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Scott D. Haley, Phillip N. Miklas, Lucia Afanador, and James D. Kelly

The objective of this study was to evaluate the degree of RAPD marker variability between and within commercially productive market classes representative of the Andean and Middle American gene pools of common bean (Phaseolus vulgaris L.). Six sets of near-isogenic lines were screened with oligonucleotide primers in the polymerase chain reaction-based RAPD assay. Simultaneous analyses with at least three sets of lines enabled us to score RAPD markers between the two major gene pools, races within the same gene pool, and different genotypes of the same race (within race). A “three-tiered” pattern of polymorphism was observed: between gene pools> between races> within races. The overall level of polymorphism between the Andean and Middle American gene pools was 83.4%. The overall level of polymorphism between races within the same gene pool was similar for Andean races (60.4%) and Middle American races (61.7%). The level of polymorphism between related commercial navy bean lines was 39.2% and between related commercial snap bean lines was 53.6 %. The inherent simplicity and efficiency of RAPD analyses, coupled with the number of polymorphisms detectable between related commercial genotypes, should facilitate the construction of RAPD-based genetic linkage maps in the context of populations representative of most bean breeding programs.

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

Common bean is by far the most widely consumed grain legume in the world ( Singh, 2001 ). Domestication of common bean took place in two, already diverged ancestral wild gene pools distributed from northern Mexico to Colombia (Mesoamerican gene pool

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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

gene pools. A prevalence of the Andean “C” and “T” phaseolin types (76%) was first detected by Gepts and Bliss (1988) , and was then confirmed by Lioi (1989) in an analysis of a large collection from Italy, Greece, and Cyprus (66% in total), by

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

Drought is an important abiotic stress that limits common bean (Phaseolus vulgaris) productivity. The objective of this study was to determine shoot traits that are associated with drought tolerance in common bean seedlings. Ten common bean genotypes consisting mainly of cultivars and breeding lines from the Mesoamerican race of the Middle American gene pool were first evaluated in the greenhouse. Genotypes were grown in a shallow soil profile to limit root growth and assess shoot phenotypes under stress. Water stress was imposed by withholding watering for 24 days after planting. Traits evaluated included wilting, unifoliate senescence, stem greenness, and recovery from drought. Biomass and number of pods/plant produced after drought recovery were evaluated to quantify the effect of early drought stress on bean growth and reproduction. A second group of 94 common bean genotypes from the Bean Coordinated Agricultural Project (BeanCAP) were evaluated using the same protocol to determine the genetic variability for the same traits in a wider range of genotypes. In general, genotypes known to possess drought avoidance in the field conferred by deep rooting traits performed poorly in these conditions suggesting that the assay could be used to identify seedling shoot traits that contribute to drought tolerance. Genotypes from race Mesoamerica showed the greatest range in wilting. Genotypes that showed a slow rate of wilting maintained a green stem and had a higher recovery rate after watering. Importantly, these genotypes demonstrated a smaller reduction in biomass and pod number under stress compared with non-stress treatments. A few genotypes recovered completely despite expressing severe wilting, whereas the majority of genotypes with high wilting rates did not recover. Among the BeanCAP materials, genotypes bred in the rainfed midwestern United States showed overall better recovery than those bred under the irrigated production system used in the western United States. Because recovery from drought is a prerequisite to plant regrowth, biomass, and pod production after drought stress, factors that contribute to recovery were studied. Stem greenness was highly positively correlated to the recovery, whereas wilting was negatively correlated to the recovery. In a regression analysis, stem greenness and slow wilting were found to be important contributors to the variability of recovery. In addition, photosynthetic rate and stomatal conductance (g S) explained variation in wilting and stem greenness. These results suggest that wilting and stem greenness might be useful traits to screen for drought tolerance in seedlings of common bean.

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Gayle M. Volk, Adam D. Henk, Christopher M. Richards, Philip L. Forsline, and C. Thomas Chao

. niedzwetzkyana . We use genotypic and phenotypic data to determine if the gene pools in the NPGS that comprise these taxa can be distinguished from one another. Materials and Methods Malus sieversii and several accessions of M. sieversii var. kirghisorum

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Yu Zong, Ping Sun, Xiaoyan Yue, Qingfeng Niu, and Yuanwen Teng

-adjusted metric of allelic richness ( A r ) was calculated using FSTAT 2.9.3 ( Goudet, 1995 ). Allele richness was standardized for 11 individuals. Genetic differentiation among populations. The number of homogeneous gene pools ( K ) was evaluated using a Bayesian

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Hisayo Yamane, Yukinobu Kashiwa, Tomomi Ooka, Ryutaro Tao, and Keizo Yonemori

endodormancy, we generated two subtraction libraries. First, we generated a SSH/MOS library containing gene pools that are expressed preferentially in endodormant buds compared with ecodormant buds to search for genes that are down-regulated by endodormancy

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Kim E. Hummer

. Many countries in both the northern and southern hemispheres are producing these healthful fruits for local use and also for export to population centers. The use of diverse species in breeding programs has broadened gene pools and has been the

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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 Nienhuis, Jan Tivang, Paul Skroch, and Joao B. dos Santos

Knowledge of relative genetic distance among genotypes is useful in a breeding program because it permits organization of germplasm resources. Genetic distance (GD) was estimated among 65 Phaselous lunatus L.. accessions, which included 4 large-seeded and 7 small-seeded cultivars and 54 germplasm accessions (landrace's) from the Caribbean and North, Central, and South America. Based on 125 polymorphic random amplification polymorphic DNA (RAPD) bands, two major clusters, which generally correspond in seed size and geographic region to [be Mesoamerican and Andean gene pools, were observed among the landraces (GD = 0.726 ± 0.041). Four Fordhook cultivars and a landrace from the United States formed a separate cluster that is more distantly related to the small- (GD) = 0.561 ± 0.039) than to the large-seeded cluster (GD = 0.303 ± 0.022). The mean GD between the Andean and Mesoamerican (0.726), Mesoamerican and Fordhook (0.561), and Andean and Fordhook (0.303) clusters were all significant. The significant GD between the Andean and Mesoamerican groups supports the hypothesized existence of two major gene pools in lima bean. The RAPD marker diversity of the Mesoamerican group was the largest (0.1 10), followed by the Andean (0.097) and Ford hook (0.062) groups. The plot of the relationship between the coefficient of variation (cv) and sample size (number of bands) indicates that cvs as low as 10% for estimating CD between Andean and Mesoamerican lima bean accessions can be achieved by sampling as few as 100 bands.