The microbial population dynamics on apples cv. Golden Delicious were analysed 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 predominant mycroflora were the filamentous fungi
Cladosporium and
Alternaria spp. and white and pink yeasts. Other genera isolated included mainly species of
Epicoccum, Fusarium and
Acremonium. However, the most important post-harvest pathogens
Penicillium expansum and
Botrytis cinerea were seldom isolated from ripening apples. Maximum total filamentous fungal populations occurred after fruit set and during early ripening [2 × 10
4cfu (colony-forming units) g
-1 approximately] while those of bacteria were maximum at bud stage (3.5 × 10
5and 3.0 × 10
4 cfu g
-1 in 1994 and 1995 respectively). White yeasts were more numerous than pink yeasts. Endophytic infection of apple buds by
Alternaria spp., responsible for core rot, was found in almost all bud tissue. By contrast,
Cladosporium spp. were initially isolated later from 12.5–50% of tissue samples during blooming and fruit set. The impact of a four-spray fungicide regime during apple development significantly decreased the total filamentous fungal populations in both years, and that of
Cladosporium spp. in 1994. However, bacterial populations were often higher on apples from fungicide-treated plots. Fungicide sprays decreased populations 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.
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