Differential Induction by Endopolygalacturonase of Beta-1,3-Glucanases in Phaseolus vulgaris Isoline Susceptible and Resistant to Colletotrichum lindemuthianum Race Beta. Claude Lafitte. Centre de Biologie et Physiologie Végétale, UA CNRS no. 1457, Université Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cédex, France. Jean-Paul Barthe, Xavier Gansel, Grégory Dechamp-Guillaume, Catherine Faucher, Dominique Mazau, and Marie-Thérèse Esquerré-Tugayé. Centre de Biologie et Physiologie Végétale, UA CNRS no. 1457, Université Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cédex, France.. MPMI 6:628-634. Accepted 6 May 1993. Copyright 1993 The American Phytopathological Society.

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.