Screening Of Low Temperature Germplasm Resources At Rice Seedling Stage And Low Temperature Regulation

Rice,as one of the main food crops in China and even the world,is susceptible to chilling injury.As the saying goes “Good seedlins equivalent to half a year's grain”,Seedling stage is a critical period for rice cultivation,if the rice seedling stage encounters low temperature and cold damage,it will inevitably affect the quality of the seedlings,thus reducing the yield,and affecting the world food security.Screening of low-temperature germplasm resources at seedling stage,effect of low temperature on seedling root in seedling stage,screening low temperature regulators and its regulatory mechanism in rice seedling stage were studied in the paper.The results are as follows:The artificial climate box was used to simulate the low temperature,there were 19 materials for cold resistance level 1,accounting for 8.26 % of the tested materials;11 materials for cold resistance level 3,accounting for 4.78 % of the tested materials;20 materials for cold resistance level 5,accounting for 8.70 % of the tested materials;48 materials for cold resistance level 7,accounting for 20.87 % of the tested materials;132 materials for cold resistance level 3,accounting for 57.40 % of the tested materials.There were only 2 materials for level 1 under the natural low temperature in early spring in bud and seedling stage,accounting for 2.13% of the tested materials;3 materials for cold resistance level 3,accounting for 3.19 % of the tested materials;7 materials for cold resistance level 5,accounting for 7.45 % of the tested materials;68 materials for cold resistance level 7,accounting for 78.34 % of the tested materials;14 materials for cold resistance level 3,accounting for 14.89 % of the tested materials.The results of early spring natural low temperature identification were basically consistent with that of the artificial climate box.2.The low temperature stress at seedling stage inhibited the growth of rice seedling roots,But there were differences between different varieties of cold tolerance.Under low temperature stress,the two indexes of root electrical conductivity and malondialdehyde content showed an increasing trend,and the root vitality gradually decreased compared to the control,the change range between varieties was different.The increaseing extend of root electrical conductivity and malonaldehyde content and the decreaseing extend of root activity in cold tolerant cultivar Sanqishiluo were less than those of cold sensitive cultivar Xiangzaoxian45;The root SOD activity of cold sensitive rice Xiangzaoxian45 was increased first and then decreased,while the cold resistant rice Sanqishiluo kept increasing.Under low temperature stress,epidermal cell of root top in cold sensitive cultivar Xiangzaoxian45 arranged irregularly and untightly,vascular bundle of connective tissue was seriously destroyed,and vascular bundle sheath cell arranged irregularly,xylem and phloem were unclear.while epidermal cell wall in vascular bundle of connective tissue in cold tolerant cultivar Sanqishiluo arranged regularly and tightly vascular bundle sheath cell and parenchyma cells arranged regularly xylem and phloem were clear.This indicates that the effect of low temperature on the root tip morphological structure of the seedlings with cold tolerant cultivar Sanqishiluo was less than that of cold sensitive cultivar Xiangzaoxian 45.3.In this 7 tested reagents,solutions of calcium chloride(0.01mol/L),uniconazole(20mg/L),potassium dihydrogen phosphate(6g/L),salicylic acid(100mg/L)and abscisic acid(10mg/L)could significantly increased the survival rate of seedlings under low temperature stress;There were 10 kind of mixed regulators,mixed with different single reagents at different scales,that could increased the living rate by more than 40 % after low temperature stress,one of the mixed reagents increased by 80%.4.Compared to the control,spraying RKHJ could increase seedling dry weight,fresh weight and SOD activity under low temperature stress,the increased scope of cold sensitive varieties was greater than that of cold resistant variety;Spraying RKHJ could reduce MDA content in the leaf and slow down the decreased tendency of chlorophyll content of seedlings after low temperature stress,cold sensitive variety was less than that of cold resistant variety.In general,spraying RKHJ could improve cold resistance of cold sensitive variety more than that of cold tolerant variety.