# Combining Ability in Maize Breeding Programs in Sub-Saharan Africa: A Systematic Review

## TL;DR

This review summarizes how combining ability analysis helps improve maize breeding in sub-Saharan Africa by identifying strong parental lines and efficient mating strategies.

## Contribution

The study provides a systematic review of combining ability applications in maize breeding across sub-Saharan Africa from 2020 to 2025.

## Key findings

- Most studies focused on yield improvement using inbred lines with high general combining ability.
- General combining ability contributed 80% to hybrid performance across 580 environments.
- Nigeria, Ethiopia, and Ghana were the main regions conducting maize hybridization research.

## Abstract

Background/Objectives: Combining ability (CA) analysis is a key tool in maize breeding for developing superior hybrids by evaluating parental genetic potential through general combining ability (GCA) and specific combining ability (SCA). Despite its widespread use, knowledge of how CA techniques help overcome major constraints to maize production in sub-Saharan Africa (SSA) is limited. This review summarizes recent applications of CA analysis in addressing maize breeding challenges across SSA. Methods: A systematic literature search was conducted using ScienceDirect, Springer, and Google Scholar for studies published between 2020 and September 2025. Search terms included maize, combining ability, and SSA. The review followed PRISMA guidelines, and 94 studies met the eligibility criteria and were included in the analysis. Results: Most studies were conducted in Nigeria (42%), Ethiopia (16%), and Ghana (14%), indicating regional concentration of maize hybridization research within SSA. Yield improvement was the dominant breeding objective across the region. Inbred lines with high GCA were predominantly used as parental materials compared with open-pollinated varieties. The line × tester mating design was the most frequently applied, followed by other mating designs. Across 580 environments, GCA contributed 80%, SCA 19%, and combined GCA/SCA 1% to hybrid performance. The predominance of GCA across traits and environments underscores high additive gene effects, largely due to the high homozygosity of inbred line parents. Conclusions: It has been observed in this systematic review that combining ability analysis remains essential for enhancing maize productivity and resilience in SSA by enabling identification of superior parents, efficient mating designs, and development of widely adapted hybrids.