INHIBITION OF APHANOMYCES-EUTEICHES F-SP PISI BY VOLATILES PRODUCED BY HYDROLYSIS OF BRASSICA-NAPUS SEED MEAL

Seed meal from Brassica napus (rapeseed) produced volatile fungitoxic compounds potentially of value in the control of Aphanomyces root rot of pea. Hyphal growth, germination of encysted zoospores, and oospore survival and inoculum potential, were determined in the presence of vo latiles produced from B. napus seed meal. Volatile compounds from B. n apus meal completely suppressed mycelial growth and germination of enc ysted zoospores on agar. In growth chamber bioassays, pea (Pisum sativ um) seed inoculated with zoospore suspensions and incubated 24 h in th e presence of volatiles from rapeseed meal had 50% lower root rot dise ase severity than in the absence of meal. Volatile compounds passing t hrough soil also significantly decreased survival and inoculum potenti al of oospores. Gas chromatographic analysis of rape seed tissues and the volatile compounds evolved from tissues showed that substrate gluc osinolates were hydrolyzed enzymatically to produce mainly isothiocyan ates. Non-autoclaved rapeseed meal produced significantly higher level s of volatile compounds than did autoclaved meal. Also, volatile compo unds produced from autoclaved meal were dominated by nitriles, whereas isothiocyanates were more common volatile products from non-autoclave d meal. Our results indicate that B. napus allelochemicals responsible for toxic effects toward A. euteiches f. sp. pisi are enzymatic hydro lysis products of glucosinolates.