| The effects of plant density, nitrogen application amount and basal: top dressing N ratio on the characteristics of population with good quality and high efficiency in weak gluten wheat cultivar Ningmai 9 (T. aestivum L) were studied on the experimental field of Crop Cultivation and Physiology Key Laboratory of Jiangsu Province, Yangzhou University in 2000-2002. The main results were as follows.1. Indices of population quality and plant type with good grain quality and a grain yield of about 6000kg/ha.1/..1 Population quality indices.The ideal number of main stems and tillers per hectare was 800 104 -900 104 at early wintering stage, 1100 104 -1200 104 at maximum, 450 104at maturity. The earing percentage of main stems and tillers should be 40%. The perfect amount of accumulated dry matter was 350-500kg/ha at wintering stage, 3 103-3.5 103kg/ha at jointing stage, 11.0 103-12.0 103kg/ha at anthesis, 14.0 103-15.0 103kg/ha at maturity, 3.0 103 -3.5 l03kg/ha from anthesis to maturity. The suitable leaf area index was 1.5-2.0 at wintering stage, 4.0-4.5 at jointing stage, 6.5-7.0 at booting stage, about 5.0 at anthesis, about 3.5 at early milk stage, about 2.0 at late milk stage.1.2 Plant type indices.1.2.1 Leaf type. The ideal order for leaf blade length was penultimate leaf>3rd leaf from top >flag leaf, for leaf width was flag leaf > penultimate leaf > 3rd leaf from top, for leaf area was penultimate leaf > flag leaf > 3rd leaf from top. The width, area and specific area weight of flag leaves and penultimate leaves were significantly positively correlated with grain yield, whereas, the ratio of length to width of flag leaves was significantly negatively correlated with grain yield.1.2.2 Stem type. The ideal plant height was about 90cm. The length proportion of basal internode to upper 5 internodes should be 1: (1.5-2): 2.5: 3: (4.5-5): (7-8) respectively. The suitable ratio of peduncle length to stem length was 36-38%. The ratioof the length of peduncle plus ear to plant height should keep 42-44%. The perfect plant height component index I1 was 0.615-0.620. The ratios of peduncle length to stem length, and the length of peduncle plus ear to plant height as well as I1 were positively correlated with grain yield.1.2.3 The number of upper layer roots. The minimum number of upper layer roots per stem should be 5-6. The number of upper layer roots per stem was positively related to spike weight and 1000-grain weight.1.2.4 Spike type. The perfect number of grains per ear was 41-45; the suitable ear weight was 1.3-1.35g. The number of seeded spikelets per ear should be 17-19. The number of grains per ear was positively related to grain yield, whereas, the number of degenerated spikelets per ear was negatively related to grain yield.2. Effects of plant density and nitrogen on plant type. Increasing basic seedling number, and reducing nitrogen applying amount and top dressing N amount could not improve plant type, which resulted in low yield.3. Physiological aspects related to flag leaf senescence. The treatment with 240 104 plants/ha, 240kg/ha N, and basal: top dressing N ratio 7:3 could delay chlorophyll's degradation of upper three leaves, keep the activities of superoxide dismutase (SOD) and peroxidase (POD) at a high level, decrease malondialdehyde (MDA) content at late growth stage, meanwhile, increase zeatin riboside (ZR), isopentenyl adenosine (iPA), gibberellin (GA3), indole-3-acetic acid (IAA) contents in leaves and decrease abscisic acid (ABA) content, which resulted in the delay of flag leaf senescence, and the coordination of grain yield and grain quality.4. Effects of plant density and nitrogen on grain starch formation. Under the same plant density and basal: top dressing N ratio, only decreasing nitrogen application amount could cause the decline of sucrose phosphate synthase (SPS) activity and sucrose content in flag leaves, but the rise of sucrose synthase (SS) activity in grains. Moreover, sucrose content in grains was decreased. ZR, iPA, GA3, IAA con...
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