Biological Control of the Grapevine Dieback Fungus Eutypa lata I: Screening of Bacterial Antagonists

Antifungal bacterial strains were assayed for antag- onistic activity towards the grapevine dieback fungus Eutypa lata in vitro and on grape wood. One hundred 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 autoclaved grape wood discs, liquid cultures from 24 of 76 selected bacterial strains (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 Serratia plymuthica and 16 actinomycete isolates. One B. subtilis strain (B1a), two E. herbicola strains (JII/E2 and JII/E4) and one actinomycete (A123) showed the highest degree of antagonism (70±100% control over a period of 4 weeks). In E. herbicola and the actino- mycete A123 the cell-free supernatant was the active fraction of the applied liquid culture (100% control); suspended cells showed no or limited e€ect. Con- versely, in B. subtilis the cells were the decisive component (50±70% control). Erwinia herbicola JII/ E2 and B. subtilis B1a inhibited growth of six di€erent E. lata isolates on wood signi®cantly. The strong antagonistic e€ect of the four bacterial strains was con®rmed by the measurement of fungal hydro- lase activity (chitinase, protease, cellulase). Activities of fungal hydrolases were highly correlated with mycelial growth on wood (r > 0.88). In B. subtilis B1a antagonistic activity and ability to colonize grape wood was further demonstrated by cryo-scanning electron microscopy.