Effects Of Shading On Sequential And Non-sequential Pattern Of Senescence And Formation Mechanism In Winter Wheat

The research was carried out at Water-saving & Irrigation Experiment Station in Northwest A&F University in 2013 and 2014. Four wheat varieties, including two sequential senescence of wheat, which are NR9405 and Xinong88yu3; two non sequential senescence, which are Wenmai19 and Lankaoaizao8. To build a simulation environment for the weak light transmittance of 70% in the shade of wheat flowering until maturity. Studied the effects of shading treatment on physiological parameters of the flag leaf and second leaf of sequential and non sequential senescence wheat, including chlorophyll content, total soluble sugar, soluble protein content, sucrose content and sucrose metabolism related enzyme activity. In order to investigate the adaptability to the anthesis shading environment of inverted senescing wheat, to provide a theoretical basis for the identification and breeding of wheat. The main results are as follows:1. After shading treatment spike weight and thousand kernels weight of the four wheat varieties reached significant level, natural conditions and shading under non sequential senescence varieties panicle weight and thousand kernels weight weight were greater than sequential senescence varieties and thousand kernels weight difference reached significant level. The thousand kernels weight of the drop in non sequential senescence varieties less than sequential senescence varieties.2. After 30% shading treatment, chlorophyll a, chlorophyll b and total chlorophyll content of flag leaf and second leaf in four wheat varieties increased, shading makes the chlorophyll a/b ratio decreased, reduction with different varieties. 30% shading treatment delayed and weakened the phenomenon of non sequential of chlorophyll content of non sequential senescence wheat in different varieties, non-sequential time of occurrence and degree in different non-sequential senescence varieties have differences.3. After 30% shading treatment, soluble sugar content and soluble protein content of the flag leaf and second leaf in the whole growth period of four varieties were significantly lower than that of natural conditions. Shading is not conducive to the synthesis of soluble sugar and soluble protein. Under 30% shading treatment, soluble sugar and soluble protein content of non sequential senescence of wheat flag leaf became lower than the second leaf, significantly later than the natural conditions and the difference between the flag leaf and second leaf decreased.4. The sucrose content and soluble total sugar content in leaves of four wheat varieties change trends are basically the same, first decreased and then increased and then decreased trend. 30% shading treatment is not conducive to the synthesis of sucrose in wheat leaves, compared to sequential senescence varieties, the top two leaves photosynthetic capacity is stronger, sucrose content is higher in non sequential senescence varieties. The differences of SPS and SS activities between the leaves of the sequential and non sequential wheat cultivars were significantly. The SPS and SS activities of sequential senescence wheat were first increased and then decreased, the SPS and SS activities of non sequential senescence wheat in flag leaf were bimodal curve which decreased and then increased and then decreased trend. 30% shading treatment significantly decreased SPS and SS activities in leaf, reduced the difference between the flag leaf and second leaf.5. Grain SS activity in four wheat varieties showed the trend of first increased and then decreased, the highest active time of different varieties difference. 30% shading treatment significantly reduced the grain SS activity, indicating that the ability of wheat grain sucrose degradation and utilization decreased. The effects of 30% shading on grain SS activity in the non sequential varieties is smaller than sequential varieties.The results show that non sequential senescence varieties have strong resistance to the weak light and have a strong adaptability to the rainy weather compared with the sequential senescence varieties. 30% shading treatment significantly decreased the yield of wheat, reduced the difference between the flag leaf and second leaf, delayed and weakened the phenomenon of non sequential of chlorophyll, soluble total sugar, soluble protein and sucrose content of non sequential senescence wheat in different varieties, non-sequential time of occurrence and degree in different non-sequential senescence varieties have differences. Although the non sequential senescence wheat show the phenomenon of the premature senility of the flag leaf than the second leaf in the shape, but the photosynthetic function of flag leaf still played a major role in late grouting, did not weaken immediately. By the end of the flag leaf photosynthetic function decline in the late filling stage, the second leaf continue to complete the grouting. Thus, the mechanism of non sequential senescence wheat in grain filling is better than that of the sequential senescence wheat. May be the important reason for the high yield of the non sequential senescence wheat.