Suppression of Botrytis cinerea by antagonists in living, moribund and dead grapevine tissue

[摘要] ENGLISH ABSTRACT:Several attempts have been made to reduce Botrytis cinerea grey mould in vineyards andin storage by means of biological control. However, the so called silver bullet approach inutilising a single antagonist, has its limitations when compared with synthetic fungicides.Often the antagonist has a limited spectrum of activity and the duration of its effectiveness isless than that provided by synthetic fungicides. Furthermore, antagonists are more likely tobe effective in preventing initial infection rather than resumption of latent infection.Therefore, due to the various infection sites in grape bunches utilised by B. cinerea and thefact that the pathogen can remain latent in the grapevine tissue, it may be possible to obtaineffective control of the pathogen by integrating fungicides and different biological controlagents each aimed at a different site in grape bunches, protecting the bunch at the variousphenological stages of growth and under different micro climatic conditions. In this study thepotential of three fungal antagonists (Glioc/adium roseum, Uloc/adium atrum andTrichoderma harzianum) and one yeast (Trichosporon pullulans) to colonise different sites ingrape bunches, and to reduce B. cinerea infection, was investigated in commercial vineyards.As the biological control agents were used in an integrated system, the effect of variousfungicides frequently applied to local vineyards on the organisms was also investigated.Fungicide trials were conducted taking into account two possible scenarios. Firstly, thepossible effect of fungicides applied to the vineyard after an application of the biologicalcontrol agent or shortly before the application of the biocontrol agent. This entailed exposingthe biocontrol agents to relatively low concentrations of the active ingredient of thefungicides, similar to the residue levels to which these organisms would be exposed underfield conditions. Secondly, the possibility of applying the organisms and the fungicides at thesame time by making use of spray tank mixtures. This meant exposing the biocontrol agentsto relatively high doses of the active ingredient of the various fungicides. Mycelial growthand germination tests were performed on agar in Petri dishes to determine the effect offungicides. It was assumed that if the fungicide effectively inhibits the antagonist at 2.5 !-lga.Uml, the fungicide and antagonist can not be used in an integrated programme. Based onthis criterium, T harzianum can not be applied to vineyards with penconazole,mancozeb/metalaxyl, pyrifenox or mancozeb. In addition T harzianum can not be applied astank mixtures with iprodione. However, T harzianum can be used in conjunction withpyrimethanil, folpan, iprodione, fosetyl-Al and copperhydroxide, provided the chemicals andthe antagonist are applied alternately. Gliocladium roseum can not be applied in a tankmixture with pyrimethanil and penconazole, but can be used on grapevine in conjunction withpenconazole, pyrifenox, pyrimethanil, iprodione and fosetyl-Al. Ulocladium atrum can notbe applied with pyrimethanil and iprodione. Ulocladium atrum can be applied in conjunctionwith penconazole, pyrifenox, pyrimethanil, iprodione, fosetyl-Al and mancozeb. The funguscan be applied in a tank mixture with penconazole and pyrifenox.The antagonists were applied as conidial suspensions to bunches at various phenologicalstages in commercial vineyards planted with the wine grape cultivar Chardonnay in theStellenbosch region, or the table grape cultivar Dauphine planted in Paarl region. Buncheswere collected 2 wk after application, surface-sterilised and used for determining antagonistcolonisation and B. cinerea infection at specific sites in the bunches. In Chardonnay, theantagonists colonised the different sites, but colonisation during the three seasons wasinconsistent and sporadic. Ulocladium atrum and G. roseum colonised floral debris to adegree in the 1996 season. However, in the 1997 season these two antagonists did notdevelop from floral debris. Trichoderma harzianum colonised floral debris extensively in the1996 season. In the 1997 season colonisation by T harzianum dropped, but unlike G. roseumand U atrum, T harzianum occurred at a low level in flowers. Ulocladium atrum onlycolonised bunches during bloom, and was not found in bunches monitored from pea-sizestage to véraison. This finding suggests that the saprophyte colonised moribund and deadflower parts occurring in bunches during full bloom to the pre-pea size stage, and is not likelyto be found in living tissue. Gliocladium roseum colonised grape berries and pedicels tosome degree and T harzianum colonised these grape parts extensively. Botrytis cinereaoccurred inconsistently and at low frequencies in the different sites in bunches. It wastherefore not possible to comment on the effectivity of the various antagonists in the threeseasons during which the trials were performed. However, it was noted that, during the peasizestage in 1996, when high levels of B. cinerea were recorded, T harzianum controlledthese infections in the pedicels more effectively than any other treatment.

[发布机构] Stellenbosch University