Biological control of foliar pathogens by means of Trichoderma harzianum and potential modes of action

There is increasing interest in the use of biological control agents (BCAs) and plant resistance stimulants to suppress botrytis bunch rot in grapes, caused by Botrytis cinerea. Numerous different filamentous fungi, bacteria and yeasts have been selected as potential BCAs for control of grey mould based upon demonstrated antagonism towards B. cinerea. Biological suppression of the pathogen arises via competition for nutrients and space, the production of inhibitory metabolites and/or parasitism. Preformed and inducible grapevine defence mechanisms also contribute to disease suppression by preventing or delaying pathogenic infection. Furthermore, various biotic and abiotic agents can stimulate grapevine defence mechanisms and so elevate resistance to B. cinerea infection. Biosuppression of B. cinerea in vineyards, using BCAs and resistance stimulants, has been inconsistent when compared with that observed in controlled glasshouse or laboratory conditions. This may be attributable, in part, to the innate variability of the field environment. Research to improve field efficacy has focused on formulation improvement, the use of BCA mixtures and combinational approaches involving BCAs and plant resistance stimulants with complementary modes of action.

Biosuppression of Botrytis cinerea in grapes

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Antibiosis, mycoparasitism, and colonization success for endophytic Trichoderma isolates with biological control potential in Theobroma cacao

Biocontrol of Botrytis-incited diseases has been extensively investigated over the last 50 years. This chapter reviews the literature on microbial control of Botrytis species with a particular emphasis on the importance of gaining a full understanding of the biological and ecological attributes of a biological control agent as a means to developing appropriate strategies for its effective use under commercial cropping conditions. The key microbial genera that have shown greatest potential for Botrytis disease control include the filamentous fungi Trichoderma, Gliocladium and Ulocladium, the bacteria Bacillus and Pseudomonas and the yeasts Pichia and Candida. Commercial success has been achieved in glasshouse and post-harvest environments where stable environmental conditions allow greater control over the application of the biocontrol agent and expression of its biological activity. Considerable progress has also been made in achieving more consistent biocontrol under field conditions, particularly in vineyards, but the complexities of the plant, microbe, environment interaction and its inherent variability will always pose a severe challenge to achieving effective and consistent field biocontrol. In recognising this, current research aims to define more clearly the biological and economic barriers that limit biocontrol efficacy and future research should focus on the strategic integration of biocontrol systems with other cultural, chemical and genetic methods to provide more sustainable disease control.

Microbial control of Botrytis spp.

Two biocontrol preparations were tested for their ability to control Sphaerotheca fusca and Botrytis cinerea on greenhouse cucumber. Trichoderma harzianum T39 (TRICHODEX) spray reduced powdery mildew severity by up to 97% but its efficacy declined to 18–55% control as the epidemic progressed. Unlike on young leaves, on older leaves the control of powdery mildew by T. harzianum T39 was poor. Ampelomyces quisqualis (AQ10) was very effective against powdery mildew, achieving up to 98% of control. Its effectiveness declined with the progress of the epidemic but unlike the other biocontrol agent it retained significant control capability on older leaves. Two aliphatic petroleum distillate oil products improved the efficacy of both biocontrol agents. The co-application of T. harzianum T39 and A. quisqualis AQ10 was tested on cucumber plants infected with powdery mildew followed by fruit gray mold infection. It resulted in no improvement of the control of powdery mildew, and in an improvement of gray mold control, the latter probably because of the use of additive oil (ADDQ) along with the second biocontrol preparation. There was no significant interference between the biocontrol agents in the co-application treatment as compared with the application of each agent alone; the level of population of T. harzianum T39 remained similar and the parasitism of S. fusca by A. quisqualis was not nullified. The application of T. harzianum T39 to soil instead of spraying it resulted in 75–90% lower powdery mildew coverage on the leaves. It was concluded that the mode of action of T. harzianum T39 in powdery mildew control is induced resistance, not mycoparasitism or antibiotic action.

Management of powdery mildew and gray mold of cucumber by Trichoderma harzianum T39 and Ampelomyces quisqualis AQ10

The efficacy of a formulation of Trichoderma harzianum T39 for control of grey mould (Botrytis cinerea) on grapevine was examined in 133 experiments conducted under diverse commercial conditions. The experiments were carried out between 1988 and 1994 in 19 countries and on 34 varieties. The average disease incidence in the untreated plots of all experiments was 42 2.3% (mean standard error). In general, the reduction of disease achieved by T. harzianum application was lower than that obtained by chemical fungicides: 36.3 2.7% disease reduction in biocontrol treatments and 52.3 2.6% in the exclusively chemical treatments. Control efficacy declined when the interval between application and assessment dates increased to 5 weeks. The experiments also included treatments in which T. harzianum was integrated with chemical fungicides, the two being applied alternately, and a reduced chemical treatment in which only chemicals were applied, and only at the times when chemicals were applied in the integrated treatm...

A. Cohen

Papers

Control of Grapevine Grey Mould with Trichoderma harzianum T39