BIOFUMIGATION POTENTIAL OF BRASSICAS - I - VARIATION IN GLUCOSINOLATEPROFILES OF DIVERSE FIELD-GROWN BRASSICAS

Biofumigation refers to the suppression of soil-borne pests and pathog ens by biocidal compounds released in soil when glucosinolates (GSL) i n Brassica green manure or rotation crops are hydrolysed. We investiga ted the potential to enhance biofumigation by considering the variatio n in GSL production in the roots and shoots of 76 entries from 13 Bras sica and related weed species grown in the field. Total plant GSL prod uction on a ground area basis at mid-flowering ranged from 0.8 to 45.3 mmol m(-2). The variation derived equally from differences in biomass and GSL concentration, which were not correlated in either root or sh oot tissues. Roots (0-0.15 m) contributed an average of 23.6% (range 2 -81%) of the total plant GSLs, their contribution limited by low bioma ss rather than GSL concentration, which was usually similar or higher than that of shoots. The GSL concentrations in root and shoot tissues did not correlate significantly with seed levels in any of the species , so selection for higher plant GSL production to enhance biofumigatio n potential cannot be based on seed GSL levels. The types of GSLs pres ent in the tissues varied considerably between species but were consis tent within species. In contrast, the concentration of individual and total GSLs in both root and shoot tissues varied four to ten-fold both between and within all species. Shoots contained predominately alipha tic GSLs, while aromatic GSLs, particularly 2-phenylethyl GSL, were do minant in the roots of all entries. Indolyl GSLs were present in all t issues but at low concentrations (<1 mu mol g(-1)). The variation in t he biomass, GSL profiles and concentrations in both roots and shoots p rovide significant scope to select or develop brassicas with enhanced biofumigation potential. Further studies on the efficacy of the variou s GSL hydrolysis products to suppress target organisms in soil are req uired to fully exploit biofumigation as a part of integrated pest mana gement.