CORRELATION OF FUNGICIDAL ACTIVITY OF BRASSICA SPECIES WITH ALLYL ISOTHIOCYANATE PRODUCTION IN MACERATED LEAF TISSUE

Brassica species were tested for production of volatile fungicidal com pounds from macerated green leaf tissue. Tissue (10, 20, and 40 g) of one cultivar each of six Brassica species was assayed for inhibition o f Fusarium sambacinum. Only cultivars of B. nigra and B. juncea suppre ssed radial growth (>50% inhibition of control). Plant introduction ac cessions (PIs) of B. juncea, B. carinata, B. nigra, and B. napus were screened for suppression of F. sambucinum. Only B, nigra, B. juncea, a nd B. carinata PIs had suppressive activity, but activity varied among PIs within these species. The concentration of allyl isothiocyanate ( AITC), a breakdown product of allyl glucosinolate, in leaf tissue was measured using gas chromatography. AITC was detected in PIs of B. nigr a, B. juncea, and B. carinata. Radial growth of F. sambucinum was nega tively correlated (P < 0.05) with AITC concentrations emitted from Bra ssica leaf tissue. All Brassica PIs with AITC concentrations greater t han 0.10 mg/g of leaf tissue were suppressive to F. sambucinum in radi al growth assays. Growth of five other plant pathogenic fungi was also suppressed by a B. juncea cultivar that contained high concentrations of AITC.