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+, Ca2+ and Mg2+ 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

Photosynthetic machinery under salinity stress: Trepidations and adaptive mechanisms

Chloroplasts and photosynthesis are the physiologically fateful arenas of salinity stress. Morphological and anatomical alterations in the leaf tissue, ultrastructural changes in the chloroplast, compromise in the integrity of the three-layered chloroplast membrane system, and defects in the light and dark reactions during the osmotic, ionic, and oxidative phases of salt stress are conversed in detail to bring the salinity-mediated physiological alterations in the chloroplast on to a single platform. Chloroplasts of salt-tolerant plants have evolved highly regulated salt-responsive pathways. Thylakoid membrane remodeling, ion homeostasis, osmoprotection, upregulation of chloroplast membrane and stromal proteins, chloroplast ROS scavenging, efficient retrograde signalling, and differential gene and metabolite abundance are the key attributes of optimal photosynthesis in tolerant species. This review throws light into the comparative mechanism of chloroplast and photosynthetic response to salinity in sensitive and tolerant plant species