Abstract:

Early-maturity is closely related to yield and quality of cotton. Cotton growing season in the north of China, especially in the early-maturing cotton area, is short. So early-maturity has decisive significance for the improvement of yield and quality of cotton in this specific area. In the special ecological environment of northern Xinjiang cotton growing region and the Yellow River growing region with wheat-cotton interplanting, improving the pre-frost lint yield primarily depends on the early-maturing cotton varieties with, shorter growth period and more pre-frost boll numbers. In the early-maturing Upland cotton area, pre-frost lint yield largely determines the proportion of high-quality cotton. However, research on molecular breeding for cotton earliness is still lacking at home and abroad. The early-, mid- and late-maturing materials with large genetic differences were used as parents in this study. The genotypes and the relative genetic effects of major loci groups based on Quantitative Trait Loci (QTL) detection system were first adopted to estimate the magnitude of heterosis for pre-frost lint yield, and to analyze the relationship between favourable loci groups and heterosis. According to Griffing’s P(P–1)/2 Incomplete Diallel Cross design, fifteen combinations were made by six cotton varieties from different origins. The results showed that the phenotypic variations explained by major loci groups (G), G×E, environment (E) and minor loci group were 36.79%, 33.46%, 10.37%, and 3.27%, respectively. The pre-frost lint yield was controlled by five isolated major gene loci groups with additive effects of 5.99^{**, –1.26**, –0.92**, –0.75, and 3.01; and dominant effects of 2.55**, 4.16**, 7.95**, 5.32**, and –7.71**, respectively. Mid-parent heterosis of lint yield for major loci groups ranged from 15.55 to 133.56%, with an average of 63.34%, whereas high-parent heterosis ranged from 15.39% to 93.82%, with an average of 44.56%. Pre-frost lint yield heterosis was mainly determined by the gene heterozygosity of major loci groups. The hybrid combination, P2×P5, had highest favorable loci aggregation and surpassed all hybrid combinations in this study in pre-frost lint yield. This shows that genes related to pre-frost lint yield exist in the early- and mid-maturing parents. On the basis of parent materials genotypic estimation, with this method, genotypes aggregating favorable loci can be identified, or the donor with unfavorable locus can be changed to achieve the strong heterotic combinations. Combined with molecular design breeding, conventional cultivars with excellent comprehensive characteristics including high-quality; resistance to insect pests, disease, stress; and other properties can be developed with enhanced breeding efficiency.}

Key words: Cotton, Pre-frost lint yield, Major loci groups, Genetic effects, MLGsxenvironment interaction