Biological Effect of Two Strains of Microorganisms Antagonistic to Botrytis Cinerea Causal Organism of Gray Mold on Strawberry
Trichoderma sp. (strain CI306) and Bacillus amyloliquefaciens (strain GAl) have shown antagonistic effect against Botrytis cinerea. These strains were formulated in an invert emulsion (water - in - oil). Conidia of strain CI306 or endospores of strain GA1 were firstly suspended in water, then introduced into the invert emulsion at the same time of mixing the ingredients. Invert emulsions developed in this study and designated IE. 1 and IE.3 have the following characteristics: i) a high stability, with an emulsification rate of 99 to 100%; ii) a low and constant viscosity of 25 centipoises for IE.1 and 35 centipoises for 1E.3; iii) a high water content ranging from 20.4 to 34.6% for IE.1 and from 16.8 to 18.6% for IE.3 after 24 hours of application at 25°C and 66 to 81% atmospheric relative humidity respectively; and iv) an excellent survival of tested microorganisms after introduction into invert emulsions especially in IE.1. Moreover, the ingredients of invert emulsion IE.1 especially the oil (Radia 7108) and the emulsifier (Radiasurf 7155) are used as food additives in Belgium. Biological efficacy of the two strains against B. cinerea was assessed using foliar discs of strawberry. Lesion development due to Botrytis was significantly reduced on treated foliar discs with these strains when were applied in formulated form at low levels of relative humidity in comparison with the non-formulated form. Trichoderma-IE.1 formulation, for example, reduced the lesion development at 45% compared to non-formulated form (MDBLCC=0.80 and 0.44 in formulated and non-formulated forms respectively). In addition, the number of Botrytis conidiophores appeared on infected surfaces was greatly inhibited on treated foliar discs with strains compared with the non-treated control. Trichoderma - IE.1 formulation, for example, decreased the number of Botrytis conidiophores to nil compared to non-treated control (MRDBC=0/+++ or 0/++ according to relative humidity level).