In vitro assessment of the effects of Brassica juncea and Raphanus sativus leaf and root extracts on the viability of Globodera pallida encysted eggs

Abstract

The biofumigation potential of leaf and root extracts of Brassica juncea and Raphanus sativus on Globodera pallida were assessed in vitro. In an efficacy study, G. pallida encysted eggs were exposed to six different concentrations of freeze-dried leaf or root extracts for 96 h and assessed for viability using hatching assays in 6-week-old potato root leachates (PRL). For B. juncea extracts an LC50 value of 0.027 mg ml−1 w/v was determined. The LC50 of Raphanus sativus root extracts was 0.032 mg ml−1, whereas leaf extracts were effective only at higher concentrations (⩾0.50 mg ml−1; w/v) and to a lesser extent. Hatching of G. pallida was enhanced in PRL following exposure to lower concentrations (0.063 mg ml−1) of R. sativus leaf extract. An analysis of the types and concentrations of glucosinolate (GSL) present in the freeze-dried tissues revealed that B. juncea leaf tissue was rich in 2-propenyl GSL (≈98%). Root tissue also had a high concentration of 2-propenyl GSL, but the leaf extracts were found to have a higher concentration (⩾90 μmol (g dry weight)−1) when compared with the root extract (⩾10 μmol (g dry weight)−1). Raphanus sativus had two-fold more root GSL, predominantly 2-phenylethyl GSL (⩾50 μmol (g dry weight)−1), when compared with the leaf tissue which was dominated by 4-methylsulfinylbutyl GSL (⩾20 μmol (g dry weight)−1). In summary, the strong suppression of G. pallida encysted eggs exhibited by lower concentrations of B. juncea extracts shows the potential of this species in G. pallida management if effectively incorporated into an integrated potato cyst nematode management scheme. In comparison with B. juncea, the biofumigation potential of R. sativus can be improved by maximising its root biomass production.