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Abstract SUMMARY Six Egyptian cotton cultivars namely; Giza 45. Giza 70. Giza 66 , Giza 67 , Giza 69 • Giza 75. were crossed in a diallel pattern and evaluated for heterosis.,.combining ability and genotypic variation • AnalY8i~of genetic component controlling the. variables. seed cottoti yield. boll weight. lint percent. seed and lint indices, micronaire reading. hair weight. staple and mean length and yarn strength was also conducted. The six parents and their 15 FI’s plus their corresponding F 2 ’s were included in a randomized complete blocks experiment. 1· The analysis of variance revealed significant differences among genotypes for all variables studied in F 1 and F gen~~rations • 2 1· Estimates of mid-parent heterosis were significant for seed cotton yield, lint percent, hair weight and mean length. Meanwhile the average BP heterosis (useful heterosis for . pl.nt breeder)w.as significant and positiveforseedC()ttonyield Moreover. positive but insignificant BP heterosis was obtained for fiber fineness (hair weight) and fiber length (mean length). While then:mrlning ~~ showed no heterotic effects over the average .BP heterosis. A considerable number of hybrids exhi bited signi fican t MP heterosis. when t only a few displayed significant BP heterosis. The parental cuI tivars Giza 67 and Giza 70 were represented in moat cases which sh showed BP heterosis for yield. 9. ThE! reciprocal crosses which exhibited true he~erosts. aLnost showed heterotic effects, however, in some cases it did n01: reach the significant level. Thus, the heterotic effects are real. 4. Mean inbreeding depression effects showed insignificant effects for all traits except for fiber length (mean length) which gave highly significant value. The individual F2 means were almost close to the mean of their MP and Fl performance for all traits. This suggested that additive and do~inance effects are more important than those for epistasis in this material. ~. Highly significant or significant estimates were calculated for GCA and SCA mean squares in the F2 generation, while the values of SCA mean squares were inconsistent in the F1 generation. ~. The GCA/SCA ratio of variance components indicated that additive genetic variance was aproximately of greAter tmportaqce for all traits. 1. The magnitude of GCA effects corresponded closely with the rank of the parental means for all traits. This indicates that selection of parents u’sed . in breeding to improve these traits~be based largely on the phenotypic performance oc the parents and also suggests the presence of a considerable additive effects. A· The reciprocal effects are significant for seed index • lint index and all fiber property traits in both F and F2 generations. They are lower in magni tude compared to GCA and SCA. Meanwhile, the FI hybrids almost showed significant effects indicating that heterosis in most traits is real. However. the results may indicate the possibility of reciprocal effects in Egyptian cotton and the traits expression in the FI hybrid may be the function of both genotype and cytoplasm. Therefore, the studies point out to the need for including reciprocal crosses in such biomettrical studies. 9. Relatively high level of heterosis and SCA effects observed for seed cotton yield and fiber fineness(hair weight) in certain crosses suggested that some potential useful combinations were present. It seems that for this material, breeding procedures used should be that maXimize both additive and dominance genetic variance. IO.Estimates of D component were greater than Hi for lint percent, lint index and hair weight in F1 generation. This suggests that additive genetic variance is more important for these traits in this material than dominance genetic variance. On the other hand. for the other remaining traits the dominance genetic variance is more i.portant • Moreov4~r, the estimator hI also indicated that the parents seemed to carry more dominant alleles than recessives for these characters studied. 11. The average degree of dominance were in the overdominance range for seed cotton yield, boll weight, seed index, microna: ire reading and staple and mean length in the Fl’ In the F2, seed index and micronaire reading showed complete and overdominance, res pee tively , while seed cot ton yield, boll weight and yarn strength were in the parential dom- Lnance range. 12. The est ima tor of the average frequency of posi tive VB negative alleles were lower than 0.25 suggesting that positive and 11egative alleles were not equally distributed among the parent LaI cuItivars. The parents seemed to carry more dominant genes than recessive, as indicated by the positive values of F component. 11. Estimates of the ratio dominant to recessive illleles in the parents, Kn/KR ’ were greater than one for all traits which indicates asymetry of the parents, this implies excess of dominant genes in the parents for these traits. 14. The number of effective factors, k , of seed cotton yield and boll weight were relatively high in both generations, whereas the remaining traits showed fairly uniform or eratic estimates over the two generations. 15. High negative correlation coefficients between the mean value of (Wr + Vr) of each array averaged over blocks and the corresponding parental means averaged over blocks , were calculated for boll weight, lint percent and lint index in the F1 and seed cotton yield and micronaire reading in the F2. This ind ica tes that the dominant a alleles are positive in ’irection, i.e., operating in the direction of heavier bolls, higher lint percent, lint index, seed cotton yield and micronaire reading. Moreover, the positive coefficient calculated for hair weight may indicate that dominant alleles are negative in direction and operating in the direction of finer fibers. I 16. High narrow-sense heritability estimates were calculated for hair weight, lint percent and lint index, whereas , reliable values were obtained for boll weight and micronaire reading and relatively lower values were estimated for the remaining traits, in the F1 generation. The heritability values calculated in the ’2 were medium to low for t he traits studied. 17. These results indicated that an effecting breeding method within this material for improving seed cotton yield and its ~elated variables along with higher fiber quality would be tlBt leeding towarde the production of varieties rather than hybrids. However, the information obtained in regard to H and degree of dominance suggests that sub_ stantial potential exists for obtaining improvements in yield, components of yield and fiber properties in this material, through the use of breeding program utilizingF1hybrids. |