The germination and hyphal growth of Fusarium oxysporum f.sp. ciceri was significantly inhibited when spores were treated with the root exudate of both the chickpea varieties CPSI and JG62 although the greatest inhibitory effect was recorded for the exudate of CPSI. The water soluble components remaining after fractionation of the exudate of either variety with ethyl acetate did not inhibit spore germination or hyphal growth. TLC analyses of the ethyl acetate fractions revealed several quantitative differences between the phenolic profiles of the resistant (CPSI) and the susceptible (JG62) varieties. Three components were visible under long wave UV and were present at visibly higher concentrations in CPSI. They were isolated by preparative TLC and two of them were shown to inhibit germination and the third inhibited hyphal growth. The inhibitory effect of these components was shown to be concentration dependent and thus the field resistance of CPSI could be attributed to the higher concentration of these compounds in the root exudate of this variety. HPLC analysis identified the pterocarpans medicarpin and maackiain in the exudate of CPSI at more than 10 times the concentration of that in JG62. Further TLC analysis showed that the relative mobility of these compounds was close to those isolated bands which inhibited germination and hyphal growth suggesting that the activity of these compounds may have been due to the constitutive presence of medicarpin and maackiain.
Acta Horticulturae (1994) 381 (2) 631-637. International Symposium on Natural Phenols in Plant Resistance