Effects Of Low Temperature And Water-Logging Stress At Bud Stage On Growth Characteristics And Yield Of Early Indica Rice

After direct seeding of early rice in Jiangxi Province,it is susceptible to bad weather such as "cold in late spring" and other phenomena such as rotten roots and rotten buds in bud stage of direct seeding early rice,which will cause serious harm to direct seeding early rice.In order to screen out drought-tolerant and sensitive varieties,large-scale direct-seeded early rice varieties were widely collected in the middle and lower reaches of the Yangtze River.Through field experiments,the effects of low temperature and flooding on growth traits and yield of drought-tolerant and sensitive varieties and their physiological mechanisms were further explored.The effect of seed soaking agent on alleviating low temperature in bud stage was explored by soaking seeds with seed soaking agent.The main results are as follows:(1)41 early indica rice were treated with three low temperature gradients(5?,8?,10?)and four time gradients(3 d,5 d,7 d,10 d)at the budding stage of early rice.The results showed that the dead seedling rate increased with the decrease of treatment temperature and the increase of duration days.The variance and variation range of the dead seedling rate of 12 treatments were the largest when treated at 8? for 10 d,which was suitable for early indica rice at budding stage.Ideal temperature for cold tolerance identification;4 extremely cold tolerant varieties,such as Zhuliangyou1 and Linglingliangyou7108,were screened out by dead seedling rate;8 strong cold tolerant varieties,such as Zhuliangyou101 and Zhuliangyou08;22 moderate cold tolerant varieties,such as Xiangzaoxian6 and Zhuliangyou819;and 7 sensitive varieties,such as Lingliangyou32 and Zhongjiazao17.(2)Deep water treatment(deep 5 cm treatment for 10 days)was carried out on 41 early indica rice varieties at bud stage.The results showed that the coleoptile,seedling height,root length,root number,aboveground biomass and root biomass of rice seedlings were significantly different from those of the control.Root-shoot ratio and root biomass contributed the most to the principal component analysis,and could best reflect the tolerance to flooding stress.By cluster analysis,41 early indica rice varieties were divided into three types: strong drought tolerance,moderate drought tolerance and non-drought tolerance.Among them,11 varieties such as Wen229 and Lingliangyou7108 were strong drought-resistant,20 varieties such as Luliangyou996 and You I651 were moderately drought-resistant,and 10 varieties such as Ganxin203 and Zhongjiazao17 were more sensitive.(3)Low temperature stress treatment at budding stage resulted in the reduction of rice yield,the slowdown of seedling growth,the extension of growth period and the decrease ofdry matter accumulation.It was also found that the effective panicle number and seed setting rate were the main reasons for the reduction of rice yield,followed by the number of grains per panicle and 1000-grain weight.The soluble protein content,SOD and POD activity of hypocotyls were significantly increased under cold stress,and the growth rate of cold-tolerant varieties was increased.The content of MDA was higher than that of sensitive cultivars,but the content of MDA was opposite.Combining yield and growth characteristics,it was found that cold tolerant varieties were more tolerant to low temperature than sensitive varieties.(4)Flooding stress at bud stage slowed down seedling growth and prolonged growth period.After flooding stress,plant height at seedling stage increased,root length,root number,shoot dry weight and root dry weight decreased.Soluble protein,SOD and POD content in leaves increased,and the rising speed of drought-tolerant varieties was significantly higher than that of sensitive varieties,while MDA content was the opposite.(5)Soaking seeds with 5 mg/L auxin IAA was beneficial to improve the Germination Effect of seeds;50 mg/L Paclobutrazol and 0.1% Shile time soaking seeds were beneficial to improve the survival rate of buds and alleviate low temperature injury under low temperature injury;50 mg/L Paclobutrazol and 0.1% Shile time soaking treatment could also improve the POD activity and soluble protein content of germs,and reduce MDA content.