| Lodging is one of the main reasons that restrict the high and stable yield of rice.Lodging mostly occurs at the base of stem,which is closely related to the amount of nitrogen fertilizer and planting density.Exploring the relationship between stem traits and lodging resistance of different types of rice varieties under different nitrogen densities can provide a theoretical basis for the breeding of high-yield and high-quality lodging-resistant varieties and the application of optimal nitrogen density planting mode in cultivation.In this experiment,six typical conventional japonica rice and hybrid japonica rice varieties with different panicle types in Liaoning Province were used as test materials.They were Beigeng 1705(Erect panicle type conventional japonica rice),Shennong 808(Curved panicle type conventional japonica rice),Liaoyou 9906(Erect panicle type hybrid japonica rice),Fengjin(Curved panicle type conventional japonica rice),Liaoyou 5206(Curved panicle type hybrid japonica rice)and Beigeng 1604(Erect panicle type conventional japonica rice).They were planted under four different nitrogen rates(CK: no nitrogen fertilizer;Low nitrogen C1: 120kg/hm2;medium nitrogen C2: 180kg/hm2;high nitrogen C3: 240kg/hm2)and three different densities(high density D1: 250000 holes per hectare;medium density D2: 200000 holes per hectare;low density D3: 167000 holes per hectare).The changes of stem morphological traits,anatomical structure,lodging resistance and yield and yield related traits were investigated.The changes of stem traits and their effects on lodging resistance and yield of different types of japonica rice varieties under different nitrogen density treatments were studied.The following conclusions were drawn:1.Nitrogen application rate had significant effects on stem morphological traits,stem base anatomical structure,lodging resistance and yield.The plant height and center of gravity of rice increased by 27.3 % and 27.2 % respectively under high nitrogen.With the increase of nitrogen application rate,the basal angle,leaf length and leaf width of upper three leaves increased,and the number and area of vascular bundles per stem decreased.However,nitrogen application increased the tiller number of rice,and the number and area of vascular bundles per plant increased with the increase of nitrogen application.The breaking resistance and stem strength of the first,second and third internodes at the base decreased with the increase of nitrogen application rate.The bending moment,lodging index,internode length,stem diameter and thrust resistance increased with the increase of nitrogen application rate.The yield reached the maximum at nitrogen application rate of 180 kg/hm2,increased by 10.7 % and 72.1 %respectively compared with 120 kg/hm2 and no nitrogen application.2.Planting density also had significant effects on stem morphological traits,anatomical structure of stem base,lodging resistance and yield.With the decrease of planting density,flag leaf width and top 3 leaf width decreased.The number and area of vascular bundles per plant increased with the decrease of planting density.The stem diameter and stem wall thickness of the third internode of the base decreased with the decrease of planting density.The lodging index of the third internode of the base decreased first and then increased with the decrease of planting density,and the minimum was at the level of 200000 holes per hectare.The thrust resistance increased with the decrease of planting density.The yield was the highest at high density,which was 13.7 % and 31.3 % higher than that under medium and low density treatments,respectively.3.The stem morphological traits,anatomical structure and yield structure of japonica rice varieties are closely related to lodging resistance.Under the influence of nitrogen density interaction,stem length,diameter,thickness,plant height,height of gravity center,basal angle of upper three leaves,length and width of upper three leaves,yield were significantly negatively correlated with folding resistance and stem strength,and positively correlated with lodging index.The neck panicle bending degree was significantly negatively correlated with the strength of the resistant stem and positively correlated with the lodging index.The number and area of vascular bundles with single stem size were significantly negatively correlated with folding resistance,and significantly positively correlated with stem strength and lodging index.Comprehensive analysis showed that the rice varieties with moderate thickness of the first internode,relatively coarse between the second and third internodes,thick wall of stem base,developed vascular bundles and low proportion of basal internode length to plant height were more resistant to lodging,and breeders should focus on these traits.4.The response of stem morphological traits,stem base anatomical structure and lodging resistance of different rice varieties to nitrogen density treatment was not completely consistent.The density of thrust resistance under different nitrogen treatments was consistent,reaching the maximum value at 250000 holes per hectare.The bending resistance of conventional japonica rice with curved panicle type was consistent.The bending resistance was the highest at the density of 200000 holes per hectare without nitrogen application and 240kg/hm2,and the bending resistance was the highest at the density of 250000 holes per hectare with nitrogen application of 120kg/hm2 and 180 kg/hm2.The breaking resistance between internodes 1 and 2 of the stem of conventional japonica rice with curved panicles was significantly reduced,and the number and area of vascular bundles per stem size,and the stem strength between internodes 1 and 2 at the base were lower than those of hybrid japonica rice and vertical conventional japonica rice.Comprehensive analysis showed that curved panicle conventional japonica rice was more affected by nitrogen density interaction than hybrid japonica rice and vertical conventional japonica rice,and curved panicle japonica rice was more prone to lodging than vertical panicle japonica rice,and conventional japonica rice was more prone to lodging than hybrid japonica rice.5.The responses of yield of different types of japonica rice varieties to N treatment were different.For conventional japonica rice with erect panicles,such as Beigeng 1705 and Beigeng 1604,it is suggested that the maximum yield should be obtained under nitrogen application rate of 240kg/hm2 and planting density of 250000 holes per hectare.For curved panicle type high quality rice varieties,such as Shennong 808 and Fengjin,in order to ensure that they can have relatively high yield without lodging,it is recommended to plant under nitrogen application rate of 120kg/hm2 and planting density of 167000 holes per hectare;for hybrid japonica rice,such as Liaoyou 9906 and Liaoyou 5206,due to their obvious heterosis,lodging resistance and barren resistance,it is not necessary to apply excessive nitrogen fertilizer.It is recommended to plant under the nitrogen application rate of 180kg/hm2 and planting density of 250000 holes per hectare,which can save cost and increase yield and income. |
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