Effects Of Weak-light Stress During Grain Filling On The Grain Yield And Starch Qualities Of Waxy Maize

The experiments of weak-light stress (shading 30% and 50% was moderate and severe weak-light stress, taken the natural sunlight as control) during grain filling on grain yield and starch quality of waxy maize were carried out on experimental farm of the Agricultural College, Yangzhou University in 2013-2014. The control varieties (Suyunuo5 and Yunuo7) in national southern waxy maize regional test were taken as materials with split block design.The main results were as follows:Weak light stress during grain filling decreased the grain volume, weight, number per ear, results in the loss of grain yield. Compared to controls, the grain volume, weight, number per ear and yield decreased 22.4%,21.3%,19.8%,35.6%, and 26.8%,26.5%,37.2%,52.8% under moderate and severe weak-light stress, respectively. The grain moisture contents in response to weak light stress dependent on variety, planting year and shading degree. The reduction in grain number per ear was the most important factor leading to yield loss. Shading increased the protein content and decreased the soluble sugar content significantly. The starch content was increased under moderate shading condition and decreased under severe shading condition, respectively.Mature waxy maize starch granules were in the shape of irregular polygons and oval. Compared to moderate weak light stress, severe weak light stress increased the proportion of large starch granules and increased the proportion of irregular polygons. Shading after pollination increased the starch granule average size and the proportion of large granules (diameter>15μm). Compared to the control, moderate shading increased the blue value, λmax and iodine binding capacity. Shading reduced the swelling power of starch, while the response were dependent on planting years. In 2013, the starch swelling power gradually decreased with the shading degree, while the value in 2014 were higher under severe shading condition than under moderate shading condition The results of correlation analysis indicated the swelling power was negatively correlated to average granule size and the proportion of starch granules (>15μm). Shading after pollination had no significant effect on the crystal pattern and all samples exhibited a typical "A" type diffraction pattern. Compared to controls, moderate shading decreased the starch peak intensity, while severe shading increased it. The crystallinity of Suyunuo5 starch gradually decreased with the decrease of light intensity, the change tendency of Yunuo7 starch crystallinity were consistent with its peak intensity, which were both first decreased and then increased with the decrease of light intensity in summer, showing a certain correlation.With the decrease of light intensity, the peak, trough, final and breakdown viscosities of flour gradually decreased. The results of correlation analysis observed that peak, trough and final viscosities was positively correlated to soluble sugar content, indicated that the decrease of soluble sugar content under shading conditions make the flour paste less viscous. The peak and breakdown viscosities of starch gradually decreased with the increase of shading degree, while no obvious tend of observed on other pasting characteristics.With the decrease of light intensity, the flour transition temperatures gradually increase, and the value reached at significant level under severe weak-light stress conditions. Compared to control, the flour gelatinization enthalpy, peak height index, retrogradation enthalpy and retro gradation percentage was positively correlated to protein content and negatively correlated to starch content. The starch gelatinization enthalpy was decreased, while peak and conclusion temperature, gelatinization range and retrogradation percentage was increased under moderate shading degree. The thermal stability under moderate shading condition was less than under severe shading condtion. The starch gelatinization enthalpy and peak height index was negatively correlated to average granule size, while peak temperature, gelatinization range and retrogradation percentage was positively correlated to starch average granule size.