Two independently assorting dominant genes conditioning resistance to bean anthracnose were identified in an F2 population derived from the highly resistant bean differential cultivar, ‘G 2333’. One gene was allelic to the Co-4 gene in the differential cultivar ‘TO’ and was named Co-4
, whereas the second gene was assigned the temporary name Co-7 until a complete characterization with other known resistance genes can be conducted. Two RAPD markers linked to the Co-4
allele were identified. One RAPD, OAS13950, co-segregated with no recombinants in two segregating populations of 143 F2 individuals, whereas the second RAPD, OAL9740, mapped at 3.9 cM from the Co-4
allele. Two 24-mer SCAR primers (SAS13), developed from the OAS13950 RAPD marker, were dominant and polymorphic, similar to the original RAPD, and supported the tight linkage between the marker(s)
and the Co-4
allele. The markers were present in germplasm with known resistance alleles at the Co-4 locus. The presence of the markers in two other differential cultivars not previously characterized and in four navy bean
cultivars suggests the existence of a gene family for anthracnose resistance at or near the Co-4 locus. Since the Co-7 gene was present only in germplasm which also possessed the Co-4
and Co-5 genes, the SAS13 markers were used in combination with standard inoculation techniques to identify F3 lines in which the Co-7 gene was homozygous and the Co-4
allele was absent. A similar strategy of marker-assisted dissection is proposed to identify resistant lines in which the
Co-5 gene is absent and the Co-7 gene is present by selecting against the OAB3450 marker, which has been shown previously to be linked to the Co-5 gene. These genes cannot be distinguished using traditional screening methods since all current races of the pathogen virulent
to the Co-5 gene are avirulent to the Co-4
and Co-7 genes. We describe the use of molecular markers tightly linked to resistance genes to facilitate the identification of an
uncharacterized resistance gene for which no discriminating race of the pathogen is known.
"Additionally, its significance has been highlighted due to its ample spectra of genetic resistance (Young et al., 1998). Therefore, it was verified that the gene present in Corinthiano is independent from the previously characterized genes: Co-1, Co-1 4 /Phg-1, Co-2, Co-3, Co-3 3 , Co-3 4 /Phg-3, Co-4, Co-4 2 , Co-5, Co-5 2 , Co-6, Co-3 5 , Co-11, Co-12, Co-13, Co-14, and Co-16 that are present in the tested cultivars. "
"(c) Mapping of the Rpsar-2 gene to the end of LG B8. SAS13 and Dj1kSCAR are two SCAR markers linked to the anthracnose Co-4 R gene (Adam-Blondon, 1994; Young et al., 1998). Oval symbols correspond to R genes. "
[Show abstract][Hide abstract] ABSTRACT: *In plants, the evolution of specific resistance is poorly understood. Pseudomonas syringae effectors AvrB and AvrRpm1 are recognized by phylogenetically distinct resistance (R) proteins in Arabidopsis thaliana (Brassicaceae) and soybean (Glycine max, Fabaceae). In soybean, these resistances are encoded by two tightly linked R genes, Rpg1-b and Rpg1-r. To study the evolution of these specific resistances, we investigated AvrB- and AvrRpm1-induced responses in common bean (Phaseolus vulgaris, Fabaceae). *Common bean genotypes of various geographical origins were inoculated with P. syringae strains expressing AvrB or AvrRpm1. A common bean recombinant inbred line (RIL) population was used to map R genes to AvrRpm1. *No common bean genotypes recognized AvrB. By contrast, multiple genotypes responded to AvrRpm1, and two independent R genes conferring AvrRpm1-specific resistance were mapped to the ends of linkage group B11 (Rpsar-1, for resistance to Pseudomonas syringae effector AvrRpm1 number 1) and B8 (Rpsar-2). Rpsar-1 is located in a region syntenic with the soybean Rpg1 cluster. However, mapping of specific Rpg1 homologous genes suggests that AvrRpm1 recognition evolved independently in common bean and soybean. *The conservation of the genomic position of AvrRpm1-specific genes between soybean and common bean suggests a model whereby specific clusters of R genes are predisposed to evolve recognition of the same effector molecules.
New Phytologist 09/2010; 187(4):941-56. DOI:10.1111/j.1469-8137.2010.03337.x · 7.67 Impact Factor
"Sixth, for the SCAR markers linked to disease-resistance genes tested in our sample, the frequency of accessions that presented the molecular marker (or amplification product) ranged from 34 to 77% of the accessions. SCAR markers have been used routinely in different common bean breeding programs for marker-assisted selection, aimed at disease resistance (Young et al. 1998; Broughton et al. 2003; Ragagnin et al. 2005). However, the presence of the marker does not guarantee the presence of the corresponding tagged genes. "
[Show abstract][Hide abstract] ABSTRACT: Brazil is the largest producer and consumer of common bean (Phaseolus vulgaris L.), which is the most important source of human dietary protein in that country. This study assessed the genetic diversity and the structure of a sample of 279 geo-referenced common bean landraces from Brazil, using molecular markers. Sixty-seven microsatellite markers spread over the 11 linkage groups of the common bean genome, as well as Phaseolin, PvTFL1y, APA and four SCAR markers were used. As expected, the sample showed lower genetic diversity compared to the diversity in the primary center of diversification. Andean and Mesoamerican gene pools were both present but the latter gene pool was four times more frequent than the former. The two gene pools could be clearly distinguished; limited admixture was observed between these groups. The Mesoamerican group consisted of two sub-populations, with a high level of admixture between them leading to a large proportion of stabilized hybrids not observed in the centers of domestication. Thus, Brazil can be considered a secondary center of diversification of common bean. A high degree of genome-wide multilocus associations even among unlinked loci was observed, confirming the high level of structure in the sample and suggesting that association mapping should be conducted in separate Andean and Mesoamerican Brazilian samples.
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