Resistance genes (QTLs and major genes) to various pathogens tend to occur in clusters at specific locations in plant genomes. In common bean (Phaseolus vulgaris), common genomic regions associated with host response to the bacterial pathogen Xanthomonas campestris pv. phaseoli and to the symbiont Rhizobium have been identified. Agrobacterium tumefaciens causes crown gall disease in common bean, and shares similar gene activation mechanisms and host recognition signals with Rhizobium. Genotypic differences in tumorigenesis have been observed and could restrict Agrobacterium-mediated bean genetic transformation. The objectives of this research were: 1) to identify wild Agrobacterium strains inducing contrasting response in bean genotypes; and 2) to identify genomic regions in a core linkage map associated with host response to Agrobacterium infection, in comparison with the position of other symbiont or pathogen resistance genes. Among 10 wild A. tumefaciens strains tested under controlled inoculations of 1-week-old seedlings, Ach5, R10, and mainly Chry5 were virulent to the genotypes tested. The genotype BAT93 was susceptible to Chry5, even at low inoculum concentration, in contrast with JaloEEP558. Increasing levels of N enhanced susceptibility to Chry5, R10 and Ach5. Fifty recombinat inbred lines of BAT93 × JaloEEP558 were inoculated with Chry5 and segregated for tumor formation, with 21 lines not forming tumors. Analysis of variance identified 25 markers in five linkage groups of the core linkage map, significantly associated with Agrobacterium resistance, sharing the same location with QTLs identified for other host-bacteria interactions. (Financed by FAPESP 97/12066-1).
Toward structural and functional genomics of Agrobacterium tumefaciens: Linkage map of the left region of linear chromosome