The role of pith, tube, and stalk density in determining sugarcane sucrose content and stalk weight.

Selection against pith and tube is one of the major criteria used to eliminate inferior sugarcane (Saccharum spp.) cultivars in early stages of new cultivar evaluation. Understanding the genetic relationships for these traits would facilitate crossing and selection decisions. This study was conducted to determine heritability, genetic coefficient of variation, and the potential for genetic advance by selection for pith, tube, and stalk density. Correlation and path-coefficient analysis studies were conducted to determine the effects of Brix, pith, and stalk density on sucrose content and the effects of stalk volume, tube, and pith on stalk weight. Eighty randomly selected cultivars (four progeny from each of 20 crosses), representing a first clonal stage of a Louisiana sugarcane breeding population, and their parents were planted at St. Gabriel/LA, and yield data were collected in 1986, 1987, and 1988. Pith and tube exhibited large genotype and genotype-by-year variation, whereas variation in stalk density was nonsignificant. Broad-sense and narrow-sense heritabilities were high, moderately high, and low for pith, tube, and stalk density, respectively. Path-coefficient analysis revealed that stalk volume was the major factor determining stalk weight. Tube and pith were factors that decreased stalk weight. As expected, Brix was the single most important factor determining sucrose content, however, high stalk density and low pith were also associated with high sucrose content. Sugarcane breeders should practice stringent selection for low pith across years to increase stalk weight and sucrose content. Since stalk density was effectively increased by high sucrose content and low pith, the use of stalk density in breeding and selection should be avoided. The minimal effect of tube on stalk weight suggests that its use as selection criteria be minimized or dropped.