STUDIES ON RICE IMPROVEMENT FOR LOWER SENSITIVITY TO COLD STRESS M. Salam * , N.K. Saha, P.S. Saha, M.U. Islam and M.R. Karim Agriculture and Food Security Program, BRAC, Bangladesh Abstract Irrigated rice becomes the major alternative to livelihood improvement in haor areas (1M ha) of Bangladesh. This crop suffers from cold stress (10-18 o C) at seedling to flowering stages. In addition, its maturity is delayed up to late-April because of prevailing minimum critical temperature in early-March at the booting stage. Consequently, the crop is submerged on mid- April especially in the rough-weather years. Chaiti group of rice varieties have lower sensitivity to critical temperature (18 o C) at booting stage and matured by mid-April. Moreover, development of varieties matured at mid-April can open the scope of four rice crops per calendar year. Therefore, efforts have been made to develop low temperature stress tolerant rice at BRAC. Rice germplasm was shared from GSR, IRTON and IRBN in cooperation with IRRI. Seeding of two consecutive years on 10 November (2011 and 2012) identified NOVATOR, UZHNEY, FLAGMAN, GAMMA, VNIIR 72807, VNIIR 8572 and VNIIR 9678 as low temperature stress tolerant similar to Chaiti variety (Hbj.B.IV). The genotypes possessed HYV characters, grains without awns and Japonica type. Therefore, crosses were made involving the germplasm and five selected crosses were studied. All these F 1 s matured 2-5 April and showed HYV characters though sterility was very high (32-76%) when seeded on 12 November. Apparently it indicates the start of developing rice with lower sensitivity to cold stress. CNI 9028 (GSR) matured on 10 April and was placed in four rice crops schedule starting from 20 March 2012. Four crops were successfully harvested in a calendar year and cumulative yield was 18.2tha -1 . Key words: Cold stress, Low sensitivity, Haor area, Irrigated rice, Mid-April maturity, Flash flood, Four rice Introduction: Flood prone irrigated low land ecosystem consisted of Haor (Basin) and Beel (Low lying) areas in Bangladesh. Originally, these areas were the habitat of Deep Water Rice (DWR) called Floating Rice. Importantly, only very small areas were planted to irrigated lowland rice at the banks of the cannels and adjacent to water sources. Chaiti group of traditional rice varieties were cultivated through human drown irrigation equipments. Theses rice varieties mature by mid-April and save the crop from flash flood. Because of the very low yields of DWR and the introduction of high yielding rice varieties iAt present, the whole Deep water rice areas are being converted to irrigated lowland rice ecosystem. It covers >1.5 million hectares. Farmers have been adopting long duration (160 days) varieties (IR8, BR3, BR19 and BRRI dhan29) and facing the high risk of flash flood during crop maturity. This problem can be solved by introducing short duration rice varieties that can mature on or before 15 April when seeded in early November. Trails of popularly grown short duration varieties viz. BRRI dhan28 and BRRI dhan45 showed maturity on or after 20 April when seeded mid- November. Furthermore, these varieties showed high sterility due to prevailing cold weather when seeded on early November.