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1
Guo, X. W., and W. G. D. Fernando. "Seasonal and Diurnal Patterns of Spore Dispersal by Leptosphaeria maculans from Canola Stubble in Relation to Environmental Conditions." Plant Disease 89, no. 1 (January 2005): 97–104. http://dx.doi.org/10.1094/pd-89-0097.
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Seasonal and diurnal patterns of spore dispersal by Leptosphaeria maculans, which causes blackleg disease of canola, were studied in two consecutive field seasons using a 7-day Burkard spore sampler and rotorod impaction spore samplers. Ascospores of L. maculans were trapped from mid-June to the end of July, whereas pycnidiospores were trapped from mid-July until the end of July or early August. Ascospores and pycnidiospores were trapped between 9:00 P.M. and 4:00 A.M., when air temperatures were 13 to 18°C and relative humidity was >80%. Peak ascospore and pycnidiospore dispersal was associated with rain events. Peak ascospore dispersal was found to occur several hours after rainfall ≥2 mm, and ascospore dispersal continued for approximately 3 days after such events. Peak pycnidiospore dispersal occurred during the same hours as rain events. More ascospores and pycnidiospores were carried in the direction of prevailing winds than in other directions. To the south of the inoculated area, the gradients of disease incidence and stem disease severity were -19.2 and -0.8 m-1, respectively. Disease incidence and stem severity declined by 50% 12.5 and 5.5 m from the inoculated area, respectively. To the north of the inoculated area, the gradients of disease incidence and stem severity were -21.5 and -0.7 m-1, respectively. Disease incidence and stem severity declined by 50% 14.0 and 5.2 m from the inoculated area, respectively. In 2001, ascospores and pycnidiospores were trapped within 25 m of the inoculated area, whereas pycnidiospores were trapped up to 45 m from the inoculated area.
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Chen, Wei-Qun, David P. Morgan, Dan Felts, and Themis J. Michailides. "Antagonism of Paenibacillus lentimorbus to Botryosphaeria dothidea and Biological Control of Panicle and Shoot Blight of Pistachio." Plant Disease 87, no. 4 (April 2003): 359–65. http://dx.doi.org/10.1094/pdis.2003.87.4.359.
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A potential microbial fungicide, Paenibacillus lentimorbus isolate CBCA-2, against Botryosphaeria dothidea, the pistachio panicle and shoot blight fungus, was obtained from healthy pistachio leaves by both in vitro and in vivo screening techniques. CBCA-2 caused 100% inhibition of pycnidiospore germination after 24 h incubation at 25°C. Malformation of pycnidiospores and hyphae, and lysis and swollen pycnidiospores of B. dothidea occurred in the presence of cell suspensions of CBCA-2. Among the five media tested, nutrient yeast dextrose broth significantly increased the production of antifungal compounds. Application of culture filtrates of CBCA-2 suppressed disease on detached pistachio leaves, but washed bacterial cells did not inhibit lesion development. Development of lesions on excised dormant stems was inhibited only when the culture filtrate was applied before fungal inoculation. Survival of the CBCA-2 after treatment with azoxystrobin (Abound), benomyl (Benlate), tebuconazole (Elite), propiconazole (Break), or trifloxystrobin (Flint) at the highest recommended concentration was not affected, but survival was affected by iprodione (Rovral). Spraying a suspension of CBCA-2 on pruning wounds before inoculation with pycnidiospores of B. dothidea significantly reduced infection compared with the unsprayed, inoculated controls.
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Zhang, Jin Xiu, W. G. Dilantha Fernando, and Allen G. Xue. "Daily and seasonal spore dispersal by Mycosphaerella pinodes and development of mycosphaerella blight of field pea." Canadian Journal of Botany 83, no. 3 (March 1, 2005): 302–10. http://dx.doi.org/10.1139/b05-003.
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Daily and seasonal spore dispersal of Mycosphaerella pinodes (Berk & Bloxam) Vestergren and the relationship of spore dispersal to distance and disease severity were investigated in a pea field in western Canada during two consecutive years. Most ascospores were released in response to rain events, during the first 2327 d after the inoculum source area was infested with naturally diseased pea residue, whereas most pycnidiospores were trapped during the first 20 d. For both ascospores and pycnidiospores, the highest peaks of spore release occurred during the first 1420 d after infestation. Few spores were trapped after day 27 after infestation. Daily peaks of ascospore and pycnidiospore release occurred between 1700 and 0400 hours. Most ascospores were released 12 d after a rain event and the largest peak appeared the first day after rain. In contrast, most pycnidiospores were released on the same day as rain occurred or the following day. The release of both spore types was associated with rainfall events ≥2 mm during the first 27 d after infestation but not with rainfall events after 27 d. Ascospore density was negatively correlated with distance from the inoculum source (r ≤ 0.92) and positively related to the disease severity (r ≥ 0.92). Disease severity decreased with increasing distance from the inoculum source. The patterns of spore dispersal associated with rain events have practical applications in the disease forecasting and spraying of chemicals to control the disease.Key words: field pea, mycosphaerella blight, rainfall, spore release.
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Dorrance, A. E., O. K. Miller, and H. L. Warren. "Comparison of Stenocarpella maydis Isolates for Isozyme and Cultural Characteristics." Plant Disease 83, no. 7 (July 1999): 675–80. http://dx.doi.org/10.1094/pdis.1999.83.7.675.
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Isolates of Stenocarpella maydis from seed companies and plant disease clinics in the United States and the Republic of South Africa were assayed for isozyme polymorphisms and cultural variability. A low level of isozyme polymorphisms was detected in this collection of isolates. Isozyme polymorphisms were detected for α-esterase, hexose kinase, and malate dehydroge-nase of the enzymes assayed. Fungi often have limited variability among isozyme profiles, and this is especially true for fungi that have host specialization such as biotrophs or fungi with formae speciales designations. Optimum growth temperature, colony color, and pycnidiospore production were also measured. All isolates had an optimum temperature of 28 to 31°C for colony growth on acidified potato dextrose agar. Colony color and pycnidiospore production were variable over the course of several experiments, indicating that these phenotypes are poor genetic markers.
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Galper, S., A. Sztejnberg, and N. Lisker. "Scanning electron microscopy of the ontogeny of Ampelomyces quisqualis pycnidia." Canadian Journal of Microbiology 31, no. 10 (October 1, 1985): 961–64. http://dx.doi.org/10.1139/m85-181.
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Observations on Ampelomyces quisqualis disclosed that the pycnidium may originate either from one cell of a single pycnidiospore, or from one hyphal cell. In the first case the pycnidiospore becomes two celled and swollen and a profuse germination of one of the two swollen spore cells can be observed. Later, the short hyphae branches, interweave, and anastomose to form a compact network around the mother spore, the pycnidium primordium. Similarly, we observed profuse branching in a single hyphal cell. The newly formed branches interweave and anastomose to form a compact network which gives rise to the pycnidium primordium. Hyphal rings were also observed throughout this study, but no pycnidia arose from these structures. During the vegetative growth of the fungus, hyphal anastomosis seems to be a frequent pattern. It seems that the pycnidial ontogeny of A. quisqualis does not conform to any known developmental type.
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Hu, Jiahuai, Evan G. Johnson, Nan-Yi Wang, Tiago Davoglio, and Megan M. Dewdney. "qPCR Quantification of Pathogenic Guignardia citricarpa and Nonpathogenic G. mangiferae in Citrus." Plant Disease 98, no. 1 (January 2014): 112–20. http://dx.doi.org/10.1094/pdis-04-13-0465-re.
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Citrus black spot, a major citrus disease caused by Guignardia citricarpa, was recently introduced in Florida. The nonpathogenic fungal endophyte G. mangiferae is commonly found in the same citrus tissues as G. citricarpa. Quantitative polymerase chain reaction (qPCR) assays based on internal transcribed spacer (ITS)-1 genes were developed to detect, quantify, and distinguish between these morphologically similar organisms in environmental samples. The primer/probe sets GCITS and GMITS were more than 95% efficient in single-set reactions in complex environmental DNA samples. Detection of 10 fg of G. citricarpa and G. mangiferae DNA was possible. Pycnidiospore disruption resulted in detection of single pycnidiospores with 78 (59 to 102; 95% confidence interval [CI]) and 112 (92 to 136; 95% CI) ITS copies for G. citricarpa and G. mangiferae, respectively. Detection was from partially decomposed leaves where fruiting bodies cannot be morphologically distinguished. Temperature and wetting period have significant effects on Guignardia spp. pseudothecia production in leaf litter. Based on relative biomass or the proportion of nuclei detected, G. citricarpa and G. mangiferae respond more strongly to wetting period than temperature. This qPCR assay will provide additional epidemiological data on black spot in tissues where G. citricarpa and G. mangiferae are not easily distinguished.
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Li, Hua, John Kuo, Martin John Barbetti, and Krishnapillai Sivasithamparam. "Differences in the responses of stem tissues of spring-type Brassica napus cultivars with polygenic resistance and single dominant gene-based resistance to inoculation with Leptosphaeria maculans." Canadian Journal of Botany 85, no. 2 (January 2007): 191–203. http://dx.doi.org/10.1139/b06-159.
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Six spring-type Brassica napus L. cultivars, either susceptible or with polygenic or monogenic resistance, were inoculated with Leptosphaeria maculans (Desmaz.) Ces. & De Not. (organism causing phoma stem canker in crucifers) to investigate differences in the responses of host stem tissues to the pathogen. At growth stage 1.06, plants were inoculated with pycnidiospores at the junction of the petiole and stem. The pre-penetration and penetration phases were examined along with the histological, ultrastructural, and histochemical responses. The processes of pycnidiospore attachment, germination, and penetration through the stomata of petioles and stems were found to be similar in all cultivars. Specific post-penetration defense reactions identified were lignification, suberisation, and additional cambium formation in the resistant cultivars. In ‘Surpass 400’, which has monogenic resistance, these responses occurred 4–5 d earlier than in polygenically resistant cultivars, and were more intense (preventing hyphal penetration of the additional cambium layer), and resulted in a hypersensitive reaction without pycnidia formation. Our study clearly emphasizes the variatiability in location, timing, and histochemistry of stem responses between compatible and incompatible interactions and will improve our overall understanding of the role and importance of the mechanisms of resistance in spring-type B. napus to L. maculans.
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Moyo, Providence, Paul H. Fourie, Siyethemba L. Masikane, Régis de Oliveira Fialho, Lindokuhle C. Mamba, Wilma du Plooy, and Vaughan Hattingh. "The Effects of Postharvest Treatments and Sunlight Exposure on the Reproductive Capability and Viability of Phyllosticta citricarpa in Citrus Black Spot Fruit Lesions." Plants 9, no. 12 (December 21, 2020): 1813. http://dx.doi.org/10.3390/plants9121813.
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Citrus black spot (CBS) is caused by Phyllosticta citricarpa, which is classified as a quarantine organism in certain countries whose concerns are that CBS-infected fruit may be a pathway for introduction of the pathogen. This study evaluated the reproductive capability and viability of P. citricarpa under simulated conditions in which the whole fruit, peel segments, or citrus pulp with CBS lesions were discarded. Naturally infected ‘Midknight’ Valencia orange and ‘Eureka’ lemon fruit, either treated using standard postharvest sanitation, fungicide, and wax coating treatments or untreated, were placed into cold storage for 5 weeks (oranges at 4 °C and lemons at 7 °C). Thereafter, treated and untreated fruit were incubated for a further 2 weeks at conditions conducive for CBS symptom expression and formation of pycnidia. The ability of pycnidia to secrete viable pycnidiospores after whole fruit and peel segments or peel pieces from citrus pulp were exposed to sunlight at warm temperatures (±28 °C) and ±75% relative humidity levels was then investigated. The combination of postharvest treatments and cold storage effectively controlled CBS latent infections (>83.6% control) and pycnidium formation (<1.4% of lesions formed pycnidia), and the wax coating completely inhibited pycnidiospore release in fruit and peel segments. Pycnidiospores were secreted only from lesions on untreated fruit and peel segments and at low levels (4.3–8.6%) from peel pieces from pulped treated fruit. However, spore release rapidly declined when exposed to sunlight conditions (1.4% and 0% after 2 and 3 days, respectively). The generally poor reproductive ability and viability of CBS fruit lesions on harvested fruit, particularly when exposed to sunlight conditions, supports the conclusion that citrus fruit without leaves is not an epidemiologically significant pathway for the entry, establishment, and spread of P. citricarpa.
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Shaw, Brian D., and H. C. Hoch. "Ca2+ Regulation of Phyllosticta ampelicida Pycnidiospore Germination and Appressorium Formation." Fungal Genetics and Biology 31, no. 1 (October 2000): 43–53. http://dx.doi.org/10.1006/fgbi.2000.1223.
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Ma, Zhonghua, and Themis J. Michailides. "Characterization of Botryosphaeria dothidea Isolates Collected from Pistachio and Other Plant Hosts in California." Phytopathology® 92, no. 5 (May 2002): 519–26. http://dx.doi.org/10.1094/phyto.2002.92.5.519.
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Eighty-six isolates of Botryosphaeria dothidea, the causal agent of Botryosphaeria panicle and shoot blight of pistachio, were collected from pistachio and other plant hosts in California. The isolates were characterized by microsatellite-primed polymerase chain reaction (MP-PCR), sequences of the nuclear ribosomal DNA internal transcribed spacer region (ITS1, 5.8S gene, and ITS2), morphological and cultural characters, osmotic and fungicide sensitivity, and pathogenicity on pistachio. Three groups of these isolates were identified based upon analysis of MP-PCR data and ITS sequences. Group I contained 43 pycnidiospore-derived isolates collected from pistachio and other hosts. Group II consisted of 20 ascosporic isolates obtained from a single sequoia plant. Group III consisted of 20 ascosporic isolates from three shoots on a single blackberry plant, two pycnidiospore-derived isolates from incense cedar, and one from pistachio. Group I predominated over the other two groups in California pistachio orchards. B. dothidea isolates of group III grew faster on acidified potato dextrose agar (APDA) than the isolates of groups I and II. Isolates of group III produced pycnidia on both APDA and autoclaved pistachio shoots, but the isolates of the other two groups produced pycnidia on only autoclaved pistachio shoots. Additionally, significant differences in osmotic and fungicide sensitivities were observed among these three groups. Results from lathhouse inoculations demonstrated that the representative isolates for each of the three groups were all capable of infecting pistachio and producing characteristic disease symptoms of Botryosphaeria blight. The virulence of group II isolates on pistachio was, however, significantly lower than that of group I isolates.
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Shaw, B. D., and H. C. Hoch. "The pycnidiospore of Phyllosticta ampelicida: surface properties involved in substratum attachment and germination." Mycological Research 103, no. 7 (July 1999): 915–24. http://dx.doi.org/10.1017/s095375629800793x.
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Szlávik, Sz, T. Barasits, and W. G. D. Fernando. "First Report of Pathogenicity Group-3 of Leptosphaeria maculans on Winter Rape in Hungary." Plant Disease 90, no. 5 (May 2006): 684. http://dx.doi.org/10.1094/pd-90-0684c.
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Blackleg, caused by Leptosphaeria maculans, is an increasing threat to winter rape (Brassica napus L.) in Hungary. The winter rape acreage has been increasing, and the occurrence and severity of the disease has become widespread in all rapeseed-growing regions throughout Hungary in a very short time. The blackleg-infected rape stubbles were collected in the autumn of 2003 in Ikervár, County Vas where the disease was severe. Ascospores were obtained from pseudothecia growing on infected rape stubble (susceptible cvs. GK Helga and Aladin). Three single-spore cultures were grown on V8 agar medium at room temperature and fluorescent light. The culture characteristics fit the type culture description for L. maculans. Pycnidiospores that formed on V8 plates were flooded with 10 ml of sterile distilled water. Seeds of cvs. Westar, Glacier, and Quinta obtained from the Department of Plant Science, University of Manitoba, Canada were sown in plastic pots containing peat mix. Seedlings were maintained in a growth chamber at 24°C with 90% relative humidity and a 16-h photoperiod. Seven days after sowing, cotyledons were wound inoculated with a 10-μl droplet of pycnidiospore suspension (1.5 × 107 spores ml-1). Interaction phenotypes (IP) were scored 10 days after inoculation using a 0 to 9 scale (1). All three isolates from Ikervár were highly virulent on cvs. Westar (8.8 to 8.9) and Glacier (8.1 to 8.3) and avirulent on cv. Quinta (0.8 to 0.9). The IP ratings indicated that these isolates belonged to pathogenicity group-3 (PG-3). To our knowledge, this is the first report of the presence of L. maculans PG-3 in Hungary. At the current time, PG-3 has caused at least 30% yield losses in susceptible cultivars of winter rape. Reference: (1) A. Mengistu et al. Plant Dis. 75:1279, 1991.
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Fernando, W. G. D., and Y. Chen. "First Report on the Presence of Leptosphaeria maculans Pathogenicity Group-3, the Causal Agent of Blackleg of Canola in Manitoba." Plant Disease 87, no. 10 (October 2003): 1268. http://dx.doi.org/10.1094/pdis.2003.87.10.1268a.
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Blackleg, caused by Leptosphaeria maculans (Desmaz.) Ces. & De Not. (anamorph = Phoma lingam) (Tode:Fr.) Desmaz.), is an economically important and serious disease of canola (Brassica napus L.) in Australia, Europe, and Canada. L. maculans isolates can be categorized into four pathogenicity groups (PGs) on the basis of the interaction phenotypes (IP) on the differential canola cvs. Westar, Glacier, and Quinta (1) by using a standard screening protocol in the greenhouse. PG1 isolates are weakly virulent and PG2, PG3, and PG4 isolates are highly virulent. In Manitoba, L. maculans population consists mainly of PG2 (virulent on cv. Westar; avirulent on cvs. Glacier and Quinta) and a few PG1 isolates (avirulent on all three differentials). The Oilseed Pathology Lab in the Department of Plant Science, University of Manitoba examines the pathogenic variability of blackleg isolates obtained from Manitoba each year. In 2002, the blackleg-resistant cv. Q2, was found to be severely infected in Roland, Manitoba. The canola stubble collected from a coop trial plot (Roland, Manitoba) and a farm in East Selkirk (60 km northeast of Winnipeg, Manitoba) was isolated for the blackleg fungus. Small pieces of stubble were cut from the pseudothecia forming section and surface sterilized with 1% sodium hypochlorite solution for 3 to 5 min and then rinsed in sterile distilled water. V8 agar medium containing 1% streptomycin sulphate was used to culture the isolates under continuous cool-white fluorescent light for 14 days. Pure cultures of the pathogen were isolated and characterized as L. maculans by means of colony morphology, pycnidia, and microscopic observations of pycnidiospores. Pycnidiospores that formed on V8 plates were flooded with 10 ml of sterile distilled water and then harvested by filtering through sterilized Miracloth and kept at -20°C. The isolates were passed once through cv. Westar to maintain their virulence. The PG test was performed with the three differential cultivars. Two additional cultivars, Q2 (resistant to PG2 isolates) and Defender (moderately resistant to PG2 isolates), were included for comparisons. Twelve 7-day-old cotyledons of each differential cultivar grown in Metro Mix were wound inoculated with a 10-μl droplet of pycnidiospore suspension (1 × 107 pycnidiospores per ml). Inoculated cotyledons were maintained in the greenhouse (16/21°C night/day and a 16-h photoperiod). The experiment was repeated twice. Disease severity on cotyledons was assessed 12 days postinoculation by using a 0 to 9 scale (2). All five isolates from Roland and East Selkirk were highly virulent on Glacier (6.4 to 7.7), Q2 (7.1 to 8.2), and Defender (7.2 to 8.4), but intermediately virulent on Quinta (4.5 to 5.4). This clearly indicated that these isolates were of PG3. Isolates of PG2 have been predominant in Manitoba for the past 25 years, and highly virulent isolates belonging to PG3 had not been detected previously. To our knowledge, this is the first report of the presence of PG3 in L. maculans in Manitoba. References: (1) A. Mengistu et al. Plant Dis. 75:1279, 1991. (2) P. H. Williams. Crucifer Genetics Cooperatives (CrGC) Resource Book, University of Wisconsin—Madison, 1985.
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Fernando, W. G. D., P. S. Parks, G. Tomm, L. V. Viau, and C. Jurke. "First Report of Blackleg Disease Caused by Leptosphaeria maculans on Canola in Brazil." Plant Disease 87, no. 3 (March 2003): 314. http://dx.doi.org/10.1094/pdis.2003.87.3.314c.
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Canola (Brassica napus L.) is a relatively new crop in Brazil, having been grown there for approximately 8 years. In 2000, leaf lesions and stem cankers were observed in cvs. Hyola 420 and Hyola 401 in farmers' fields in the state of Rio Grande do Sul. Cankered stems were received at the University of Manitoba, Canada, from Rio Grande do Sul for disease identification. Small pieces of the stem were cut from the cankered area, and standard protocol was followed to surface sterilize the stem pieces. Stem pieces were plated on V8 agar medium and incubated under light for 12 days. Typical fungal colonies with concentric rings containing pycnidia formed on the V8 agar. The colony characteristics were typical of the blackleg pathogen, Leptosphaeria maculans (Desmaz.) Ces. & De Not. (anamorph = Phoma lingam) (Tode:Fr.) Desmaz.). Blackleg is an economically important and serious disease in many parts of the world including Australia, Canada, the United States, and Europe. L. maculans strains can be characterized in four pathogenicity groups (PG1 through PG4) based on differential testing procedures giving interaction phenotype (IP) reactions (2). Two weeks after plating on V8 media, plates were flooded with sterile distilled water, and pycnidiospores were harvested. Flats of multipots filled with Metro Mix were seeded with three cultivars (Westar, Glacier, and Quinta). One-week-old cotyledons from the three cultivars were inoculated with pycnidiospore suspensions (2 × 107 pycnidiospores per ml) of seven Brazilian isolates, numbered 7, 8, 9, 11, 15, 16, and 18, respectively. Each cotyledon leaf, punctured in the center with a needle, was inoculated with a 10-μl droplet of the inoculum. Disease evaluations were made 11 days after inoculation using a 0 to 9 rating scale (1). This screening was repeated three times from February 2001 to October 2001. After the second repeat, the isolates from Rio Grande do Sul were passed through the highly susceptible canola cv. Westar. Results from all four trials were consistent, and yielded one PG1 isolate (No. 7) and six PG3 isolates. PG1 is classified as a nonaggressive strain, whereas PG3 isolates are classified as aggressive. PG3 isolates would have an IP reaction of 7 to 9, 7 to 9, and 3 to 6 on cvs. Westar, Glacier, and Quinta, respectively. PG2 is the most commonly found aggressive strain in the Canadian prairies. PG3 is predominantly found in Australia, the United Kingdom, and the United States. To our knowledge, this is the first report of blackleg disease caused by L. maculans on canola in Brazil. Differential testing fulfilled Koch's postulates and determined the PG groups found in Brazil (PG1 and PG3). References: (1) P. A. Delwiche. Genetic aspects of blackleg (Leptosphaeria maculans) resistance in rapeseed (Brassica napus) Ph.D. thesis. University of Wisconsin-Madison, 1980. (2) A. Mengistu et al. Plant Dis. 75:1279, 1991.
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Fernando, W. G. D., K. Ghanbarnia, and M. Salati. "First Report on the Presence of Phoma Blackleg Pathogenicity Group 1 (Leptosphaeria biglobosa) on Brassica napus (Canola/Rapeseed) in Iran." Plant Disease 91, no. 4 (April 2007): 465. http://dx.doi.org/10.1094/pdis-91-4-0465a.
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Canola/rapeseed (Brassica napus L.) is a new crop in Iran, grown since 1996. In 2006, 180,000 ha were planted. During the same year, leaf and upper stem lesions (3) were observed on cv. Hyola 401 at rosette and flowering stages in the Gorgan Province in northern Iran. Field disease incidence ranged from 1 to 40%. Several isolates from stem lesions were sent to the Department of Plant Science, Blackleg Research Lab, University of Manitoba, Canada from the Agricultural and Natural Resources Research Center of Golestan Province of Iran for pathogenicity group identification. The blackleg pathogen is divided into several pathogenicity groups on the basis of phenotypic interaction (IP) of isolates on differential cvs. Westar, Glacier, and Quinta. Isolates PG2, PG3, PG4, and PGT are highly virulent, but PG1, which recently has been named Leptosphaeria biglobosa (2), is weakly virulent. Colonies of the blackleg pathogen were reisolated from their original medium, potato dextrose agar, and grown onV8 agar medium and incubated under light for 2 weeks. Pure cultures of the pathogen were then characterized by colony morphology, pycnidia, and measurement and microscopic observation of pycnidio-spores. Fungal colonies formed with concentric rings containing pycnidia with pink ooze on V8 agar. Pycnidia were globose and as much as 200 μ 200 μm. They had a prominent beak on the ascomata that was enlarged, cylindrical, central, terete, erect, and 150 to 200 × 100 μm. Pycnidiospores were cylindrical, straight, 4 to 5 × 2 μm, and hyaline (2). To identify the pathogenicity group of the Iranian isolates, pycnidiospores were harvested from single-spore cultures after 14 days of incubation under continuous cool-white fluorescent light (1). One-week-old cotyledons from the differential cvs. Westar, Glacier, and Quinta were inoculated with pycnidiospore suspension concentration of 2 × 107 spores per ml of the four Iranian isolates. Each cotyledon lobe was punctured with forceps and inoculated with a 10-μl droplet of spore suspension. Disease evaluations were made 10 to 14 days after inoculation using a 0 to 9 rating scale. Inoculations were repeated twice with identical results yielding only the PG1 type reaction. To our knowledge, this is the first report of the presence of L. biglobosa (PG1; B-type) on canola in Iran. Differential testing fulfilled Koch's postulates. L. biglobosa seems to be less damaging compared with L. maculans, but severe phoma stem lesion epidemics have been associated with the L. biglobosa in Poland (3). The importance of this weakly virulent pathogen, whenever the relative humidity increases, has been demonstrated in greenhouse conditions (A. El-Hadrami, W. G. D. Fernando, and F. Daayf, unpublished data). Since the relative humidity in northern Iran is high, an epidemic may occur if appropriate management practices are not utilized to minimize inoculum levels. References: (1) W. G. D. Fernando and Y. Chen. Plant Dis. 87:1268, 2003. (2) R. A. Shoemaker and H. Brun. Can. J. Bot. 79:412, 2003. (3) J. S.West et al. Plant Pathol. 48:161, 2001.
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Ojiambo, Peter S., Harald Scherm, and Phillip M. Brannen. "Temporal Dynamics of Septoria Leaf Spot of Blueberry and its Relationship to Defoliation and Yield." Plant Health Progress 8, no. 1 (January 2007): 68. http://dx.doi.org/10.1094/php-2007-0726-05-rs.
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In field trials on Premier rabbiteye blueberry in Georgia, onset of Septoria leaf spot (caused by Septoria albopunctata) occurred between late April and mid-June. Average disease severity increased sigmoidally until late September, after which it declined due to the abscission of severely affected leaves. Disease severity was highest on early-emerging leaves and on those located on shoots closer to the ground. Pycnidiospore inoculum was present throughout the season, and leaves became infected by S. albopunctata season-long. Disease severity, defoliation, flower bud set, and next season's yield were interrelated; severely affected leaves abscised earlier in the fall than those with low disease severity, and shoots with severely diseased leaves and/or high levels of defoliation had reduced flower bud set. Furthermore, such shoots consistently had low yields the following year. The results form the basis for identifying disease levels that can be tolerated during specific periods of crop development without negatively impacting flower bud set and yield. Accepted for publication 15 March 2007. Published 26 July 2007.
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Dorrance, A. E., K. H. Hinkelmann, and H. L. Warren. "Diallel Analysis of Diplodia Ear Rot Resistance in Maize." Plant Disease 82, no. 6 (June 1998): 699–703. http://dx.doi.org/10.1094/pdis.1998.82.6.699.
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A diallel cross of seven inbreds and one synthetic line of maize were analyzed in 1994 and 1995 for their reaction to Diplodia ear rot. An additional inbred line was included in the 1995 analysis. Plants were inoculated by placing a pycnidiospore suspension (5 × 103 spores per ml) of Stenocarpella maydis in the whorl at the V14 to V15 growth stage. Crosses were evaluated for disease incidence of Diplodia ear rot at harvest, and the percentage of plants with Diplodia ear rot in a plot was used for analysis. In both years, general combining ability (GCA) effects were significant. In 1995, specific combining ability effects were also significant. There were no reciprocal effects. There was no significant interaction between year and genotypes, indicating that crosses reacted the same in both years. Inbred lines B37, H111, B68, and MS had negative GCA effects that contributed toward resistance in both years. VA26, with intermediate resistance to Diplodia ear rot, contributed toward susceptibility. Only inbred lines with a high degree of resistance should be used as parents.
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Tan, Kar-Chun, Joshua L. Heazlewood, A. Harvey Millar, Gordon Thomson, Richard P. Oliver, and Peter S. Solomon. "A Signaling-Regulated, Short-Chain Dehydrogenase of Stagonospora nodorum Regulates Asexual Development." Eukaryotic Cell 7, no. 11 (September 5, 2008): 1916–29. http://dx.doi.org/10.1128/ec.00237-08.
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ABSTRACT The fungus Stagonospora nodorum is a causal agent of leaf and glume blotch disease of wheat. It has been previously shown that inactivation of heterotrimeric G protein signaling in Stagonospora nodorum caused development defects and reduced pathogenicity [P. S. Solomon et al., Mol. Plant-Microbe Interact. 17:456-466, 2004]. In this study, we sought to identify targets of the signaling pathway that may have contributed to phenotypic defects of the signaling mutants. A comparative analysis of Stagonospora nodorum wild-type and Gα-defective mutant (gna1) intracellular proteomes was performed via two-dimensional polyacrylamide gel electrophoresis. Several proteins showed significantly altered abundances when comparing the two strains. One such protein, the short-chain dehydrogenase Sch1, was 18-fold less abundant in the gna1 strain, implying that it is positively regulated by Gα signaling. Gene expression and transcriptional enhanced green fluorescent protein fusion analyses of Sch1 indicates strong expression during asexual development. Mutant strains of Stagonospora nodorum lacking Sch1 demonstrated poor growth on minimal media and exhibited a significant reduction in asexual sporulation on all growth media examined. Detailed histological experiments on sch1 pycnidia revealed that the gene is required for the differentiation of the subparietal layers of asexual pycnidia resulting in a significant reduction in both pycnidiospore size and numbers.
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Sprague, Susan J., Stephen J. Marcroft, Kurt D. Lindbeck, Andrew H. Ware, Ravjit K. Khangura, and Angela P. Van de Wouw. "Detection, prevalence and severity of upper canopy infection on mature Brassica napus plants caused by Leptosphaeria maculans in Australia." Crop and Pasture Science 69, no. 1 (2018): 65. http://dx.doi.org/10.1071/cp17140.
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Blackleg, caused by Leptosphaeria maculans, is the main disease constraint for canola production in Australia. The fungus infects all aboveground and belowground parts of the canola plant. Yield loss in Australia and worldwide is generally associated with cankers at the crown, which arise from leaf infections during the early stages of seedling growth. Infection of flowers, peduncles, siliques, main stems and branches, with resultant lesions and canker formation, are typically uncommon symptoms. We propose the term ‘upper canopy infection’ to encompass symptoms on all of these plant parts because they generally occur together on the same plant and appear after the plant has undergone elongation. Branch and stem lesions observed in a commercial crop in 2010 were confirmed as L. maculans. Since then, assessment of upper canopy symptoms at 25 sites across the canola-producing regions of Australia between 2011 and 2016 show that symptoms are more prevalent, although they differed between sites and seasons. In 2011, symptoms were present at a single site, and this increased to seven sites in 2013 and 23 sites in 2016. Preliminary data indicate that infection arises from both ascospore and pycnidiospore inoculum, and that earlier onset of flowering is a key risk factor for more severe upper canopy infection. Evidence suggests that host genetic resistance may be an effective control for upper canopy infection.
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Bradley, C. A., P. S. Parks, Y. Chen, and W. G. D. Fernando. "First Report of Pathogenicity Groups 3 and 4 of Leptosphaeria maculans on Canola in North Dakota." Plant Disease 89, no. 7 (July 2005): 776. http://dx.doi.org/10.1094/pd-89-0776c.
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Blackleg, caused by Leptosphaeria maculans (Desmaz) Ces. & de Not (anamorph = Phoma lingam), is an economically important disease of canola (Brassica napus L.) worldwide and was first detected in North Dakota in 1991 (3). L. maculans can be categorized into one of several pathogenicity groups (PGs) on the basis of the interaction phenotypes in differential canola cvs. Westar, Glacier, and Quinta by using a standard screening protocol in the greenhouse (4). With this system, PG1 strains are weakly virulent and PG2, PG3, and PG4 are highly virulent. The predominant strains of L. maculans in North Dakota are PG1 and PG2 (3). In cooperation with the Oilseed Pathology Lab in the Department of Plant Science, University of Manitoba, blackleg-infested canola stubble was collected arbitrarily from fields in North Dakota during August and September of 2003. Isolates of the pathogen were obtained by plating surface-sterilized (2% NaOCl), collected stubble on V8 agar containing 0.03% chloramphenicol at 22°C under continuous cool-white fluorescent light. Pycnidiospores were harvested from single pycnidia after 14 days of incubation with the Miracloth filtering method (2) and stored at -20°C. Each isolate was passed once through cv. Westar to maintain virulence. Isolates were confirmed as being L. maculans by the presence of characteristic pink pycnidia formed on V8 agar and the characteristic symptoms caused on inoculated cotyledons of cv. Westar. The PG test was performed using a standard screening protocol (4) and was repeated three times for each isolate. For each isolate, 12 7-day-old cotyledons of each differential cultivar were wound inoculated with 10 μl of a pycnidiospore suspension (1 × 107 per ml). Disease severity on cotyledons was assessed 12 days after inoculation with a 0 to 9 scale (0 to 2 = resistant; 3 to 6 = intermediate; and 7 to 9 = susceptible). A total of 106 isolates were obtained from the stubble collected from 47 fields. Of these isolates, three were characterized as PG1, 94 as PG2, six as PG3, and one as PG4; two isolates could not be characterized according to the PG system as described (4). PG3 isolates originated from two fields in Cavalier County and one field in Ward County. The PG4 isolate was from Cavalier County. To our knowledge, this is the first time highly virulent strains of PG3 and PG4 have been detected in North Dakota. PG3 and PG4 strains of L. maculans were found only recently in western Canada (1,2). The discovery of these PGs in North Dakota and western Canada has immense implication to canola breeding programs and blackleg control, since these PGs may cause greater levels of blackleg severity on canola cultivars that are resistant to only PG2 type isolates. References: (1) Y. Chen and W. G. D. Fernando. Plant Dis. 89:339, 2005. (2) W. G. D. Fernando and Y. Chen. Plant Dis. 87:1268, 2003. (3) H. A. Lamey and D. E. Hershman. Plant Dis. 77:1263, 1993. (4) A. Mengistu et al. Plant Dis. 75:1279, 1991.
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Reszka, E., E. Arseniuk, A. Malkus, K. R. Chung, N. R. O'Neill, Q. J. Song, and P. P. Ueng. "A New Biotype of Phaeosphaeria sp. of Uncertain Affinity Causing Stagonospora Leaf Blotch Disease in Cereals in Poland." Plant Disease 90, no. 1 (January 2006): 113. http://dx.doi.org/10.1094/pd-90-0113b.
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A new Phaeosphaeria sp. biotype was isolated from winter ryes in Poland during 1995. Two isolates, Sn23-1 and Sn48-1, were obtained from diseased leaves of cvs. Motto and Dańkowskie, respectively. The rye Phaeosphaeria sp. represented by isolate Sn48-1 has similar pycnidiospore morphology and induces disease symptoms in cereals similar to Phaeosphaeria nodorum, the causal agent of Stagonospora nodorum blotch disease (4). The pathogen (Sn48-1) produces hyaline, cylindrical pycnidiospores that are mostly three-septate and measure 12.8 to 23.7 × 2.1 to 3.2 μm (average size = 16 × 2.6 μm) on water agar. A molecular comparison of several genes in isolates Sn23-1 and Sn48-1 revealed that the rye Phaeosphaeria sp. was different from P. nodorum. In the conserved alpha-box sequence (1,93 bp) of the MAT1-1 gene, a four nucleotide difference occurred between the wheat-biotype P. nodorum and isolates Sn23-1 and Sn48-1 (GenBank Accession Nos. AY072933 and AF322008). In addition, the length of the internal transcribed spacer (ITS) region of the nuclear rDNA was the same for the wheat-biotype P. nodorum and the two rye Phaeosphaeria sp. isolates. However, a six nucleotide discrepancy was found in the ITS region (GenBank Accession Nos. U77362 and AF321323). The beta-glucosidase (bgl1) and beta-tubulin (tubA) genes differ in length between the wheat-biotype P. nodorum and two rye Phaeosphaeria sp. isolates (2,3). The main difference was due to the intron sizes of these two genes. One extra nucleotide was found in the intron2 of the bgl1 gene (GenBank Accession Nos. AY683619 and AY683620) and the intron1 of the tubA gene (GenBank Accession Nos. AY786337 and AY786331), respectively, in these two rye Phaeosphaeria sp. isolates. Disease severity on the fifth leaf (GS15) of Polish wheat (Alba, Begra, and Liwilla), triticale (Bogo and Pinokio), and rye (Zduno) cultivars was assessed with one (resistant) to nine (susceptible) scales 14 days after inoculation. Aggressiveness of wheat-biotype P. nodorum isolate Sn26-1 and rye Phaeosphaeria sp. isolate Sn48-1 was significant (P < 0.01) in five cultivars except in the moderately resistant wheat cv. Liwilla. The rye Phaeosphaeria sp. isolate Sn48-1 severely affected Polish rye Zduno (8.3) and two triticale cultivars (6.5), while the infection by isolate Sn26-1 was moderate (3–4). On the contrary, the wheat-biotype P. nodorum isolate Sn26-1 was more aggressive on wheat (4.1 on moderately resistant Alba and 6.2 on highly susceptible Begra) than the rye Phaeosphaeria sp. isolate Sn48-1, which had a scale of 2.2 and 4.3, respectively. Under laboratory conditions, the rye isolate Sn48-1 was able to cross with the wheat-biotype P. nodorum isolate Sn26-1 that has an opposite mating-type (MAT1-2) gene, but few viable ascospores were produced (1). References: (1) P. C. Czembor and E. Arseniuk. Mycol. Res. 104:919, 2000. (2) A. Malkus et al. FEMS (Fed. Eur. Microbiol. Soc.) Lett. 249:49, 2005. (3) E. Reszka et al. Can. J. Bot. 83:1001, 2005. (4) M. J. Richardson and M. Noble. Plant Pathol. 19:159, 1970.
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Zhao, Xinbei, Yunxia Ni, Xintao Liu, Hui Zhao, Jing Wang, Yung-Chun Chen, Weidong Chen, and Hongyan Liu. "A Simple and Effective Technique for Production of Pycnidia and Pycnidiospores by Macrophomina phaseolina." Plant Disease 104, no. 4 (April 2020): 1183–87. http://dx.doi.org/10.1094/pdis-08-19-1795-re.
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Production of pycnidia and pycnidiospores by Macrophomina phaseolina is not often seen in vitro. The objective of this study is to develop a simple and effective technique to obtain pycnidiospores of M. phaseolina isolates in vitro and to evaluate germination rates and pathogenicity of pycnidiospores. We found M. phaseolina isolates can produce pycnidia on oatmeal agar (OMA) under ultraviolet light with 365 nm wavelength (UV). For evaluating the effect of OMA and UV on growth of M. phaseolina, combinations of two agar media and three lighting conditions were tested. The results confirm that all six M. phaseolina isolates produced pycnidia only on OMA under UV. The pycnidiospores produced on OMA under UV had germination rates higher than 90%. In pathogenicity tests, inoculation with the pycnidiospores showed symptoms later than inoculation with hypha-colonized toothpicks. Significant differences in the pathogenicity is detected between isolates Mp2014003 and Mp2014024 when inoculation is done with the pycnidiospores (P < 0.001), but not when hypha-colonized toothpicks are used as inoculum (P = 0.091). This study provides a new method for obtaining pycnidiospores of M. phaseolina for future investigations.
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Sudha, Appusami. "Volatile Organic Compounds of some Antagonists against Lasiodiplodia theobromae, a Pathogen of Coconut." International Journal of Agriculture and Biology 26, no. 06 (December 1, 2021): 731–40. http://dx.doi.org/10.17957/ijab/15.1889.
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Biocontrol agents are the potential microbes and used for the control of aerial and soil-borne pathogens present in all crops. An attempt was made on identification, morphological and molecular characterization of Lasiodiplodia theobromae, a pathogen causing disease in nuts and leaves of coconut. A virulent isolate Lasiodiplodia theobromae L26 was selected based on the growth parameters and pycnidiospore production. Three efficient biocontrol agents (BCAs) namely Trichoderma asperellum, Bacillus subtilis and Streptomyces rochei, were selected for in vitro studies. Among these, T. asperellum showed a significantly higher percentage of inhibition (81%) in dual culture assay against L26. The inhibition was also confirmed in light microscopic observation, the mycelium of L26 was distorted, lysis of cell wall during the interaction. Volatile organic compounds (VOCs) emitted from BCAs inhibited the fungal growth of L26 by 59.61–47.03% in sealed plate method. Solid-phase microextraction GC-MS analysis revealed numerous new VOCs compounds emitted from the BCAs, whereas the dominant compound was identified as peptaibols, 2,4-di-tert-butylphenol, 2-piperidinone. The strength of peaks of these compounds augmented during the interaction of BCAs with L26, the peak intensity for terpenoids was the predominant class, followed by phenols and heterocyclic organic compound. Crude metabolite (75 μL) of each antagonist tested through agar well method against L26 and showed a complete inhibition. This study demonstrated the ability of BCAs to produce volatile and nonvolatile antifungal compounds, showing that there could a major mechanism involved in and that will be responsible for the successful inhibition of L26 under in vitro. In future combination of these three strains as commercial formulation may be a better management practices for leaf blight and malformation of nuts in coconut. © 2021 Friends Science Publishers
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Ma, Zhonghua, Eric W. A. Boehm, Yong Luo, and Themis J. Michailides. "Population Structure of Botryosphaeria dothidea from Pistachio and Other Hosts in California." Phytopathology® 91, no. 7 (July 2001): 665–72. http://dx.doi.org/10.1094/phyto.2001.91.7.665.
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Genetic diversity was investigated among California populations of Botryosphaeria dothidea, causal agent of Botryosphaeria panicle and shoot blight of pistachio, with random amplified polymorphic DNA (RAPD) and microsatellite-primed polymerase chain reaction (MP-PCR). We surveyed 120 isolates, 112 of which originated from the California Central Valley and included pistachio isolates (n = 52) and isolates from other plant species (n = 60). Out-group isolates (n = 8) were obtained from pistachio in Greece. There was a strong correlation (r = 0.99; P < 0.0001) between the RAPD- and MP-PCR dissimilarity data sets. Little genetic variation (haplotypic diversity [Hs] < 0.002) was detected among B. dothidea isolates collected from central and southern California pistachio plantings. We observed relatively high diversity for isolates from a northern California pistachio orchard (Hs = 0.0146), where the disease was first diagnosed, and from the Chico U.S. Department of Agriculture Germ Plasm Repository (Hs = 0.0726), where the first pistachio trees were planted in California in 1929. Isolates obtained from other hosts, especially those associated with the rare occurrence of the sexual stage of this fungus, showed the highest levels of diversity (Hs = 0.1689). Thirty-eight pistachio isolates (73.1%) had DNA fingerprints identical to 28 pycnidiospore-derived isolates (56.0%) obtained from other host species. Greenhouse inoculations demonstrated that all isolates obtained from other hosts were capable of infecting pistachio and produced characteristic disease symptomology. Thus, California populations of B. dothidea from pistachio are, for the most part, genetically uniform, with the sexual stage rare to absent. However, the rare occurrence of the sexual stage of B. dothidea on other hosts, and more importantly, the capacity of these isolates to infect pistachio, indicate that other host species may serve as sources of inoculum and genetic variation.
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Chen, Y., and W. G. D. Fernando. "First Report of Canola Blackleg Caused by Pathogenicity Group 4 of Leptosphaeria maculans in Manitoba." Plant Disease 89, no. 3 (March 2005): 339. http://dx.doi.org/10.1094/pd-89-0339b.
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Leptosphaeria maculans (Desmaz.) Ces. & de Not., causal agent of blackleg of canola (Brassica napus L.), was initially placed in several pathogenicity groups (PG) on the basis of the interaction phenotypes (IP) of L. maculans isolates on the differential canola cvs. Westar (W), Glacier (G), and Quinta (Q) (4). PG1 isolates are weakly virulent and PG2, PG3, and PG4 isolates are highly virulent. In Manitoba, the L. maculans population consists mainly of PG2 isolates (virulent on W and avirulent on G and Q), a few PG1 isolates (avirulent on W, G, and Q), and PGT (virulent on W and Q, but avirulent on G) (3). Since the blackleg fungus is known to have a high level of evolutionary potential, the Oilseed Pathology Laboratory at the University of Manitoba, Winnipeg, Canada, examines the pathogenic variability of L. maculans isolates from the Canadian Prairies and North Dakota each year. During 2002, the presence of PG3 (virulent on W and G and avirulent on Q) was reported in Manitoba (1). During 2003, a canola field located at La Riviere, Manitoba, 200 km southwest of Winnipeg, was found to be severely affected by blackleg. Stubble from this field was arbitrarily collected in mid-April 2004, and 98 single-pycnidia pure cultures were obtained by isolating fungi from surface-sterilized (2% sodium hypochlorite), infested residue, cultured on V8 agar at room temperature under cool-white florescent light for 24 h. Pycnidiospores were harvested after 14 days of incubation using the Miracloth filtering method (1). PG testing was performed using the three differential cultivars in the greenhouse. Known PG2, 3, and 4 isolates, 86-12, Liffole-6, and PL30.2, respectively, were included as positive controls. For each of the 98 isolates, 12 7-day-old cotyledons of each differential cultivar grown in Metro Mix were wound-inoculated with 10 μl of a pycnidiospore suspension (1 × 107 per ml) (1). Inoculated plants were maintained in the greenhouse (16/21°C night/day and a 16-h photoperiod with cool-white florescent light). The experiment was repeated three times. Disease severity on cotyledons was assessed 12 days after inoculation with a 0 to 9 scale (0 to 2 = resistant; 3 to 6 = intermediate; and 7 to 9 = susceptible). Of the 98 isolates tested, five were PG1, 51 were PG2, 24 were PG3, 13 were PGT, and five were PG4. The isolates classified as PG4 gave IP reactions of 7 to 9, 7 to 9, and 6.6 to 8.2, on W, G, and Q, respectively. PG3 was reported one year ago, but highly virulent isolates belonging to PG4 have not been previously detected in Manitoba. To our knowledge, this is the first report of the occurrence of PG4 isolates of L. maculans, and the first report of PG4 causing canola blackleg in Manitoba. The appearance of PG4 may be evidence of pathogen population changes occurring under high-selection-pressure exerted by resistance genes in commercial cultivars (2), or through importation of PG4 isolates with canola seed. References: (1) W. G. D. Fernando and Y. Chen. Plant Dis. 87:1268, 2003. (2) B. J. Howlett. Can. J. Plant Pathol. 26:245, 2004. (3) M. Keri et al. Can. J. Plant Pathol. 23:199, 2001. (4) A. Mengistu et al. Plant Dis. 75:1279, 1991.
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Cordo, C. A., C. I. Mónaco, R. Altamirano, A. E. Perelló, S. Larrán, N. I. Kripelz, and M. R. Simón. "Weather Conditions Associated with the Release and Dispersal of Zymoseptoria tritici Spores in the Argentine Pampas Region." International Journal of Agronomy 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/1468580.
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The abundance of Zymoseptoria tritici ascospores and conidia in a field was examined throughout two one-year periods (1998-1999 and 1999-2000) establishing the relationship between spore release and weather variables. Radiation, temperature, intensity of rainfall, and relative humidity significantly affected the dispersal of ascospores and pycnidiospores of this pathogen. Spore traps collected both types of spores, at weekly intervals, at two different stages of the wheat crop (vegetative and wheat stubble stages) and different distances from the sources. Ascospores were the predominant sources of inoculum in the field. The numbers of ascospores and pycnidiospores declined with the increase of distance from the sources. The release of pycnidiospores was associated with the increase in rainfall intensity 7 days before the released event and the increase in radiation 60 days before the same event. Relative humidity 3 and 15 days before the release event was positively correlated with ascospores release and negatively correlated with radiation and temperature in all the sampling interval. Also for the first time, a positive correlation between radiation and pycnidiospores dispersal is reported. Understanding the relationship between environment conditions and spores dispersal event could improve the control strategies of the disease.
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Li, H., K. Sivasithamparam, and M. J. Barbetti. "Breakdown of a Brassica rapa subsp. sylvestris Single Dominant Blackleg Resistance Gene in B. napus Rapeseed by Leptosphaeria maculans Field Isolates in Australia." Plant Disease 87, no. 6 (June 2003): 752. http://dx.doi.org/10.1094/pdis.2003.87.6.752a.
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Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus) grown in Canada, Europe, and Australia. Cv. Surpass 400 was released in Australia in 2000 as the most resistant cultivar to L. maculans. It carries a single dominant resistance gene from B. rapa subsp. sylvestris. This cultivar usually shows a hypersensitive response to L. maculans characterized by small, dark brown lesions that are necrotic, localized, and without pycnidia on cotyledons, leaves, and stems. However, in 2001 on a Western Australian experimental farm, a small proportion of the lesions on the lower stem and crown region of cv. Surpass 400 were typical of those observed in susceptible cultivars, which were brown, necrotic lesions with a darker margin, but they contained fewer pycnidia. Forty seedlings of cv. Surpass 400 and susceptible cv. Westar were inoculated with pycnidiospore suspensions (106/ml) of each of 18 isolates taken from lesions on cv. Surpass 400. All 18 isolates caused collapse of cotyledons of susceptible cv. Westar. Four of these isolates caused large cotyledon lesions with some pycnidia on cv. Surpass 400. Three of these four isolates were subsequently inoculated onto 60 seedlings per isolate, at each of the four cotyledon lobes of each seedling of the two cultivars. Inoculated plants were assessed for disease severity on cotyledons and transplanted to the field 14 days after inoculation. The cotyledons of inoculated cv. Surpass 400 showed characteristic large, necrotic lesions with pycnidia, while the cotyledons of cv. Westar had collapsed and contained a mass of pycnidia. Blackleg disease severity in the crown region of the stem was assessed at 2 weeks before harvest. Fifty-four percent of the cv. Surpass 400 transplanted inoculated plants subsequently developed susceptible symptoms of crown cankers on stems. These symptoms were deep, girdling, brown lesions on the plant crowns with some pycnidia. One hundred percent of cv. Westar plants were infected and dead at this stage. This confirmed the ability of these field isolates to overcome the single dominant resistance gene present in cv. Surpass 400. To our knowledge, this is the first report of breakdown of a single dominant B. rapa subsp. sylvestris gene based resistance to blackleg in oilseed rape in the field.
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Shaw, B. D., KerChung Kuo, and H. C. Hoch. "Germination and Appressorium Development of Phyllosticta ampelicida Pycnidiospores." Mycologia 90, no. 2 (March 1998): 258. http://dx.doi.org/10.2307/3761301.
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Brennan, R. M., B. D. L. Fitt, J. Colhoun, and G. S. Taylor. "Factors Affecting the Germination of Septoria nodorum Pycnidiospores." Journal of Phytopathology 117, no. 1 (September 1986): 49–53. http://dx.doi.org/10.1111/j.1439-0434.1986.tb04359.x.
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Morant, M. A. "A Synthetic Medium for Mass Production of Pycnidiospores ofStenocarpellaSpecies." Plant Disease 77, no. 4 (1993): 424. http://dx.doi.org/10.1094/pd-77-0424.
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Brennan, R. M., B. D. L. Fitt, G. S. Taylor, and J. Colhoun. "Dispersal of Septoria nodorum Pycnidiospores by Simulated Rain and Wind." Journal of Phytopathology 112, no. 4 (April 1985): 291–97. http://dx.doi.org/10.1111/j.1439-0434.1985.tb00806.x.
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del Río Mendoza, L. E., A. Nepal, J. M. Bjerke, M. Boyles, and T. Peeper. "Identification of Leptosphaeria maculans Pathogenicity Group 4 Causing Blackleg on Winter Canola in Oklahoma." Plant Disease 95, no. 5 (May 2011): 614. http://dx.doi.org/10.1094/pdis-11-10-0789.
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Winter canola (Brassica napus L.) is a relatively new crop to Oklahoma and other southern U.S. states where it is considered a desirable rotation crop with wheat. In 2009, approximately 15,000 ha of winter canola were harvested in Oklahoma (3); that area is expected to almost double in 2010. Blackleg, a potentially devastating canola disease, was detected in Oklahoma in 2009. Blackleg is caused by Leptosphaeria maculans (Desmaz.) Ces. & de Not (anamorph = Phoma lingam (Tode:Fr.) Desmaz.). In early 2010, leaf samples showing typical symptoms of blackleg were collected from four canola fields near the town of Enid in Garfield County, OK. Small portions of infected tissues were surface disinfested in an aqueous solution of NaOCl (0.5% a.i.) for 1 min, rinsed twice in sterile distilled water, and plated on V8 medium. Seven colonies were isolated and when grown in pure culture, all produced 2 × 4.5 μm guttulate, unicellular, hyaline spores in pycnidia that ranged from 200 to 480 μm in diameter. These morphological characteristics correspond with those of P. lingam (1). To verify the pathogenic nature of the isolates and establish the pathogenicity group (PG) to which they belong, a standard inoculation protocol was followed on a set of three differential cultivars, Quinta, Glacier, and Westar (2). Briefly, for each isolate, tiny puncture wounds were made with sterile needles on the cotyledons of six 10-day-old plants of each differential and a 10-μl aliquot of a pycnidiospore suspension (1 × 107 spores ml–1) was deposited on the wounds. Also, a set of differentials were inoculated with distilled water (mock inoculation). Inoculated plants were incubated overnight in a misting chamber at 21°C in the dark and returned the next day to the greenhouse. Disease severity was recorded 10 days after inoculation using a 0 to 9 scale in which 0 to 2 = resistant, 3 to 6 = intermediate, and 7 to 9 = susceptible. This process was repeated three times. Two of the seven isolates evaluated were highly virulent on all three differentials, an indication they belong to pathogenicity group 4 (2). The other five isolates produced small lesions on Westar (resistant reaction) but failed to develop symptoms on the other two differentials. This phenotypic reaction has been associated with strains of PG-1. Mock-inoculated plants did not develop lesions. To our knowledge, this is the first time blackleg isolates from Oklahoma have been identified to the PG level. While this information will assist breeders in the development of both spring and winter canola lines with resistance to blackleg, additional studies are necessary to determine the relative prevalence and diversity of the various PG in Oklahoma. References: (1) G. H. Boerema. Trans. Br. Mycol. Soc. 67:289, 1976. (2) A. Mengistu et al. Plant Dis. 75:1279, 1991. (3) USDA. National Agricultural Statistics Service. Retrieved from http://www.nass.usda.gov/Statistics_by_State/Ag_Overview/ AgOverview_OK.pdf , September 20, 2010.
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Arseniuk, E., T. Góral, and A. L. Scharen. "Seasonal Patterns of Spore Dispersal of Phaeosphaeria spp. and Stagonospora spp." Plant Disease 82, no. 2 (February 1998): 187–94. http://dx.doi.org/10.1094/pdis.1998.82.2.187.
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The spatial and temporal patterns of discharge and dissemination of airborne spores of Phaeosphaeria spp. and Stagonospora spp. were studied. Both ascospores and pycnidiospores of the pathogens were deposited at various densities on microscope slides used as spore samplers. The maximum deposition of the spores was observed during the period of August to October. A multiple regression analysis was used to determine which weather factors significantly explained the variation measured in the numbers of ascospores that settled on microscope slides. Rainfall, air temperature, and relative air humidity were influential in the release of Phaeosphaeria spp. ascospores into the air. The amount of airborne ascospores was a function of the variables and remained largely under their control. The liberation of ascospores was favored by air temperature above 0°C, rainfall greater than 1 mm, and high relative humidity. The range of atmospheric conditions stimulating air dispersal of ascospores was wider than that for pycnidiospores. Pycnidiospores were sampled only during rainy days. Their release was affected adversely by air temperature below 5°C. Multiple regression models based on weather data were developed and verified for their predictive ability and accuracy by jackknife and cross-validation procedures, as well as by comparisons of observed and predicted mean numbers of deposited ascospores per microscope slide after a substitution of each period data set with a set of data of the other respective time interval. The numbers of airborne ascospores predicted by the regression models were in a good agreement with the observed values. The jackknife and cross-validation techniques allowed use of the limited data sets for both the parameter estimation and validation processes in a development of simulation models. The airborne inoculum appeared to be omnipresent over cereal areas year round, except during periods with freezing temperatures and a snow cover. Such an omnipresence of inoculum of the pathogens poses a danger to crops and could be of importance in the epidemiology of Stagonospora (= Septoria) blotches under the climatic conditions of central Poland.
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Brennan, R. M., B. D. L. Fitt, G. S. Taylor, and J. Colhoun. "Dispersal of Septoria nodorum Pycnidiospores by Simulated Raindrops in Still Air." Journal of Phytopathology 112, no. 4 (April 1985): 281–90. http://dx.doi.org/10.1111/j.1439-0434.1985.tb00805.x.
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Bannon, F. J., and B. M. Cooke. "Studies on dispersal of Septoria tritici pycnidiospores in wheat?clover intercrops." Plant Pathology 47, no. 1 (February 1998): 49–56. http://dx.doi.org/10.1046/j.1365-3059.1998.00200.x.
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Aderiye, B. I., S. A. Laleye, and B. Ojo. "Toxicity of citric and succinic acids for the pycnidiospores ofBotryodiplodia theobromae." Folia Microbiologica 43, no. 2 (March 1998): 147–50. http://dx.doi.org/10.1007/bf02816500.
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Zivkovic, Svetlana, Sasa Stojanovic, Jelica Balaz, and Veljko Gavrilovic. "Characteristics of Phomopsis sp. isolates of plum trees origin." Zbornik Matice srpske za prirodne nauke, no. 113 (2007): 83–91. http://dx.doi.org/10.2298/zmspn0713083z.
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Twelve isolates of Phomopsis sp. were obtained from the branches and the trunk of plums (Prunus domestica L) with decay symptoms in Valjevo, Ljig Koceljeva and Ub vicinity during 2004-2006. Morphological, pathogenic and growing characteristics were studied. Pathogen caused tissue necrosis of branches around the inoculate seats, and wrinkling and watering of plum fruits. All media were suitable for pathogen development, except prune agar. The best growth of isolates was at medium pH 5,5. The optimal temperature for growth and germination of pycnidiospores was 25?C.
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Kuo, KerChung, and H. C. Hoch. "Visualization of the extracellular matrix surrounding pycnidiospores, germlings, and appressoria ofPhyllosticta ampelicida." Mycologia 87, no. 6 (November 1995): 759–71. http://dx.doi.org/10.1080/00275514.1995.12026597.
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Kuo, KerChung, and H. C. Hoch. "Visualization of the Extracellular Matrix Surrounding Pycnidiospores, Germlings, and Appressoria of Phyllosticta ampelicida." Mycologia 87, no. 6 (November 1995): 759. http://dx.doi.org/10.2307/3760852.
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Travadon, R., L. Bousset, S. Saint-Jean, H. Brun, and I. Sache. "Splash dispersal of Leptosphaeria maculans pycnidiospores and the spread of blackleg on oilseed rape." Plant Pathology 56, no. 4 (August 2007): 595–603. http://dx.doi.org/10.1111/j.1365-3059.2007.01572.x.
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Kempenaar, C., P. J. F. M. Horsten, and P. C. Scheepens. "Spore germination and disease development after application of pycnidiospores ofAscochyta caulina toChenopodium album plants." European Journal of Plant Pathology 102, no. 2 (January 1996): 143–53. http://dx.doi.org/10.1007/bf01877101.
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Hong, Sung-Jun, and Sung-Chul Yun. "Effects of Dryness, Moisture Interruption, and Temperature on Germination of Diaporthe citri Pycnidiospores on Yuzu." Research in Plant Disease 24, no. 2 (June 30, 2018): 132–37. http://dx.doi.org/10.5423/rpd.2018.24.2.132.
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Vanniasingham, Vasanthi M., and C. A. Gilligan. "Effects of biotic and abiotic factors on germination of pycnidiospores of Leptosphaeria maculans in vitro." Transactions of the British Mycological Society 90, no. 3 (April 1988): 415–20. http://dx.doi.org/10.1016/s0007-1536(88)80150-5.
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Sosnowski, M. R., E. S. Scott, and M. D. Ramsey. "Temperature, wetness period and inoculum concentration influence infection of canola (Brassica napus) by pycnidiospores ofLeptosphaeria maculans." Australasian Plant Pathology 34, no. 3 (2005): 339. http://dx.doi.org/10.1071/ap05036.
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LI, HUA, NICOLE TAPPER, NEREE DEAN, MARTIN BARBETTI, and KRISHNAPILLAI SIVASITHAMPARAM. "Enhanced Pathogenicity of Leptosphaeria maculans Pycnidiospores from Paired Co-inoculation of Brassica napus Cotyledons with Ascospores." Annals of Botany 97, no. 6 (March 13, 2006): 1151–56. http://dx.doi.org/10.1093/aob/mcl062.
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Ojiambo, P. S., and H. Scherm. "Temporal Progress of Septoria Leaf Spot on Rabbiteye Blueberry (Vaccinium ashei)." Plant Disease 89, no. 10 (October 2005): 1090–96. http://dx.doi.org/10.1094/pd-89-1090.
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Septoria leaf spot, caused by Septoria albopunctata, is an important disease on blueberry in the southeastern United States, yet its epidemiology is largely unknown. Disease severity and dissemination of pycnidiospores were monitored from 2002 to 2004 in a planting of susceptible Premier rabbiteye blueberry to characterize the temporal progress of the disease and determine the effect of inoculum dynamics and selected leaf attributes on disease development. Disease onset was observed between late April and mid-June, followed by a rapid increase in disease severity until mid- to late September; thereafter, disease severity decreased until the end of the season due to abscission of severely infected leaves. A logistic model was fitted to disease severity data using nonlinear regression, and parameter estimates were used to compare the effects of leaf position on the shoot and shoot location in the canopy on disease progress. Based on this model, the highest absolute rate of disease increase and the highest upper asymptote of disease severity were predicted for leaves in intermediate positions on the shoot and for shoots in the lower canopy. Data collected with funnel spore samplers showed that splash-dispersed pycnidiospores of S. albopunctata were available throughout most of the period from April through late October. Final disease severity on individual leaves was more strongly correlated with cumulative spore numbers throughout the entire season (from leaf emergence to the end of the assessment period in November) than with cumulative spore numbers during shorter periods around the time of leaf emergence; this suggests that infection is not limited to young, expanding leaves, but rather that leaves at all developmental stages can become infected by S. albopunctata seasonlong. Disease incidence on leaves of potted trap plants exposed to natural inoculum in the field during rain events in 2003 and 2004 was >70.0% irrespective of leaf developmental stage at the time of exposure. Taken together, the results of this study indicate that inoculum of S. albopunctata is present throughout most of the growing season and that infection can occur season-long on leaves of any age, giving rise to a polycyclic epidemic.
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Wang, L., and P. Vincelli. "Coniothyrium minitans on Apothecia of Sclerotinia trifoliorum." Plant Disease 81, no. 6 (June 1997): 695. http://dx.doi.org/10.1094/pdis.1997.81.6.695d.
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During a study of apothecial dynamics of Sclerotinia trifoliorum at the University of Kentucky Spindletop Farm at Lexington, an apothecium with small black patches on the surface of the hymenium was found. The affected apothecium was incubated in a moist chamber at room temperature. After 3 days, white, cottony mycelium was observed on the surface of the hymenium; pycnidia formed in the mycelium and around the stipe of the apothecium several days later. The apothecium eventually decayed and shrunk. Pycnidia measured 168 to 520 μm (mean 311 μm). Pycnidiospores were dark brown en masse; they were ovoid to ellipsoid, measuring 3.1 to 8.2 μm (mean 6.0 μm) in length and 3.1 to 4.1 μm (mean 3.7 μm) in width, and were faintly verrucose. Fresh sclerotia of S. trifoliorum were produced in vitro and then inoculated with pycnidiospores produced on potato dextrose agar. Inoculated sclerotia were incubated in a moist chamber at room temperature. After 7 to 10 days, inoculated sclerotia shriveled and decayed, pycnidia formed on their surfaces, and the same fungus was isolated. The fungus was identified as Coniothyrium minitans Campbell. Among 58 apothecia examined in the field on 1 November, three were apparently parasitized; pycnidia developed on one of these following a 3-day incubation. Weather conditions during the preceding 2 weeks had been generally humid with above-normal temperatures (daily mean air temperature range and interquartile range were 4.0 to 20.0 and 8.9 to 16.1°C, respectively), which may have favored activity of the mycoparasite. C. minitans was reported by Campbell (1) in California on sclerotia formed in cultures of Sclerotinia sclerotiorum. It causes decay of sclerotia of several Sclerotinia spp., some Botrytis spp., and Sclerotium cepivorum in soil. Consequently, it may have considerable biological control potential. It has been recorded in 29 countries and on all continents except South America (2). The fungus previously has been isolated from only sclerotia or, in a few instances, directly from soil. This is the first report on C. minitans parasitic on apothecia collected from the field. References: (1) W. A. Campbell. Mycologia 39:190, 1947. (2) C. Sandys-Winsch et al. Mycol. Res. 97:1175, 1993.
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Hur, Kil-Hyun, and Seur-Kee Park. "Sporulation and Dissemination of Pycnidiospores of Diaporthe citri in Yuzu Tree (Citrus junos Sieb) in Jeonnam Area." Research in Plant Disease 11, no. 1 (June 1, 2005): 16–20. http://dx.doi.org/10.5423/rpd.2005.11.1.016.
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GOTT, KATHLEEN A., R. B. MAUDE, and T. H. THOMAS. "Fungitoxicity of plant growth regulators (PGRs) and PGR/fungicide mixtures in soak treatments to Septoria apiicola pycnidiospores." Plant Pathology 38, no. 1 (March 1989): 21–25. http://dx.doi.org/10.1111/j.1365-3059.1989.tb01423.x.
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Mims, C. W., and R. L. Doudrick. "Ultrastructure of spermatia and spermatium ontogeny in the rust fungus Cronartium quercuum f.sp. fusiforme." Canadian Journal of Botany 74, no. 7 (July 1, 1996): 1050–57. http://dx.doi.org/10.1139/b96-129.
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Spermogonia of Cronartium quercuum f.sp. fusiforme developed just beneath the bark on galled regions of infected pine seedlings. Spermogonia consist of flattened, spreading, island-like masses of fungal tissue covered with a thin layer of liquid containing large numbers of spermatia. Spermatia arose in an annellophoric fashion from the tips of long, slender sporogenous cells produced in a distinct layer. Each sporogenous cell contained a large prominent nucleus that underwent mitosis as each spermatium initial developed. One of the resulting nuclei moved into the initial while the other remained in the sporogenous cell. Once a spermatium was delimited, it was pushed away from the tip of the sporogenous cell as another spermatium initial developed below it. Once delimited, a spermatium underwent specific morphological changes as it matured. A mature spermatium was subpyriform in shape and surrounded by a thin wall. In addition to a single large nucleus each spermatium contained ribosomes, mitochondria, lipid bodies, strands of endoplasmic reticulum, vacuole-like inclusions, and many small vesicles that packed its base. Keywords: transmission electron microscopy, pycnidia, pycnidiospores, spermogonia.