Genetic variation within natural host-pathogen populations : Phaseolus vulgaris, Colletotrichum lindemuthianum
1994
Neema, C. | Sicard, D. | Adam, A.F. | Buchet, S. | Cattan, I. | Dron, Michel
Wild common beans and their associated Colletotrichum lindemuthianum strains were collected from diverse ecogeographical regions in Argentina, the South Andean center of origin of Phaseolus vulgaris. Simultaneous study of genetic variability of both host and pathogen populations was carried out to understand the genetic interaction which occurs in natural plant communities. Sixty isolates of C. lindemuthianum were obtained from 200 plants, collected in 21 locations. The isolates were characterized for their virulence on a differential host range of 12 cultivars and 14 different races, at least, were identified. This racial diversity was not specific of a geographic region and it exists also within isolates originating from the same location. The genomic variability of the isolates was confirmed using a PCR-based technique, involving the random amplification of polymorphic DNA (RAPD). The majority of the isolates were only virulent on the South Andean cultivars of the host range, suggesting the same origin with their hosts. The total samples of 200 wild beans from Argentina, were screened for variability of phaseolin seed protein. They showed 3 different phaseolin types: "T, I and J", which had been previously identified in wild material from that region. The distribution of the 3 types amongst the regions was uneven. The region of Salta was significantly less diverse than the 2 other regions (Tucuman and Jujuy). This variability is now assessed using the RAPD method. C. lindemuthianum races were tested for pathogenicity on their wild bean hosts. A Duncan statistic analysis displayed significant different virulence classes of pathogen which correspond to significant different susceptible classes of wild beans. The occurrence of an adaptation of the pathogen races to their wild host is discussed.
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