Biocontrol of Botrytis cinerea with Trichoderma spp is generally believed to result from direct interaction of the biocontrol agent with the pathogen or from a Trichoderma-induced change in environmental conditions that affects B cinerea development In this work we provide arguments for the participation of induced plant defence in T harzianum T39 control of B cinerea In tomato, lettuce, pepper, bean and tobacco, T harzianum T39 application at sites spatially separated from the B cinerea inoculation resulted in a 25–100%percnt; reduction of grey mould symptoms, caused by a delay or suppression of spreading lesion formation Given the spatial separation of both micro-organisms, this effect was attributed to the induction of systemic resistance by T harzianum T39 The observation that in bean the effect of T harzianum T39 was similar to that of the rhizobacterium Pseudomonas aeruginosa KMPCH, a reference strain for the induction of systemic resistance, confirmed this hypothesis Since B cinerea control on tobacco leaves sprayed with T harzianum T39 was similar to the control on leaves from T harzianum T39 soil-treated plants, induction of plant defence might also participate in biocontrol on treated leaves

Induced systemic resistance in Trichoderma harzianum T39 biocontrol of Botrytis cinerea

SUMMARY Rhizosphere-competent fungi of the genus Trichoderma are widely used as biofertilizers and biopesticides in commercial formulates because of the multiple beneficial effects on plant growth and disease resistance. In this work, we demonstrate that genetic variability among wild and cultivated tomato lines affects the outcome of the interaction with two ‘elite’ biocontrol strains of T. atroviride and T. harzianum.The beneficial response, which included enhanced growth and systemic resistance againstBotrytis cinerea,was clearly evident for some,but not all, the tested lines.At least in one case (line M82), treatment with the biocontrol agents had no effect or was even detrimental. Expression studies on defence-related genes suggested that the fungus is able to trigger, in the responsive lines, a long-lasting up-regulation of the salicylic acid pathway in the absence of a pathogen,possibly activating a priming mechanism in the plant. Consequently, infection with B. cinerea on plants pretreated with Trichoderma is followed by enhanced activation of jasmonate-responsive genes, eventually boosting systemic resistance to the pathogen in a plant genotype-dependent manner. Our data indicate that, at least in tomato, the Trichoderma induced systemic resistance mechanism is much more complex than considered so far, and the ability of the plant to benefit from this symbiotic-like interaction can be genetically improved.

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The beneficial effect of Trichoderma spp. on tomato is modulated by the plant genotype

Mechanisms involved in the biological suppression of infection and inoculum potential ofBotrytis cinerea are numerous and variable and the involvement of two or more mechanisms has been demonstrated in several systems Reported combinations include antibiosis with enzyme degradation ofB cinerea cell walls; competition for nutrients followed by interference with pathogenicity enzymes of the pathogen or with induced resistance; and alteration of plant surface wettability combined with antibiosis Since germinatingB cinerea conidia are dependent on the presence of nutrients, competition for nutrients is regarded as important in systems where biocontrol is involved Conidial viability and germination capacity are also potentially affected by the presence of antibiotics produced by biocontrol agents and present in the phyllosphere Slower in action are mechanisms involving induced resistance in the host plant and production of hydrolytic enzymes that degradeB cinerea cell walls The latter has been demonstrated much more convincinglyin vitro than in the phyllosphere Biocontrol in established lesions and reduction of sporulation on necrotic plant tissues is a means to minimize the pathogen inoculum

Mechanisms involved in the biological control of Botrytis cinerea incited diseases

Botrytis cinerea Persoon: Fries (known as “grey mould fungus”) causes serious preand post-harvest diseases in at least 235 plant species (Jarvis, 1977), including a range of agronomically important crops, such as grapevine, tomato, strawberry, cucumber, bulb flowers and ornamental plants. Graminaceous monocots are generally considered as poor hosts for grey mould. Disease control frequently relies on chemicals, although efforts to develop biological control strategies are increasingly successful (e.g. Kohl et al., 1995; Elad, 1996) and biocontrol agents are marketed. The name of the asexual stage or anamorph, Botrytis cinerea, is preferred to the name of the teleomorph, Botryotinia fuckeliana (de Bary) Whetzel (XIth International Botrytis Symposium, 1996, Wageningen, The Netherlands). The teleomorph has rarely been detected in the field during the last century, but molecular population studies recently provided clear evidence that sexual reproduction occurs more frequently than previously anticipated (Giraud et al., 1997). The pathogen is a typical necrotroph, inducing host cell death resulting in serious damage to plant tissues, culminating in rot of the plant or the harvested product. There are extensive descriptions of microscopic and biochemical studies on infection mechanisms (reviewed by Staples and Mayer, 1995). Comprehensive insight in the infection process, however, is hampered by the fact that various groups used different fungal strains and different host species for their studies.

Infection Strategies of Botrytis cinerea and Related Necrotrophic Pathogens

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.

https://apsjournals.apsnet.org/doi/pdfplus/10.1094/PHYTO.1997.87.3.332

Incorporation of Weather Forecasting in Integrated, Biological-Chemical Management of Botrytis cinerea.

The effectiveness ofTrichoderma harzianum in suppression of tomato stem rot caused byBotrytis cinerea was examined on tomato stem pieces and on whole plants. Ten days after simultanous inoculation withB. cinerea andT. harzianum, the incidence of infected stem pieces was reduced by 62–84%, the severity of infection by 68–71% and the intensity of sporulation by 87%. Seventeen days after inoculation of wounds on whole plants, the incidence of stem rot was reduced by 50 and 33% at 15 and 26 °C, respectively, and the incidence of rot at leaf scar sites on the main stem was reduced by 60 and 50%, respectively. Simultanous inoculation and pre-inoculation withT. harzianum gave good control ofB. cinerea (50 and 90% disease reduction, 10 days after inoculation). The rate of rotting was not reduced by the biocontrol agent once infection was established. However, sporulation byB. cinerea was specifically reduced on these rotting stem pieces. Temperature had a greater effect than vapour pressure deficit (VPD) on the efficacy of biocontrol. Suppression ofB. cinerea incidence byT. harzianum on stem pieces was significant at 10 °C and higher temperatures up to 26 °C. Control of infection was significantly lower at a VPD of 1.3 kPa (60% reduction), than at VPD<1.06 kPa (90–100% control). Reductions in the severity of stem rotting and the sporulation intensity of grey mould were generally not affected by VPD in the range 0.59–1.06 kPa. Survival ofT. harzianum on stems was affected by both temperature and VPD and was greatest at 10 °C at a low VPD and at 26 ° C at a high VPD.

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Papers

Biological control of Botrytis cinerea on tomato stem wounds with Trichoderma harzianum