Zur besiedlung von apfelblättern, -blüten und -zweigen mit epiphytischen mikroorganismen

Abstract

Summary Results of three years-lasting studies on the epiphytic microflora of apple trees (flowers, leaves and twigs) in connection with an artificial contamination by the causal agent of fire blight, Erwinia amylovora ( Burrill ) Winslow et al., are presented. By colony traits and pigmentation more than 160 groups of bacteria as well as some yeasts and filamentous fungi could be distinguished. Agreeing with the studies of Stadelmann (1976) and others in Switzerland the qualitative and quantitative alterations of the resident microflora observed mainly depended on the season. Thus, in second half of the season the concentration of chromogenic bacteria increased. In a dry year (1986) the bacteria occurring on the twigs remarkably decreased during summer and showed a typical population maximum in autumn. In the third year of monitoring (1987) only a short-term reduction of the population of epiphytic bacteria could be proved. Obviously, the differences in the colonization density between the years under test were dependent on the specific meteorological conditions of each season (years resp. periods with few or high precipitations). In all test years the epiphytic fungi showed population maxima in spring time and in autumn. The Erwinia amylovora population artificially applicated survived mostly 2, seldom 3 months on the surface of the plant organs treated. The results are discussed concerning the possible suppression of the pathogen by resident microorganisms.