Morphophysiological Diversity and Haplotype Analysis of Saltol QTL Region in Diverse Rice Landraces for Salinity Tolerance

Rice is sensitive to salinity stress at both the seedling and reproductive stages.The present study used 145 rice genotypes comprising of 100 landraces and 45 advanced breeding lines collected from different regions of India.These genotypes were evaluated in hydroponics under control[electrical conductivity(ECe)~1.2 dS/m]and saline(ECe~10.0 dS/m)environments along with susceptible(IR29)and tolerant(FL478)checks.The stress susceptibility index for eight morphophysiological traits was estimated.Analysis of variance showed significant differences among the genotypes for all the parameters studied in control,stress and relative stress conditions.We identified 3 landraces(Kuttimanja,Tulasimog and IET-13713I)as tolerant and 14 lines as moderately tolerant to salt stress.Strong correlations in the morphological(root and shoot lengths)and physiological traits(shoot Na^(+),Ca^(2+)and Mg^(2+)contents,and Na^(+)/K^(+)ratio)were observed under all the conditions.The hierarchical cluster analysis grouped the genotypes into five clusters,among which cluster Ⅱ comprised salt-tolerant lines.Haplotyping of Saltol region using 11 simple sequence repeat markers on 17 saline tolerant and moderately tolerant lines was conducted.Markers AP3206F,RM10793 and RM3412b,located close to SKC1 gene(11.23‒12.55 Mb),displayed diverse allelic variations and they were not related to the FL478 type.In this region,tolerant lines like Kuttimanja,IET-13713I and Tulasimog have new alleles.As a result,these lines may be suitable candidates for novel genomic regions governing rice salinity tolerance.Salt-tolerance ability of Kuttimanja,Tulasimog and IET-13713I was validated in two years in three salinity stress environments.These promising lines can be used in breeding programs to broaden the genetic base of salinity tolerance in rice,and it may help to dissect key genomic regions responsible for salinity tolerance.

Haplotyping of Rice Genotypes Using Simple Sequence Repeat Markers Associated with Salt Tolerance

Salt stress is a major problem in most of the rice growing areas in the world. A major QTLSaltol associated with salt tolerance at the seedling stage has been mapped on chromosome 1 in rice.This study aimed to characterize the haplotype diversity at Saltol and additional QTLs associated withsalt tolerance. Salt tolerance at the seedling stage was assessed in 54 rice genotypes in the scale of 1to 9 score at EC = 10 dSm^-1 under controlled environmental conditions. Seven new breeding linesincluding three KMR3/O. rufipogon introgression lines showed similar salt tolerant ability as FL478 andcan be good sources of new genes/alleles for salt tolerance. Simple sequence repeat （SSR） markerRM289 showed only two alleles and RM8094 showed seven alleles. Polymorphic information contentvalue varied from 0.55 for RM289 to 0.99 for RM8094 and RM493. Based on 14 SSR markers, the 54lines were clearly separated into two major clusters. Fourteen haplotypes were identified based onSaltol linked markers with FL478 as the reference. Alleles of RM8094 and RM3412 can discriminatebetween the salt tolerant and susceptible genotypes clearly and hence can be useful in marker-assistedselection at the seedling stage. Other markers RM10720 on chromosome 1 and RM149 and RM264 onchromosome 8 can also distinguish tolerant and susceptible lines but with lesser stringency.