Diagnose und Vorkommen bakterieller Naßfäuleerreger in Kartoffellagerbeständen

Abstract

Summary From 1971 to 1976 soft-rotting potato tubers out of 6 districts of the GDR were studied upon the occurrence of bacterial soft rot pathogens. For this purpose bacterial strains were isolated from diseased tissue after enrichment on potato slices and identified (1971–1974) or bacteria isolated out of soft-rotted tissue were directly differentiated on various selective media without pre-enrichment (1975–1976). Tuber samples from 39 different sites were analyzed and more than 2,400 pathogenic bacterial strains were isolated thereout. By both methods in the most years 30–40% of the isolates obtained could be identified as Erwinia carotovora subsp. atroseptica , the causal agent of the black-leg disease of potato. Further E. carotovora subsp. carotovora (3–33%), pectolytic Pseudomonas (2–29%) and Bacillus spp. (9–82%) frequently were found. In contrast, Clostridium strains could be isolated continuously but in a lower frequency (2%). Bacteria from other genera ( Enterobacter, Klebsiella, Alcaligenes and others) occurred only very seldom. The results we obtained show, that out of the 26 possible combinations and 5 single variants of soft rot pathogens, only 18 in the samples studied were realized. In all combinations frequently found, the strains of both subspecies of Erwinia carotovora participated as a component. In the extreme dry year 1976 a considerable alteration of the normal pathogen population was to observe. Under these conditions Bacillus strains occupied 80 per cent of the pectolytic isolates. The importance of the results obtained for successful control of tuber soft rot is discussed, concerning the fact that all soft rot pathogens found can infect the tubers only pathing wounds or lenticells.