A STUDY OF GENETIC VARIABILITY AND QUANTITATIVE TRAIT LOCI (QTL) FOR SALINITY TOLERANCE IN RICE (Oryza sativa L.)
ABSTRACT
Sub-soil salinity is the leading physiological stress limiting rice productivity in inland and coastal regions of West Africa. Thus, rice productivity could be enhanced through the development of improved rice varieties with tolerance to salt stress. The objectives of this study were to characterize the essential traits for salt tolerance breeding in Sahelian regions by evaluating BG90-2 and Jarmissa cross for tolerance to salt stress at the early seedling and reproductive stages, and mapping Quantitative Trait Loci (QTLs) for grain yield (GY) and yield related traits under salt stress. At the seedling stage, one hundred and twenty-two progenies were found to possess tolerance higher than the international tolerant check (FL478) at 12dSm-1. Root dry weight was found to be the most significant trait for discriminating salt tolerance at seedling stage, making it suitable for indirect selection for salt tolerance at seedling stage. The flame photometry analysis of sodium (Na+) and potassium (K+) ion content in roots and leaves of plants grown under stress and non-stress conditions, revealed plants exhibited three tolerance mechanisms; restricted ion transport, selective K+ absorption and tissue tolerance. Yield and related traits were evaluated under reproductive stage stress to identify progenies that showed good yield and stable performance across environments. Yield reduction due to salt stress (4 – 6 dSm-1) was attributed mainly to reduced number of grains per panicle and reduced weight of grains and panicle. These traits could be used for indirect selection for yield under salt stress. The study identified progenies BGJ-001, BGJ-002 and BGJ-223 which, produced yield greater than the recurrent parent (BG90-2) and local checks (Sahel 108 and Sahel 208) in stress environments. These progenies could be used as donors in a salt tolerance improvement programme. Progenies BGJ-046 and BGJ-047 were the most stable across environments whereas progeny BGJ-068 was high yielding and showed repeated performance in the stress environment
in the two years the trail was conducted. Progeny BGJ-015 was found to be high yielding under stress and non-stress conditions. Six tolerant progenies including BGJ-001, BGJ-002, BGJ-127, BG-053, BGJ-223 and BGJ-245 were identified. These could be used in breeding programmes for improving rice for salt tolerance. QTL analysis based on a linkage map generated from 701 polymorphic marker loci, generated from Rice 6K SNP array identified three QTLs for tiller number (qTN-2, qTN-6.2 and qTN 6-2), one QTL for spikelet sterility (qSTER-8) and two QTLs for yield (qYLD-9 and qYLD-12). The QTL qYLD-12 has large effect (24.2%) and co-localizes with previously mapped QTLs for important agronomic traits and blast resistance and has potential for post QTL analysis for gene discovery.