Yellowing, stunting, and seedling death associated with cold stress is a common problem in many Asian countries for winter rice cultivation. Improvement of cultivars through marker-assisted selection of QTLs for cold tolerance at seedling stage from locally adapted germplasm/cultivar is the most effective and sustainable strategy to resolve this problem. A study was undertaken to map QTLs from 151 progenies of a cross between a cold susceptible variety, BR1 and a locally adapted traditional cultivar, Hbj.BVI. A total of six significant QTLs were identified for two cold tolerance indices-cold-induced leaf discoloration and survival rate after a recovery period of seven days on chromosomes 6, 8, 11, and 12. Among these QTLs,-- and -- being co-localized into RM7027-RM339 on chromosome 8 and -- and -- into RM247-RM2529 on chromosome 12 showed 12.78 and 14.96% contribution, respectively, to the total phenotypic variation for cold tolerance. Validation of QTL effect in BCF population derived a cross between a cold susceptible BRRI dhan28 and Hbj.BVI showed dominating effect of -- on cold tolerance at seedling stage and it became stronger when one or more other QTLs were co-segregated with it. These results suggest that the QTLs identified in this study are stable and effective on other genetic background also, which warrant the use of these QTLs for further study aiming to cultivar development for seedling stage cold tolerance.
Article HistoryAbiotic stresses limit crop growth at different growth stages resulting low yield of rice. Molecular characterization of parental materials gives precise information on the extent of genetic diversity exists between them. A set of 60 SSRs randomly distributed over 12 chromosomes were used to analyze eight cultivars intend to be used as parent in breeding programs to address cold and drought tolerance, and nutritional quality of rice. A total of 300 alleles were detected across the cultivars for 51 polymophic markers with 5.88 alleles per loci. On average 30.6% of the genotypes shared a common allele at any given locus. UPGMA cluster analysis showed that 67% common alleles were shared by the cultivars. The cultivars were clearly grouped into two distinct clusters at 67.0% genetic similarity. Hbj. BVI showing high tolerance to cold stress at seedling stage differed from cold susceptible BR1, BRRI dhan28 and BRRI dhan29 by 33% alleles while BR18 that showed moderately cold tolerance differed by 29.0 -29.9% alleles which indicated that only 3-4% alleles difference caused higher cold tolerance in Hbj. BVI. The moderate genetic distance between cold tolerant Hbj. BVI and high yielding BRRI dhan28 and BRRI dhan29 indicated that there is higher possibility of obtaining high yielding cold tolerant segregants from the crosses between them. On the other hand, Kalobokri, which had 31.7 mg zinc a kilogram of polished rice differed by 33.0% alleles from the drought tolerant rainfed low varieties BRRI dhan56 and BRRI dhan57 having moderate level of zinc (~20 mg/kg), which also indicated that crosses between them might produce progenies with higher nutritional quality under drought environment. Contribution/ Originality:This study is one of the few studies which have investigated the genetic distance between the parental lines that are intended to be used in the breeding program to address abiotic stresses, like drought and cold tolerance with high yield potential and enhanced nutritional quality, particularly zinc content in rice.
Rice plants are sensitive to cold stress at various growth stages starting from germination to maturity. Exploitation of cold tolerance for the development of cold tolerant varieties may help in saving crop loss or cost of production in the cold prone environment. Introgression of quantitative trait loci (QTLs) conferring cold tolerance in the elite variety may be the most effective and sustainable approach to address this issue. A F2:3 mapping population of a cross between a cold susceptible variety (BR1) and a cold tolerant variety (BR18) was used to map QTLs for cold tolerance at seedling stage. Three significant QTLs on chromosomes 1, 3 and 12 associated with cold tolerance were mapped between the markers intervals of RM220-RM10829, RM546-RM7 and RM27877-RM463, respectively at a threshold LOD of 4.3 through composite interval mapping. Phenotypic contributions of these QTLs were 50.7, 39 and 52.7%, respectively. Marker information of such a large effect QTL could be used in the breeding program after necessary validation to develop cold tolerant high yielding rice varieties.
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