Genetic architecture of grain yield and its components in hexaploid and octoploid triticale

Abstract

The genetic basis of yield and its components were characterized in two sets of diallel crosses obtained from seven lines of hexaploid and five lines of octoploid triticale. The analysis were made according to Griffing's method 2 and model 1, and Morley Jones analysis of half diallel table derived from Hayman and Jinks model. The findings of these analysis are discussed in the context of potentials for genetic improvement of yield among the populations under study. In the hexaploid population, both the GCA and SCA variances were highly significant for all the nine characters studied, but the GCA (additive gene effect) was more preponderant in controlling yield and yield components, except for 1000 grain weight and plant height which were predominantly governed by non-additive gene effects. In the octoploid population, non-additive gene effects govern the expression of most of the characters, except for days to heading which was controlled by additive gene effect and spike length where both gene effects were equally in control. Combining ability analysis suggested that Aranui, Swans, Till and Salvo gave consistently high general combining ability effects for at least more than half of the characters studied, suggesting that their crosses should produce desirable segregates for improvement. None of the octoploid lines however was a good general combiner, except for FCT and Pavon which showed significant GCA for days to heading. The (Wr, Vr) graphical analysis in the hexaploid population indicated the presence of partial dominance for all the characters studied, except for 1000 grain weight which showed complete dominance. Partial dominance were also controlling all the characters of the octoploid population except for plant height and grains per spike which showed over dominance. However the over-dominance could be spurious ones arising from presence of epistasis. The distribution of dominant and recessive genes in the parents, also indicated that most of the higher yielding lines in the hexaploid, namely Salvo, Swans and Aranui have mostly recessive alleles, suggesting that high yield is inherited as a genetic recessive, while low yield was inherited mainly by genetic dominance. Narrow sense heritability was found to be high in the hexaploid population for grain yield per plant, spike fertility, spikelets per spike, spike length and days to heading, suggesting these characters will respond to selection. For the octoploid, all characters exhibited low narrow sense heritability. Correlation coefficient analysis revealed that grain yield per plant was positively and significantly correlated with grains per spike, main spike fertility, 1000 grain weight and spikelets per spike indicating that these are strong yield components. Further more, the high correlated response of yield per plant, indicated that selecting for yield directly could be rewarding in the hexaploid population, though selecting for spike fertility could also be a good alternative for improving grain yield per plant. None of the octoploid characters will respond to selection. Specific combining ability effects were good predictors of heterotic responses, but the per-se performances of F₁'s were not able to predict high SCA effects in all characters. Only in the strong yield components were the correlations highly significant, thus per-se performance could be used to select best cross-combinations in these characters. Heterosis for grain yield over the commercial variety was quite high in the hexaploid population. If such heterotic effect exist under normal planting conditions then it would be worthwhile to exploit it for commercial production. There was no heterosis for grain yield among the octoploid hybrids. Exploitation of heterosis in triticale requires some efficient techniques with which to remove the male reproductive organs from the spikes. With this in mind an investigation was also conducted to evaluate the possibility of producing hybrid seeds by hand emasculations and chemical hybridizing agent CHA. The results revealed that cross pollination by wind readily occurs under Canterbury conditions, giving a high percentage seed set, indicating that hybrid seeds could easily be produced in a limited quantity in triticale. The results of the CHA agent was also highly effective on triticale, revealing its potentials as a gametocide for use in commercial exploitation in hybrid triticale production. Both diallel mating designs were found to be effective in characterizing the genetic architecture of the hexaploid population, but an inappropriate design in the octoploid, due to failures of some of the underlying assumptions. The overall implication therefore is that the hexaploid population has great potentials to respond to improvement, while the octoploids should be used to improve the hexaploids mainly.