In vitro antagonism of Botrytis cinerea by phylloplane yeasts

The influence of inoculum and nutrient concentrations on the in vitro antagonism of Botrytis cinerea by phylloplane yeasts was investigated with detached leaf disk and conidial germination assays. Rhodosporidium toruloides Y-1091 significantly reduced lesion development after 96 h on geranium leaf disks when co-inoculated at 1 x 10(6) or 1 x 10(7) yeast cells/mL with B. cinerea conidia at 1 x 10(4) or 1 x 10(5) conidia/mL. No effect on lesion development was observed when yeast and fungus were co-inoculated at a 1:1 ratio. Biocontrol activity of R. toruloides was greatest in 20 mM glucose and 20-fold dilute yeast nitrogen base. Twenty-five phylloplane yeasts exhibited a wide range of biocontrol activity when screened for antagonism of B. cinerea on geranium leaf disks (1 x 10(6) yeast cells/mL, 1 x 10(5) conidia/mL). Lesion development was significantly reduced by yeasts initially identified as poor antagonists when inoculated at higher concentrations (5 x 10(6) or 1 x 10(7) yeast cells/mL) with B. cinerea. Both poor and good antagonists significantly reduced in vitro germination of B. cinerea conidia. The presence of B. cinerea conidia had a greater effect on the growth of two poor antagonists compared with two good antagonists on leaf disks. These data suggest that many phylloplane yeasts will antagonize B. cinerea under conditions of low nutrient availability and with high antagonist to pathogen ratios.