Genetic Dissection of Seedling Cold Tolerance in Rice (Oryza sativa L.).

Cultivated rice (Oryza sativa L.) is sensitive to temperatures below 15 to 20°C. Under low temperature conditions, rice plants respond in several ways and their sensitivity to cold can be manifested at all stages of development. Given the wide-ranging effects of low temperature on rice and the serious impact on productivity, tolerance to this stress is of considerable importance to temperate rice growing regions of the world such as the USA. Efforts to improve cold tolerance typically focus on the early and the reproductive stages of development, which have the greatest impact on production.

Cold stress at the early stages of development results in poor germination and growth. The increased seedling mortality and negative impact on plant development results in poor stand establishment and non-uniform crop maturation. Seedling cold tolerance is of particular importance in the USA where virtually all rice is planted using direct seeding methods that greatly increase exposure to low temperature stress compared to the transplanting of well-established seedlings common in Asia and Africa. One of our goals is to understand the molecular genetic basis of seedling cold tolerance in rice.

M202 is the predominant rice variety grown in California. Among its many positive attributes is good seedling cold tolerance. Previous genetic analysis of M202, a temperate japonica, has resulted in the identification of two major QTL, qCTS12 and qCTS4, which confer seedling cold tolerance to IR50, a cold sensitive indica variety from the Philippines. The effect of qCTS12 is observed under temperature conditions that result in wilting and necrosis in IR50 while qCTS4 provides tolerance to conditions that cause chlorosis and stunting. We have recently fine mapped the qCTS12 and qCTS4 loci. Progress towards isolation and characterization of the genes underlying qCTS12 and qCTS4 will be presented.