Seasonal changes in the apple phylloplane microflora

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Abstract
Microbial populations in the phylloplane of unsprayed ‘Dougherty’ apple trees were estlfllated by maceration-dilution platmg and spore fall methods during two growing seasons in Auckland, New Zealand. The dense microflora within unopened flower buds declined rapidly as the buds opened and the rosette leaves unfurled; some species of the bud microflora disappeared from the phylloplane within a few days, and new species derived from the air spora became established. Newly unfurled shoot leaves did not have a distinctive microflora derived from the vegetative buds; they supported a sparse microflora which included air spora-derived species. Population densities declined during leaf expansion, then increased when leaves attained full size. Mould populations were evenly distributed between the two leaf surfaces, and increased only slightly during summer. In March, Tilletiopsis minor Nyland increased markedly, predominantly on the abaxial surface, and maintained a high population density until leaf fall in mid June. Yeast and bacterial populations were always approximately twice as dense on the abaxial surface as on the adaxial. Yeast densities increased throughout spring and early summer, but decreased during autumn. The proportion of carotenoid-pigmented yeasts (particularly Sporobolomyces roseus Kluyver et van Neil) in the total yeast population also increased during spring and decreased during autumn. S. roseus ballistospore discharge occurred predominantly from the adaxial surface, and was depressed by heavy rain. Bacterial densities increased throughout spring and early summer, decreased in late summer, and then increased again in late autumn.

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