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With 1 figure and 8 tables Abstract The genetic effects and heterosis of the colour and quality of brown fibres were analysed in this paper through the complete 5 × 5 diallel crossing among two brown cotton cultivars and three white cotton cultivars in upland cotton (Gossypium hirsutum). Parents and F1 were arranged in a randomized block design in three locations. The results showed that the inheritability for all the traits has exceeded 50%, with significant dominance effect at the 0.01 level. The additive effect of fibre colour, lint percentage, elongation and strength was also significant at the 0.01 level, reaching 85.6%, 29.7%, 16.1% and 19.1%, respectively. The ratio of residual variance of lint percentage and fibre qualities was 29.5 – 45.9%, that of colour was only 1.1%. Fibre colour had significant negative correlation with lint percentage, fibre length, uniformity, elongation and strength. The mid-parent heterosis of fibre colour was negative, which was −0.7%; those of lint percentage, fibre length, uniformity and strength were 3.5%, 4.2%, 1.7% and 2.6%, respectively, reaching the significant level. The simple correlation coefficient between heterosis of fibre length and strength and SSR genetic distance was 0.718 and 0.724, respectively, with a significant level. For the heterosis utilizing, the fibre quality of F1 could be predicted via the mean value of the fibre qualities of parents or the SSR genetic difference among varieties (lines). Selection among the early hybrid generations was suggested. Regional planning could be applied to improve lint percentage and fibre qualities by taking advantage of environmental variation.

With 2 figures and 4 tables Abstract A novel super-dwarf mutant, named AS98, was discovered from an interspecific hybrid in 1998. Compared to the normal line LHF10W99, plant height and internode length were significantly shorter in AS98, but it had only slightly (3–5%) fewer internodes. Therefore, the shorter plant height was the result of shorter internodal length. AS98 was crossed with LHF10W99, and the F1, F2, BC1, and BC2 populations were used for genetic analysis of the dwarf trait. The results showed that the trait was controlled by a single incomplete-dominant gene. Exogenous application of gibberellin acid (GA3), brassinosteroid and indol acetic acid showed a significant response to GA3, which could restore plant height in AS98. The results thus provide a basis for utilizing the dwarf trait in breeding and studying the biosynthesis of GA or signal transduction in cotton.