Correlation of Fungicidal Activity of<i>Brassica</i>Species with Allyl Isothiocyanate Production in Macerated Leaf Tissue

Abstract

Brassica species were tested for production of volatile fungicidal compounds from macerated green leaf tissue. Tissue (10, 20, and 40 g) of one cultivar each of six Brassica species was assayed for inhibition of Fusarium sambucinum. Only cultivars of B. nigra and B. juncea suppressed radial growth (>50% inhibition of control). Plant introduction accessions (PIs) of B. juncea, B. carinata, B. nigra, and B. napus were screened for suppression of F. sambucinum. Only B. nigra, B. juncea, and 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. nigra, B. juncea, and B. carinata. Radial growth of F. sambucinum was negatively correlated (P < 0.05) with AITC concentrations emitted from Brassica leaf tissue. All Brassica PIs with AITC concentrations greater than 0.10 mg/g of leaf tissue were suppressive to F. sambucinum in radial growth assays. Growth of five other plant pathogenic fungi was also suppressed by a B. juncea cultivar that contained high concentrations of AITC.