Genetic studies on traits related to cold tolerance in rice (Oryza sativa L.).
Low temperature stress is commonly associated with rice cultivation in temperate growing areas where successful cultivars have to possess a high degree of cold tolerance at sensitive growth stages. This research was conducted to identify and tag quantitative trait loci associated with low temperature tolerance at the seedling and booting stage of rice. Cold tolerance was assessed using several parameters measured in replicated experiments under controlled environment and natural field conditions using 191 recombinant inbred lines developed from a cross between the japonica cultivar M-202 and the indica cultivar IR50. A genetic map composed of 181 microsatellite loci was constructed for QTL analysis implemented using the composite interval mapping approach. At the seedling stage, a major QTL associated with cold- induced wilting in the growth chamber experiment was identified on chromosome 12 accounting for 41% of the phenotypic variation. Another QTL with large effect on chromosome 1 explained 68% of the phenotypic variation for cold tolerance in the field. At the booting stage, two QTL on chromosomes 2 and 9 were associated with spikelet fertility assessed in the growth chamber and greenhouse; both explained a total of 18% of the phenotypic variation. QTL associated with heading date, plant height, panicle exsertion and length, number of grains per panicle and tillering were also identified in this research. To elucidate the relationships between several cold tolerance parameters and agronomic trait measurements using controlled and field environments, correlation analysis was performed. Several interesting QTL have been identified as potential targets in breeding for cold tolerant rice and for further study.