Construction of near-isogenic lines to investigate the efficiency of different resistance genes to anthracnose.

A suitable experimental model was designed with the aim of investigating the specific effect of different resistance genes in the Phaseolus vulgaris - Colletotrichum lindemuthianum interaction. The four resistance genes examined were chosen because they confer a different phenotype (resistance or susceptibility) to the lines carrying them when challenged by a range of C. lindemuthianum races. These different resistance genes were introgressed independently into the same susceptible recipient line. The isogenicity of the five near-isogenic lines (NILs) thus obtained (four resistant lines, one susceptible line = recipient line) was assessed by a RAPD analysis. The hypersensitive reaction occurred at the same time after infection, whatever the resistance gene present, when the NILs were challenged by the avirulent race 9 of the pathogen. In contrast, the pathogen development was arrested more or less rapidly in the different NILs. At the first stages of the infection process, the transcripts encoding phenylalanine ammonia-lyase were accumulated to a different extent in the different resistant NILs but always to a higher level than in the susceptible recipient line. These results suggest that the different resistance genes operate through more than one way in the production of defense factors.