2 AVIRULENT RACES OF COLLETOTRICHUM-LINDEMUTHIANUM TRIGGER DIFFERENT TIME COURSES OF PLANT DEFENSE REACTIONS IN BEAN

A bean resistant line, carrying the ARE resistance gene, was challenge d with two avirulent races of Colletotrichum lindemuthianum (races 1 a nd 9), the causal agent of bean anthracnose. The time course of the pl ant defense reaction was monitored by the observation of symptom devel opment, fungal infection process, and accumulation of bean phenylalani ne ammonia-lyase, chitinase, and hydroxyproline-rich glycoprotein mRNA s in infected leaves. Race 9-infected beans displayed a faster inducti on and a different pattern of all these events. When compared to previ ous results with an isogenic susceptible line, both race 1 and race 9 provoked an earlier induction of PAL and CHT mRNAs accumulation in inc ompatible interactions than in compatible ones. However, with race 1, the maximum of accumulation occurred almost at the same time after inf ection 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 acc umulated in the resistant line, whereas they were not accumulated at a ll in the susceptible line. In contrast, the pattern of induction of H yp 4.1 mRNA was similar in these race 1-infected lines.