CONTROL OF STORAGE DECAY OF APPLES WITH SPOROBOLOMYCES-ROSEUS

The biocontrol potential of an antagonist occurring naturally on pome fruit surfaces against postharvest diseases of apple (Malus X domestica) was investigated. Pink yeast, Sporobolomyces roseus (isolate FS-43-238), isolated from pear fruit reduced blue mold (Penicillium expansum) from 100 to 0% and gray mold (Botrytis cinerea) from 78 to 0% on wounded fruit drop-inoculated with suspensions containing 7.9 X 10(6) and 6.3 X 10(5) cfu/ml yeast cells, respectively, and then challenged with the pathogen at 10(4) conidia per milliliter. The reduction in the percentage of infected wounds and in average lesion diameter followed a similar pattern and was effected by the antagonist and pathogen concentrations. On wounded apples dipped in the pathogen or antagonist-pathogen suspensions and stored for 3 mo at 1 C, the incidence of rots was reduced from 33 to 0% for P. expansum and from 92 to 4% for B. cinerea at yeast concentrations of 7.9 and 5.3 X 10(6) cfu/ml, respectively. In spray application, where S. roseus was mixed with both pathogens (each at 10(4) conidia per milliliter), less than 1% of fruit developed lesions in the antagonist-pathogen treatment, compared to 15% in the control and 9% in the thiabendazole treatment, after 6 mo in storage at 1 C. Wounds wee readily colonized by S. roseus, and the populations increased from 4.3 to 6.1 log cfu/ml in drop-application experiments after 48 hr at 18 C and from 4.1 to 6.4 log cfu/ ml in spray-application experiments after 3 mo at 1 C. In addition to its effectiveness at relatively low concentrations, S. roseus shows promise for commercial development because it is ubiquitous in nature, occurs commonly on fruits, and does not grow at 36 C.