Littérature scientifique sur le sujet « Trichoderma harzianum T39 »

Gray mold (Botrytis cinerea) is an important disease of tomato (Solanum lycopersicum). This study examined defense-related gene expression involved in the resistance to B. cinerea that is induced in tomato plants by benzothiadiazole and Trichoderma harzianum T39 soil drench. In whole plants, transcriptional changes related to salicylic acid and ethylene were induced by the application of a 0.01% benzothiadiazole solution, whereas changes related to jasmonic acid were induced by the application of a 0.4% T39 suspension. On detached leaves, soil treatment by T39 led to enhanced resistance to B. cinerea infection that was proportional to the concentration of the T39 suspension. By 5 days after pathogen inoculation, the plants that had received the 0.04% T39 drench exhibited 62% less severe disease than the untreated plants. The 0.4% T39 drench led to an 84% reduction in disease severity. Observations of B. cinerea infection in leaves harvested from plants grown in the treated soils revealed that drenching with a T39 suspension induces systemic resistance against B. cinerea and primes salicylic acid- and ethylene-related gene expression in a manner proportional to the concentration of the biocontrol agent. Benzothiadiazole treatment induced resistance to gray mold independently of salicylic acid and led to strong priming of two genes known to be involved in defense against B. cinerea, Pti5 and PI2.

Enhancement of plant defense through the application of resistance inducers seems a promising alternative to chemical fungicides for controlling crop diseases but the efficacy can be affected by abiotic factors in the field. Plants respond to abiotic stresses with hormonal signals that may interfere with the mechanisms of induced systemic resistance (ISR) to pathogens. In this study, we exposed grapevines to heat, drought, or both to investigate the effects of abiotic stresses on grapevine resistance induced by Trichoderma harzianum T39 (T39) to downy mildew. Whereas the efficacy of T39-induced resistance was not affected by exposure to heat or drought, it was significantly reduced by combined abiotic stresses. Decrease of leaf water potential and upregulation of heat-stress markers confirmed that plants reacted to abiotic stresses. Basal expression of defense-related genes and their upregulation during T39-induced resistance were attenuated by abiotic stresses, in agreement with the reduced efficacy of T39. The evidence reported here suggests that exposure of crops to abiotic stress should be carefully considered to optimize the use of resistance inducers, especially in view of future global climate changes. Expression analysis of ISR marker genes could be helpful to identify when plants are responding to abiotic stresses, in order to optimize treatments with resistance inducers in field.

A strategy for integrated biological and chemical control of Botrytis cinerea in nonheated greenhouse vegetables was developed. The biocontrol agent used was a commercial preparation developed from an isolate of Trichoderma harzianum, T39 (Trichodex). Decisions concerning whether to spray the biocontrol agent or a fungicide were made based on a weather-based disease warning system. The integrated strategy (BOTMAN [short for Botrytis manager]) was implemented as follows: when slow or no disease progress was expected, no spraying was needed; when an outbreak of epidemics was expected, use of a chemical fungicide was recommended; in all other cases, application of T. harzianum T39 was recommended. Future weather information (a 4-day weather forecast provided by the Israel Weather Forecast Service) was more useful for disease warnings than immediate past weather. The integrated strategy was compared with weekly applications of fungicide in 11 experiments conducted over 3 years in greenhouse-grown tomato and cucumber. Disease reduction in the integrated strategy (63.9 ± 3.0%) did not differ significantly (P < 0.05) from the fungicide-only treatment (70.1 ± 3.6%). The number of fungicide sprays in the integrated strategy ranged from 2 to 7 (mean 4.2) compared to 7 to 13 (mean 10.5) in the fungicide treatment. The integrated strategy averaged 5.9 sprays of T. harzianum T39. For the integrated strategy, one treatment omitted use of T. harzianum T39 to estimate the contribution of this agent to disease control. Disease reduction in that treatment (49.1 ± 4.8%) was significantly (P < 0.05) inferior to the combined chemical and biological strategy, indicating that the T. harzianum T39 sprays had a measurable effect on disease control.

Biocontrol agents can control pathogens by reenforcing systemic plant resistance through systemic acquired resistance (SAR) or induced systemic resistance (ISR). Trichoderma spp. can activate the plant immune system through ISR, priming molecular mechanisms of defense against pathogens. Entomopathogenic fungi (EPF) can infect a wide range of arthropod pests and play an important role in reducing pests’ population. Here, we investigated the mechanisms by which EPF control plant diseases. We tested two well studied EPF, Metarhizium brunneum isolate Mb7 and Beauveria bassiana as the commercial product Velifer, for their ability to induce systemic immunity and disease resistance against several fungal and bacterial phytopathogens, and their ability to promote plant growth. We compared the activity of these EPF to an established biocontrol agent, Trichoderma harzianum T39, a known inducer of systemic plant immunity and broad disease resistance. The three fungal agents were effective against several fungal and bacterial plant pathogens and arthropod pests. Our results indicate that EPF induce systemic plant immunity and disease resistance by activating the plant host defense machinery, as evidenced by increases in reactive oxygen species production and defense gene expression, and that EPF promote plant growth. EPF should be considered as control means for Tuta absoluta. We demonstrate that, with some exceptions, biocontrol in tomato can be equally potent by the tested EPF and T. harzianum T39, against both insect pests and plant pathogens. Taken together, our findings suggest that EPF may find use in broad-spectrum pest and disease management and as plant growth promoting agents.

Grapevine (Vitis vinifera L.) is one of the major fruit crops worldwide and varieties used for table grape or wine production are susceptible to several pathogens. Downy mildew caused by the oomycete Plasmopara viticola is an important grapevine disease that threatens leaves and young berries and, to avoid yield losses, control of the disease is based on the application of chemical fungicides. Genetic analysis of pathogen’s population structure in field indicated that germination of oospores, causing primary infections occurs for a long period, alongside secondary infection cycles, and few P. viticola genotypes are dominating during an epidemic. Alternative methods for controlling downy mildew have been studied, including the use of microbial biocontrol agents. Application of Trichoderma harzianum T39 (T39) has been shown to reduce downy mildew symptoms in grapevine by activating the plant mediated resistance mechanism. Induced resistance offers the prospect of broad-spectrum disease control using the plant’s own defenses and represents a promising low-impact tool for controlling crop diseases. However, the potential of induced resistance has yet to be fully realized, mainly due to its only partial control of the disease and its inconsistency under field conditions. Induced resistance is a plant-mediated mechanism, and its expression under field conditions is likely to be influenced by a number of factors, including environment, genotype and crop nutrition. Concerns about the impact of abiotic stresses on agriculture have been raised in the last decade, especially in light of the predicted effects of climate changes. High temperatures and drought associated with heat waves may occur with increased frequency as a result of climate change, threatening crop production and influencing interactions with both pathogenic and beneficial microorganisms. Aim of this project was to study the downy mildew disease form the pathogen and from the host plant point of views, in order to maximize the control of the disease with low-impact natural methods. To evaluate the efficacy of the T39-induced resistance under non-optimal conditions and to study pathogen’s infection dynamics of different P. viticola isolates we evaluated i) the T39-induced resistance in plants exposed to heat and drought stresses, ii) the T39-induced resistance in different grapevine cultivars and iii) the possible selection mechanisms of different P. viticola isolates. The work was structured in three distinct sections where, at first, we could assess that co-inoculated P. viticola isolates competed for the infection of the host, although being equally infective when singularly inoculated. Competition was not related to the origin of the isolate and we hypothesized that competitive selection was modulated by differences in the 2 secretion of effector molecules, which explained the establishment of dominant genotypes over an epidemic season. In other two sections we demonstrated that T39-induced resistance was found to be reduced in plants exposed to the combination of heat and drought stresses, moreover, variable levels of efficacy were observed in different grapevine cultivars. Modulation of the marker genes in the T39-induced resistance was partially attenuated in plants under heat and drought stress. The molecular mechanisms activated in response to the resistance inducer were different and complex among cultivars, indicating that specific receptors are probably involved in the regulation of the plant response. The work presented in this thesis provides a deeper understanding to current knowledge of the biology of this grapevine pathogen and of the mechanisms of the induced resistance. Different P. viticola genotypes reacted differently when co-existing on a unique substrate, indicating that plant-pathogen interactions seem to be more complex than mere colonization of the plant tissue. The environmental conditions and the plant genotype are key factors affecting the T39-induced resistance. Therefore, prevention of predominant genotypes during an epidemic season and consideration of the variable responsiveness of the plant to the resistance inducer applied are important strategies for the improvement of biocontrol methods against downy mildew of grapevine