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Crop wild relatives that have experienced multiple and independent domestication events provide an excellent model for understanding adaptation processes in crop populations and a first and relevant aspect to investigate is the geographic origin of landraces. The aim of this research was to establish the origin of Mesoamerican and Andean Lima bean (Phaseolus lunatus L.) landraces by analyzing chloroplast DNA and ITS polymorphisms in a sample of 59 wild and 50 landrace accessions. According to seed size, genetic distance analyses, and haplotype networks, at least two independent domestication events are proposed. The first one would have taken place in the Andes of southern Ecuador--northwestern Peru and would have given rise to the large-seeded landraces collectively known as the 'Big Lima' cultivars. The second one would have taken place in central--western Mexico, more likely in the area to the north and northwest of the Isthmus of Tehuantepec. This event, along with post-domestication migrations of landraces in South America, would have given rise to the great variety of small-seeded Mesoamerican landraces that exist today. We did not find any evidence supporting the existence of two discrete groups within Mesoamerican landraces that might correspond to the previously proposed 'Sieva' and 'Potato' cultigroups. A severe reduction in genetic diversity because of domestication, known as the 'founder effect', was detected, which may have implications for the conservation of genetic resources in this species. doi: 10.2135/cropsci2009.12.0706

Tepary bean (Phaseolus acutifolius A. Gray), a low-rainfall crop from the Sonoran desert, is thought to have low diversity; however, its relationship to its wild relatives is poorly understood. In this study, a total of 147 accessions were evaluated by means of AFLP markers to (i) establish the taxonomic relationships within and between the Acutifolii and other sections and (ii) to understand tepary bean domestication. The structure among the 10 species analyzed corresponded to currently recognized sections: Phaseolus glabelus and Phaseolus lunatus L. were equally distant from the phaseoli and coccinei sections and the rugosi section included Phaseolus angustissimus, Phaseolus carteri and Phaseolus filiformis. We also compared the gene pool differences for common (Phaseolus vulgaris L.) and lima bean (P. lunatus) with differences observed within the Acutifolii section. The wild relative, Phaseolus parvifolius persistently separated from the bulk of both cultivated and wild tepary, validating its status as a separate species; while within the wild accessions, there was no obvious grouping along the foliar variants. On the basis of our results, one of two Mexican states, Sinaloa or Jalisco, could have been the domestication center, although the hypothesis of multiple domestication events cannot be discarded. Furthermore, domesticated tepary bean was most likely derived from wild genotypes of var. acutifolius rather than genotypes of var. tenuifolius.

The genus Phaseolus includes important cultivated species as well as wild species with diverse ecological adaptations. Characterization of the ecological adaptations of the wild species would be useful for improved understanding, conservation, and utilization of these genetic resources. Salinity tolerance during vegetative growth was evaluated for 132 accessions for 14 wild Phaseolus species (P. acutifolius A. Gray, P. angustissimus A. Gray, P. carteri Freytag & Debouck, P. filiformis Bentham, P. glabellus Piper, P. leptostachyus Bentham, P. lunatus L., P. micranthus Hook & Arnold, P. microcarpus Mart, P. mcvaughii A. Delgado, P. oligospermus Piper, and P. vulgaris L.) and 11 accessions representing five cultivated species (P. acutifolius, P. coccineus L., P. lunatus L., P. polyanthus Greenman, and P. vulgaris) in nutrient solution containing 0 and 180 m M sodium chloride for 21 d. When plants were salinized after the emergence of the first trifoliate leaf, wild accessions of P. acutifolius, P. filiformis, P. lunatus, and P. vulgaris showed a wide range of variation in their salinity tolerance as defined by total dry weight reduction (PR) as a percentage of the unsalinized controls, salt susceptibility index (SSI), and root: shoot ratio (RSR). SSI and PR were correlated positively, indicating either trait could be used to select salt-tolerant accessions. Cluster analysis revealed substantial intraspecific and interspecific variation in salinity tolerance. Salinity tolerance was observed in wild P. micranthus, P. mcvaughii, P. lunatus, cultivated P. coccineus, and several accessions of wild P. filiformis, and P. vulgaris. Of these, P. filiformis was noteworthy in having 9 of 11 accessions rated as highly tolerant. Wild P. vulgaris was more salinity tolerant than the three cultivated P. vulgaris accessions included in the study. Many tolerant accessions originated in arid, coastal, or saline areas. We conclude that the genus Phaseolus has substantial diversity in salinity tolerance., EXCESSIVE SOIL SALINITY is an important constraint limiting the distribution of plants in natural habitats, and is an increasingly severe agricultural problem in arid and semiarid regions (Shannon, 1986). Various [...]

Edited by J.M.M. Engels, V. Ramanatha Rao, A.H.D. Brown, and M.T. Jackson. CABI Publishing, 10 E 40th St., Suite 3203, New York, NY 10016. 2002. Hardcover, 487 pp., $140.00. ISBN [...]