Combining Ability Analysis and Identification of Testers for Biomass Yield and Forage Quality Traits in Guineagrass (Megathyrsus maximus)

Guineagrass (Megathyrsus maximus), a key tropical forage species, presents breeding constraints due to apomixis, polyploidy and a narrow sexual gene pool. This study quantified the genetic architecture of biomass and forage quality traits and identified apomictic testers using an incomplete North Carolina II mating design. A total of 175 F1 families derived from 27 sexual female parents and nine apomictic male parents were evaluated. Agronomic traits were evaluated across three contrasting environments in Colombia, whereas nutritional quality traits were assessed in one location. Mixed models were used to estimate variance components, combining ability, heritability, and genetic interactions with locations. General combining ability accounted for 58.6% to 80.1% of the main genetic variance depending on the trait. Full-sib family mean broad-sense heritability was high for agronomic traits (H2FS = 0.89–0.95) and moderate for nutritional quality traits (H2FS = 0.56–0.66), supporting selection at the family level. Male half-sib family mean heritability was consistently high, indicating reliable estimation of apomictic tester effects. Mombaça (CIAT_6962) was the most consistent productivity tester, whereas CIAT_6799 and CIAT_6986 showed favorable predicted effects for nutritional quality traits under Palmira Location. These results provide a quantitative basis for recurrent selection using testers and family validation in guineagrass breeding.