TOXICITY OF GLUCOSINOLATE DEGRADATION PRODUCTS FROM BRASSICA-NAPUS SEED MEAL TOWARD APHANOMYCES-EUTEICHES F-SP PISI

Brassica tissues are potentially useful in the control of Aphanomyces root rot of peas (Pisum sativum), but identity of the responsible comp ounds and specific impacts of those compounds on the pathogen's infect ion potential remain uncertain. Brassica napus seed meals and water ex tracts from these meals were used to determine the effect of glucosino late hydrolysis products on Aphanomyces euteiches f. sp, pisi. B. napu s meal ('Dwarf Essex') containing glucosinolates and intact myrosinase , the enzyme responsible for glucosinolate hydrolysis, completely inhi bited infection by A, euteiches f. sp. pisi oospores. Water extracts f rom this meal, likewise, severely inhibited infection by oospores, as well as mycelial growth. Extracts from autoclaved 'Dwarf Essex' meal, in which myrosinase was denatured, and a low glucosinolate B. napus va riety ('Stonewall') produced little disease reduction and had less imp act on mycelial growth. Gas chromatographic analysis of Brassica tissu es and water extracts confirmed that glucosinolates remained in autocl aved 'Dwarf Essex' meal and that 'Stonewall' meal contained low glucos inelate concentrations. 5-Vinyloxazolidine-2-thione was identified by mass spectrometry as a dominant glucosinolate hydrolysis product in aq ueous extracts of the inhibitory meal. Bioassays conducted with aqueou s solutions of this compound reduced mycelial growth, but not to the e xtent of those from intact 'Dwarf Essex' meal. Water-soluble compounds produced from the hydrolysis of glucosinolates in B. napus tissues re duced A. euteiches oospore infection and inhibited mycelial growth, th us, demonstrating potential utility of Brassica species in the control of A. euteiches.