Analysis Of Genetic Variation Of Main Economic Traits Of Interspecific Hybrid Between Gossypium Hirsutum L. And G. Barbadense L. And Its Backcross Populations

At present, the genetic diversity of Upland cotton cultivars(Gossypium hirsutum L.) in China is narrow. There are few breakthrough varieties, and the fiber strength of varieties is low. The existing cultivars are difficult to meet the needs of the production of high-quality yarn in textile industry. However, G. Barbadense L. cultivars have better fiber quality and resistance to verticillium wilt. So it is essential to transfer the genes which effect these outstanding traits into the G. hirsutum varieties to effectively enrich the germplasm of G. hirsutum cultivars and in the same time to improve the quality of cotton fiber and yield of fiber.In this paper,the genetic variance on fiber quality and yield traits was analyzed for the hybrids through diallel cross combinations of G. hirsutum and G. barbadense, and their advanced backcross populations, which lays a foundation for future researches as screening of chromosome single segment substitution lines, QTL fine mapping, gene cloning and gene pyramiding, etc.1. The 2-year experiment data of 12 F1 hybrids obtained from the diallel cross combinations of 4 G. hirsutum varieties (lines) and 3 G.Barbadense cultivars are analyzed with Zhu Jun's AD genetic model software. The results indicated that there existed significant or extremely significant dominant effects for all fiber traits, and extremely significant additive effects for the other 4 traits except micronaire, and small interactions with the environmental factors for all fiber traits. Micronaire was only controlled by dominant effects. Strength was controlled mainly by additive effects and dominant effects was comparatively smaller. Length, uniformity and elongation were controlled by additive effects and dominant effects together and their dominant effects were higher than their corresponding additive efffects. The results showed that dominant effects was more evident for fiber traits of interspecific hybrid of G. hirsutum×G.barbadense, except strength, than that in intraspecific hybrid of G. hirsutum×G. hirsutum or that in intraspecific hybrid of G. barbadense×G. barbadense. The population mean heterosis of length, strength, uniformity and elongation expressed significant positive value. The population mean heterosis and the better-parental heterosis of micronaire expressed significant negative value.The results also indicated that there existed extremely significant additive effects and dominant effects and small interactions with the environmental factors for boll-weight and lint-percentage traits. Boll-weight was controlled mainly by additive effects and dominant effects was comparatively smaller. Lint-percentage were controlled by additive effects and dominant effects all together. The population mean heterosis of boll-weight and lint-percentage expressed significant negative heterosis. The results showed that it was good for strength and boll-weight to be selected in early generation and for other traits to be selected after middle generation.2. The frequency distribution of fiber quality and yield traits, coefficient of variation, population average, the percentage of excellent individuals and the percentage of individuals which are better than the backcross parents were analyzed in the BC₃F₁-BC₇F₁ populations from CCRI-41×Hai1 combination and in the BC₄F₁-BC₆F₁ populations from Zhong-394×Hai1 combination. The results showed that the backcrossing times of interspecific hybrid of G. hirsutum×G. barbadense is not the more, the better. The best backcrossing times differed slightly under different genetic backgrounds. Overall, 4-5 times are appropriate.3. Based on the comparative analysis of BC₄F₁ and BC₅F₁ populations obtained from family backcross method (CCRI-45×Hai1 and CCRI-36×Hai1) and regular backcross method (CCRI-41×Hai1 and Zhong-394×Hai1), the results showed that the average values of fiber length, strength and micronaire in the population obtained by family backcross method was relatively high. And its frequency distribution was skewed towards the high value. Its percentage of the excellent individuals which were better than the recurrent parent was relatively high, and its percentage of high-quality individuals of F2 selfing generation of advanced backcross populations was also relatively high. However, these values are relatively lower in the populations obtained from the regular backcross method.42 pairs of SSR primers were used for molecular polymorphisms. The preliminary results were BC4F1 family population for CCRI-45×Hai1 obtained by family backcross method reserved more introgressed segments of G. barbadense, ranging from 2 to 20, with an average of 10.17 for each family, while BC4F1 plant population for CCRI-41×Hai1 obtained by regular backcross method reserved relatively less introgressed segments, ranging from 0 to 11, with an average of 3.86 for each individual. Therefore, the preliminary conclusion was that family backcross method is superior to regular backcross method. Up to now, there is still no other report on the comparative research of the two backcross methods in cotton.4. The relevance of the fiber quality and yield traits was analyzed comparatively for BC₃F₁-BC₇F₁ populations from CCRI-41×Hai1 combination, and BC₄F₁-BC₆F₁ populations from Zhong-394×Hai1 combination, BC4F1 population from CCRI-45×Hai1 combination, BC5F1 population from CCRI-36×Hai1 combination and their F₂ selfing generation The results showed that the advanced backcrossing could not break the significant or highly significant positive correlationship among fiber length, strength and uniformity, which further illustrate a very close linkage among the three fiber quality traits. But, backcrossing could break or reduce the negative linkage between fiber quality and boll weight or lint-percentage. The negative correlation between fiber quality and lint-percentage still existed, which means that it is still difficult to improve fiber quality and lint-percentage simultaneously.Therefore, the next working step needs to be carried out. Specific plant traits should be selected out from the advanced backcross populations and hybridized with each other, which can pyramid the genes which control yield and quality traits. Single plant with excellent fiber quality should be selected out and hybridized or backcrossed with G. hirsutum varieties (lines) with high lint-percentage to increase yield and quality simultaneously. Chromosome single segment substitution lines should be screened in whole cotton genome for QTL fine mapping, gene cloning.