| Three new two-line intersubspecific hybrid rice combnations: zhu Is/Guangjing 1, Lu 1 Ss/Guangjing 1 and Xiang Zao 2-2s/Guangjing 1 (expressed as A, C and E ); two two-line super hybrid rice contrastive combinations:Pei'ai 64s/E32 and Pei'ai 64s/9311 (expressed as B and D)and a three-line high-yeild check combination Shanyou 63 (expressed as F) were used in the study.Under the conditions of five sowing times (April 5, April 20, May 5, May 20 and June 4), the yield and main economical characters and traits, growing period, dynamic state of growth and developments, canopy-architecture, main physiological characters of three uppermost leaves in the later growth stage and rice quality were studied comparatively. The main results are as follows:1. The A's average yield of five sowing times is the highest (540.0 kg/mu) among six provided combinations. It increased 4.1%, 3.5% and 7.7% over B,D and F respectively. And with putting off sowing times, the increasing trend of yield is very obvious, the yield of the fifth sowing times is the highest. By variance analysis ,the yield of A is higher singnificalntly than other combinations, but the divergence of C and E is not singnificnat compared with three contrasts. On the aspect of indivdual biological yield ,the yields of A, C and E are 140.3g,139.1g and 137.1g respectively, all they are higher significantly than three contrasts.2. The average total growing periods of A, C and E are 148.8d, 151.8d and 146.4d respectively, which are 23.6d, 26.2d and 21.2d longer respectively than contrastive combinations. By variance analysis, the total growing periods of three combinations are longer significantly than three contrasts. In additions, the total growing periods of provided six combinations were shorten with putting off sowing times, the shortened ranges in order from the large to the small are: C, A, E, D, B and F. From the results combing with the yield, three Tow-line intersubpecific super rice combinations should be sowed in changsha in early June and cultivated as single late maturing rice or delayed late maturing rice.3. The average plant height of A, C and E are 149.9cm, 153cm and 148.8cm respectively, which are higher obviously than three contrasts. The largest seedline number per plant of A , C and E are 19.6, 21.3 and 21.5 respectively, which are lower obviously than three contrastive combinations,but the spike ratioes are all above 70% which are higher obviously than contrasts. The total leaf number per plant of A, C and E are 17.9, 17.9 and 17.4 respectively, which are more one leaf or so than three contrasts, and their leaf-emerging rates are slow obviously compared with contrasts.4. From the leaf length of three uppermost leaves,compared with three contrastivecombinations, all leaf length of the uppermost leaf 2 and 3 are longer than three contrasts combinations except that flag leaf are shorter than combination B. All leaf width of three uppermost leaves are wider singnificantly than three contrastive combinations. All leaf areas of three uppermost leaves are large significantly compared with three contrasts. From the leaf posture, the flag leaf angle of A, C and E are smaller significantly than F and larger singnificantly than B and D; their flag leaf droopy angles are similar to that of B and D and significantly smaller than F. To sum up,the canopy-architecture shapes of A, C, E are obviously superior to the three-line combinations F and inferior to super hybrid rice contrastive combinations D and B.5. The analytical results about physiological characters of leaf nitrogen content, soluble sugar content and dry-matter contribution dynamic of three uppermost leaves in later growing period are: leaf nitrogen content of different combinations have great divergence, that of D is lower obviously than other combinations; With putting off sowing times, all nitrogen content of every combination appeared descendent trend, the desendent rates are not obvious among provided combinations. The effect of dynamic change that sowing times taked on the nitro...
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