Thesis Abstract

The patterns of gene effects on agronomic and some quality traits of eight genotypes ofrice (Oryza sativa L.) and their progenies were studied using Diallel analysis method 1involving parents, F1 hybrids and their reciprocals. The eight genotypes studied wereselected for their agronomic performance and protein content from thirty genotypesevaluated in a randomized complete block design and replicated three times at theTeaching and Research Farm of the Federal University of Technology, Owerri, Nigeriaduring the planting seasons of 2005 and 2006. The results of the Diallel analysisconducted during the 2007 planting season indicated larger magnitude of additivecomponents of variance in attributes like number of tillers per plant, number of days toanthesis, panicle length , number of secondary branches per panicle, 1000-seed weight,grain width and grain length/grain width ratio. Non-additive variance was more importantfor plant height at flowering, number of seeds per secondary branch of panicle, grainlength and percentage protein content. The nature and magnitude of general combiningability(GCA) and specific combining ability(SCA) effects, as well as the direction ofheterosis assessed by the SCA effects, seemed to differ for different traits and variouscross combinations. No parental line consistently had negative SCA effects for all the

traits.

Additive gene effects with high GCA values could be exploited in WITA 4 andMax for higher tillering ability, NERICA 1, Fofifa 16 and WAB 96-1-1 for earliness;WITA 4 and NERICA 1 for production of hybrids for greater number of secondarybranches per panicle; CT 7127-49 and EMPASC 105 for development of hybrids withgreater number of spikelets per panicle; NERICA 1, CT7127-49 and EMPASC 105 forproducing hybrids with more fertile grains; CT7127-49 and NERICAI for developingprogenies with more seeds per secondary branch of panicle; IR57689-73 and Fofifa 16for 1000-seed weight and CT 7127-49 and WITA 4 for developing long and fine grains.WITA 4 and EMPASC 105 were observed to be semi-dwarfs and offer themselves ascandidate genotypes for reduction of plant height to reduce stem lodging and increaseyield. The phenotypic generation means of the parental lines (P1 and P2), F1 andreciprocal cross and the BC1 and BC2, evaluated during the 2009 planting season for thestudy on genetic effects of the characters on the breeding lines generated, indicated thatthe F1 generation means were higher than their mid-parent values especially forpercentage protein content. The F1 and F2 generation means were not significantlydifferent in the majority of the cases except for lowland x upland and upland x lowlandhybrids for percentage fertile spikelets and numbers of spikelets per panicle. Variedgenetic effects were observed on the characters for generation mean analysis on sixparameter model. Additive and dominance as well as epistatic gene effects were involvedin the inheritance of most characters. Digenic interactions were significant for most of thetraits. Presence of significant dominance effect combined with duplicate epitasisrestricted the scope for simple selection for most of the characters. Reciprocal and

maternal effects were also implicated for most of the traits.

Thesis Overview