Understanding the waxy maize starch physicochemical properties response to heat stress during grain filling could improve starch quality.The effects of heat stress during early（1-15 days after pollination,DAP） and late（16-30 DAP） grain filling stages on the starch physicochemical properties of four waxy maize varieties were evaluated.Crystallinity only increased in Suyunuo 5 after exposure to high temperature at late grain filling stage.The effects of heat stress on digestibility and swelling power were dependent on varieties and stages.Generally,swelling power was increased by heat stress at early grain development stage and digestibility was increased by high temperature at late grain filling stage,respectively.The results of correlation analysis indicated the starch with large granule size could swell well and easy digest.Peak,trough,final,and breakdown viscosities in response to heat stress were dependent on stages and varieties.In general,peak,trough and final viscosities were decreased and increased by heat stress at early grain formation and late grain filling stages,respectively;whereas the breakdown and setback viscosities were similar among the three treatments.Heat stress increased the gelatinization temperatures and retrogradation percentage.Gelatinization range decreased under heat stress at 1-15 DAP but remained constant under heat stress at 16-30 DAP in all varieties.The starch exposed to high temperature at 16-30 DAP presented higher digestibility and peak viscosity and lower retrogradation percentage than those at 1-15 DAP.Therefore,heat stress at early grain formation stage severely affects the physicochemical properties of starch.
Grain physicochemical properties determine the table quality of fresh waxy maize. Two waxy maize varieties, Suyunuo 5 （shading tolerant） and FHN003 （shading sensitive）, were used to estimate the effect of shading （plants received 30% less radiation than control） during grain filling （from 0 d to 23 d after pollination） on physicochemical properties of fresh waxy maize grain. Shading decreased the grain fresh weight of Suyunuo 5 and FHN003 by 8.4 and 19.1%, respectively. Shading increased the grain water content of FHN003, whereas that of Suyunuo 5 was not affected. In both varieties for shading treatment, soluble sugar, starch and protein contents were decreased, whereas zein content was increased. The changes in globulin, albumin and glutenin contents under shading were variety dependent. In both varieties, shading decreased λmax, iodine binding capacity and the percentage of large starch granules （diameter 〉17 μm） but increased crystallinity. The results of rapid visco analysis showed that the viscosity characteristics （except for pasting temperature） of both varieties were decreased by shading; however, FHN003 was more severely affected than Suyunuo 5. Under shading, Antet and %R were decreased in both varieties, whereas the changes in △Hgol and transition temperatures were variety dependent. Hardness, cohesiveness and chewiness were decreased in both varieties. Significant differences in physicochemical characteristics were observed between the two varieties.
为探明不同施氮水平下玉米超高产（≥13 500 kg hm 2）群体氮磷钾积累及分配规律,通过苏玉20、浚单20两品种3年不同氮肥运筹方案的试验,实现了籽粒最高产量14 753 kg hm 2的目标。结果表明：（1）随着生育进程,两品种氮磷钾在植株、籽粒中积累逐渐增大,在叶片、茎秆、叶鞘中呈先单峰变化趋势,叶片氮钾峰值在大口期,磷峰值在开花期。增大灌浆期植株氮积累量及叶片氮转移率,促使成熟期籽粒氮磷较大积累量,利于超高产玉米群体的形成。（2）籽粒产量、1 kg氮生产籽粒量、氮肥的农学效率、氮素利用率、植株（叶片、茎秆、叶鞘、籽粒等器官）氮磷钾含量在450 kg hm 2施氮水平时达到最大值,其值（苏玉20）分别为14 753 kg hm 2、44.0 kg、19.24%、38.63%、335.4kg hm 2、178.2 kg hm 2、230.7 kg hm 2,过高过低施氮均使氮磷钾积累量及产量下降。（3）由两品种产量与施氮水平的回归方程,确定了超高产时的最佳施氮量、超高产施氮水平和最佳施氮范围,苏玉20分别为457.0 kg hm 2、418.3~495.7 kg hm 2、418.5~495.4 kg hm 2;浚单20分别为452.7 kg hm 2（最佳施氮量）、410.8~494.6 kg hm 2（最佳施氮范围）。
