Increasing population with decreasing resources and increasing climate vulnerability appeared as the great challenges to sustain food security of Bangladesh. Cold stress adversely affects growth and productivity of rice (Oryza sativa L.). Systematic studies have been carried out to improve understanding on rice cold tolerance. Two adverse conditions, such as low temperature stress at reproductive stages and flash flood at maturity affect the Boro rice in the haor areas of Bangladesh. Any deviation of these two phenomena is enough to cause disaster in haor areas. Here, we summarized different types of cold injury, rice cold injury scenario and cold tolerant rice varieties/genotypes available in different countries. Moreover, we discussed on rice cold tolerant barrier and flash flood risk in Boro rice cultivation at haor areas of Bangladesh. Based on the authors’ own research and available data, the concept of overcoming cold and flash flood damage was proposed. According to this concept there were distinguished possible ways how to improve cold tolerance and flash flood problem in Boro rice cultivation in BangladeshBangladesh Rice j. 2017, 21(1): 13-25

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46Variations in concentration and distribution of health-related elements affected by environmental and genotypic differences in rice grains Ren Xue-liang, Liu Qing-long, Wu Dian-xing, and Shu Qing-yao 45 QTL mapping of low temperature on germination rate of rice

Photosensitive rice varieties have higher advantages in delayed planting. The present study was undertaken to figure out the degrees of delayed planting and evaluate the performance of six modern Aman rice varieties (BR11, BR22, BR23, BRRI dhan46, BRRI dhan54) against three sets of delayed planting. Each rice variety showed considerable variations for plant height, days to panicle initiation, flowering and maturity. BR22, BR23, and BRRI dhan54 showed a drastic reduction in days to panicle initiation and varied from 65 to 58 days, 69 to 60 days, and 62 to 55 days respectively, while it varied from 76 to 80 days for the control variety BR11. Similarly, days to flowering of BR22 and BRRI dhan54 showed a gradual decrease following different planting time and varied from 92 to 86 days, and 83 to 77 days respectively, while it varied from 109 to 107 days for the control variety BR11. For the above traits, BRRI dhan44 and BRRI dhan46 showed a moderate reduction depending on the three sets of planting time. Grain yield of BR22, BR23 reduced at the third set with a value ranging from 5.8 to 5.0 t/ha, 6.1 to 5.1 t/ha respectively, while BRRI dhan54 showed consistency in grain yield with a range from 5.3 to 5.2 t/ha. In contrast, grain yield of remaining rice varieties ranged between 5.7 to 4.5 t/ha for BRRI dhan46, 6.2 to 3.9 t/ha for BRRI dhan46 while severe reduction for the control variety BR11 with a range from 4.4 to 2.0 t/ha was observed. In conclusion, BRRI dhan54 was found more suitable rice variety in delayed planting compared with other photosensitive rice varieties. In future, BRRI dhan54 could be used as benchmark rice variety in a special rice breeding programme designed for delayed planting. Bangladesh Rice j. 2019, 23(1): 65-72