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Estimating Genetic Variance in Sugarcane Using a Factorial Cross Design¹

Progeny from seven factorials of crosses were studied to examine the quantitative genetics of a breeding population of clones used in the Hawaiian sugarcane (Saccharum spp. L.) breeding program and the applicability of quantitative genetic theory to sugarcane. Nonadditive genetic effects were equally important to additive genetic effects, which suggests that increased yields could result from utilizing both polycrosses and crosses where both parents are known. There was relatively little genetic variability for sugar content as measured by refractometer solids compared to the genetic variability for yield of cane as measured by volume. Thus, the greatest progress in breeding and selection is more likely to come from increasing the yield of cane rather than from increasing sugar content.

The estimates of additive genetic variance, ²_A1 and ²_A2, were obtained, respectively, from the regression of progeny means on mid-parent means and the progeny analysis; the estimates of total genetic variance, ²_G! and ²_G2 were obtained, respectively, from the analysis of parental clones and the progenies. The ratios of ²_A1/²_A2 and ²_G1/²_G2, however, were generally less than one, which suggests that the assumptions underlying quantitative inheritance analysis were violated. This is probably because the clones in the breeding population were highly selected for yield potential.

Key Words: Saccharum spp. • Heritability • Degree of genetic determination • Selection, Genotype x environment interaction • Additive genetic variance • non-additive genetic variance • Epistasis

² Respectively, senior geneticist, Bureau of Sugar Exp. Stn., Brisbane, Australia; associate plant breeder; former head of Genetics and Pathology Dep., Exp. Stn., Hawaiian Sugar Planters' Assoc.

Received for publication September 17, 1979.