| In recent years, the increasing greenhouse effect and the frequent extreme heat weather had made a serous harm to the crop yield and quality. The research on the heat tolerance identification and its physiological mechanism of soybean cultivars were conducted, which were significant for breeding heat-tolerance soybean cultivars and soybean high yield cultivation. The heat-talerance of 155 soybean cultivars(lines) were uesd as experimental materials to evaluate comprehensively, and selecting heat-tolerance tolerant cultivar Changnong17 and heat sensitive cultivar Jinzhou 4-1 to research the heat resistant physiological mechanism at different growth stages. The major results of the studies were as below:1. The 155 soybean cultivars (lines) were classified into six types at both treatment stages, which were strong heat-tolerance type, heat-tolerance type, medium heat-tolerance type, medium sensitive type, sensitive type and strong sensitive type. Considering the identification results of flowering and seed-filling heat-tolerance, the study screened 4 very heat-tolerance soybean cultivars (lines) and 63 heat-sensitive soybean cultivars (lines). 100-seeds weight, seed weight per plant, pods per plant, stem length, stem diameter, internode length and shoot dry weight per plant could be used as identification indexes of heat tolerance at flowering stage. Seed weight per plant, seeds per plant, seeds per pod, stem length, internode length, shoot dry weight per plant and fat content could be used as identification indexes of heat tolerance at seed filling stage.2. The results of heat stress in different growth stage showed as below. High temperature at seedling stage, the souble sugar content, ASA content, POD activity and chlorophll a/b ratio were reduced, and MDA content, SOD activity and chlorophyll content were inscreased. proline content was most with 30±2℃, but it was declined with the increase of temperature stress. High temperature at flowering stage, the souble sugar content, ASA content, POD activity and chlorophll a/b ratio were reduced with the increase of temperature, and proline content, MDA content, SOD activity and chlorophyll content were enhanced with the increase of temperature. With the treatment of 35±2℃ and 40±2℃ at seed-filling stage, the souble sugar content and chlorophll a/b ratio were reduced, and MDA content, SOD activity and POD activity were increased. Meanwhile, the ASA content, proline content and chlorophyll content had significant difference between Changnongl7 and Jinzhou4-1. The reduction of souble sugar content, chlorophll a/b ratio and MDA content were less than those of Jinzhou4-1, and the increases of MDA content of Changnong17 was less than it of Jinzhou4-1. The proline content, ASA content, SOD activity and POD activity of Changnong17 were higher than those of Jinzhou4-1.3. The seed weight per plant of soybean was significantly decreased under the high temperature stresses of 35±2℃ and 40±2℃ on flowering stage and seed-filling stage, and seed weight per plant was decreased even more by high temperature at the time of seed-filling stage. The yield per plant of heat-sensitive Jinzhou4-1 was decreased more than heat-tolerance Changnong17. Through the correlation analysis, seed weight per plant was significantly positively correlated with that of the content of soluble sugar, chlorophyll a/b and negatively correlated with MDA content. The accumulation of MDA was negatively correlated with soluble sugar content, ASA content, POD activity and chlorophyll a/b ratio. POD were significantly positively correlated with ASA and SOD, respectively. In conclusion, the more serious the membrane lipid peroxidation, the lower soluble sugar content in soybean leaves, the weaker the antioxidant capacity, the more obvious the imbalance of chlorophyll a /b ratio, the more the seed weight per plant decreased. ASA, POD and SOD had synergistic effect on scavenging reactive oxygen, which could remove active oxygen radicals effectively, and enhanced the heat resistance of soybean. |
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