Combining ability and gene action for flowering, plant height, grain size, and yield in rice (Oryza sativa L.) genotypes

Rice ( Oryza sativa L .) is one of the most fundamental staple cereal crops feeding more than half of the global population. General Combining Ability (GCA) is the average performance of a genotype across multiple hybrid combinations, mainly due to additive genetic effects while Specific Combining Ability (SCA) is the deviation from expected performance in specific crosses, attributed to non-additive genetic effects such as dominance and epistasis. The aim of the current study was to determine combining ability and gene action of 4 key rice traits such as flowering, plant height, grain size and yield. The study was carried out at Lifuwu Agricultural Research Station – Experimental Fields in Salima District (in Malawi) during the 2024/2025 rainy season in a Randomized Complete Block Design (RCBD) with 3 replications using a total of 15 rice genotypes. Since genetic variance components are not directly observable, crossing methods such as North Carolina Design II (NCD II) was therefore used in the current study to reveal those parameters. Gen stat 19th edition was used for the analysis of majority of the dataset in the current study and Analysis of variance showed significant differences among genotypes, indicating substantial genetic variability across traits. Kudya rice genotype exhibited the highest positive GCA effects (1.015) indicating its strong potential as a grain yield contributor in hybrid combinations. The highest positive SCA effect was exhibited in a cross between Kudya and Kayanjamalo rice germplasm, indicating strong non-additive genetic contribution to yield performance. The highest mean grain yield per plant was recorded in the cross of Kudya × Kayanjamalo (19.0 g), while the lowest was observed in Uwemi × Kilombero (10.3 g). The implication of this study in rice breeding is that superior parents and hybrid combinations for grain yield, earliness to maturity and grain quality were identified for future breeding programmes.