Recovery ofAthelia bombacinafrom Apple Leaf Litter

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Abstract
A semiselective medium (PAB: potato agar amended with 50 .mu.g a.i. / ml of benomyl, 100 .mu.g/ml of chlortetracycline HCl, and 200 .mu.g/ml of streptomycin sulfate) was developed for detection in apple leaf litter of Athelia bombacina, an antagonist to Venturia inaequalis. The efficiency of PAB depended on inoculum level and varied between 14% (close to the detection threshold of 0.14 .times. 103 cfu/ml) and 81%, when expressed as recovery from inoculated, initially sterile leaves. Bacteria were eliminated and filamentous fungi and yeasts were reduced by 99.6 and 82.1%, respectively, on PAB as compared with potato-dextrose agar. The one other isolate of A. bombacina available did not grow on PAB. A mixture of inoculated and uninoculated apple leaves was incubated on the ground in mesh bags from November 1986 to May 1987 and November 1987 to mid-April 1988. Leaves were sampled every 4-8 wk and leaf pieces were incubated on PAB. During 1986-1987, recovery of A. bombacina from inoculated leaf pieces averaged 85% in the last four samples. During 1987-1988, recovery from inoculated leaf pieces averaged 96% in all samples. Recovery (averaged over all samples in both experiments) from uninoculated leaves was 21% less than that from inoculated leaves. The fungus grew 15 cm (1.2% recovery at this distance) across a mat of uninoculated leaves but did not cross a 1-cm gap of turf between adjacent mesh bags. Thus, extensive coverage by initial inoculum and a high survival rate of A. bombacina are probably the most important factors leading to extensive colonization of leaf litter.