PHYTOALEXIN ACCUMULATION IN THE ROOTS OF CHICKPEA (CICER-ARIETINUM L)SEEDLINGS ASSOCIATED WITH RESISTANCE TO FUSARIUM-WILT (FUSARIUM-OXYSPORUM F-SP CICERI)

Four cultivars of chickpea which differed in their reaction to Fusariu m oxysporum f.sp. ciceri, the pathogen causing wilt, were grown in wil t infested soil. The root xylem of plants showing wilt symptoms was he avily occluded by hyphae. Hyphal occlusion of stem xylem was also reco rded up to the fifth internode. The roots of resistant cultivars were penetrated but hyphal growth was very slow. No localized cell death (h ypersensitivity) or gross structural changes (lignification) were obse rved in the vicinity of invading hyphae in resistant cultivars, sugges ting that the resistance was dependent upon chemical rather than physi cal mechanisms. The concentration of the pterocarpans medicarpin and m aackiain in the roots increased in the presence of two races of the pa thogen. Both pre- and post-induction concentrations of pterocarpans we re significantly greater in wilt-resistant cultivars indicating an ass ociation between phytoalexin induction and resistance. Medicarpin and maackiain showed antifungal activity to F. oxysporum f.sp. ciceri at s imilar concentrations to those recorded in wilt-resistant chickpea roo ts. No significant difference in the sensitivity of races 1 and 2 to t he antifungal activity of the pterocarpans was detected, bur. the accu mulation of phytoalexins in response to the more virulent pathotype ra ce 2 was lower in ail cultivars than those produced in response to rac e 1. We conclude that they are fundamental components of the resistanc e mechanism of chickpeas to wilt. (C) 1997 Academic Press Limited.