Analysis On Maize Plant Type Via Mixed Inheritance Model Of Major Genes Plus Polygenes

Plant type is one of the major research contents in maize genetic improvement in recent years. This research on genetic laws of maize plant type can provide theoretical references for maize plant type breeding.2crosses, PH4CV/Chang7-2(cross Ⅰ) and PH6WC/7873(cross Ⅱ) were formed from4maize inbred lines with great differences. The six generations (P1, P2, F1, B1, B2and F2) of2crosses were investigated in spring sowing environment (environment Ⅰ) and summer sowing environment (environment Ⅱ). The joint segregation analysis of major genes plus polygenes mixed inheritance model was conducted to study the genetic rules of leaf angle above and below uppermost ear, leaf orientation value above and below uppermost ear, leaf area near three leaves, plant height, ear height, leaf spacing, stem diameter, tassel length and branch number, with a view to providing genetic information for maize plant type breeding. The results were:1Genetic model analysis on plant typeThe optimal model was model D-2in leaf angle above uppermost ear (environment Ⅰ), leaf angle below uppermost ear (environment Ⅱ) and leaf area (environment Ⅰ) in cross Ⅱ. Under both environments, leaf orientation value was controlled by model E-1. And leaf area (environment Ⅱ) was also controlled by model E-1. The optimal model in leaf angle above uppermost ear (environment Ⅰ) and leaf orientation value below uppermost ear was model D-3and D-4, respectively. In environment Ⅱ, leaf angle below uppermost ear was governed by model C-0without any major gene detected. Leaf orientation value was controlled by model B-1in environment Ⅰ.Both plant height and ear height were controlled by model E-3in cross Ⅰ while these traits were governed by model E-1under both environments. In summer sowing environment, the optimal model of plant height and ear height was C-0model in cross Ⅱ. But in spring sowing environment, the model of plant height and ear height in cross I differed, and was controlled by C-0model and D-3model, respectively. The optimal model of leaf spacing respectively was model E-1and C-0in cross Ⅰ while that was model D-4and D-2in cross Ⅱ under both environments, respectively. Stem diameter was controlled by model D-2in cross Ⅰ under two environments. In cross Ⅱ, the optimal model of stem diameter was model E-1in spring sowing environment while that was D-2model in summer sowing environment.In spring sowing environment, the tassel branch number was controlled by E-1in both2crosses. The optimal model was C-0in cross Ⅰ, and that was E-3model in cross Ⅱ in summer sowing environment. In both environments, the tassel length was governed by model D-2in cross Ⅰ, whereas the optimal model was model D-3in cross Ⅱ.2Genetic parameter estimates on plant type The polygenes heritability of leaf angle above the uppermost ear in cross Ⅱ was the highest in B2generation, and was91.15%in spring sowing environment, and was87.36%in summer sowing environment. It had the highest choosen efficiency when leaf orientation value above uppermost ear was selected in F2generation in cross Ⅱ in both environments because of higher major genes heritabilities in F2generation. In spring sowing environment, the major genes heritability of leaf angle below uppermost ear in B1generation was the biggest, and was85.75%. Under the same environment, the highest polygene heritability of leaf orientation value below uppermost ear in cross Ⅱ appeared in B2generation, and was71.35%. In summer sowing environment, the polygenes heritabilities of leaf angle below uppermost ear were the largest in F2generation, i.e.90.39%in cross Ⅱ under summer sowing environment. The highest major genes heritability of leaf orientation value below uppermost ear was84.12%in F2generation in cross II under summer sowing environment. The highest heritability of leaf area near three leaves in cross Ⅱ was87.22%in B1generation in spring sowing environment. But leaf area near three leaves in cross Ⅱ had the highest major genes heritability in F2generation, and the value was75.82%.Plant height and ear height of2crosses had the highest chosen efficiency in F2generation under both environments. In spring sowing environment, the major genes heritabilities of plant height in F2of cross Ⅰ and cross Ⅱ were58.57%and74.78%, respectively. In summer sowing environment, the polygenes heritabilities of plant height in F2generation of cross Ⅰ and cross Ⅱ were94.34%and94.39%, respectively. In spring sowing environment, the ear height in F2generation of cross Ⅰ and cross Ⅱ had the highest major genes heritabilities which were70.69%and90.94%, respectively. In summer sowing environment, the ear height in F2generation of cross Ⅰ and cross Ⅱ had the highest polygenes heritabilities and were95.61%and87.28%, respectively.The highest major genes heredities of leaf spacing of cross I were85%in F2generation in spring sowing environment, and were93%in B2as well as in F2in summer sowing environment. In spring sowing environment, the largest major genes heritabilities of stem diameter in cross Ⅰ and cross Ⅱ were69.01%and85.43%, respectively. In summer sowing environment, the largest polygenes heritabilities of stem diameter in cross I and cross Ⅱ were77.26%and82.08%, respectively.The highest major genes heritabilities of tassel length in cross Ⅰ and cross Ⅱ were72.24%and59.43%in F2generation in spring sowing environment, respectively. The highest polygenes heritabilities of tassel length in cross Ⅰ and cross Ⅱ were87.99%and68.94%in B2generation in summer sowing environment, respectively. In summer sowing environment, the highest polygenes heritability of leaf spacing in cross Ⅱ was92.02%in B2generation.3Genetic law analysis on plant typeIn spring and summer sowing environment, leaf angle above and below uppermost ear in cross Ⅱ were controlled or mainly controlled by polygenes. Leaf orientation value above uppermost ear was mainly controlled by major genes in cross Ⅱ under both environments. Leaf orientation value below uppermost ear in cross Ⅱ was governed by major genes and mainly controlled by polygenes in spring and summer sowing environment, respectively. Leaf area near three leaves was mainly controlled by polygenes in spring sowing environment while that was mainly controlled by major genes in summer sowing environment. In2crosses, plant height, ear height and stem diameter were mainly controlled by major genes in spring sowing environment while these traits were controlled by polygenes model or mainly controlled by polygenes in summer sowing environment. In spring sowing environment, leaf spacing showed major genes inheritance. However, leaf spacing of2crosses showed polygenes inheritance in summer sowing environment. In spring sowing environment, tassel length in2crosses was mainly controlled by major genes. In summer sowing environment, the tassel length in cross Ⅰ and cross Ⅱ showed polygenes inheritance. The tassel branch number in cross Ⅰ was mainly controlled by major genes in summer sowing environment. In summer sowing environment, tassel branch number in cross Ⅱ was controlled by polygenes. The tassel branch number of cross Ⅰ(environment Ⅱ), tassel branch number of cross Ⅱ (environment Ⅰ) and leaf spacing of cross Ⅱ (environment Ⅰ) didn’t show obvious major-polygenes effects. In order to improve the efficiency of maize breeding, single cross recombination or simple backcross could be adopted for the traits belonging to typical major gene inheritance or mainly controlled by major gene, and polymerization backcross or recurrent selection could be adopted for the traits belonging to typical polygene inheritance or mainly controlled by polygene. The relative effects of major gene and polygenes should be considered simultaneously for the traits controlled by both major genes and polygenes.