Quantitative genetics of sugarcane : I. Analysis of variation in a commercial hybrid sugarcane population.

1. The statistical techniques of quantitative genetic analysis have been applied to the study of variation in a sugarcane breeding population of interspecific hybrid origin. 2. A comparison has been made of estimates of heritability based on sire or dam components of variance alone. The overall equality of these two statistics has been taken as evidence that pollen contamination, self-fertilization and parthenogenetic reproduction are unimportant sources of disturbance in the genetic analysis of the population. 3. From an analysis of plot means it has been concluded that all twenty-four primary characters show significant clonal variation, the overall mean value for clonal repeatability being 0.48. For sixteen of the variables, the estimate of heritability based on the component of variance among full-sib family groups was also significant, the mean value of this parameter being 0.29. 4. For ten of the primary characters, the estimate of clonal repeatability differed significantly from the estimate of heritability. In every case the repeatability value was the greater of the two. It cannot be concluded that nonadditive genetic variance is the major factor responsible, since the use of selected clones as parental material, and disassortative mating for some easily observed characters, appear to provide a sufficient explanation of the disparity. 5. The irregular transmission of unpaired chromosomes derived fromS. spontaneum, S. robustum andS. sinense may possibly contribute to the observed difference between heritability and repeatability. No other serious departure was observed from expectations based on diploid inheritance. 6. The analyses show fibre percent fresh weight and sucrose percent dry matter to be particularly strong clonal characters. The measure of sucrose per plot, which includes variability for yield of cane, has a heritability of 0.24, a repeatability of 0.43, and a high coefficient of variation (46%). 7. Comparisons of the breeding population with two commercial standards have indicated that selection among genotypes within the present population could lead to significant improvement in any one of the commercially important characters. Further gains with subsequent cycles of hybridization and selection are also strongly indicated. No information has as yet been obtained on the magnitude of genotype×years interaction effects.