Molecular Genetics of Cold Tolerance at Germination and Seedling Stages in Rice

Abstract

Low temperature stress is a major constraint for rice production in temperate and high altitude areas of the world. Delayed germination coupled with reduced seedling vigor hinders crop establishment and crop growth resulting in reduced rice productivity. Mapping of chromosomal regions controlling cold tolerance will accelerate marker-assisted breeding of cold tolerant rice varieties. A recombinant inbred line (RIL) mapping population involving a rice cultivar ‘Bengal’ and a US weedy rice accession ‘PSRR-1’ was evaluated for cold tolerance at both germination and seedling stages. Observations on germinating ability and seedling vigor were recorded under both low temperature (13oC) and optimum temperature (28oC) at germination stage. ‘PSRR-1’ performed better than ‘Bengal’ under cold stress. Forty-nine QTL distributed over ten chromosomes were identified for 11 traits. The number of QTL varied from one to nine with phenotypic variability of each QTL ranging from 3.5 to 12.7%. For 18 QTL, ‘Bengal’ alleles were adaptable, whereas ‘PSRR-1’ alleles improved germination and seedling vigor under cold stress in 31 QTL. Three major QTL were observed for coleoptile length and seedling shoot length. The QTL were clustered in six chromosomal regions. The congruency of a QTL cluster on chromosome 11 in this study with earlier studies suggests a potential target for cloning cold tolerance genes at germination stage. Evaluation of cold tolerance at seedling stage was conducted by exposing rice seedlings at the 3rd leaf stage to 18/8 oC day/night temperature for 18 days and scoring of visual damage on a 1-9 scale. ‘Bengal’ showed higher tolerance to cold stress than ‘PSRR-1’. Twenty-three QTL for four cold tolerance traits were detected along all twelve chromosomes at seedling stage. The number of QTLs varied between four and eight per trait and each QTL contributed 2 to 42% of the total phenotypic variation. Bengal alleles increased cold stress tolerance in 10 QTL and PSRR-1 alleles in rest 13 QTLs. The most prominent one was on chromosome 11 which harbored a cluster of cold tolerance QTLs at both germination and seedling stage. This study demonstrated that weedy rice can be a valuable donor for enhancing cold tolerance in rice cultivars.