Screening Of Density Tolerant Soybean Varieties And Study On High Yield Agronomic Traits

In order to explore the germplasm resources of soybean with dense planting tolerance,82soybean varieties were used as experimental materials in a two-factor randomized group design with density as the main zone and variety as the secondary zone,and two treatments were set up for conventional density and high density,with densities of 200,000/hm~2and 300,000/hm~2,respectively.Agronomic traits,yield,stem bending resistance,chlorophyll content and other 18traits were collected and the density tolerance index of each soybean variety was clarified by principal component analysis and membership function methods,etc.Based on yield and lodging index,they were classified into three categories:type I,without density tolerance;type II,neutral density tolerance;and type III,density tolerance.and five dense high-yielding varieties were screened,and the physiological and agronomic traits of dense high-yielding varieties were analyzed:(1)The effect of planting density on chlorophyll content of soybean.With increasing density,the chlorophyll content of the upper layer showed a significant decrease in all fertility stages.The chlorophyll content of the lower layer at high density was significantly lower than that of the conventional density at the pod and bulge stage.With the increase of density,the chlorophyll content in the upper layer of different dense-tolerant varieties tended to decrease,and the chlorophyll content of density tolerant varieties was more stable,while the chlorophyll content of neutral density tolerant and without density tolerance varieties decreased significantly.The decrease in chlorophyll content in the lower layer of density tolerance varieties was the smallest,and the decrease in the without density tolerance varieties was the largest,with the fastest rate of leaf senescence.(2)The effect of planting density on leaf area index and dry matter accumulation of soybean.The leaf area index increased significantly and the rate of dry matter accumulation per plant decreased significantly under high density compared to conventional density.Compared to the neutral density tolerance and without density tolerance varieties,the leaf area index of the density tolerance varieties increased more and the dry matter per plant decreased less.The increase in leaf area index of the without density tolerance varieties was the smallest,and the corresponding decrease in dry matter per plant was greater under high density planting compared with conventional density,indicating that the higher leaf area index of the intolerant varieties in the middle and late stage was beneficial to the accumulation of dry matter in the later stage.(3)The effect of planting density on stalk folding resistance and inversion grade of soybean.The number of lodging level was significantly higher under high density planting compared to conventional density planting,and lodging level were significantly and positively correlated with plant height,balance point and average internode length;stem bending resistance was significantly and positively correlated with stem diameter,and lodging level were negatively correlated with stem bending resistance.As planting density increased,without density tolerance varieties exhibited a more apparent lodging phenomenon and a greater decrease in stem bending resistance.In contrast,density tolerance varieties displayed less lodging and the smallest decrease in stem bending resistance.(4)The effect of planting density on agronomic traits of soybean.With increasing density,plant height,balance point,senescence leaf node position,bottom pod height and average internode length showed a significant increase;stem diameter,number of main stem nodes and number of branches all showed a significant decrease.The plant height,balance point,senescence leaf node position,bottom pod height and average internode length of different densely tolerant varieties increased to different degrees under high density planting,with the without density tolerance varieties showing the greatest increase,followed by neutral density tolerance varieties,while density tolerance varieties showed the smallest increase.Stem diameter,number of main stem nodes and number of branches decreased to the greatest extent for the without density tolerance varieties,followed by the neutral density tolerance type,and the least for the density tolerant type.(5)The effect of planting density on soybean yield.After increasing planting density,the number of pods per plant,the number of grains per plant and the grain weight per plant all decreased significantly,while the hundred-grain weight and yield increased significantly.The number of pods per plant,number of grains per plant,and grain weight per plant of different densely tolerant varieties decreased to different degrees under high density planting,with the greatest decrease in the without density tolerance varieties,followed by the neutral density tolerance ones,and the least in the density tolerance ones.Compared with conventional density planting,the hundred-grain weight of density tolerance varieties increased the most.Under high density planting,the plot yield of density tolerant varieties was significantly higher than that of conventional density,the yield increase of neutral density tolerance varieties was small and insignificant,and the yield of without density tolerance varieties was significantly lower.In summary,five densely tolerant and high-yielding soybean varieties(Hefeng 50,Heinong93,Suinong 30,Heinong 64,and Ji Soybean No.5)were screened,and the results of the study provide a material basis for future theoretical research on densely tolerant soybean and selection and breeding of new densely tolerant varieties.