Raising also markedly reduced by imposing drought treatment for

Raising of seedlings is practiced in different rice-growing countries in a different way for transplanting. Usual practice of raising seedling is to sow seeds in the wet beds, which is very common in Bangladesh and other rice-growing countries of the world (Begum et al. 2002). In some countries in Asia and Africa, dry beds are also used to raise seedlings. An ideal seedbed is important for good germination and healthy seedling growth. Thus, special seedbed management is needed to improve crop establishment in areas where low winter temperature limits germination. Poor germination and leaf discoloration is the main problem in the seedbeds of winter rice. Covering of seedbeds with white ploythene has been shown to reduce cold injury in at seedling stage (Hayashi1961, Hoshikawa et al.1995). In a study at Bangladesh Rice Research Institute (BRRI), it was found that white polythene covering over the seedbeds at day time during cold spell reduces cold injury (BRRI 2015). However, Shathi et al. (1982) reported that coverage over the nurseries during night time (which raised night temperature 4.5?C) increased the number of tillers, seedling dry weight, reduced sterility and increased yield. The rate of germination can also be increased by covering the dry seedbeds for 7-10 days starting from the day of seeding. Chilling hardening is another approach of increasing cold tolerance in rice seedlings. It is well known that sudden exposure to low temperature during crop growth is more injurious than gradual exposure. During seasonal periodic cold stress plants have to be acclimated gradually to this type of stress to cope up with. Lee et al. (1989) observed increased cold tolerance when seedlings grown in polythene tunnel are hardened repeatedly by removing and replacing the cover 2-3 times during each day for 3-4 days before transplanting. Selection of land for seedbed is another crucial cultural practice. Seedbeds at sunny place produce heathy seedlings that can survive well in the main field after transplanting even during low temperature season. Chilling injury is also markedly reduced by imposing drought treatment for four hours prior to exposure the seedlings to low temperature (8-10?C) (Que and Rui-chi 1986). They found that cold injury of rice seedlings can be reduced by salt treatment on foliage (0.1 mol/L NaCl solution).