Microbial populations associated with buds and young leaves of apple

Abstract

Apple buds and developing leaves and floral parts were assessed for microbial populations by a washing procedure and scanning electron microscopy (SEM) at six stages ranging from dormancy through early tight cluster. Densities of yeasts, filamentous fungi, and bacteria associated with dormant buds were on an order of magnitude of 5 × 105 propagules per gram fresh weight of tissue. Populations tended to peak as buds swelled and to diminish during subsequent developmental stages. External surfaces of buds were colonized extensively. Internal surfaces, particularly those of the peripheral scales, also supported abundant microflora. Evidence from SEM suggested that few microorganisms were associated with floral and leaf primordia. Surface sterilization was not found to be an adequate method to discriminate between external and internal bud microflora. A partial list of microorganisms included fluorescent pseudomonads, Aureobasidium pullulans, and species of Cryptococcus, Sporobolomyces, Rhodotorula, Coniothyrium, Alternaria, Phomopsis, Phoma, Epicoccum, Cladosporium, Acremonium, Fusarium, Stachybotrys, and Sclerotium. These data are pertinent to the microbial ecology of the gemmisphere and to the prospective biological control of foliar pathogens.