Abstract
This study investigated the biofumigation potential of nine Brassica species/cultivars by determining the levels of 2-propenyl glucosinolate in their roots and shoots, and their in-vitro suppression of four major soil-borne pathogens of vegetable crops. Hydrolysis of 2-propenyl GSL produces volatile isothiocyanate (ITC) compounds which are known to have anti-fungal activity. HPLC results showed that 2-propenyl GSL only occurred in root and shoot residue of flowering plants of four Brassica cultivars developed for green manuring (Caliente 199?, Mustclean?, Nemfix? and BQ Mulch?) and in the standard (mustard seed meal) treatment Fumafert?. Levels of 2-propenyl GSL varied several fold within the four Brassica cultivars, with 77-88% of the total concentrations recorded in the shoot tissues. In in vitro assays, the level of fungal suppression by volatiles emitted by hydrated shoot and root residues related to their content of 2-propenyl GSL, and the dose of residue applied to five soilborne test pathogens (S. minor, Rhizoctonia solani, Fusarium oxysporum, Pythium dissotocum and Rhizoctonia solani). The variation in 2-propenyl GLS levels found in the Brassica green manure crops tested provides scope for selecting cultivars with greater potential for biofumigation, and to control multiple soil-borne disease problems in vegetable farms.
Highlights
Many soil-borne diseases are persistent problems in Australian vegetable farms, resulting in productivity losses due to reduced marketable yield, reduced plant growth, and lower quality
The aim was to determine if suppression of four important soil-borne pathogens of vegetable crops by the Brassica biofumigants could be demonstrated in-vitro, and if the level of suppression was related to concentration of 2-propenyl GSL in root and shoot tissues
The compound 2-propenyl GSL only occurred in shoot and root tissue of flowering plants of four Brassica green manure crops, and the soil treatment Fumafert (Figure 1)
Summary
Many soil-borne diseases are persistent problems in Australian vegetable farms, resulting in productivity losses due to reduced marketable yield, reduced plant growth, and lower quality. Biofumigation is a term used to describe the suppression of pest and soil-borne pathogens by biocidal compounds, principally ITCs, released when GSLs in Brassica rotation or green manure crops are hydrolysed in soil [7] [8]. In Australia, few studies have compared the GSL profiles and production in tissues of biofumigant crops, and the role of volatile compounds released from their hydrolysed root and shoot tissues against fungal pathogens [3] [8]. The aim was to determine if suppression of four important soil-borne pathogens (species of Sclerotinia, Fusarium, Rhizoctonia and Pythium) of vegetable crops by the Brassica biofumigants could be demonstrated in-vitro, and if the level of suppression was related to concentration of 2-propenyl GSL in root and shoot tissues
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