Mixed Inheritance And QTL Location Study On Earliness And Its Related Traits Of Short Season Cotton

There is limited cultivated land per capita in China, and cotton main production cultivated land is also crop main production cultivated land, so the breeding and extension of short season cotton variety is the efficient way to deal with the contradictory of using cultivated land between cotton and crop, and acquire double good harvests of cotton and crop as soon as possible. The genetic research about earliness and its related traits of short-season cotton and findings of the molecular markers closely linked with earliness genes are significant to short season cotton breeding. In this study, major gene-polygene mixed inheritance model and joint analysis method for six generations were used to analyze the genetics of earliness and its related traits of short-season cotton, while location of QTL and its distribution characteristic were illustrated by using composite interval mapping.Mixed Inheritance of earliness and its related traits of short-season cottonMajor gene-polygene mixed inheritance model was generated to analyze the genetics of earliness and its related traits of short-season cotton by using six generations including earliness variety Baimian 2 (P2) and genetic standard line TM-1 (P1) in upland cotton (Gossypium hirsutum L.), and their F1, B1, B2 and F2 grown in Yellow River Valley Region (Xinxiang, Henan, environmentⅠ) and Northwest Inland Region (Shihezi, Xinjiang, environmentⅡ), respectively. The results were as follows:1. Major genes were always detected under two environments in all traits except flower and boll period as well as lint percentage, which showed that the universality of major genes existing in earliness and its related traits of short-season cotton.2. Under two environments, optimum genetic models of growth period were identical, and the tendencies of their major gene heritability proportion were also consistent as well as that of polygene, indicating that the genetics of growth period was more stable than other traits under different environments; although optimum genetic models of fruit branch beginning site under two environments were identical as well as that of boll weight, the tendencies of their major gene heritability proportion were opposite as well as that of polygene, so their genetic rules need further discussion; just like bud period, flower and boll period, and lint percentage, optimum genetic models of seedling period were all different under two environments, and the tendencies of their major gene heritability proportion were deeply different from that of polygene, indicating that gene expression of which were affected by environments, the selection should be applied in special environments in order to improve breeding efficiency.3. By estimating and comparing the major gene plus polygenes heritabilities of separating generations in earliness and its related traits of short-season cotton, the highest efficient generation of each trait was determined; under two environments, total heritability tendencies of growth period, seedling period, bud period, height of fruit branch beginning site and fruit branch beginning site were more stable than other traits, in which total heritability of growth period, as the important indicator of cotton earliness, was always the highest of all, indicating selection was efficient in early generation under different ecological environments. Height of fruit branch beginning site and fruit branch beginning site might be considered as credible morphological indices to identify earliness of short-season cotton.4. Under two environments, the genetic pattern of each trait was not all different. Growth period, bud period and height of fruit branch beginning site were all mainly controlled by major gene; seedling period, flower and boll period, fruit branch beginning site and lint percentage were all mainly controlled by major gene and polygene, respectively; boll weight was mainly controlled by polygene and major gene, respectively. To improve breeding efficiency, single cross recombination or simple backcross should be adopted for the traits mainly controlled by major gene, while polymerization backcross or recurrent selection to cumulate positive alleles should be adopted for the traits mainly controlled by polygene.QTL location of earliness and its related traits of short-season cottonIn this study, 188 F2 individuals were obtained through Baimian 2×TM-1 group as mapping population. SSR molecular marker and Joinmap 3.0 software were applied in constructing molecular genetic linkage map. The composite interval mapping method of WinQTLCart2.5 software were used to locating QTL in F2 population of earliness and its related traits of short-season cotton. The results were as follows:1. 152 SSR molecular markers were assigned to 40 linkage groups with a total map distance of 1,010.3 cM and an average distance of about 5.91 cM between the two markers, covering approximately 22.6% of the total recombinational length (4500cM) of the cotton genome. According to the information from the backbone linkage maps, 40 linkage groups were tentatively assigned to 21 chromosomes. This linkage map laid a good foundation for molecular genetic map construction of short season cotton.2. The results indicated that 22 QTL for earliness and related traits were identified including 4 QTL for growth period, 2 QTL for seedling period, 5 QTL for bud period, 3 QTL for flower and boll period, 1 QTL for height of fruit branch beginning site, 1 QTL for fruit branch beginning site, 2 QTL for boll weight and 4 QTL for lint persentage, which separately explained 1%-16%, 8%-44%, 5%-46%, 1%-10%, 10%, 6%, 6%-7% and 5%-24% of the phenotypic variance.3. Major QTL identified and major genes as the first part mentioned have been complimentary verified well. Different QTL affecting earliness and its related traits were always detected within the same or closer chromosome region, suggesting that highly repeated rich gene regions might be located in cotton genome and genes controlling earliness and its related traits might be linked closely or the result of pleiotropy, and explaining genetic relation among them from molecular level. 72.7% QTL positive alleles mainly came from Baimian 2 and 27.3% from TM-1 indicating that the resource of positive alleles mainly came from Baimian 2. The addictive QTL were 31.8%, the dominant QTL 45.5% and the over-dominant 22.7%, which suggested that the QTL controlling earliness and its related traits might mainly be dominant. The molecular markers linked closely to the major QTL can be used in MAS (marker-assisted selection) breeding of short season cotton.