| Rice is the staple food for Chinese. Improving unit yield of rice is an important way to safeguard our food security with the background of increasing population, decreasing cultivated land and soil fertility degradation.In recent years, plant height of most hybrid rice cultivars in production is more than 100cm, and some of which even up to 130cm, nearly twice than semi-dwarf rice cultivars in 1960s. Maybe higher-stem rice will be cultivated in production in the future. The higher of rice plant, the more possible of lodging. Therefore, study on lodging resistance is a significant part to keep high yield of rice. Due to the study conditions, semi-dwarf hybrid rice cultivars were selected as materials in previous studies, which focused on the relationship between ability to resist lodging and basal internodes where lodging occurred usually. However, relationship between ability of lodging resistance and physical characteristics of semi-high-stem hybrid rice plant, including physical character of the whole plant, such as plant height, fresh weight, height of gravity center and reverse-force of the plant, physical characteristics of all the internodes. length and diameter of internodes, thickness of culms wall, was rarely reported. With the purpose of investigating relationship between ability of lodging resistance and physical characteristics of semi-high-stem hybrid rice plant,14 semi-high-stem hybrid rice cultivars had been selected for one experiment of the study. And four nitrogen fertilizer levels and different plant growth regulations were set to investigate reflection of ability of lodging resistance and physical characteristics of two kinds of semi-high-stem hybrid rice plant in another experiment of the study. In addition, ability of lodging resistance of rice plant was judged by lodging index and lodging percentage at mature stage. Lodging index was calculated by the following formula. LI=BM/RM X 100.BM is short of bending moment, product of fresh weight with plant height. RM is short for reverse-force moment, product of the mechanics to slope a plant 45 ° divided gravitational constant (9.8N/kg) and then multiplied by 20 centimeters, height of the mechanics on rice plant. The main consequences were as follows.1. Relationship between ability of lodging resistance and internodes configuration of semi-high-stem hybrid rice12 semi-high-stem hybrid rice cultivars were cultivated in the first experiment to analysis correlation between lodging index and physical characters of plant. configuration of internodes. The results showed there was very significant negative correlation between lodging index and reverse-force, reverse-force moment(r1=-0.87**, r2=-0.87**), but significant positive correlation with length of D4,D6.and both the proportion of total length from D5～D6 and D4～D6 (r1=0.61*, r2=0.63*),insignificant correlation with plant height, height of gravity center and fresh weight. Proportion of total length of some basal internodes of Zhunliangyou527 is higher than other 11 cultivars, which got lodging at mature stage.2. Effects on internodes configuration and ability of lodging resistance of semi-high-stem hybrid rice by nitrogen fertilizer levels.Two kinds of semi-high-stem hybrid rice, Zhunliangyou527 (easy to lodging) and Guangliangyou1128 (resist lodging), and four levels of nitrogen fertilizer(N1:180kg/hm2, N2:240kg/hm2, N3:300kg/hm2, N4:360kg/hm2) were set in the second experiment. The results were as following. As increased of nitrogen fertilizer application, lodging index increased and plant height, height and relative height of gravity center got higher as well. Zhunliangyou527 had higher sensitivity on nitrogen fertilizer than Guangliangyou1128, plant height, height and relative height of gravity center of which increased 3.2cm,1.6cm,0.8% at N3 compared with N1, respectively. Plant height, height and relative height of gravity center of Guangliangyou1128 increased significantly 8.7cm,5.8cm,2.4% at N4 compared with N1, respectively. D4 of Zhunliangyou527 significantly elongated 4.0% at N2 compared with N1 and D5 elongated 8.0% at N3 compared with Nl. Thickness of culms wall and diameter of Zhunliangyou527 had tendency of reducing. Length of D2 and D3 of Guangliangyou1128 significantly elongated 6.7% and 8.4% at N4 compared with N1 while D5 elongated as much as 13.9% at N4 compared with N1. Basal internodes of D5 and D6 of Guangliangyou1128 enlarged significantly at N4 compared with other three treatments. The same as Zhunliangyou527. thickness of Guangliangyou1128 reduced as nitrogen fertilizer increased.3. Effects on internodes configuration and ability of lodging resistance of semi-high-stem hybrid rice by spraying two kinds of plant growth regulations.Same as experiment two. Zhunliangyou527 and Guangliangyou1128were selected in experiment three. And two kinds of plant growth regulations. Lifengling(plant growth retardant) and gibberellins (plant growth promoter). were sprayed in this experiment. The results were as follows. Lifengling had good effects on enhancing lodging resistance of semi-high-stem hybrid rice plants. especially of Zhunliangyou527. It significantly reduced plant height of Zhunliangyou527 and Guangliangyou11284.0cm,7.0cm. respectively; and significantly lowed height and relative height of gravity center of hybrid rice plants. Length of D3, D5 and D6 of Zhunliangyou527 and D4.D5 of Guangliangyou1128 significantly shortened as much as 22.5%-27.6%. and diameter of D1～D5 of Guangliangyou1128 significantly reduced by spraying Lifengling. Internodes thickness of the both cultivars increased. However, gibberellins had the opposite effects on ability of lodging resistance, plant height, height and relative height of gravity center of semi-high-stem hybrid rice. It reduced its reverse-force moment, weakened the ability of lodging resistance of rice plants, which made Guangliangyou1128 got slight lodging. It increased the plant height of Zhunliangyou527 and Guangliangyou1128 as high as 4.3cm and 7.1cm, respectively. By spraying the plant growth promoter, length of D2 and D3 of the both cultivars significantly elongated 10.2%-18.4%. and increased diameter of some internodes. While it had little effects on thickness of the culms wall.4. Correlation between lodging index and internodes configuration after the regulators by nitrogen and plant growth regulations.Correlation analysis showed that there was significant negative correlation between lodging index and reverse-force, reverse-force moment(r1A1= r2A1=-0.97**, r2A1=r2A2=-0.90**,A1,Zhunliangyou527.A2.Guangliangyou1128, and same as follows), significant positive correlation with plant height, height and relative height of gravity center(r1A1=0.90**, r2A,=0.77*,r3A1=0.83*, r,A2=0.94**,r2A2=0.93**,r3A2=0.92**) in one cultivar.but insignificant correlation with fresh weight and bending moment. There was significant correlation between lodging index and length of D3. diameter of D2, thickness of culms wall of D1 and D3 of Zhunliangyou527. length of D2, D3 and D5, diameter of all the six internodes of Guangliangyou1128. Stepwise regression analysis showed length of Dl and diameter of D2 had negative effect on lodging index of Zhunliangyou527. while length of D3 and D6 had positive effect on lodging index of Zhunliangyou527. Length of D4 and D6 had positive effect on lodging index of Guangliangyoull28 while length of D1. diameter of D3 and D4 had negative effect on lodging index.To sum up. ability of lodging resistance of semi-high-stem hybrid rice plant depended on its reverse-force, reverse-force moment. Lodging index had insignificant correlation with Length of D4. D6 and proportion of total length from D3～D6 in plant height. Plant height has little effect on ability of lodging resistance of semi-high-stem hybrid rice. Both excess application of nitrogen fertilizer and plant growth promoter could weaken ability of lodging resistance of semi-high-stem hybrid rice plant while plant growth retardant enhance ability of lodging resistance of semi-high-stem hybrid rice plant. The change of lodging index contributed on regulation of physical characters and physical characteristics of internodes. Whether keep the balance of yield and lodging resistance with reasonable nitrogen application and plant growth regulation needs further researches. |
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