Genetic Diversity in Cultivated Common Bean: II. Marker-Based Analysis of Morphological and Agronomic Traits

Knowledge of patterns of genetic diversity enhances the efficiency of germplasm conservation and improvement. This study examined the organization of diversity for morphological and agronomic characteristics in 306 landraces of cultivated common bean (Phaseolus vulgaris L.) from Latin America and its relationship with phaseolin seed protein and allozyme diversity of the landraces. Data on pigmentation, growth habit, and leaflet, pod, seed, and phenology traits, as well as reaction to four important diseases and an insect pest, obtained from field evaluations at three locations in Colombia during the 1987-1988 cropping season, were analyzed by multivariate statistical analyses. In addition, these same 306 landraces were characterized by electrophoresis for phaseolin seed protein and nine allozymes. Results permitted separation of these landraces into Mesoamerican and Andean groups, confirming prior phaseolin and allozyme data. A marker-based multivariate analysis, using phaseolin or allozymes as an initial classification criterion, followed by a corroborating analysis of morpho-agronomic traits, suggested the existence of subgroups within each of the major Andean and Mesoamerican groups, with distinctive morphology, adaptation, and disease resistances. Molecular analyses in conjunction with morphological and agronomic evaluations of gene bank accessions are recommended, because these provide complementary information and increase the resolving power of genetic diversity analyses. C COMMON BEAN is a morphologically diverse crop (Hedrick, 1931). Strikingly large variations are found for growth habit, pigmentation, pod, seed, phenology, and other characters (Leakey, 1988; Singh, 1989; Vanderborght, 1986). This diversity reflects the wide range of ecological and human environments under which the crop has evolved over millennia. In spite of the importance of these traits, the organization of their genetic diversity is poorly understood. Study of patterns of variation for phaseolin seed protein (Gepts and Bliss, 1985; Gepts et al., 1986) and allozymes (Koenig and Gepts, 1989; Singh et al., 1991) has revealed the existence of two major groups, a Mesoamerican and an Andean, within common bean germplasm. Attempts have been made to suggest subdivisions within the Mesoamerican and Andean germplasm. Evans (1976) and Vanderborght (1986) proposed classifications relying primarily on growth habit. Singh et al. (1989) identified three races within each of the Mesoamerican and Andean groups, and Singh (1988, 1989) proposed the existence of 12 gene pools in dry bean on the basis of growth habit and seed, morphological, and adaptational traits. S.P. Singh, J.A. Gutierrez, A. Molina, and C. Urrea, Bean Program, Int. Ctr. for Tropical Agric. (CIAT), Apartado aereo 6713, Call, Colombia; and P. Gepts, Dep. of Agron. and Range Sci., Univ. of California, Davis, CA 95616. Received 15 Dec. 1989. •Corresponding author. Published in Crop Sci. 31:23-29 (1991). 24 CROP SCIENCE, VOL. 31, JANUARY-FEBRUARY 1991 Multivariate statistical methods have been used previously to analyze patterns of genetic diversity. For example, Polignano and Spagnoletti-Zeuli (1985) examined variation of 10 morphological and agronomic traits in Mediterranean populations of Vicia faba L. with canonical discriminant and factor analyses. They were able to distinguish populations of different geographic origins within the Mediterranean basin, and they identified the specific traits responsible for the differences among them. In common bean, Vanderborght (1986) analyzed the morphological diversity Mesoamerican and Andean germplasm using cluster ̄ analysis and principal component analysis. Our objectives were to study patterns of diversity for morphological and agronomic traits in cultivated common bean and their relationship with patterns of diversity for phaseolin seed protein and allozymes. MATERIALS AND METHODS