Effect Of Shading During The Grain Filling Period On Photosynthetic Characteristics Of Flag Leaf And Grain Yield Formation In Sorghum

Sorghum is the fifth largest grain crop in the world,and it is an important grain crop in China.Sorghum is a typical C4 crop that prefers high temperature and light conditions.Its leaves have strong photosynthetic capacity,and it has a high demand for light.However,the low-light stress caused by continuous rain and little light during the filling period of sorghum is extremely unfavorable to growth,development and grain formation in sorghum.To investigate the response of sorghum photosynthesis and yield to shading stress,in this study,Jinza34(tolerant of shading stress)and Jinza22(sensitive to shading stress)were adopted.We investigated the changes in the leaf morphological structure,chlorophyll content,photosynthetic characteristics,chlorophyll fluorescence characteristics,grain-filling characteristics and yield components.The results were as follows:(1)Shading stress during the filling period reduced the specific leaf weight and thinned the functional leaves,and the thinning of the sorghum leaves was mainly due to decreases in epidermal cells,mesophyll cells and vascular bundles.(2)The chlorophyll content of sorghum leaves increased,but the chlorophyll a/b content showed a decreasing trend.JZ34 had a higher content of chlorophyll b under the shading treatment,indicating that JZ34 had a stronger ability to capture light under shading stress.(3)Shading stress during the filling period significantly affected sorghum photosynthesis.Under shading stress,the net photosynthetic rate,transpiration rate,stomatal conductance and intercellular carbon dioxide concentration of the two cultivars decreased.The influence of shading on gas exchange parameters was more serious in JZ22 than in JZ34.Shading also significantly affected the chlorophyll fluorescence parameters of the flag leaves during the sorghum filling period.The chlorophyll fluorescence parameters decreased under shading stress in both cultivars.Compared to those in JZ22,JZ34 had a higher photochemical quenching coefficient and a lower non-photochemical quenching coefficient under the shading treatment,indicating that JZ34 had a higher light energy utilization rate under shading stress.(4)Shading in the filling period significantly affected grain filling in both cultivars and reduced the maximum filling rate of sorghum and the grain yield of sorghum.Grain filling in JZ22 was more obviously affected by shading stress than that in JZ34.These results revealed the different effects of shading stress on growth,development and yield formation in both cultivars.This study provides a reference and guidance for sorghum breeding and cultivation for shading stress tolerance.This study has important theoretical and practical significance for achieving high and stable sorghum yields under complex meteorological conditions.