Microbial population dynamics on Golden Delicious apples from bud to harvest and effect of fungicide applications

The microbial population dynamics on apples cv. Golden Delicious were analy sed every 15 days between bud and harvest in a fully replicated experiment in northern Spain in 1994 and 1995. The total microbial populations varied with developmental stage, and with prevailing climatic conditions. The pred ominant mycroflora were the filamentous fungi Cladosporium and Alternaria s pp. and white and pink yeasts. Other genera isolated included mainly specie s of Epicoccum, Fusarium and Acremonium. However, the most important post-h arvest pathogens Penicillium expansum and Botrytis cinerea were seldom isol ated from ripening apples. Maximum total filamentous fungal populations occ urred after fruit set and during early ripening [2 x 10(4) cfu (colony-form ing units) g(-1) approximately] while those of bacteria were maximum at bud stage (3.5 x 10(5) and 3.0 x 10(4) cfu g(-1) in 1994 and 1995 respectively ). White yeasts were more numerous than pink yeasts. Endophytic infection o f apple buds by Alternaria spp., responsible for core rot, was found in alm ost all bud tissue. By contrast, Cladosporium spp. were initially isolated later from 12.5-50% of tissue samples during blooming and fruit set. The im pact of a four-spray fungicide regime during apple development significantl y decreased the total filamentous fungal populations in both years, and tha t of Cladosporium spp. in 1994. However, bacterial populations were often h igher on apples from fungicide-treated plots. Fungicide sprays decreased po pulations of Cladosporium, Alternaria and white yeasts for a maximum of up to 15-30 days after application. Fungicide application had little effect on endophytic infection of apples by Alternaria spp. between bud and harvest.