Academic literature on the topic 'Cercospora zonata'

The temporal and spatial dynamics of Cercospora leaf spot on susceptible and resistant lines of faba bean grown in or at defined distances from soil with residues infested by Cercospora zonata were examined in South Australia in 2005 and 2006. The disease was first observed on susceptible seedlings 49 days after sowing (DAS) in soil that had been sown with faba bean every 3 years since 1997 (positive soil zone for C. zonata) but was delayed by 1 week in adjacent soil (0 to 16 m away) with no history of cultivation of faba bean (negative soil zone). The incidence of diseased seedlings from 49 to 63 DAS showed a gradient from 4 to 16 m from the infested soil and was significantly greater for susceptible plants grown in the positive versus negative soil zones in field trials conducted in 2005 and 2006 (92 versus 30% in 2005, χ21 = 32.2, P < 0.001; 98 versus 55% in 2006, χ21 = 12.1, P < 0.001). The incidence of Cercospora leaf spot on the resistant line 1322/2 was significantly less (χ26 = 171.7; P < 0.001) than on the susceptible line ‘Farah’ at that time in both years, with fewer than 5% of the seedlings showing the disease. However, a gradient was shown at 70 to 84 DAS, where disease incidence was significantly greater on line 1322/2 in the positive soil zone than on plants in the negative soil zone in both years (62 and 18%, respectively, with χ21 = 27.9, P < 0.001 in the 2005 trial; and 47 and 6%, respectively, with χ21 = 33.3, P < 0.001 in the 2006 trial). At peak disease severity on Farah, Cercospora leaf spot mean leaf area diseased (%LAD) was severe (85 ± 4.3%) on leaves of the three nodes closest to the soil surface, and much less severe (1 ± 0.6%) in the upper canopy. Defoliation combined with %LAD was used to describe the loss of photosynthetic leaf area (%LPLA) in both cultivars, on both soil zones, in each year. Nonlinear regression analyses using a logistic model described disease development over time on susceptible plants grown in infested soil (e.g., for +12-m blocks within infested soil, y = 2.66 + 46.08/[1 + exp(−0.23 × [X − 40.92])] in 2005 and y = 0.49 + 5.02/[1 + exp(−0.14 × [X − 28.30])] in 2006, where X = DAS and y = %LPLA, with both regressions significant at P < 0.001), whereas an exponential model (e.g., for −12-m blocks from infested soil, y = 0.23 + 0.77 × 1.04X in 2005 and y = 0.44 + 0.56 × 1.04X in 2006, both at P < 0.001) best described disease gradients with increasing distance from the inoculum source. Paired t tests of %LPLA at 77 and 98 DAS showed significant differences in disease severity in the positive versus negative soil zones and a steep gradient in %LPLA from 0 to 4 m from the inoculum source. The role of infested faba bean residue in survival of C. zonata over time was also examined using a pot-bioassay and in situ field assay. When residues were removed from the soil surface or depleted rapidly by animal grazing, the amount of C. zonata inoculum in the soil was significantly less (P < 0.001) than for soil with residue remaining on the soil surface. C. zonata survived in soil and remained infective for at least 30 months after harvest of an infected faba bean crop.

In the spring of 1996, diseased plants of Trigonella coerulea were noted in an experimental area at Kazanlak, Bulgaria. The primary symptoms were leaf spots 8 to 2 mm in diameter, light brown then becoming gray and slightly zonate, and surrounded by a diffuse chlorotic margin. When single lesions occur the disease normally develops as a typical leaf spot. However, the development of more than one spot is followed rapidly by yellowing and withering of entire leaflets. Stem lesions usually begin at the point of leaf attachment, extend both directions about 15 to 20 mm, and often encircle the stems. Isolations on potato dextrose agar (PDA) yielded a slow-growing, gray fungus. Conidia from the isolated fungus when inoculated at 3.104 spores per ml on potted T. coerulea seedlings and kept in a moisture chamber for 48 h caused foliar spots in 5 to 8 days and sporulating structures similar to those seen in field observations. Simultaneous inoculation of T. foenum-graecum (fenugreek) plants produced similar symptoms, but the percentage of successfully inoculated leaves (3.6%) was lower than in T. coerulea (27.6%). Conidiophores of the fungus are dark, arising in clusters, unbranched, septate (1 to 3), and have small conidial scars. Conidia are hyaline, straight, multicelled (1 to 17), tapering at the base, and measured 30 to 212 × 4 to 6 μm. The pathogen was identified as Cercospora traversiana Sacc. and this is the first report of its occurrence in Bulgaria.

To assess the prevalence and severity of sorghum diseases in western Kenya, a 2-year survey was conducted (July 1995 and 1996), in 91 and 109 farmers' fields, respectively. Fields were generally <0.5 ha and production environment ranged from warm-humid to warm-semi-arid. Fourteen foliar and six panicle diseases were observed, with limited variation in disease prevalence and severity between the 2 years. The most common foliar diseases observed were (in decreasing order of prevalence) oval leaf spot (Ramulispora sorghicola), rust (Puccinia purpurea), ladder leaf spot (Cercospora fusimaculans), zonate leaf spot (Gloeocercospora sorghi), gray leaf spot (Cercospora sorghi), leaf blight (Exserohilum turcicum), and anthracnose (Colletotrichum sublineolum); with prevalence ranging from 95 to 97% of fields for oval leaf spot, and 44 to 65% of fields for anthracnose. Head smut (Sporisorium reilianum), was observed in 73 to 75% of fields, covered kernel smut (S. sorghi) 42 to 43% of fields, and loose smut (S. cruenta) 14 to 24% of fields. Head smut incidence was >25% in 3% of fields surveyed. Grain yield reduction from smut diseases alone was estimated to be 5%. Out of eight probability distribution functions compared, the double Gaussian model best described the frequency of disease severity levels for most diseases. Based on the best-fitting model, the proportion of fields with disease severity level thought to cause yield loss (severity rating >5 on a 1 to 9 scale, where 1 = no disease) was calculated as 26.6% for oval leaf spot, 15.3% for rust, 14.8% for anthracnose, 4.8% for ladder leaf spot, and 1.5% for leaf blight. The production environment influenced the prevalence of disease severity. Severe anthracnose, leaf blight, and ladder leaf spot were confined to fields in the humid LM1 and LM2 agro-ecological zones, rust was ubiquitous, and severe gray leaf spot was more prevalent in the dryer LM4 zone.

A survey was conducted in 2014 to determine the prevalence of fungal diseases on sorghum across different agroecological zones in Tanzania and Uganda. In Tanzania, 37 sorghum fields were sampled in Dodoma and Singida Provinces, representing the central drier areas, and in Simiyu, Shinyanga, Mwanza, and Mara Provinces, representing the lake-zone region. In Uganda, 134 fields were sampled across four agroecological zones of Teso, Western, Northern, and West Nile. Farmers were purposively selected, and at least 30 plants per field along two diagonal transects were visually assessed for disease. Ten and 14 diseases were identified in Tanzania and Uganda, respectively. Among the major diseases identified, those more prevalent in Tanzania than in Uganda were leaf blight caused by Setosphaeria turcica (P = 0.0031) and rust caused by Puccinia purpurea (P < 0.0001). Major diseases more prevalent in Uganda than in Tanzania were anthracnose caused by Colletotrichum sublineola (P = 0.0207) and zonate leaf spot caused by Gloeocercospora sorghi (P = 0.0312). We report for the first time the occurrence of ladder leaf spot caused by Cercospora fusimaculans in Uganda and confirm its occurrence in Tanzania. This is the first comprehensive sorghum disease survey report in over 15 years in both countries.

Ultrastructural alterations in epidermal and mesophyll cells and variations in endogenous zeatin riboside (ZR) concentrations were studied in leaves of Hedera helix, Pelargonium zonale, Pru-nus avium, and Rubus ulmifolius infected by Colletotrichum trichellum, Puccinia pelargonii-zonalis, Cercospora circumscissa, and Phragmidium violaceum, respectively. Infected tissues showed a marked increase in vesicles, myelin-like structures, and electron-dense bodies associated with plasma membranes. The main changes to the chloroplast included thylakoid swelling and disruption of the chloroplast envelope. The ZR content of the green islands was always higher than that of the yellow, senescent parts of the same leaves; the highest levels of ZR were observed in the green areas of infected Prunus avium (462.2 pmol g-1 fresh weight [FW]) and Rubus ulmifolius (441.6 pmol g-1 FW), followed by Pelargonium zonale (263.8 pmol g-1 FW) and Hedera helix (219.8 pmol g-1 FW); the yellow zones of the same leaves had lower ZR contents (78.3, 73.9, 73.6, and 18.1 pmol g-1 FW, respectively). The green islands had almost the same ZR content as the controls (green healthy leaves). These results suggest a relationship between ultrastructural alterations and ZR content of these plant species (blackberry, cherry, English ivy, geranium) in reacting to this type of biotic stress and could confirm the role of cytokinins as senescence-delaying hormones.

Se realizó un análisis del achiote Bixa orellana L. como posible alternativa productiva de desarrollo industrial para el departamento del Meta, mediante la recopilación de información de investigaciones sobre esta planta y las experiencias de países como Perú, en los cuales el achiote es uno de los principales productos de exportación. En primer lugar, se generó un marco de referencia centrado en las características fenológicas, requerimientos climatológicos, aspectos agronómicos, de procesamiento y mercados. Esta especie amazónica, se encuentra distribuida en 19 de los 32 departamentos del país, se adapta a suelos químicamente pobres, siempre que presente buenas condiciones físicas (texturas franco arenosas) para el desarrollo radicular, las mejores producciones se logran en altitudes menores a los 800 msnm, es un buen demandante de agua y para evitar problemas patológicos a nivel de las semillas, es importante no tener humedades relativas por encima del 80%. Los principales insectos que causan daño son los chupadores como los chinches (Leptoglossus zonatus), los masticadores como las hormigas (Atta mexicana) y barrenadores de la capsula (Milgithea melanoleuca). Entre los principales patógenos que pueden afectar el cultivo están los hongos Oidium bixaea, Collectotrichum gloeosporioides, Crinipellis perniciosa, Fusarium sp. y Cercospora bixae. La producción de cápsulas por hectárea puede variar dependiendo de la zona y sobre todo del manejo del cultivo, encontrando producciones por hectárea mayores a 5 toneladas y menores de 1 tonelada. En conclusión, la creciente demanda mundial de colorantes naturales, la oferta agroclimatológica del departamento del Meta, la cercanía a la capital como principal mercado para la comercialización de este producto en la cadena productiva de plantas aromáticas y medicinales son oportunidades para el desarrollo económico de esta planta.

Abstract A description is provided for Cercospora zonata. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Vicia species including V. faba, V. narbonensis and P. saliva; also Lens esculenta.DISEASE: Leaf spot. GEOGRAPHICAL DISTRIBUTION: Africa: Ethiopia, Libya, Malawi, Mauritius, Zambia; Asia: India, Iran, Nepal; Europe: British Isles, Cyprus, Malta, Rumania; North America: USA. TRANSMISSION: Presumably by air-borne, or rain-splash dispersed, conidia.

A total of 115 Chinese accessions from six provinces with diverse climate, topography and farming systems were screened for reaction to three fungal diseases Ascochyta blight, (Acochyta fabae), chocolate spot (Botrytis fabae) and Cercospora leaf spot (Cercospora zonata). Not all the accessions were included in three disease screening trials due to a limited number of seeds for some accessions. However, a majority of lines were included in all three disease screening trials and the remaining at least for two trials. In the Ascochyta blight screening trial 96 Chinese accessions were evaluated and while the majority of lines were susceptible a number of lines including 1688, 1689 (Gansu), 1729 (Guangxi), 1750 (Jiangsu), 1998 and 1999 (Qinghai) were identified with a significant degree of heterogeneity including a low proportion of resistant plants. Single plants with a disease score of either 1 (resistant) or 3 (moderately resistant) could be used for the development and selection of resistant lines. The effect of three concentrations of B. fabae inoculum was observed on four cultivars 1714-1, Nura, Fiesta and Icarus. The disease development was proportional to the amount of inoculum irrespective of cultivars but the relative responses of cultivars varied between treatments, consistent with partial resistance. The lines 1714-1 and Icarus were most resistant at all treatments. A medium dose of inoculum provided the opportunity for cv. Nura to express resistance compared to cv. Fiesta, while at a low and high inoculum concentration, there was no significant difference between the two cultivars. A total of 99 Chinese accessions from six provinces were evaluated for chocolate spot resistance. Germplasm from Qinghai, Guangxi, Jiangsu and Gansu were more resistant as compared to germplasm from Yunnan and Guangdong. Qinghai Province lines 1982, 1983, 1988, 1994, 1998 and 1999 were the least susceptible among all the Chinese lines and could be valuable sources of resistance against the chocolate spot disease. A total of 45 faba bean lines, 22 from six different regions of China, identified in the preliminary screening as having some degree of resistance, 13 regional lines previously reported as resistant to chocolate spot and 10 Australian cultivars were evaluated for chocolate spot resistance. Germplasm from Qinghai, Jiangsu and Yunnan regions were comparatively resistant and particularly accessions 1983 and 1985 from Qinghai province showed a moderately resistant reaction. Accession 1714-1, a selection from Acc 1714 from Gansu, was the most resistant among all lines including Icarus and Farah. None of the other Chinese lines was equivalent to Australian resistant cultivars Icarus and Farah. In Cercospora leaf spot screening trial, a total of 72 Chinese accessions and two local check lines were screened for disease resistance. The only resistant line was the local check, however, three lines 1673, 1727 and 1890 from Gansu, Guangxi and Yunnan, respectively expressed a minor level of resistance and there is potential to develop resistant lines through single plant selection from these heterogeneous accessions. There was significant defoliation due to disease. The genetics of inheritance of resistance to A. fabae (isolate 86/03) was investigated in five faba bean lines. The resistance of cvs. Farah and Ascot was under the control of different genes in the two cultivars. The F₂ populations of the crosses of these two cultivars with susceptible cv. Icarus segregated in different distribution patterns for resistance and susceptibility that indicated a dominant gene controls resistance in Farah while resistance in Ascot is controlled by a recessive gene. The cross 1783/2*Ascot (Acc 1783/2 of Tunisian origin) did not segregate in the F₂ generation, with the exception of a single plant rated 5, indicating resistance in both cultivars is controlled by the same gene(s). Two crosses out of three from 1689/1*Ascot (Acc 1689/1 susceptible and of Chinese origin) segregated in the ratio 1:3 indicating the resistant gene of Ascot is recessive to 1689/1. Seventeen isolates of A. fabae from southern Australia were characterised for a number of characters including pathogenicity on cv. Icarus, growth on medium, growth patterns, pycnidial formation and distribution, size of spores and colour. The isolates were variable in most of the features. Pycnidial formation and growth on media were positively associated with disease severity, but there was no association between the other traits in culture with disease severity. This project has identified variation within Chinese germplasm in response to the fungal diseases Ascochyta blight, chocolate spot and Cercospora leaf spot. Lines with a degree of resistance to Ascochyta blight and Cercospora leaf spot were heterogeneous and screening of larger populations of identified lines and selection of individual resistant plants could lead to the development of new resistant lines. Genetic studies of resistance to Ascochyta blight comparing Ascot and Farah confirmed that there are alternative genes controlling resistance, and resistant Chinese lines might provide additional resistance genes. Identification of chocolate spot resistance in Acc 1714-1 is a significant finding as the majority of previously identified sources of resistance to this disease originated from the Andean region. Further characterization and utilization of these new sources of disease resistance should contribute to a long-term strategy of breeding disease resistant faba bean cultivars.
Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2009