Identification of putative genes in bean (Phaseolus vulgaris) genomic (Bng) RFLP clones and their conversion to STSs.

A set of 79 previously mapped bean (Phaseolus vulgaris) genomic (Bng) clones were partially sequenced. BLAST database searches detected homologies between 59 of these clones and genes from a variety of plants, especially Arabidopsis thaliana. Some matches in the database to the Bng clones included a putative P-glycoprotein-ABC transporter from Arabidopsis, an early nodulin-binding protein (ENBPI) from Medicago truncatula, a lon-protease protein from spinach, a branched-chain amino-acid aminotransferase from Arabidopsis, and a vacuolar sorting receptor (BP-80) from Pisum sativum. Additional matches were found for genes involved in isoprenoid biosynthesis, sulfur metabolism, proline biosynthesis, and floral development. Sequence tagged site (STSs) were produced for 16 of the clones, 2 of which contain simple sequence repeats (SSRs). Polymorphisms were detected for six of the STSs.

Mapping genetic factors affecting the reaction to Xanthomonas axonopodis pv. phaseoli in Phaseolus vulgaris L. under field conditions.

The objectives of the present study were to evaluate the field effects of Xanthomonas axonopodis pv. phaseoli (Xap), which causes common bacterial blight (CBB) on common bean (Phaseolus vulgaris L.), and to identify genetic factors for resistance to CBB using a linkage map constructed with random amplified polymorphic DNA (RAPD), restriction fragment length polymorphism (RFLP), simple sequence repeat (SSR), and amplified fragment length polymorphism (AFLP) markers. One hundred and forty-two F2:4 lines, derived from a cross between 'OAC Seaforth' and 'OAC 95-4', and the parents were evaluated for their field reaction to CBB. In the inoculated plots, the reaction to CBB was negatively correlated with seed yield, days to maturity, plant height, hypocotyl diameter, pods per plant, and harvest index. A reduction in seed yield and its components was observed when disease-free and CBB-inoculated plots were compared. The broad-sense heritability estimate of the reaction to CBB was 0.74. The disease segregation ratio was not significantly different from the expected segregation ratio for a single locus in an F2 generation. The major gene for CBB resistance was localized on linkage group (LG) G5. A simple interval mapping procedure identified three genomic regions associated with the reaction to CBB. One quantitative trait loci (QTL), each on LG G2 (BNG71Dra1), G3 (BNG21EcoRV), and G5 (PHVPVPK-1) explained 36.3%, 10.2%, and 42.2% of the phenotypic variation for the reaction to CBB, respectively. Together, these loci explained 68.4% of the phenotypic variation. The relative positions of these QTL on the core common bean map and their comparison with the previous QTL for CBB resistance are discussed.

Identification of RAPD markers linked to common bacterial blight resistance genes in Phaseolus vulgaris L.

Seven hundred and fifty-six random primers were screened with bulks of genomic DNA from common bacterial blight (CBB) resistant and susceptible bean plants. The plants were from a breeding population derived from an interspecific cross between Phaseolus acutifolius and Phaseolus vulgaris. Four RAPD markers, named R7313, RE416, RE49, and R4865, were found to be significantly associated with CBB resistance in this population. Forty-nine molecular markers segregating in the population were clustered into 8 linkage groups by a MAPMAKER linkage analysis. The largest linkage group was 140 cM long and contained 25 marker loci, including marker R4865. Markers R7313, RE416, and RE49 were clustered on another linkage group. A regression analysis indicated that the markers in these two groups together accounted for 81% of the variation in CBB resistance in the population. The addition of another marker, M56810, which was not individually associated with CBB resistance, increased the total contribution to the trait to 87%.