| Cottonseed (Gossypium spp.) is the most important byproduct of cotton production. As the most basic material for cotton production, cottonseeds are widely used in food, feed and pharmaceutical industries. Cottonseed quality traits consist of physical and nutrition qualities. The physical quality traits are those included seed index (SI), kernel index (KI), kernel percentage (KP), and kernel/hull (K/H), which directly affect the sowing quality of cotton. The nutritional ones are those included oil and fatty acid contents, protein and amino acid contents, and gossypol content, which directly affect the cottonseed value in utilization. The studies of cottonseed traits and their QTL mapping can help to improve the quality of cottonseeds for sowing as well as its nutritional quality through cotton breeding and also enhance their economic values in utilization. The genetic effect, inheritance and correlation based on embryo, maternal plant, and the cytoplasm genomes were studies, used a backcross population with376combinations from the188inbred lines and their parents. At the same time, the QTLs of some physical and nutrition traits were mapped analyzed based on embryo genome and maternal plant genome, used the immortalized F2population derived from same recombination inbred population. The main results are as follows:(1) A backcross populations comprising of376backcrosses and an immortal F2population with402crosses were constructed using a set of recombination inbred lines (RIL) developed from the hybrid of HS46x MARCABUCAG8US-1-88. All the cottonseed quality traits were distributed followed continuous normal distribution for both of the two populations, which were suitable for the genetic research and QTL mapping.(2) The inheritance and genetic effects of cottonseed quality traits were studied using the backcross population with376backcross hybrids. As the results shown that, the gene presses of those SI, KP, K/H and KI were controlled by the main genetic effects, mainly by maternal genetic effects, followed by embryo genetic effects, but without cytoplasmatic effect. Among the cottonseed physical qualities, SI was mainly affected by maternal additive effects, following by maternal additive effects, maternal dominance effects, and embryo dominant effects. KP was mainly affected by maternal additive effects, maternal additive effects, and embryo dominant effects, then by maternal additive interaction effects and embryo dominant interaction effects. K/H was mainly controlled by maternal additive effects and maternal dominant effects, and next by maternal additive interaction effects, maternal dominant interaction effects, and embryo dominant interaction effects. KI was mainly controlled by maternal additive effects, embryo additive and dominant effects, then by maternal additive interaction effects and maternal dominance effect.Oil content and oleic acid contents were mainly controlled by maternal additive effects and maternal dominant effects, and maternal additive interaction effects and embryo additive interaction effects were important as well. The contents of palmitic acid and linoleic acid were mainly controlled by embryo additive interaction effects and maternal dominant interaction effects. The results illustrated that the traits of oil content and some fatty acid contents were greatly influenced by the environment and it should be considered during the studies of breeding for cottonseed qualities. Maternal additive effects were greatly for protein and amino acid contents and cytoplasm interaction effects were also important. While the gossypol content was mainly controlled by embryo additive effects and maternal additive effects, then by the effects of the cytoplasm and maternal dominant interactions.(3) Heritability analysis of seed quality traits shown that the maternal heritability was the most important for SI, KP, K/H, and KI, and the next was the embryo genetic heritability. The normal cytoplasm and cytoplasm interaction heritability were not discovered in this experiment. So the selection for those traits could be carried out according to the performance of the embryo and maternal plants. The maternal heritability and embryo heritability were the most important effect for oil content, as well as the contents of palmitic acid, oleic acid, and linoleic acid contents. At the same time, the heritabilities of embryonic interaction and maternal interaction were higher. The maternal heritability was the most important for protein and amino acid contents, and wheir cytoplasm interaction heritability was found significantly. However, the maternal heritability and cytoplasm interaction heritability were significant for the gossypol content.(4) The genetic correlation analysis of cottonseed quality traits showed that the physical traits were influenced by additive correlation, and the maternal additive and dominance correlation were obvious as well. There were significantly embryo dominance, maternal additive, and maternal dominant correlations between SI and oil content. The relationship between SI and protein content were mainly controlled by positive maternal additive and negative embryo dominant effect. While that between SI and gossypol content was mainly controlled by embryo dominance interactions, and that between KP and oil content was mainly controlled by maternal additive and dominant positive correlation. The relationship between KP and oleic acid content were influenced by maternal additive and maternal dominant negative correlation, and that between KP and protein content, and between KP and gossypol content were influenced by maternal additive correlation. Between K/H and oil content, the maternal additive and dominant positive correlation were significant. Between K/H and oleic acid content, there was significant maternal additive and dominant negative correlation. Between K/H and linoleic acid content, there was significantly positive maternal dominance correlation. The maternal additive correlation was significant between K/H and protein content, K/H and gossypol content. While between KI and oil content, KI and palmitic acid contents, KI and oleic acid contents, and KI and linoleic acid contents the maternal additive and dominance correlation were significant. There was significant maternal additive correlation between KI and protein content. KI was negatively related to the gossypol content in embryo additive and embryo dominant interactions. The significant embryo dominance negative interaction was found between oil content and protein content, significant embryo dominance positive interaction was found between oil and gossypol contents, and main negatively correlation in embryo dominant interactions and maternal additive interaction were found between protein and gossypol contents.(5) QTL mapping and QTL genetic effects for several cottonseed quality traits were analyzed using the immortal F2population obtained from the random mating among the188recombinant inbred lines which derived from a cross of between HS46 and MARCABUCAG8US-1-88. With the newly developed QTL mapping method that includes embryo and maternal main effects, as well as their genotype×environment (GE) interaction effects on quantitative traits of dicotyledonous seeds, two QTLs were detected for SI, which could explain59.73%of the phenotypic variation. Two QTLs were detected for KI explaining32.95%of the phenotypic variation. In addition, one pair of epistatic QTLs was detected for SI. Three QTLs were detected for oil content explaining14.94%of the phenotypic variation. One QTL was detected for hexadecanoic acid (C16-0), explaining1.70%of the phenotypic variation. Two QTLs were detected for oleic acid (C18-1) content, which explained11.8%of the phenotypic variation. In addition, a pair of epistatic QTLs for palmitic acid (C16-0) content, a pair of epistatic QTLs for oleic acid (C18-1) content, and four pair of epistatic QTLs for linoleic acid (C18-2) content were detected in this experiment. |
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