BIOLOGICAL-CONTROL OF BOTRYTIS-CINEREA IN APPLE BY YEASTS FROM VARIOUS HABITATS AND THEIR PUTATIVE MECHANISMS OF ANTAGONISM

Twenty-eight yeasts isolated from habitats other than apple were scree ned for their potential to protect wounds of Golden Delicious apples d uring storage from gray mold caused by Botrytis cinerea. All isolates reduced (P < 0.05) decay severity and 23 reduced decay incidence after 7 days at 22-24 degrees C when applied at 5 x 10(6) CFU per wound 1-2 h earlier than 8 x 10(3) conidia of B. cinerea (P < 0.05). When selec ted isolates were tested at 5 x 10(5) CFU per wound on apples stored f or 30 days at 4 degrees C, Cryptococcus humicola NRRL Y1266, Filobasid ium floriforme NRRL Y7454, and Rhodosporidium toruloides NRRL Y1091, p reviously unreported gray mold antagonists, reduced both incidence and decay severity as well as chlorothalonil and Sporobolomyces roseus FS -43-238, a reported biocontrol agent. Experiments at 22-24 degrees C i ndicated that, with the exception of R. toruloides, protection general ly required yeast inoculation into wounds before conidia. Nine yeasts protected wounds at 5 x 10(6) CFU per wound, whereas only three of nin e were effective at 5 x 10(2) CFU per wound, a density calculated to b e too low to preemptively carpet the wound, even though selected yeast s increased at least one log unit in the first 24 h following inoculat ion into wounds. In vitro utilization of C-14-labeled sucrose by the y easts was greater than that by the conidia after 12-48 h incubation, s upporting nutrient competition as a mechanism of antagonism. Cell-free , dilute sucrose solutions that were preincubated with effective bioco ntrol yeasts for 24 h significantly inhibited conidium germination; ho wever, a solution preincubated with a sucrose-utilizing but less effec tive yeast did not. Results suggest that nutrient competition may have played a significant role in biocontrol, but the contribution of pree mptive physical exclusion and antifungal metabolites to a complex bioc ontrol process cannot be dismissed. (C) 1996 Academic Press, Inc.