Article

Marker-assisted dissection of the oligogenic anthracnose resistance in the common bean cultivar, ‘G2333’

Theoretical and Applied Genetics (Impact Factor: 3.66). 12/1997; 96(1):87-94. DOI: 10.1007/s001220050713

ABSTRACT  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

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, 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

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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

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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

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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

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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

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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

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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.

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