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Marko Maras, Jelka Šuštar-Vozlič, Wolfgang Kainz, and Vladimir Meglič

) and from southern Peru to northwestern Argentina (Andean gene pool) ( Gepts et al., 1986 ; Khairallah et al., 1990 ; Koenig and Gepts, 1989 ). After the initial domestication phase, the common bean spread between Mesoamerica and South America and

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Marko Maras, Barbara Pipan, Jelka Šuštar-Vozlič, Vida Todorović, Gordana Đurić, Mirjana Vasić, Suzana Kratovalieva, Afrodita Ibusoska, Rukie Agić, Zdravko Matotan, Tihomir Čupić, and Vladimir Meglič

suggests that the set of 15 accessions represents additional variation within the Andean gene pool. Bayesian clustering was employed in Structure software to identify genetic populations, assign accessions to these populations, and identify admixed

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R.S. Balardin and J.D. Kelly

Sixty-two genetically diverse modern and traditional Phaseolus vulgaris L. cultivars from Brazil, the Dominican Republic, Honduras, Mexico, the Netherlands, and the United States, representative of the Andean and Middle American gene pools, were selected to study the interaction with distinct races of Colletotrichum lindemuthianum (Sacc. & Magnus) Lams.-Scrib. Principal component and phenetic analyses were conducted on the disease reaction to inoculation with 34 races of C. lindemuthianum from Argentina, Brazil, Colombia, Costa Rica, the Dominican Republic, Honduras, Mexico, Peru, and the United States. The principal component analysis revealed four clusters in which only one cluster consisted of cultivars from both gene pools. Bean genotypes clustered based on the gene pool origin of the resistance genes present, regardless of the actual gene pool of the host genotype. Middle American genotypes in cluster A carried Andean resistance genes. Further grouping of genotypes based on overall level of resistance within each gene pool was observed. Clusters A and C consisted of the most resistant genotypes from both gene pools. The distribution of genotypes generated by the phenetic analysis, placed the most resistant and susceptible genotypes of the anthracnose differential series at the extremities of the phenogram, providing support for the range in genotypic resistance exhibited by members of the differential series. Races of C. lindemuthianum isolated from Middle American genotypes showed broad virulence on germplasm from both gene pools, whereas races with Andean reaction showed high virulence only on Andean germplasm. The reduced virulence of Andean races on Middle American genotypes suggests selection of virulence factors congruent with diversity in P. vulgaris. In addition, races of C. lindemuthianum formed two clusters corresponding to the Middle American and Andean reaction groups based on the phenetic analysis. In the principal component analysis, most races with the Andean reaction were observed in the clusters C and D, except races 15 and 23 which clustered with Middle American races in cluster B. Only races 38, 39 and 47 from the Dominican Republic showed high similarity in both multivariate analyses and clustered based on geographic origin. Races from other countries showed no geographic effect. The overlapping of specific races, however, with races from different reaction groups might indicate that this group of isolates possesses factors of virulence to both host gene pools. Data based on virulence supports variability in C. lindemuthianum structured with diversity in P. vulgaris.

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James D. Kelly and Veronica A. Vallejo

Resistance to anthracnose in common bean is conditioned primarily by nine major independent genes, Co-1 to Co-10 as the Co-3/Co-9 genes are allelic. With the exception of the recessive co-8 gene, all other nine are dominant genes and multiple alleles exist at the Co-1, Co-3 and Co-4 loci. A reverse of dominance at the Co-1 locus suggests that an order of dominance exists among individual alleles at this locus. The nine resistance genes Co-2 to Co-10 are Middle American in origin and Co-1 is the only locus from the Andean gene pool. Seven resistance loci have been mapped to the integrated bean linkage map and Co-1 resides on linkage group B1; Co-2 on B11, Co-3 on B4; Co-4 on B8; Co-6 on B7; and Co-9 and Co-10 are located on B4 but do not appear to be linked. Three Co-genes map to linkage groups B1, B4 and B11 where clusters with genes for rust resistance are located. In addition, there is co-localization with major resistance genes and QTL that condition partial resistance to anthracnose. Other QTL for resistance may provide putative map locations for the major resistance loci still to be mapped. Molecular markers linked to the majority of major Co-genes have been reported and these provide the opportunity to enhance disease resistance through marker-assisted selection and gene pyramiding. The 10 Co-genes are represented in the anthracnose differential cultivars, but are present as part of a multi-allelic series or in combination with other Co-genes, making the characterization of more complex races difficult. Although the Co-genes behave as major Mendelian factors, they most likely exist as resistance gene clusters as has been demonstrated on the molecular level at the Co-2 locus. Since the genes differ in their effectiveness in controlling the highly variable races of the anthracnose pathogen, the authors discuss the value of individual genes and alleles in resistance breeding and suggest the most effective gene pyramids to ensure long-term durable resistance to anthracnose in common bean.

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Charles J. Wasonga, Marcial A. Pastor-Corrales, Timothy G. Porch, and Phillip D. Griffiths

) were from the Andean gene pool and included ‘Early Gallatin’ ( Ur-4 ), ‘Redlands Pioneer’ ( Ur-13 ), ‘Montcalm’ (unknown rust-resistance genes), ‘Pompadour Checa (PC) 50’ ( Ur-9, Ur-12 ), ‘Golden Gate Wax’ ( Ur-6 ), and ‘PI 260418’ (unknown rust

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Charles J. Wasonga, Marcial A. Pastor-Corrales, Timothy G. Porch, and Phillip D. Griffiths

grouped into Ur-4 , Ur-6 , Ur-9 , Ur-12 , and Ur-13 , which originate from beans of the Andean gene pool and Ur-3 , Ur-5 , Ur-7 , and Ur-11 from the Middle American gene pool ( Pastor-Corrales et al., 2007 ; Steadman et al., 2002 ). The Ur-3

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Gerardine Mukeshimana, Amy L. Lasley, Wayne H. Loescher, and James D. Kelly

, from the Andean gene pool was used in the earlier experiments and was later replaced by the otebo cultivar, Fuji, that was previously shown to be very susceptible to drought under field conditions. ‘Zorro’ is a high-yielding, widely grown black bean