Genetic diversity analyzed by microsatellite markers among rice (Oryza sativa L.) genotypes with different adaptations to saline soils

The success of salt tolerance breeding programs employing traditional screening and selection has been limited in the past decades. This study was designed to characterize the genetic diversity within a subset of rice germplasm with different adaptations to saline soils using microsatellite markers. Salt tolerance was then analyzed among molecularly characterized genotypes. Plants of 33 genotypes were grown in sand tanks under greenhouse condition and irrigated with Yoshida nutrient solution. Two salt treatments were imposed with electrical conductivities of 0.9 dS m(-1) (control) and 6.5 dS m(-1) (6:1 molar ratio of NaCl and CaCl2). A total of 123 alleles were generated at 25 microsatellite loci among the 33 genotypes. Genotypes of japonica rice grouped into three clusters and those of indica rice grouped into two clusters based on microsatellite markers. Thirty percent of the alleles detected in 20 breeding lines were not identified in the cultivars analyzed. These alleles may provide favorable allelic combinations if the breeding lines are used for intercrosses. Physiological and morphological characters under salt stress were significantly (P = 0.05) different among microsatellite clusters. There was a highly significant correlation (r = -0.25; P = 0.005) between the matrices of Jaccard genetic similarity based on microsatellite markers and taxonomic distance based on ion data. These results indicate that the adaptation of rice to saline soils is different among genotypes with diverse genetic backgrounds. Implications for engineering salt tolerance are: (1) Improving salt tolerance can be achieved by selecting parental genotypes prior to intercrossing based on microsatellite markers. (2) Phenotypic variation of ion contents in segregating populations can be increased by selecting parental genotypes prior to intercrossing based on microsatellite markers. (3) Different salt tolerance components can be combined into a cultivar by intercrossing genotypes from different microsatellite clusters with diverse salt tolerance mechanisms. (C) 2003 Elsevier Ireland Ltd. All rights reserved.