Two Avirulent Races of Colletotrichum Iindemuthianum Trigger Different Time Courses of Plant Defense Reactions in Bean. Aline Mahé. Phytopathologie Moléculaire, Département de Biologie Moléculaire Végétale, URA CNRS 1128, Bat. 430, Université Paris XI, 91405 Orsay Cedex, France. Jeanine Grisvard, and Michel Dron. Phytopathologie Moléculaire, Département de Biologie Moléculaire Végétale, URA CNRS 1128, Bat. 430, Université Paris XI, 91405 Orsay Cedex, France.. MPMI 6:423-428. Accepted 15 March 1993. Copyright 1993 The American Phytopathological Society.

A bean resistant line, carrying the ARE resistance gene, was challenged with two avirulent races of Colletotrichum lindemuthianum (races 1 and 9), the causal agent of bean anthracnose. The time course of the plant defense reaction was monitored by the observation of symptom development, fungal infection process, and accumulation of bean phenylalanine ammonia-lyase, chitinase, and hydroxyproline-rich glycoprotein mRNAs in infected leaves. Race 9-infected beans displayed a faster induction and a different pattern of all these events. When compared to previous results with an isogenic susceptible line, both race 1 and race 9 provoked an earlier induction of PAL and CHT mRNAs accumulation in incompatible interactions than in compatible ones. However, with race 1, the maximum of accumulation occurred almost at the same time after infection in both interactions. Instead, with race 9, it was observed 40 hr earlier in the incompatible interaction than in the compatible one. After infection by race 9, Hyp 4.1 transcripts were only slightly accumulated in the resistant line, whereas they were not accumulated at all in the susceptible line. In contrast, the pattern of induction of Hyp 4.1 mRNA was similar in these race 1-infected lines.