DIFFERENTIAL INDUCTION BY ENDOPOLYGALACTURONASE OF BETA-1,3-GLUCANASES IN PHASEOLUS-VULGARIS ISOLINE SUSCEPTIBLE AND RESISTANT TO COLLETOTRICHUM-LINDEMUTHIANUM, RACE-BETA

A bioassay allowing absorption of pure endopolygalacturonase (EndoPG) of Colletotrichum lindemuthianum race beta by near-isogenic lines of Phaseolus vulgaris was designed to measure the elicitor effect of the enzyme. beta-1,3-Glucanases were retained as defense markers in this system. In response to endoPG, we found that beta-1,3-glucanase activity is induced earlier in resistant than in susceptible cultivars to this race of the fungus. Two endo-beta-1,3-glucanases that correlated to the appearance of two transcripts of molecular size 2 and 1.6 kb accounted for this increased activity. Elicitation of defense was a time-dependent, saturable phenomenon. It was abolished by the addition of exopolygalacturonase to the bioassay, suggesting that pectic fragments of a critical size are required for endoPG-mediated defense in bean seedlings. The differential ability of an endoPG to elicit near-isogenic lines had not been previously reported.