| Although rice planting area is only the one third of total crop planting area,it is considered that rice prodcution consume 60%of total agricultural water consumption in China.Therefore,developing and screening rice variety with drought-resistance is significant for saving-water agriculture,and extensive researches on drought resistance are extremely necessary in rice.In this study,the mini-core germplasm collections of rice were employed for investigating root-related characteristics and its relationships with rice drought resistance in 2006,2007 and 2008 years,respectively.Similar drought stress was applied at same stage(booting to anthesis) on each rice plant grown in PVC pipes.Once more than 80%leaves were rolled,the plants were rewatered and irrigated normally,and then the root-related traits were investigated at maturity stage.Based on the root biomass, the mini-core germplasm collections were devided into 3 groups in different years and water-supply conditions.The mean membership index value(F) was considered as the index for the drought resistance,the relationships of root-related traits and drought resistance were further investigated by the method of correlation and path analysis.On the basis of the relationships,the traits closely related to drought resistance were identified.The different mechanisms of drought resistance of rice varieties were revealed by studing the root growth characteristics with different types of drought resistance.The main results are as follows:1.Under different water conditions,genetic analysis and variance analysis of root-related traits showed that the genotypes of all traits were extremely significant differences.Comparing of the heritability under different water-supply conditions,the heritability of deep root traits were lower than that of shallow root traits,the heritability of root-related traits under well-watered condition were lower than that of water-stress condition.Correlation analysis on root-related traits showed that the identical traits were significant positive correlation cross the two years.2.Based on the root biomass,the mini-core germplasm collections were devided into 3 groups in different years and water-supply conditions.Sanbangqishiluo,Xiangdao, Qitoubaigu were simultaneously ranked into grade three under the well-watered condition, which is large-sized root biomass system;Haomake(K),Sanbangqishiluo,Zhonghua8, Bawangbian1,Xiangdao,Maguzi,Hengxianliangqiu were simultaneously ranked into grade three under the water-stress condition.Nipponbare,Qingsian16B,LimingB, Weiguo,Dandong upland rice,Qiuqianbai,Xuanenchangtan,Honggu,Xiangzaoxian7, 80B,Funingzipi,Zhenshan97B,Yelizanghua,Jindaol,Heijing2,Guanlaotou83 were simultaneously ranked into grade one with small-sized root biomass system under different water conditions3.The mean membership index value(F) was using for evaluated the drought resistance of mini-core germplasm collections.Four and fifteen varieties were identified as drought resistant ones,seven and six as drought sensitive ones in 2006 and 2007, respectively.Maguzi,Aihechi,Xibaizhan,Bawangbian1,Aimakang,Menjiading2, Zhonghua8,and Gui603 were drought-resistant varieties in two years.The correlation analysis among relative value of root traits and RPW,RSL and mean membership index value of drought resistance(F) showed that the relative value of RDWs and RDWt had the highest correlation coefficient with RPW,RSL and F.The study showed that the relative value of RDWs and RVs have the greatest effect on mean membership index value(F).4.Based on both the relative value of root traits and physiological characteristics,the 19 drought-resistant varieties were classified into 3 clusters.The first cluster consisted of four varieties with higher proline content and osmotic adjustment ability,which is considered to be drought-tolerant mechanism.The second clusters consisted of two varieties,of which relative maximum root length and relative deep root dryweight were significantly higher than the other varieties in two clusters and acquire water for growth by root growth downward.So,the varieties of the cluster were considered to be droughr-avoid mechanism.The third cluster consisted of 13 varieties,the relative root traits,osmotic adjustment and proline contents were on the middle level,suggesting the two mechanisms were in effect.
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