Combining ability analysis over F1-F5 generations in diallel crosses of bread wheat
SummaryCombining ability studies for grain yield and its primary component traits in diallel crosses involving seven diverse wheat cultivars of bread wheat (Triticum aestivum L.) over generations F1-F5 are reported. The general and specific combining ability variances were significant in all generations for all the traits except specific combining ability variance for number of spikes per plant in the F5. The ratio of general to specific combining ability variances was significant for all the traits except grain yield in all the generations. This indicated an equal role of additive and non-additive gene effects in the inheritance of grain yield, and the predominance of the former for its component traits. The presence of significant specific combining ability variances in even the advanced generations may be the result of an additive x additive type of epistasis or evolutionary divergence among progenies in the same parental array. The relative breeding values of the parental varieties, as indicated by their general combining ability effects, did not vary much over the generations. The cheap and reliable procedure observed for making the choice of parents, selecting hybrids and predicting advanced generation (F5) bulk hybrid performance was the determination of breeding values of the parents on the relative performance of their F2 progeny bulks.
Hermaphroditism: A Primitive Sex Form for Improving Plant Architecture, Earliness and Yield Traits in Monoecious Ridge Gourd (Luffaacutangula Roxb.)
The present experiment was carried out to evaluate the breeding value of Satputia inbreds and to formulate suitable breeding strategies following 7 × 7 half-diallel mating design for genetic improvement of ridge gourd (Luffaacutangula Roxb.). Twenty-one F1 hybrids along with seven parental lines, including two hermaphrodite inbreds, were evaluated in randomized block design with three replications. The highly significant mean squares due to parents, hybrids and parents versus hybrids for all the eleven traits studied indicate the presence of sufficient amount of genetic variation. Prevalence of additive genetic variance indicates the usefulness of hybridization followed by selection approaches for plant stature and earliness parameters, while heterosis breeding would be suitable to improve yield potential as indicated by predominance of non-additive genetic variance. Plant stature and earliness are peculiar traits of hermaphrodite ridge gourd which is inherited in its progenies. The parents DRG-2, Satputia Long and Satputia Small were good combiners for a number of characters, including yield/plant. Ten crosses having hermaphrodite inbred as one of the parents, excelled for high per se performance along with desirable specific combining ability effects. The present findings reveal the breeding value and potentiality of hermaphrodite Satputia lines in the genetic improvement for “ideal plant type” in ridge gourd.
The isolation of ‘pure lines’ from F1 hybrids of tomato, and the problem of heterosis in inbreeding crop species
1. The problem of inbreeding and the fixation of apparent heterosis in the cultivated tomato and in inbreeding crop species generally is discussed. The case is argued that ‘heterosis’ as normally understood in out-breeders is not likely to exist as a general phenomenon in inbreeding species. 2. Selections were made among segregating progenies of two successful, commercial F1 hybrids, and the performance of the selected lines, up to the F4 generation, shows that the superiority of the hybrids over their parents can be fixed in purebreeding lines. 3. Owing to selection effects in inbreeding species of crops the best parents will differ in respect of fewer quantitative loci than is to be expected from general experiments on quantitative inheritance. In the present material, desirable recombinants were isolated at a frequency of 1 in every 1000–1500 F2 individuals. 4. The utility of F1 hybrids in the tomato thus depends on the economy of effort involved in their development as compared with the isolation of pure lines. It is concluded that the production of hybrids is to be favoured only when reliable methods of prediction of their performance are available, and then as an interim measure while pure-line forms become available.