Grain Yield, Starch Quality And Their Formation Of Winter Wheat In Responses To Shading Stress After Anthesis

The field experiment was carried out at the Experimental Station of Shandong Agricultural University from 2005 to 2006. Two wheat cultivars, Jimai20 (JM20) and Shannong1391 (SN1391), were used for investigating the effects of shading stress at different grain filling stages on yield and grain starch quality formation of winter wheat. The field was shading by the black nets with 90% shading over the plants in early (6~9d after anthesis, S1), middle (16~19d after anthesis, S2) and late (26~29d after anthesis, S3) grain filling. The principal results are follows:1. Effects of shading stress at different grain filling stages on yield and starch quality of winter wheatShading stress at grain filling stage had a great effect on grain yield. Compared with control (CK), three shading stages all caused a significant decrease in the yield. The yield had great difference in treatments of two cultivars, and the trend as following: CK>S3>S1>S2 (JM20) and CK>S1>S2>S3 (SN1391), which demonstrated that different sensitive stage to shading after anthesis. The decreasing amplitude on grain yield of JM20 was higher than that of SN1391.Shading stress after anthesis significantly decreased the grain weight. The grain weight had great difference in treatments. The low light stress of S1 treatment reduced the kernel number per spike. In fact, it reduced the upper kernel number per spike, and the decrease extent of grain weight of S1 treatment was lower than S2 and S3 treatment. The deceases in grain weight in shading took place mainly basal kernels. Simulating the process of grain filling of basal and upper kernels in different treatments with Logistic Equation, and correlation analysis showed that it was mean grain filling rate and gradual increase period grain filling rate, but not grain filling duration that declined the grain weight under shading stress.The grain test weight of flour swelling power were significantly decreased at three shading stress, and the falling number was remarkably increase in S2 and S3 treatment. Peak viscosity, trough viscosity and final viscosity of shading stress excluding S3 treatment were lower than CK. In conclusion, shading stress after anthesis went against the development of wheat starch quality.2. Effects of shading stress at different grain filling stages on the contents of the starch and starch components in the maturityThe total starch and amylopectin content of shading stress after anthesis in two cultivars were significantly lower than that of CK, however, the amylose content of shading stress after anthesis in two cultivars was significantly higher than that of CK at maturity. Then, the ratio of amylose and amylopectin was enhanced by the low light of shading stress. Low light of shading stress reduced the total starch accumulation, amylose accumulation and amylopectin accumulation. It was amylopectin accumulation that decreased starch accumulation under shading stress. The decreased values of amylose accumulation were lower than the decreased values of amylopectin accumulation under shading stress. At maturity, the A starch granule population occupied 56%, 61.76%, 71.1%, 66.61% (JM20), 63.3%, 63.7%, 69.79%, 73.46% (SN1391) of the total volume, respectively. And the B starch granule population occupied 44%, 38.24%, 28.9%, 33.39% (JM20), 36.7%, 36.3%, 30.21%, 26.54% (SN1391) of the total volume, respectively. The volume% of the A granule was increased, and the volume% of the B granule was decreased in the maturity through shading stress. It was obvious that the effects of shading stress after anthesis on the volume distribution of starch granule were consistent with the effects of shading stress after anthesis on amylose and amylopectin content.Simulating the process of the starch accumulation in different treatments with Logistic Equation, and correlation analysis showed that it was mean starch accumulation rate and gradual-increase period starch accumulation rate, but not starch accumulation duration that decreased the grain starch accumulation under shading stress.3. Effects of shading stress at different grain filling stages on the photosynthetic traitsThe net photosynthesis rate and photosynthetic pigment contents of wheat flag leaves were significantly decreased at three shading stages. The ratio of chlorophyll b and chlorophyll a in shading stress treatments was higher than that of CK. It was stomatal limitations of JM20 S2 treatment and not stomatal limitations of other treatments of two cultivars that reduced net photosynthesis rate. The content of chlorophyll a was more sensitive to shading than chlorophyll b. Net photosynthesis rate and photosynthetic pigment contents were recovered after the shading, compared with CK.4. Effects of shading stress at different grain filling stages on the starch formationThe sucrose and total soluble sugar content in S1 treatment flag leaves of two cultivars increased after shading stress. Transport of sucrose and total soluble sugar in S1 treatment flag leaves was restrained by shading stress. Then, sucrose and total soluble sugar accumulation in S1 treatment flag leaves increased after shading stress. But the shading was relieved in the S1 treatment, the sucrose and total soluble sugar content of S1 treatment flag leaves was lower than that of CK. The sucrose and total soluble sugar content of S2 and S3 treatment flag leaves were lower than that of CK from shading stress to maturity. It showed that shading stress made against synthesize of sucrose and total soluble sugar.After 4d shading stress, the sucrose and total soluble sugar contents in three shading stress treatments reserved organs, such as stem, sheath, glume and so on, declined sharply. However, the sucrose and total soluble sugar contents of three shading stress treatments reserved organs at 35d after anthesis much higher than that of CK. It showed that shading stress went against reserve and transport of sucrose and total soluble sugar in the reserved organs.The sucrose contents in grains had great difference in treatments of two cultivars. The sucrose content of S1 treatment sharply decreased, and it was sucrose providing capacity to grain that decreased the grain sucrose content. The sucrose content of S2 and S3 treatment markedly increased. After the shading was relieved, the sucrose contents of shading stress treatments grain at 35d after anthesis much higher than that of CK. It suggested that shading stress went against transform from sucrose to starch.The activities of SPS in flag leaves and SS in grains significantly declined from stress to 35d after anthesis, which also demonstrated that sucrose synthesis in flag leaves and sucrose degradation were restrained by shading stress. The activities of AGPase in grains significantly declined from stress to maturity. It showed that shading stress reduced sucrose providing capacity, and restricted starch synthesis.The activities of GBSS of S1 treatment increased and the activities of SSS of S1 treatment increased declined after 4d shading stress. After the shading was relieved, the activities of GBSS and SSS of S1 treatment in two cultivars increased sharply. The activities of GBSS and SSS of S2 and S3 treatment in two cultivars decreased markedly from shading stress to maturity. It demonstrated that the low value of starch synthase didn't effect the S1 treatment starch accumulation, especially at the middle and late grain filling stages, but inhibited from the S2 and S3 treatment starch accumulation. Combined starch synthase with grain sucrose content, we suggested that it was substance providing capacity that decreased starch accumulation of S1 treatment, and it was the activities of starch synthase and substance providing capacity that declined starch accumulation of S2 and S3 treatment. It showed that shading stress inhibitted the photosynthesis in leaves (source), and also reduced the sink activities in grains and the transport capacity in translocation.