The Environment Strongly Affects Estimates of Heterosis in Hybrid Sweet Sorghum

Abstract

Sweet sorghum [Sorghum bicolor (L.) Moench] has potential as a biofuel feedstock, but hybrid cultivars are needed to support an industry based on this crop. The purpose of this study was to compare five inbred sweet sorghum lines and 15 hybrids derived from them and to determine the extent of environmental effects on estimates of hybrid vigor (heterosis) and heritability for various agronomic traits. The test was repeated across 2 years (2013 and 2015) and three planting dates each year (April, May, and June) at Tifton, GA, USA. Environmental conditions were highly variable, and thus, estimates of heterosis for various traits, as well as correlations between hybrids and midparents (average of the inbred parents), were also variable. In the 2015 season, a new insect pest, sugarcane aphid (Melanaphis sacchari Zehntner), appeared to cause reduced juice Brix in the April planting. Hybrids generally flowered earlier than their inbred male-parent lines, and flowering time was highly correlated between midparents and hybrids. Hybrids frequently had greater lodging percentage than inbreds, but lodging was also correlated between midparents and hybrids in four environments. Heterosis for juice Brix and sugar yield was uncommon, while heterosis for panicle (grain) yield was frequently observed. Based on this study, it will be difficult to predict hybrid performance for juice Brix, sugar yield, and panicle yield based on inbred performance. Testing in multiple environments will be essential for the development of sweet sorghum hybrids, and there is a critical need for sweet sorghum cultivars with resistance to sugarcane aphids.