| Two experiments were carried out in field conditions in the farm of Henan Agricultural University in growing seasons of 2004-2005 and 2005-2006. Experiment one was a factorial combination of five sowing dates and six cultivars. Experiment two was a simulation-trial, in which the temperature was enhanced by covering wheat seedlings with man-made plastic box. Thus different temperature regimes were established for wheat after anthesis to evaluate temperature effects on grain quality traits, such as starch content and its components, starch paste properties, protein concentration and its components, farinograms and extensograms parameters. The main results were as follows:1 Both sowing dates and heat stress significantly influenced starch content and its components in grains of different special-used wheat cultivars. With the delay of sowing date, contents of starch and its component increased in the strong-gluten wheat cultivar Yumai 34 and the medium-strong gluten wheat Yumai 49. For weak-gluten wheat Yumai 50, total starch content and amylopectin content were gradually increased with delay of sowing date. In Experiment 2, heat stress at different grain filling stages decreased starch content and its component in all the three wheat cultivars. Compared with different periods of heat stress, we found that the effect occurred in early grain filling stage was much greater than in late and middle stages (The magnitude of influence was early stage>late stage>middle stage) in both Yumai 34 and Yumai 49. But for Yumai 50, the influence of heat stress in late stage was greater on amylopetin and total starch content, but influence occurred in early stages was greater on amylose.2. Flour paste parameters were significantly influenced by sowing dates in weak-gluten wheat Yumai 50 and Waxy wheat 1, while little influence was found in strong-gluten cultivar Yumai 34 and medium-strong-gluten cultivar Yumai 49. With delay of sowing dates, paste parameters (such as peak viscosity ) behaved increased significantly in Yumai 50 and waxy 1, while in Yumai 34 and Yumai 49, no difference was obtained among treatments of sowing dates. Heat stress occurred in early stage of grain filling significantly decreased the paste properties such as PV in all the three wheat cultivars. But for late stages of heat stress, the response was different among the three cultivars. Comparison of magnitude of the influence of heat stress, early stage of heat stress had relatively greater influence on paste properties in Yumai 34 and Yumai 49, but in Yumai 50, influence of middle stage of heat stress was greater.3. Protein content and its compositions in Waxy 1 were significantly influenced by sowing dates, whereas relatively smaller influence was obtained in common wheat cultivars in Experiment one. With delay of sowing date, protein content and its compositions showed a decreasing tendency in grains of Yumai 34, but the ratio of glutenin to gliadin increased. In grains of Yumai 49, only content of total protein and albumin decreased obviously, other compositions wasn't affected by sowing dates. In grains of Yumai 50, total protein content and its compositions (except for gliadin ) increased with delay of sowing dates, showing a negative effect for this weak-gluten cultivar.Total protein content was significantly increased by heat stress occurred in the early stage of grain filling, mainly caused by the enhance of gliadin (Yumai 49) and glutenin (Yumai 34) . While in middle or late stages of grain filling, contents of protein compositions were less influenced by heat stress. Compared with the three wheat cultivars, the effect of heat stress on protein compositions was much greater in Yumai 34 than in Yumai 49 and Yumai 50.4. Farinograms parameters were significantly influenced by sowing dates in Yumai 34, whereas less influenced in Yumai 49, Yumai 50 and Waxy 1. In strong-gluten cultivar Yumai 34, the minimum and maximum values of lour development time, stability time and Farinograms were obtained in B3 and B5, respectively.In Experiment two, stability time and Farinograms quality number were significantly decreased by heat stress at different grain filling stages in strong-gluten wheat cultivar Yumai 34, whereas relative smaller influence was found in weak-gluten wheat cultivar Yumai 50. For the medium-strong gluten wheat cultivar Yumai 49, the stability time and Farinograms quality number improved by heat stress occurred in early stage of grian filling, but decreased in the middle- or later stages of grain filling.5. Maximum resistance and R/E were significantly influenced by sowing dates in Yumai 34 and Yumai 49. With the delay of sowing dates, they decreased compared with the first sowing treatment (treatment of B3 obtained the smallest values and the differences were significant with treatments of B1 and B2 ) in Yumai 49, but increased in the later sowing treatments. While in Yumai 50 and Waxy 1, parameters such as the maximum resistance and R/E of Yumai 49 were little influenced by sowing dates.Under heat stress conditions, parameters such as the resistance and maximum resistance decrease in all the three wheat cultivars. And the greatest drop was obtained in cultivar Yumai 34. Parameters such as extensibility showed different changes among cultivars and heat stress at different grain filling stages.We concluded from the above results that, (1) different responses of quality traits to temperature regimes were obtained among the cultivars. In generally, strong-gluten wheat cultivar Yumai 34 showed relative sensitive to temperature changes and heat stress in grain filling stages. (2) Under conditions of minor magnitude of increasing temperature (with the delay of sowing dates), most quality traits in strong-gluten wheat cultivar were improved. While theses parameters (especially the processing quality traits) significant declined under heat stress conditions, indicating that wheat quality traits' response was different to various temperature regimes. (3) in wheat production, the optimum sowing dates should be chosen according to not only the quality changes in different cultivars varieties but also the grain yield. And Cultivating measures should be taken to avoid or relieve damages of heat stress at later growth stages. |
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