Biological control of the grapevine dieback fungus Eutypa lata I: Screening of bacterial antagonists

Antifungal bacterial strains were assayed for antagonistic activity towards the grapevine dieback fungus Eutypa lata in vitro and on grape wood. One h undred and twenty-one of 188 isolates (64%) exhibited antagonistic activity towards E. lata in vitro (> 83% of the tested actinomycetes, Bacillus and Erwinia herbicola strains and 32% of the Pseudomonas strains). On autoclave d grape wood discs, liquid cultures from 24 of 76 selected bacterial strain s (32%) caused at least 50% suppression of mycelial growth over a period of 2 weeks. Among these were two Bacillus subtilis, four E. herbicola, two Se rratia plymuthica and 16 actinomycete isolates. One B. subtilis strain (Bl alpha), two E. herbicola strains (JII/E2 and JII/E4) and one actinomycete ( A123) showed the highest degree of antagonism (70-100% control over a perio d of 4 weeks). In E. herbicola and the actinomycete A123 the cell-free supe rnatant was the active fraction of the applied liquid culture (100% control ); suspended cells showed no or limited effect. Conversely, in B. subtilis the cells were the decisive component (50-70% control). Erwinia herbicola J II/ E2 and B. subtilis Bloc inhibited growth of six different E. lata isola tes on wood significantly. The strong antagonistic effect of the four bacte rial strains was confirmed by the measurement of fungal hydrolase activity (chitinase, protease, cellulase). Activities of fungal hydrolases were high ly correlated with mycelial growth on wood (r > 0.88). In B. subtilis Bloc antagonistic activity and ability to colonize grape wood was further demons trated by cryo-scanning electron microscopy.