Assessment of rice genotypes for salt tolerance using microsatellite markers associated with the saltol QTL

A major quantitative trait locus (QTL) for salt tolerance named Saltol was mapped on chromosome 1 using F8 recombinant inbred lines (RILs) of Pokkali/IR29 cross, which is responsible for low Na super(+), high K super(+) uptake and maintaining Na super(+)/K super(+) homeostasis in the rice shoots. To test the usefulness of microsatellite (SSR) markers associated with Saltol QTL, a collection of 36 diverse rice genotypes were used. Phenotypic response of the genotypes to salt stress with EC=12 was assessed under controlled environmental conditions at seedling stage using a visual score of 1 to 9 scale. Thirty three polymorphic SSR markers located on chromosome 1 were also used to determine the impact of these markers associated with salt tolerance in rice. The results of phenotypic response of rice genotypes to salinity stress at the seedling stage indicated the varied genotypic responses. The genotypes were classified into five groups from highly tolerant (score 1) to highly sensitive (score 9). Number of alleles of the SSR markers ranged from 3 for RM10702 to 14 for RM8094. Polymorphic information content (PIC) value varied from 0.28 for RM8095 to 0.88 for RM8094 with an average of 0.73. The SSR marker, RM8094, was found to be superior for analysis of genetic diversity in this study. Cluster analysis of the rice genotypes based on SSR data divided the genotypes into three groups each of which having 12, 8 and 16 genotypes including highly salt-tolerant IRRI elite lines (cluster 1), salt tolerant and moderate tolerant genotypes as well as Pokkali and FL478 (cluster 2), sensitive and highly sensitive genotypes (cluster 3), respectively. The impact of chromosome 1 for tolerance to salinity at the seedling stage in rice was emphasized by the results. Thirty six rice genotypes divided into 18 different haplotypes based on Saltol QTL located on chromosome 1 using Pokkali cultivar as the reference. The haplotypes possessing RM8094 and RM10745 markers could discriminate the tolerant genotypes and hence could be useful for marker-assisted selection of Saltol QTL.