Letteratura scientifica selezionata sul tema "Mycoherbicide"

A water-corn oil (unrefined) emulsion has promise as a carrier for application of the mycoherbicide,Colletotrichum truncatum.We investigated this formulation (normal emulsion; oil in water) for influences on conidia germination, appressoria formation, and mycoherbicidal activity ofC. truncatum.Germination of conidia after application to hemp sesbania leaves was increased from 30% in water alone to 92% in the water-corn oil emulsion (water:oil, 1:1, by vol). The emulsion did not affect appressoria formation. of the several other oils tested, safflower seed oil enhanced in vitro germination but did not enhance germination and mycoherbicide activity when the conidia-emulsion formulation was applied to hemp sesbania leaves. Application ofC. truncatumconidia in the unrefined corn oil emulsion to hemp sesbania seedlings resulted in 89 to 97% control of the weed after a 24 to 72 h dew delay. The emulsion enhanced mycoherbicide efficacy by stimulating conidia germination by protecting the conidia during a dew-free period, hence, increasing weed infection when a dew occurred.

Periodic surveys were conducted to seek potential indigenous fungal agents for development as mycoherbicides against horse purslane, a major weed of agricultural fields in India. Pathogenic fungal species were isolated and identified from naturally infected horse purslane. The biocontrol potential of these pathogens for horse purslane was evaluated by studying their host range and virulence under growth chamber and greenhouse conditions. Three candidates,Alternaria alternata, Fusarium oxysporum, andPhoma herbarum, were identified as potential candidates for biological control of horse purslane. Preliminary host-range tests and pathogenicity studies, conducted using 45 crop and weed plants belonging to 18 families, demonstrated thatP. herbarumprovided effective weed control and was safe to most of the plant species tested. Further mycoherbicidal application ofP. herbarumas plant spray under field condition caused mortality of horse purslane 60 d after application of the inoculums.Phoma herbarumis a good mycoherbicide candidate against horse purslane.

A fungal pathogen, Helminthosporium gramineum Rabehn f.sp. echinochloae (HGE), has been developed as a mycoherbicidal agent for the control of barnyardgrass in China. Under greenhouse conditions, the effect of the pathogen on disease incidence, mortality, and dry weight reduction of barnyardgrass was tested to determine the potential of this mycoherbicide. Field experiments during 2007 and 2008 showed that the conidia of HGE displayed excellent activity on barnyardgrass and good activity on a few other weed species. The HGE treatment increased the rice yield when compared with the untreated control and had no negative impact on the rice plant. In addition, the progression of HGE infection and the alteration of cellular ultrastructure in infected barnyardgrass were observed by using scanning and transmission electron microscopes. After infection, cell membranes of barnyardgrass leaves were found dramatically changed, and the ultrastructure of cells was severely deformed. This study clearly shows the scope of HGE as a potential mycoherbicide for control of barnyardgrass in agricultural cropping systems and has laid the groundwork for further studies on the mode of infection and the nosogenesis of HGE.

Except for a small number of cases in which biocontrol agents were introduced from the site of origin of a weed (classical biocontrol), there have been few cases where a pathogen was virulent enough to perform cost effectively in the field as a mycoherbicide. Mycoherbicides are typically weed species specific, so compatibility with herbicides used to control other weeds is often studied. There can be a synergy between mycoherbicides and herbicides at the field level due to overlapping weed spectra (such synergies are not discussed in depth herein). Two approaches have been used to ascertain whether there is synergy in controlling the target weed: (1) random screening with herbicides; (2) using herbicides as antimetabolites to inhibit specific pathways, enhancing virulence. Glyphosate is the most common herbicide to synergize mycoherbicides, possibly due to its dual function as an inhibitor of biosynthesis of phenylpropanoid phytoalexins by suppressing enolphosphate-shikimate phosphate synthase, or by suppressing callose production (by inhibiting callose synthase) as well as inhibiting other calcium-dependent pathways due to the calcium-chelating properties of glyphosate.

The Stagonospora cirsii mycelium is considered as the infectious basis of a potential mycoherbicide for the control of Canadian thistle and perennial sow thistle. Successful commercialization of mycoherbicides is often constrained by poor drying survival. In this study was shown that the highest viability of mycelium S. cirsii during drying is achieved in the stationary phase of growth. The mycelium in the stationary phase is characterized by maximum level of carbohydrates. We suggest the level of arabitol as a criterion evaluation of the mycelium resistance to drying. Culturing conditions, and especially the fermentation time, allow prediction of polyols and trehalose levels, which are very critical in enhancing the storage life and efficacy of biological control agent.

With increasing intensification of forest management and limited options for control of competing vegetation, there is need for research on alternative vegetation management methods, including biological control. Most forest weeds in Canada are native species with useful as well as detrimental roles, and therefore classical biological control with introduced natural enemies generally cannot be considered. At present, use of native fungal pathogens, or mycoherbicides, is one of the most promising approaches, and recent advancements in agriculture indicate that effective, site-specific controls using mycoherbicides are possible. Mycoherbicide use in forestry appears attractive because of the likelihood of fewer off-target effects than present vegetation management methods and because it could provide either selective controls for specific weeds or broad spectrum controls.Vegetation management in forestry has some unique aspects which will make the development of biological controls different from that in agriculture. There are many indigenous plant pathogens that are potential mycoherbicides, but their efficacy will need to be enhanced by adjuvants, stress treatments, and integration with other vegetation control practices. Currently, at three Canadian institutions and several other locations worldwide, there are research programs on biological control of forest vegetation.

Two experiments were conducted in which mycelial fragments of the plantpathogenic fungus Sclerotinia sclerotiorum were applied with an organic food source to Cirsium arvense shoots with and without prior wounding In the first experiment more shoots developed disease when the fungus was applied to crush wounds on stems (100 of stems diseased) than when applied to the wound of decapitated stems (38) or to the uppermost leaf axil of decapitated stems (13) In the second experiment reduction in the autumnal shoot dry mass of C arvense due to the mycoherbicide (broadcast in early December at 60 kg/ha) was greater when the shoots were wounded with a spade before applying the mycoherbicide (49 reduction) than when not wounded (26) These results imply a greater susceptibility of wounded C arvense tissues to S sclerotiorum that could be exploited to enhance the efficacy of this fungus as a mycoherbicide

The anthropic interference in aquatic ecosystems favors the disordered colonization of T. domingensis, damaging the production of hydroelectric power and river traffic. Because of this, studies report the efficacy of fungal mycoherbicides, with control rates reaching as high as 90%. Thus, the objective of this study was to evaluate the potential of C. typhae as a mycoherbicide in bio control of T. domingensis, at in vitro and greenhouse conditions. 107 samples of symptomatic T. domingensis leaves were collected in flooded areas of rivers in Brazil, with identification and isolation of the collected fungal species. The concentration of inoculum was determined to evaluate the incidence and severity of the disease, the influence of temperature on mycelial growth and conidia germination, the effect of temperature and leaf wetness period on T. domingensis infection by C. typhae and the host range test in vitro. The growth of the colonies of C. typhae was higher at 25 to 30 ºC. There was no interference of the photoperiod on germination of the spores, but the highest percentage of germination was occurred at 20 ºC. The influence of environmental conditions on infection of inoculated leaves of T. dominguensis revealed that at 15 ºC and the period of leaf wetness of 48 hours the highest incidence of the disease was observed, as well as the severity for the same period of leaf wetness. The specificity test showed that C. typhae is specifically pathogenic to T. domingensis. This the first report of the occurrence of this pathogen in aquatic macrophytes of this species and in T. domingensis, a potential mycoherbicide for the control of this aquatic weed.

A foliar pathogen identified as a member of the genus Alternaria was isolated from blighted Sphenoclea zeylanica (gooseweed) collected in 1991 from a rice field near Los Banos, Laguna, Philippines. Inoculum density, dew period, and plant height are factors influencing biocontrol of S. zeylanica with this indigenous pathogen. Significantly higher percent reductions in plant height and dry weight were obtained and all plants were killed at higher inoculum concentrations with 8 h of dew. The number, germination, and virulence of conidia were significantly affected by production techniques, temperature, light condition, and incubation period. Exposure to continuous near-ultraviolet (NUV) light at 28$ sp circ$C stimulated sporulation on agar media and on solid substrates. Overall, the best production technique was the use of sorghum seeds using an equal quantity of sorghum seeds and water (w/v) incubated for four weeks. Another conidia production method using the sporulation medium (S-medium) technique was evaluated with the addition of 20 g L$ sp{-1}$ of calcium carbonate (CaCO$ sb3)$ and 2 ml of sterile distilled water. Primary 1/2 PDA at 18$ sp circ$C in the dark produced the most virulent conidia. This technique produced conidia relatively rapid, but was labour intensive. Host range studies using 49 plant species in 40 genera representing 20 families, selected by using a modified centrifugal phylogenetic and variety strategy indicated that only S. zeylanica was susceptible in the absence and presence of supplemental dew. On the basis of morphological and cultural characteristics, pathogenicity on the host, host specificity, and the absence of a previous record of this fungal pathogen on S. zeylanica, the binomial A. alternata f. sp. sphenocleae is proposed.

L’objectif de cette thèse était le développement d’un mycoherbicide efficace contenant les propagules stables de Plectosporium alismatis, un mycoherbicide potentiel de riz. Le champignon produit des conidies (109 L-1) et des chlamydospores (108 L-1) dans les erlens. Le nitrate est essentiel pour la production de chlamydospores qui ont une survie élevée (6. 6% germination après 4 mois) comparée aux conidies. Des agrégats hétérogènes (contenant les clilamydospores) ont été aussi observés en milieu liquide contenant du nitrate. Ces agrégats pouffaient augmenter la résistance de P. Aljymatis contre les stresses environnementaux. La production d’agrégats homogènes sphériques (les pellets) est nécessaire pour améliorer la reproductibilité. Un milieu « Aggregate Production Medium (APM) » a été développé dans lequel des pellets (~2. 8 x 105 L-1), des conidies (~6. 5 x 109 L-1) et des chlamydospores (~9. 6 x 108 L-1) ont été produits. Après la dessiccation et l’exposition aux UV, le nombre maximal de propagules libres (~104 conidies et ~2 x 102 chlamydospores) n’a pas infecté la feuille alors qu’un seul pellet était suffisant pour causer la nécrose. Nous avons donc conclu que ces pellets étaient plus pathogènes car probablement plus résistants aux UV et à la dessiccation que les conidies. Les études de survie ont montré que la formulation diatomite contenant des conidies libres, des chlamydospores libres et des pellets, stockée à 4°C, survivait après 9 mois de conservation (12% de germination) et restait pathogène. En conclusion, P. Alismatis peut produire des pellets en milieu APM, et la formulation diatomite contenant ces pellets pourrait répondre aux qualités exigées d’un mycoherbicide efficace
The objective of this thesis was to develop an efficient mycoherbicide based on the stable propagules produced by Plectosporium alismatis, a potential mycoherbicide in rice crops. The fungus produced conidia (109 L-1) and chlamydospores (108 L-1) in shake-flasks. Nitrate was required for production of chlamydospores which had a ligher shelf-life (6. 6% germination after 4 months) compared to conidia. The presence of aggregates (containing chlamydospores) ws also observed in nitrate-based medium. These aggregates may increase P. Alismatis resistance against environmental constraints. To overcome the lack of culture reproducibility due to aggregates’ heterogeneous nature, an alternative, the production of homogeneous spherical aggregates (i. E. , pellets) was developed. In a new medium “Aggregate Production Medium (APM)” in which up to 2. 8 x l05 pellets L-1, 6. 5 x l09 conidia L-1 and 9. 6 x 108 chlamydospores L-1 were produced. When maximal number of free propagules (~104 conidia and ~2 x 102 chlamydospores) was not able to infect leaf when dried and exposed to U, only a single pellet was required to induce disease in the same conditions. We conclude that pellets were far more pathogenic and tolerant to desiccation and UV compared to conidia. In shelf-life experiments, diatomite formulation containing free conidia, free chlamydospores and pellets, stored at 4°C survived for a long period (12% germination after 9 months) and remained pathogenic. In conclusion, P. Alismatis can produce pellets in APM, and diatomite formulations based on these pellet-containing cultures could satisfy the requirements for an efficient mycoherbicide

Amaranthus retroflexus L. (redroot pigweed) is a major weed of many crops in North America including corn, soybean, and potato. It can be readily controlled by chemical and cultural methods. However, some populations of A. retroflexus have developed resistance against the application of triazine herbicides. Biololical control could be an alternative method to control this weed species. In 1990, a Macrophoma sp. causing foliar lesions was isolated from redroot pigweed and the potential of this plant pathogenic fungus as a mycoherbicide was evaluated. Large numbers of infective propagules were produced in solid substrate fermentation with chickpeas. When inoculated with 10$ sp8$ or 10$ sp9$ conidia m$ sp{-2}$, plants at the cotyledon to 2-leaf stage showed the most severe damage. Disease developed over a wide range of dew period durations (6 hr to 24 hr) and temperature regimes (14 C to 26 C), and the most rapid and destructive disease development occurred following a 24-hr dew period at 18 C. In controlled environment studies, this Macrophoma sp. was pathogenic to the genus Amaranthus and the closely related genus Celosia.

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Acacia cyclops, an invasive weed in South Africa, was initially imported to stabilize the sand dunes in the southern Cape. The spread of A. cyclops is a major threat to the fragile biodiversity of the strandveld and limestone fynbos vegetation. Acacia cyclops dieback has been observed for some time, although the causative agent, Pseudolagarobasidium acaciicola, has only recently been described. This fungus is nominated for development as a mycoherbicide to control A. cyclops. Although current biological and mechanical control efforts are proving to be partially effective, A. cyclops is still causing major damage to natural ecosystems. The introduction of a mycoherbicide would increase the cost effectiveness of controlling this weed in the long term. The majority of the literature that was reviewed supports the use of mycoherbicides as biocontrol agents, especially when taking into account the decrease in acceptance and availability of chemical control agents. Considering that the Pseudolagarobasidium genus consists of saprobes, opportunistic facultative pathogens and endophytes, P. acaciicola is predicted to have similar biological characteristics. The species is also highly likely to be indigenous, although with a wider distribution range than previously envisaged. Strict precautions should still however be taken to ensure that non-target species will not be threatened. This study consists of a unique risk assessment comprising different sections. A field survey was performed to record disease incidence among indigenous woody plant species around 100 diseased A. cyclops trees. Subsequently, DNA extractions were made from the roots of the diseased indigenous plants and A. cyclops trees to verify the presence of P. acaciicola. Of the 2432 indigenous woody plants observed, 22 (0.9%) were dead or dying, while P. acaciicola was detected in 10 of these (0.4%), representing six species. Pseudolagarobasidium acaciicola was detected in 47% of the A. cyclops trees. Although P. acaciicola could be a weak pathogen in a broad range of indigenous plant species, the extremely low disease incidence is an indication of a low level of risk associated with using P. acaciicola as a mycoherbicide. Additionally, pathogenicity trials on indigenous plant species were conducted to give an indication of host susceptibility. A total of 30 indigenous plant species were wound inoculated at two field sites, and potted plants representing 17 indigenous plant species were wound and soil inoculated in a nursery. The optimum growth temperature for P. acaciicola was determined in order to understand it’s seasonal and landscape preference. Mortality was recorded in five of nine indigenous Fabaceae species, while a single plant each of four other non-Fabaceae species died after inoculation. No plants outside the Fabaceae family died in the field. Only A. cyclops seedlings died following soil inoculation. Longitudinal sections of stem inoculated plants revealed no systemic infection in Fabaceae species that survived inoculation. Infection in susceptible Fabaceae species was generally more extensive than infection in susceptible non-Fabaceae species. The optimum growth rate for P. acaciicola was determined at 35°C, indicating an adaptation to summer conditions. Indigenous Fabaceae species do display greater susceptibility than species from other families, indicating some level of specificity, although susceptible species can not be phylogenetically circumscribed. Aside from being a facultative pathogen on A. cyclops, results from this study suggest that P. acaciicola is primarily a saprophyte and an occasional opportunistic pathogen on some indigenous Fabaceae, possibly only being a weak opportunistic pathogen on some non-Fabaceae species. However, the risk of not effectively managing A. cyclops populations in these threatened vegetation types outweighs the risk associated with using P. acaciicola as a mycoherbicide. Therefore the use of P. acaciicola as a mycoherbicide on A. cyclops would be recommended, provided that sufficient monitoring of treated sites is implemented that primarily focus on the indigenous Fabaceae species. The effective control of A. cyclops could be achieved when P. acaciicola is used to compliment current mechanical, biological and chemical control methods in an integrated management strategy.
AFRIKAANSE OPSOMMING: Acacia cyclops, ook bekend as rooikrans, is ‘n indringerplant in Suid-Afrika wat oorspronklik vanaf Australië ingevoer is om die sandduine in die Kaap te stabiliseer. Die verspreiding van rooikrans bedreig die sensitiewe biodiversiteit van die strandveld en kalksteen fynbos. Rooikrans terugsterwing is al vir ‘n geruime tyd opvallend in die grootste deel van die plant se verspreiding in Suid-Afrika, alhoewel die veroorsakende organisme, Pseudolagarobasidium acaciicola, eers onlangs beskryf is. Hierdie swam is as ‘n geskikte kandidaat vir die ontwikkeling van ‘n biologiese onkruiddoder om rooikrans te beheer, genomineer. Alhoewel die huidige biologiese- en meganiese beheer metodes vir rooikrans gedeeltelik suksesvol is, hou dié indringer steeds ‘n ernstige bedreiging vir die natuurlike ekosisteme in. Die gebruik van ‘n swam-gebaseerde onkruiddoder sal die beheer van rooikrans oor die langtermyn meer koste-effektief maak. Die oorgrote meerderheid van die literatuur wat hersien is, ondersteun die gebruik van swam-gebaseerde onkruiddoders as biologiese beheermiddels, veral as die afname in aanvaarbaarheid en beskikbaarheid van chemiese beheermiddels in ag geneem word. Aangesien die Pseudolagarobasidium genus uit saprofiete, opportunistiese fakultatiewe patogene en endofiete bestaan, word daar voorspel dat P. acaciicola ‘n soortgelyke biologiese karakter sal hê. Dit is hoogs waarskynlik dat hierdie swamspesie inheems is, alhoewel die verspreiding wyer mag wees as wat oorspronklik voorspel is. Streng maatreëls moet egter steeds in plek wees om te verseker dat nie-teiken plantspesies nie bedreig word nie. Hierdie studie bestaan uit ‘n unieke risiko-analise met verkeie onderafdelings. ‘n Veld-opname is uitgevoer om die siekte-voorkoms van die inheemse houtagtige plantspesies rondom ‘n 100 siek rooikrans plante te bepaal. DNA ekstraksies is vervolgens vanuit die wortels van siek inheemse plantspesies en -rooikrans uitgevoer, om uiteindelik die teenwoordigheid van P. acaciicola binne die hout te kon bevestig. Uit ‘n totaal van 2432 inheemse houtagtige plante wat aangeteken is, was 22 (0.9%) siek of dood, terwyl die teenwoordigheid van P. acaciicola in 10 van hierdie plante (0.4%), wat ses spesies teenwoordig, bevestig is. Die teewoordigheid van P. acaciicola is ook in 47% van die rooikrans bevestig. Alhoewel P. acaciicola moontlik ‘n swak opportunistiese patogeen op ‘n verskeidenheid inheemse plantspesies is, dui die lae verhouding van dooie inheemse plante teenoor gesonde plante in die veld op ‘n lae risiko vir die gebruik van P. acaciicola as ‘n biologiese onkruiddoder. Patogenisiteitstoetse is op inheemse plantspesies uitgevoer om ‘n aanduiding van gasheervatbaarheid te verkry. Wond-inokulasies is op ‘n totaal van 30 inheemse plantspesies by twee veldstudie-areas uitgevoer, terwyl wond- en grond-inokulasies op 17 inheemse spesies potplante in die kweekhuis uitgevoer is. Die optimale temperatuur waarby P. acaciicola groei, is bepaal om die swam se seisoenale- en habitatsvoorkeure beter te verstaan. Plante van vyf uit die nege inheemse Fabaceae spesies het doodgegaan, terwyl ‘n enkele plant van vier nie-Fabaceae spesies doodgegaan het. Alle plante buite die Fabaceae familie het oorleef in die veld na inokulasie. Slegs rooikranssaailinge het na grond inokulasie doodgegaan. Lengtedeursnee van die stam en wortels van elke geïnokuleerde plant het bevestig dat daar geen sistemiese infeksie in Fabaceae spesies wat inokulasie oorleef het, plaasgevind het nie. Infeksies in vatbare Fabaceae spesies was oor die algemeen meer ernstig as infeksies in vatbare nie-Fabaceae spesies. Die optimale groei van P. acaciicola het by 35°C plaasgevind, wat aandui op ‘n voorkeur vir somerstoestande. Inheemse Fabaceae spesies het meer vatbaar as vatbare plantspesies van ander families voorgekom. Hierdie verskynsel dui op ‘n sekere vlak van spesifisiteit, alhoewel daar geen duidelike filogenetiese grense vir vatbare spesies bepaal kon word nie. Behalwe vir die feit dat P. acaciicola ‘n fakultatiewe patogeen op rooikrans is, stel resultate van hierdie studie voor dat hierdie swam hoofsaaklik ‘n saprofiet is wat soms ook ‘n opportunisties patogeen op sekere inheemse Fabaceae is en moontlik slegs ‘n swak opportunistiese patogeen op plantspesies buite die Fabaceae familie is. Die swak en oneffektiewe bestuur van rooikrans in hierdie bedreigde plantegroeitipes hou egter ‘n groter bedreiging in as die gebruik van P. acaciicola as ‘n biologiese onkruiddoder. Pseudolagarobasidium acaciicola word daarom aanbeveel vir die beheer van rooikrans, mits voldoende monitering, wat fokus op inheemse Fabaceae spesies, gepaard gaan met die gebruik van hierdie biologiese onkruiddoder. Rooikrans kan effektief beheer word as P. acaciicola ingespan word om huidige meganiese-, biologiese- en chemiese beheermetodes in ‘n geïntegreerde bestuurstrategie te komplimenteer.

Chenopodium album is considered one of the most important weeds adversely affecting agricultural production due to its highly competitive influence on field crops. Chemical herbicides have increased the efficiency of farming, but recently problems of herbicideresistant weed populations and herbicide residues in soil, water, food products and effects on non-target organisms have increased, consequently, other methods of control of weeds by using specific fungi as herbicides have been suggested. The purpose of this research was to evaluate the biological control of the weed Chenopodium album by the fungus Ascochyta caulina. Some of the factors which control dormancy and germination of Chenopodium album seeds have been investigated to understand better the weed population dynamics. The results showed that seeds from two populations (UK and Libya) differ in their response to factors such as light, chilling, and burying in soil. This could have implications for effective control of the weed in different regions. Two formulations of mycoherbicides (Tween 80 and Gelatine based applications) were tested in the laboratory, and showed promise in reducing growth of the weed, especially the formula of Tween 80. There was extensive shoot fresh and dry weight reduction of inoculated Chenopodium album, as well as reduced root growth. Highest disease severity rates were observed on plants in the first three week of life. A field trial revealed similar results but less disease severity was observed, possibly because of dry weather. However, it was concluded that the fungus Ascochyta caulina is a potentially useful biological control agent but many factors still can be modified in relation to application of the mycoherbicide to increase its efficacy.
Libyan Government

Chenopodium album is considered one of the most important weeds adversely affecting agricultural production due to its highly competitive influence on field crops. Chemical herbicides have increased the efficiency of farming, but recently problems of herbicideresistant weed populations and herbicide residues in soil, water, food products and effects on non-target organisms have increased, consequently, other methods of control of weeds by using specific fungi as herbicides have been suggested. The purpose of this research was to evaluate the biological control of the weed Chenopodium album by the fungus Ascochyta caulina. Some of the factors which control dormancy and germination of Chenopodium album seeds have been investigated to understand better the weed population dynamics. The results showed that seeds from two populations (UK and Libya) differ in their response to factors such as light, chilling, and burying in soil. This could have implications for effective control of the weed in different regions. Two formulations of mycoherbicides (Tween 80 and Gelatine based applications) were tested in the laboratory, and showed promise in reducing growth of the weed, especially the formula of Tween 80. There was extensive shoot fresh and dry weight reduction of inoculated Chenopodium album, as well as reduced root growth. Highest disease severity rates were observed on plants in the first three week of life. A field trial revealed similar results but less disease severity was observed, possibly because of dry weather. However, it was concluded that the fungus Ascochyta caulina is a potentially useful biological control agent but many factors still can be modified in relation to application of the mycoherbicide to increase its efficacy.