Abstract
Upland cotton (Gossypium hirstum L.), which produces more than 95% of the world natural cotton fibers, has a narrow genetic base which hinders progress in cotton breeding. Introducing germplasm from exotic sources especially from another cultivated tetraploid G. barbadense L. can broaden the genetic base of Upland cotton. However, the breeding potential of introgression lines (ILs) in Upland cotton with G. barbadense germplasm integration has not been well addressed. This study involved six ILs developed from an interspecific crossing and backcrossing between Upland cotton and G. barbadense and represented one of the first studies to investigate breeding potentials of a set of ILs using a full diallel analysis. High mid-parent heterosis was detected in several hybrids between ILs and a commercial cultivar, which also out-yielded the high-yielding cultivar parent in F1, F2 and F3 generations. A further analysis indicated that general ability (GCA) variance was predominant for all the traits, while specific combining ability (SCA) variance was either non-existent or much lower than GCA. The estimated GCA effects and predicted additive effects for parents in each trait were positively correlated (at P<0.01). Furthermore, GCA and additive effects for each trait were also positively correlated among generations (at P<0.05), suggesting that F2 and F3 generations can be used as a proxy to F1 in analyzing combining abilities and estimating genetic parameters. In addition, differences between reciprocal crosses in F1 and F2 were not significant for yield, yield components and fiber quality traits. But maternal effects appeared to be present for seed oil and protein contents in F3. This study identified introgression lines as good general combiners for yield and fiber quality improvement and hybrids with high heterotic vigor in yield, and therefore provided useful information for further utilization of introgression lines in cotton breeding.
Highlights
Heterosis, i.e., hybrid vigor, describes performance superiority of a hybrid over the average of its genetically distinct parents in morphological, physiological and biochemical characteristics such as body size, growth rate, fertility, and productivity
Analyses of variance were performed for the three hybrid generations separately, and the results are shown in Table 1 for seedcotton yield, lint yield, yield components, fiber quality, and seed quality traits
Except for micronaire in F1, no significant variances for reciprocal effects were detected in F1 and F2; they were detected for seedcotton yield, lint yield, micronaire, seed oil, and protein contents in F3
Summary
I.e., hybrid vigor, describes performance superiority of a hybrid over the average of its genetically distinct parents (i.e., mid-parent value) in morphological, physiological and biochemical characteristics such as body size, growth rate, fertility, and productivity. Hybrid cotton seeds in China are predominantly produced through a hand emasculation and pollination process, while genetic and cytoplasmic male sterility systems [7, 8, 9, 10] have not been widely utilized in China. There are several issues in hybrid cotton research and production in China [6]. Due to the fact that 90% of the hybrid cotton seeds were produced through hand emasculation, it is labor-intensive and time consuming, and expensive. The purity of hybrid seeds is questionable due to the lack of quality control measurements in hand emasculation and pollination. Most of the hybrids do not produce superior fiber quality. Fifth, identifying high heterotic hybrids is difficult due to a lack of genetic diversity of parental lines
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