ROOT EXUDATES ASSOCIATED WITH THE RESISTANCE OF 4 CHICKPEA CULTIVARS (CICER-ARIETINUM) TO 2 RACES OF FUSARIUM-OXYSPORUM F-SP CICERI

The germination of race 1 spores of Fusarium oxysporum f. sp. ciceri w as significantly inhibited by the root exudate of the wilt-resistant c hickpea cvs CPS1 and WR315 compared to untreated spores and spores tre ated with root exudates from susceptible cultivars. The effect was con centration dependent, such that the exudate from 1 g of root in 2 ml o f water almost completely inhibited spore germination, whereas the exu date from 1 g of root in 20 ml water did not do so. The inhibitory eff ects of the active exudates were negated when the apolar components of the exudates were removed by extraction with ethyl acetate. The root exudates of the susceptible cv. JG62 and the late wilting cv. H208 did not inhibit germination. The hyphal growth of germinated spores was a lso strongly inhibited by the concentrated exudates of CPS 1 and WR315 , and diluted exudates were less potent. The highest concentration of the exudate of the susceptible cv. JG62 showed some inhibition of hyph al growth, whereas none of the exudates of H208 were found to contain any antifungal activity. The effect of the exudates on the spores of r ace 2 was similar to that reported for race 1, except that the water-s oluble components of the crude root exudate of WR315 after ethyl aceta te extraction were also found to inhibit germination significantly. Ov erall, the spores of race 2 appeared to be mon susceptible to the effe cts of the exudates. The ethyl acetate fractions of the root exudates of CPS 1 and WR315 strongly inhibited germination and hyphal growth of both race 1 and race 2, the effect being concentration dependent. The results suggest that the resistance of chickpeas to vascular wilt dep ends, at least in part, upon the antifungal activity of the root exuda tes. Differences in the expression of resistance in the field could de pend upon the concentration or rate of production of constitutive anti fungal components by the root.