The Photosynthetic Characteristics Of Wheat Cultivars (Triticum Aestivum L.) Released At Different Period

Eight wheat cultivars (Triticum aestivum L.) released in different period and popularized in winter wheat fields of Yellow River and Huaihe River district were compared in physiological indexes such as net photosynthetic rate (Pn) of flag leaves, chlorophyll content, soluble protein content, malondialdehyde (MDA) content, activities of antioxidative enzymes, canopy apparent photosynthetic rate and dry matter translocation. The wheat varieties selected in this study were Bima1, Fengchan3, Xiaoyan6, Xiaoyan54, Jinan 17 and Xiaoyan 81, 81-24, 41-16, which were released in 50s, 60-70s, 80s, 90s of the 20th century and at present respectively. At the same time, 33 wheat cultivars with different leaf gesture, different leaf type and different harvest index were used as materials to study the the relation among leaf area, photosynthetic rate of flag leaf and yield. The main results are as follows:1. Changes of photosynthetic characteristics and activities of antioxidative enzymes with variety renewal(1)Changes of photosynthetic characteristics in flag leaves of different wheat varietiesNet photosynthetic rate (Pn) in flag leaves of eight wheat varieties increased from booting stage to flowering and reached their maximal Pn about 10 days after anthesis, and after that, declined gradually. The Pn of modern wheat varieties was higher and the high Pn value had continued for a relatively long period. Changes of stomatal conductance (Gs) and transpiratory rate (Tr) had the same trend as Pn. However, the intercellular CO2 concentration (Ci) decreased from booting stage to about 10 days after anthesis, and then increased. The present wheat varieties maintained a lower Ci level than the old ones.Chlorophyll content in flag leaves during anthesis and grain filling stages had the same trend as Pn. From the beginning of flowering to the 11th day, there were no appreciable differences among different wheat varieties. Compared with the varieties released in earlier period, Xiaoyan 81 and Xiaoyan 54 had relatively higher chlorophyll content during grain filling stage and its Chl content decreased gradually at late grain filling stages.(2)Changes of soluble protein content, MDA content and activities of antioxidative enzymes in flag leaves of different wheat varieties during grain filling stageSoluble protein content in flag leaves increased after anthesis, and reached its maxima at about 5 days after anthesis, thereafter, decreased. The differences in soluble protein content among different wheat cultivars were pronounced at all the determined time. However, modern wheat cultivars maintained relatively higher soluble protein content than the older ones. MDA content in the flag leaves increased significantly after anthesis in all the wheat varieties. Nevertheless, the present varieties maintained lower MDA content in flag leaves and increased more slowly than in wheat cultivars released in earlier years.Changes of activities of antioxidative enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX) and peroxidase (POD) in flag leaves had the same trend with Pn. While the activity of CAT decreased from anthesis. During late grain filling stages, activities of antioxidative enzymes of the present wheat cultivars decreased more slowly and maintained a relatively higher level compared with the older ones.2. Changes of canopy apparent photosynthesis and dry matter translocation characteristics with variety renewalCanopy apparent photosynthetic rate (CAP) showed an increase trend with variety renewal. CAP of the present wheat varieties was about 1.2 ~1.5 times of the older ones at anthesis stage and 1.5~1.7 times during grain filling stage. There was a positive correlation between CAP and yield at anthesis stage and grain filling stages.The plant height of wheat decreased with variety renewal. The plant height of Bima 1 was about 110 cm, but the height of the newly bred wheat varieties was only about 70 cm. However, the leaf area index (LAI) increased gradually with variety renewal. LAI of older varieties was only approximately 3, however, LAI of Xiaoyan 81, the newly bred wheat variety could be about 5. Specific leaf weight (SLW) also showed the same trend as LAI. Dry matter translocation efficiency (DMTE) and the proportion of dry matter translocation in grain (DMTP) during grain filling also increased gradually with variety renewal, which accorded with the changes of harvest index (HI).3. The relationship among leaf area, photosynthetic rate and yieldThe correlations among the top-three leaf area and plant biomass, economic yield were significantly positive. However, there were no appreciable correlations among area of the other leaves at bottom and plant biomass, economic yield. There were positive correlations among photosynthetic rate of flag leaves and biomass, economic yield, but these correlations were not significant. Nevertheless, the correlations among the product of photosynthetic rate of flag leaves and flag leaf area and biomass, economic yield were positively remarkable.