The Selection Response Of Genetic Gain Of Maize Selection Population To Planting Density

High density circulation breeding strategies gradually be taken seriously in our country,and become an important technology to create maize breeding new material.But there is no test data reveal breeding material character on the choice of different planting density response.In this study,the Chinese and American maize inbred lines of SS and NSS groups(SS groups: Zheng 58 x LH196,NSS group: Chang 7-2×MBUB)at the five densities of 4000,6000,8000,10000,12,000 Plants/MU were selected.Through mixed selection method,generation C1,C2,C3 and C4 of each selected group were obtained.And then,used these different generation as experiment materials,through incomplete block test design,evaluated growth period,resistance,plant type,yield,photosynthesis traits and genetic gain performance of different generations to explore the response regularity of maize generations agronomic traits genetic gain to planting density to provide theoretical basis for high density circulation breeding strategies.The main research results are as follows:(1)The Combined Variance Analysis shows that the character of silking stage,powder period,plant height,ear height and tassel branch number,angle of panicle,lov,yield,ear row number,kernels per row,hundred-grain weight,ear diameter,ear length,bare tip length,grain depth,bulk density and SPAD et al.have highly significant difference among the generations,besides lodging rate and bending rate.(2)Under 4000-8000 Plants/MU of the low density conditions,with the increase of planting density,the growth period was shortened,the plant type gradually changed worse and the SPAD gradually decreased first and then increased in the SS selected population,and with the increase of planting density,the yield decreased gradually,the growth period shortened,the plant type first became worse and then changed better and SPAD gradually decreased in the NSS selected population.(3)Under 8000-12000 Plant/mu of the high density conditions,with the increase of planting density,the yield decreased gradually,the growth period shortened,the plant type gradually improved and the SPAD decreased first and then increased in the SS selected population,and the yield increased first and then decreased,the growth period gradually lengthened,and the plant type gradually became better and SPAD increased first and then decreased in the NSS selected population.(4)With the change of planting density,the yield and growth period of the selected group was negatively correlated,but the yield and both the ear height and plant height that were positively correlated.Therefore,in the process of improving the density condition when we select the single plant.We should pay attention to selecting the excellent single plant with earlier growth period.However,the selection criteria for high ear level should be lowered appropriately.(5)after 4 generations of continuous improvement,the average genetic gain of the two types of selection lines decreased first and then increased with the increase of planting density,in which the SS selection population was the highest in 4000 / mu,the lowest in 8000 plants / mu,the highest in the 12000 plant / mu and the lowest in 10000 / mu,the average genetic gain of plant type traits was changed and produced.The average genetic gain in the growth period decreased gradually,and the average genetic gain of the chlorophyll content two groups showed the opposite trend,the SS selection group showed a gradual increase,and the NSS selection group showed a gradual decrease.(6)The genetic gain of each generation was analyzed separately.The two class selection line group C1 to C3 generation,the yield and growth period genetic gain was higher in 8000-12000 plant / mu high density,C4 generation,the two type of line selection group yield and growth period were higher in 4000,6000 plant / mu low density,and the remains gain in high density was mostly negative gain.(7)Comprehensive evaluation of the characteristics of generations and genetic gain of the two types of selected populations,the results showed that the response of the two selected populations to planting density was influenced by the genetic background and generation.At the same time,the optimum planting density of the C1-C3 generation in the SS selected population was 8000-12000 plants/MU.And the planting density should be increased with the improvement.Otherwise,the optimum planting density of C1-C3 generation in NSS selected population was 8000-10000 plants/MU.Both of the SS and NSS population,which the optimum planting density of C4 generation all was 4000 plants/MU.