Glucosinolate profiles of Australian canola (Brassica napus annua L.) and Indian mustard (Brassica juncea L.) cultivars: implications for biofumigation

The glucosinolate (GSL) profiles in root, shoot, and seed tissues of 22 Australian canola (Brassica napus) and 15 Indian mustard (Brassica juncea) entries were measured in the field. The Indian mustard lines included 12 low seed GSL lines from a breeding program aimed at producing canola-quality B. juncea cultivars and 3 high seed GSL condiment cultivars. The aromatic glucosinolate, 2-phenylethyl GSL, was the major GSL found in the roots of both species although Indian mustard also contained 2-propenyl GSL in the roots. The concentration of glucosinolates in the roots varied from 5 to 35 µmol/g in B. napus, from 2.5 to 25 µmol/g in low seed GSL B. juncea, and from 10 to 21 µmol/g in high seed GSL B. juncea, but was not correlated with seed glucosinolate concentrations in either species. Breeding for low seed GSLs in Indian mustard reduced the concentration of 2-propenyl GSL in both root and shoot tissues, but levels of 2-phenylethyl GSL in the roots were unaffected. The results indicate that high yielding and agronomically adapted varieties of both species could be developed with higher levels of root GSL for enhanced biofumigation potential without compromising seed quality. The GSLs which liberate isothiocyanates on hydrolysis were found primarily in the taproot and larger lateral roots (>2 mm) of both species, whereas younger fine roots (<2 mm diameter) had higher levels of indolyl GSLs. Correlations between root GSLs and susceptibility of brassicas to root pests and pathogens will need to take account of these differences in GSL profiles among different root classes.