Abstract
Resistance to common bacterial blight, caused by Xanthomonas axonopodis pv. phaseoli, in Phaseolus vulgaris is conditioned by several loci on different chromosomes. Previous studies with OAC-Rex, a CBB-resistant, white bean variety of Mesoamerican origin, identified two resistance loci associated with the molecular markers Pv-CTT001 and SU91, on chromosome 4 and 8, respectively. Resistance to CBB is assumed to be derived from an interspecific cross with Phaseolus acutifolius in the pedigree of OAC-Rex. Our current whole genome sequencing effort with OAC-Rex provided the opportunity to compare its genome in the regions associated with CBB resistance with the v1.0 release of the P. vulgaris line G19833, which is a large seeded bean of Andean origin, and (assumed to be) CBB susceptible. In addition, the genomic regions containing SAP6, a marker associated with P. vulgaris-derived CBB-resistance on chromosome 10, were compared. These analyses indicated that gene content was highly conserved between G19833 and OAC-Rex across the regions examined (>80%). However, fifty-nine genes unique to OAC Rex were identified, with resistance gene homologues making up the largest category (10 genes identified). Two unique genes in OAC-Rex located within the SU91 resistance QTL have homology to P. acutifolius ESTs and may be potential sources of CBB resistance. As the genomic sequence assembly of OAC-Rex is completed, we expect that further comparisons between it and the G19833 genome will lead to a greater understanding of CBB resistance in bean.
Highlights
Phaseolus vulgaris L., a member of the Fabacaea family, is the most important food legume in the world and is widely cultivated in Asia, North and South America and Africa, The Phaseolus genus is comprised of over 50 members, with P. vulgaris being the most commonly cultivated species
Quantitative Trait Loci (QTL) AND CONTIG IDENTIFICATION The pseudochromosome sequences from G19833 were interrogated with the sequences for the molecular markers Pv-CTT001, SAP6 and SU91
Our comparisons were somewhat hampered by the presence of N-containing regions on chromosome 8, and by a lack of genetic markers on chromosome 4, but comparisons for all three regions showed that 85% of the gene content was conserved between the two lines in the same physical space
Summary
Phaseolus vulgaris L. (common dry bean), a member of the Fabacaea family, is the most important food legume in the world and is widely cultivated in Asia, North and South America and Africa, The Phaseolus genus is comprised of over 50 members, with P. vulgaris being the most commonly cultivated species. (common dry bean), a member of the Fabacaea family, is the most important food legume in the world and is widely cultivated in Asia, North and South America and Africa, The Phaseolus genus is comprised of over 50 members, with P. vulgaris being the most commonly cultivated species. The primary gene pool of P. vulgaris is comprised of two geographically isolated pools: the Mesoamerican, and the Andean (Evans, 1973; Koening and Gepts, 1989; Koening et al, 1990; Singh et al, 1991; Debouck et al, 1993), which are distinguished by differences in seed size and color that define different market classes, in general, the beans of Mesoamerican origin have smaller seeds than those of Andean origin (Singh et al, 1991). The pathogen is endemic in the soil of most regions where dry beans are cultivated, and the ability of the pathogen to colonize the seeds of infected plants greatly increases the risk of pathogen carry-over from year to year
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