BIOFUMIGATION POTENTIAL OF BRASSICAS - II - EFFECT OF ENVIRONMENT ANDONTOGENY ON GLUCOSINOLATE PRODUCTION AND IMPLICATIONS FOR SCREENING

Biofumigation refers to the suppression of soil-borne pests and pathog ens by biocidal compounds released by Brassicaceous green manure and r otation crops when glucosinolates (GSLs) in their tissues are hydrolys ed. We investigated the effect of environment and ontogeny on the GSL production, and thus biofumigation potential, of eight entries from fi ve Brassica species. The environments included autumn and spring sown field plots (FA and FS) and potted plants grown under ambient conditio ns (PAM) or in a temperature controlled glasshouse at 20 degrees C/12 degrees C (PTC). GSL concentration was measured in the root and shoot tissue at buds-raised, flowering and maturity. Of particular interest was the suitability of the pot-grown plants for screening large number s of brassicas for GSL production. The type of GSLs present in the tis sues and their relative proportions remained relatively constant acros s environments and at different growth stages, with the exception of a n increase in indolyl GSLs in the FS environment suspected of being in duced by insect attack. Total GSL concentration generally declined fro m buds-raised to flowering in all environments, and was lowest at matu rity. The exceptions were B. campestris, which had higher GSL concentr ation at flowering than at buds-raised, and the PTC environment in whi ch most species also showed an increase at flowering. Despite GSL type s and their proportions remaining relatively constant, the total GSL c oncentration in the root and shoot tissue of all entries varied signif icantly with environment (3-10-fold) and was generally ranked FS>PAM>F A>PTC. Interactions between species and environments meant that the ra nking of the Brassica entries for total shoot and root GSL concentrati on changed with environment. However within three entries from B. napu s, the ranking was consistent across the environments. The added effec t of environment on phenological development and biomass production fu rther influenced GSL production (the product of GSL concentration and biomass) on a ground area basis. The results suggest that glasshouse e nvironments can be used to determine the types and proportions of GSLs present, and to rank entries within, but not between species for the total concentration in the tissues. However the influence of the envir onment on both GSL concentration and biomass production suggests that an accurate estimate of GSL production on a ground area basis to asses s biofumigation potential will require measurement in the target envir onment.