Effects Of Shading On Ear Differentiation And Grain Filling Of Spring Maize In Northeast China

It is important to study the effects of shading on spring maize ear characteristics and yield,which can provide important references to maintain a high and stable yield of spring mazie under the situation of climate change and dense planting.Therefore,a shading experiment was carried out with two cultivars(Zhongdan909: ZD909;and Shenyu21: SY21)at Gongzhuling City,Jilin Province in 2015 and 2016.Four shading treatments(ambient control CK,shading from jointing stage to tassel flower stage S1,shading from tassel flower stage to mature stage S2,and shading from jointing stage to mature stage S3)were chosen to investigate the effects of shading on ear differentiation characteristics,grain development and yield of spring maize in Northeast China.The main results are as follows:(1)Shading before flowering affected the progress of ear differentiation of spring maize significantly.Shading before flowering delayed maize anthesis and silking stages and especially postponed silking stage that resulted in the increase of anthesis-silking interval(ASI).Since the increase of ASI,the rate of silk and pollinate plants decreased,final empty bar rate raised.About ASI,pre-flowering shading(S1 and S3 treatments)had more influence contrasted with the post-flowering shading,and the impacts of shading on SY21 were greater than ZD909.Besides these,shading reduced the length and diameter of ear significantly,post-flowering shading(S2 and S3 treatments)affected more than the pre-flowering shading and they had superimposed effect.No significant difference was found in the number of tassel branches under shading,whereas pre-flowering shading could decrease the length of tassel while post-flowering shading had no obvious effects.(2)All Shading treatments increased grain abortive rate significantly.The response sizes of shading on the number of total florets varied with cultivars.Shading bofore flower stage reduced the number of total florets of ZD909 but had no significant impact on SY21.Shading increased the ratio of total abortive florets and decreased final grain number.S2 and S3 treatments increased the total abortive ratio of florets while S1 treatment showed smaller effects.Pre-flowering shading mainly reduced the number and rate of fertilized florets,hardly had effect on the fertilized florets after restoring natural light.However,post-flowering shading increased the ratio of abortion of fertilized florets.In general,post-flowering shading had more influence on forming final grain compared with the pre-flowering shading,and shading had less influences on ZD909 compared to SY21.(3)Shading had significant effects on grain filling characteristics.The grain dry matter weight and grain filling rate all decreased under all shaded conditions.As to grain filling parameters,shading delayed the emergence time of maximum grain filling rate,prolonged active grain filling period,declined mean grain filling rate and the final grain weight.The S1 treatment of ZD909 had less influence on the maximum grain filling rate,maximum grain fresh weight and volumn,while S2 and S3 affected these indicators significantly.Different with ZD909,these three indicators at SY21 all decreased significantly under all shading treatments.So,the effects of pre-flowering shading on grain filling for ZD909 are less than SY21.And the degree of grain filling in response to different shading regimes showed that S2 affected it most.(4)Significant impacts on yield were found among different shading treatments.Pre-flowering shading could increase the height of plant and ear,and decrease the stem diameter;nevertheless,post-flowering shading hardly had effect on these indicators.Leaf area decreased under shading especially in the period after flowering,the capacity of photosynthetic declined and the amount of dry matter lowered.Meanwhile,shading effected the normal growth of root,resulted in the decrease of root dry matter weight and root length.Pre-anthesis shading reduced the root/shoot ratio,but post-flowering shading had little effect on it.Shading decreased the number of ears per hectare,kernels per ear and 100-grains weight,and reduced the ear length,ear diameter,row per ear and the number of kernel per row significantly.The ratio of empty plant and lodging rate had increased significantly under the shading treatments.Shading decreased spring maize yield significantly.Except that 100-kernels weight was more influenced by S2 than other treatments,the response size of shading on yield and its related traits showed that S3>S2>S1.