Indirect selection for increased sucrose yield in early sugarcane testing stages

Abstract

A plant breeder may base selection on components of yield when direct selection for yield has proven ineffective. The objective of this research was to study ways of effectively improving sucrose yield, via indirect selection, in the first clonal testing stage of sugarcane ( Saccharum spp.) improvement programs. The components of sucrose yield measured were: stalk weight, stalk volume, stalk density, stalk height, stalk diameter, sucrose content, Brix, purity, and pith. A Louisiana sugarcane breeding population represented by 80 randomly-selected genotypes (four progeny from each of 20 crosses among 19 parents) from a first clonal testing stage was studied. The clones were planted at the St. Gabriel Research Station in a randomized complete block design with three replications. Data were collected in 1986, 1987, and 1988 from the plant cane, first ratoon, and second ratoon, respectively. As expected, path-coefficient analysis revealed that purity and Brix were the main factors increasing sucrose content. Indirect effects suggested that selection for low levels of pith will increase levels of Brix and purity. Stalk volume had a positive and much larger effect on stalk weight than stalk density, while increased stalk diameter and stalk height had positive and near equal effects on increasing stalk volume. When selection for cane yield cannot be accomplished directly, then selection for stalk weight can be used. Stalk weight can be effectively increased by visual selection for stalks with large volumes, which can be accomplished by emphasizing stalk diameter and stalk height. Selection emphasis based on high Brix and low pith should increase sucrose content. Maintaining high levels of sucrose content in high cane-yielding selections should best increase sucrose yield.