PARENTAL SELECTION, GENETIC VARIANCES AND HERITABILITY FOR EARLY SUGAR CONTENT IN SUGARCANE

Abstract

Cropping sugarcane (Saccharum spp.) varieties with high sucrose content and early accumulation of it, allow increases of sugar yield as well as an earlier start of the harvest season, with marginal increase in the production costs. With the aim of detecting varieties with higher sugar content and to study the genetic variability and heritability of the early sucrose content, two groups of varieties of sugarcane were evaluated: the first one (G1) integrated by 20, and the second one (G2) by 32. In addition, two groups of crosses obtained from G1 were evaluated as well: 27 crosses (CR27) planted with seedlings from sexual seeds, and a subset of 12 (CR12) planted with stem cuttings (setts) obtained from those seedlings. For G1 and G2, sucrose, total solutes, purity and fiber content were recorded at 8, 10 and 12 months for two harvest seasons; and for CR27 and CR12 the same information was recorded at 12 months in one harvest season. Variance components and broad sense heritability (H²) for variety means were estimated for G1 and G2, and narrow sense heritability (h²) was estimated for CR27 and CR12. For variety trials, the genetic variance tended to be reduced through harvest time (age), and broad sense heritability showed medium to high values. At least 11 varieties showed higher sugar content than the commercial check. For crosses from sexual seeds (CR27) the within family variance and error variance values tended to be high, which gave relatively low values of narrow sense heritability; meanwhile, in the cross trial planted with setts, the within family variance and error variance values were low and heritability resulted high. The option of obtaining setts from seedlings in a mating design for sugarcane may be less time consuming procces and produce a better genetic variance estimates, which may impact in the same way for selection purposes.