Research On Drought-Resistant Response Ability, Genetic Diversity And Association Analysis Of Different Ecotypes Of Soybeans In Shanxi Province

In this study, different ecotypes of soybean cultivars in Shanxi Province were use as materials tested. Drought stress in fields, pot experiments and yield measurement in fields were applied to research response to drought stress, change of the root and stem under drought, yield ability, genetic diversity of population, population structure, and association between traits and markers of cultivars, additionally, comprehensively evaluate low-temperature tolerance of cultivars under low temperature stress at the seedling stage for optimize the system of soybean’s stress tolerance. The results were as following:1. Taking 48 different ecotypes of soybean cultivars as materials tested, drought stress were used to the materials. At the seedling stage and pod-flowering stage, under normal and stress treatments, relative water content, proline content, relative electric conductance, chlorophyll content, activities of POD, SOD and CAT, and four photosynthetic indexes were determined. GGE bipolt was used to analyze the effect of the traits on treatments and subordinate function was used to classify the cuoltivras. The results showed （1）Under drought stress, relative water content and chlorophyll content declined, praline content and relative electric conductance ascended. Relative water content had the most obvious effect on response to drought in the normal treatment at pod-flowering stage. Chlorophyll content had the most obvious effect on response to drought in the normal treatment at seedling stage. Proline content and relative electric conductance had the most obvious effect on response to drought in the stress treatment at pod-flowering stage. Traits had significant correlations with each other. （2）Activities of protective enzymes ascended under drought, and they had different effect on response to drought in different treatments. They had significant correlations with each other. （3）All of the photosynthetic indexes declined under drought, they had different effect on response to drought in different treatments. They had significant correlations with each other.（4）Using subordinate function, among 48 cultivars, there were 2 drought-resistant cultivars,35 medium drought-resistant cultivars and 11 non-drought-resistant cultivars.2. Taking 12 different ecotypes of soybean cultivars as materials tested, pot experiments were employed and 3 treatments of normal water, low drought and strong drought were set. Photosynthetic indexes, chlorophyll content and leaf area were determined. After harvest, dry matters of above ground part, root length, and root weight were determined to calculate harvest index and root-shoot ratio. The results showed （1）Leaf area significantly reduced as the degree of drought increased.（2） Chlorophyll content significantly changed as as the degree of drought increased and the tendencies were not same. （3）Pn, Gs, TR and Ci all declined as the degree of drought increased. （4）Yield of seeds significantly declined at the strong stress and harvest index correspongdingly declined. （5）Most root length of the cultivars significantly declined as the degree of drought increased, so did root weight, and root-shoot ratios of most cultivars increased as the degree of drought increased.3. Taking 48 different ecotypes of soybean cultivars as materials tested, correlation, principal component analysi, cluster and GGEbiplot were used. Based on the twelve traits including plant height, weight per plant, mainstem pod number, mainstem node number, stem thickness, pods per plant, branch number, valid branch number,100-seed weight, pest-biiten seed number, seeds per plant and yield per plant, yield ability of cultivars tested were investigated, the resultis showed that （1） Plant shape traits had significant correlation between each, so did yield traits and they had more abundant correlation. （2）The first four principal components were extracted from the 12 traits of 48 cultivars, they were yield factor, plant shape factor, seed weight factor and seed weight II, each trait had different contribution to different components, （3）48 cultivars could be classified into 4 groups according to cluster, the first one was medium yield and potential cultivars, the second one was low yiled cultivars, the third one was medium-high yield cultivars, the fourth one was special and only one which was high yield cultivar.（4） Mainstem node number, stem thickness, plant height,100-seed weight had obvious effect on the third group of cultivars. Valid branch number, branch number, pods per plant, pest-biiten seed number, seeds per plant, weight per plant and mainstem pod number had obvious effect on the fourth group of cultivar.4. Using a natural population consisting of 102 soybean cultivars for polymorphism by using 59 SSR markers., the genotyping data of 50 SSR markers selected was used to analyze population structure, and then association analysis between SSR markers and 15 soybean agronomic traits were performed to discover elite alleles using TASSEL2.1 MLM （Mixed Linear Model） programs. The results showed:（1） A total of 157 alleles were found from 50 markers which appeared to be polymorphic among the 59 markers. Polymorphism information content （PIC） ranged from 0.038 to 0.761 with the mean of 0.431 and Shannon index ranged from 0.0973 to 1.6684 with the mean of 0.8449. （2） Markers classified the population into 3 groups at the position of GD=0.805. （3） Population structure analysis showed that the population of these materials was composed cf 4 subpopulations. （4） 8 SSR markers were found to associate with plant height, weight per plant, mainstem nod number, valid branch number, mainstem pod number, branch number shrunken seed number, pest-bitten seed number, protein content and oil content Excellent allelic genes, such as Satt248-A129, Satt168-A226, Sat₂99-A286 and Sat₂99-A2862 and so on, were found.5. We selected three different eco-types of soybean cultivars [Jinda53 （National Approval 2001006）, Jinda70（National Approval 2003006）and Jindou24（Shanxi Approval S-301）] bred and grown widely in Shanxi province as materials tested. At seedling stage, stress treatments of three kinds of low temperature and a control treatment were set in growth cabinets. The cabinets were set to keep respective constant temperature. The three stress treatments of low temperature were respectively 14℃,17℃ and 20℃. The control treatment of temperature was 23℃. When the treatments were finished, the cultivars were transplanted in a greenhouse for pot experiments. In the study, values of photosynthetic traits [including net photosynthetic rates （Pn）, intercellular CO2 concentration （Ci）, stomatal conductance（Gs） and transpiration rate（TR）]of the cultivars at the seedling stage were determined. Also, yield traits （plant height, plant weight, pods per plant and yield per plant） of the cultivars after harvest were determined. Furthermore, GGE biplot was employed for analysis of effect of traits on the cultivars, and correlations among the traits. Then, subordinate function was applied for comprehensive evaluation of low-temperature tolerance in the cultivars at seedling stage. The results showed that （1） Under the stress treatments of temperature, the seedling stages of all cultivars tested were elongated 1-12 days. （2） Under the stress treatments of temperature, values of four photosynthetic traits at seedling stage of the three cultivars all declined, the decline rates of stomatal conductance （Gs） and transpiration rate （TR） of the cultivars were significantly higher than the ones of the other two traits. The decline rate of each value of photosynthetic trait of Jinda53 was significantly lower than the one of each photosynthetic trait of the other two cultivars, which revealed that photosynthetic capacity of Jinda53 performed stronger low-temperature tolerance. Additionally, Jinda70 maintained higher Pn values than the other two, which was beneficial to its accumulation of dry matter. （3） Values of four yield traits of the cultivars tested all significantly declined under the stress treatments. The decline rates of plant weight and pods per plant were significantly higher than the ones of the other two traits. Among the three cultivars, the decline rates of plant weight and pods per plant of Jinda70 were lower than the ones of the two traits of the other two cultivars. Furthermore, the decline rates of yield per plant of Jinda70 under all stress treatments were lower than 50%, indicating that low temperature had the least effect on Jinda70’s yield. （4） GGE Biplot analysis revealed that decline rates of TR and Gs had the most obvious effect on Jinda70, decline rate of Pn had the most obvious effect on Jindou24, decline rate of Ci had effect on both Jinda70 and Jindou24, and no decline rate of photosynthetic trait values had obvious effect on Jinda53. Meanwhile, the Biplot indicated that there were significantly positive correlations among decline rates of TR, Gs, Ci, and Pn. Analysis of yield traits using the Bipolt showed decline rates of plant height and plant weight had the most obvious effect on Jinda53, decline rate of yield per plant had the most obvious effect on Jindou24, decline rate of pods per plant had effect on both Jinda53 and Jindou24, and no decline rate of yield trait values had obvious effect on Jinda70. There were significantly positive correlations among decline rates of plant weight, plant height, pods per plant, and yield per plant. Hence, the traits were able to be evaluation indexes for low-temperature tolerance. Using subordinate function, the order of low-temperature tolerance in the three cultivars at seedling stage from most to least was found to be Jinda70, Jinda53, Jindou24.