Genetic study of earliness components in upland cotton, Gossypium hirustum L

Typescript (Photocopy).Seven early-maturing lines and one full-season cultivar of cotton were used to gain information on the inheritance and interrelationships of earliness components, yield, and fiber properties. This study was initiated in 1981 by making all the possible crosses, without reciprocals, among the eight parents. Field evaluation of the eight parental genotypes and the 28 F(,1)'s was made in 1982 in a randomized complete block design with four replications. Data were collected on morphological, fruiting, product-quantity, yield, and fiber properties. Except for bloom index and boll maturation period, genetic differences for all the traits were verified by the significant differences among the parents. Validity of the diallel assumptions was evidenced by the lack of significant differences in the analysis of variance of the (Wr-Vr) arrays for all the traits studied. The component of variation due to the additive gene effects (D) was significant for node to the first fruiting branch, plant height, date to first flower, date to first open boll, horizontal flowering interval, total blooms, maturity index, mean maturity date, percentage of seed cotton harvested at second picking, length of fiber, fiber uniformity, fineness of fiber, fiber strength, fiber elongation, and lint percentage. Component of variation due to the dominance effects of the genes (H(,1) or H(,2)) was significant for all traits except for lint percentage, fiber elongation, and date to first open boll. Average degree of dominance ranged from partial dominance to overdominance. Heritability estimates varied from 0.02 for production rate index to 0.46 for fiber length. Correlation analysis among components of earliness suggested that, in general, the lower the node to the first fruiting branch and the shorter the plant, the earlier the onset of squaring, flowering, and boll opening (expressed as a number of days from planting). Also, genotypes with these characteristics tended to have shorter boll maturation period and required fewer days to reach 50 percent cumulative maturity. Moreover, such genotypes also tended to have more flowers at a specified date, to produce flowers and open bolls faster, and, consequently, to have higher amounts of seed cotton ready to be harvested at the first and second pickings. However, correlation analysis between earliness components and fiber properties and yield indicated that fiber properties and yield decreases as earliness of a genotype increases, suggesting either genetic linkage or physiological correlations between earliness and fiber properties and yield