Incorporating male sterility increases hybrid maize yield in low input African farming systems

Sub-Saharan Africa (SSA) faces a critical challenge in maize production, with yields significantly lower than global averages. Meeting future food security needs requires substantial yield increases, which cannot be achieved solely by expanding cultivated land. Current approaches focus on modern breeding programs, collaboration with seed companies, and development of stress-tolerant varieties. However, seed production remains a significant bottleneck, particularly due to the labor-intensive and costly manual detasseling required for hybrid maize production in SSA. Hybrid maize, produced by crossing two distinct parent lines, leverages heterosis (hybrid vigor) for increased yield. Three-way hybrids are common in SSA due to their lower production costs, although yields are generally lower than other hybrid types. This research explores a new seed production technology (SPT) that addresses both cost and quality issues in hybrid maize production. The SPT system, initially developed and deployed using a recessive male sterility gene (*ms45*), was adapted using a dominant male sterility gene (*Ms44*). This *Ms44*-based SPT system eliminates detasseling in both hybridization steps for three-way hybrids. Previous research showed that 50% non-pollen producing (FNP) hybrids using this system increased yields by 8.5% under controlled, low-nitrogen conditions. This study aims to validate these findings under diverse on-farm conditions in SSA, assessing yield improvements across various environments, genetic backgrounds, and low-input conditions typical of smallholder farms. Participatory research methods were incorporated to understand and address farmer needs and preferences, ensuring the technology's practical applicability and adoption.

Existing literature highlights the urgent need for increased maize productivity in SSA to improve livelihoods and food security. Studies have shown the potential of improved maize genetics and agronomic inputs to alleviate poverty. However, seed production remains a major constraint, with manual detasseling significantly increasing production costs and impacting seed quality. The use of biotechnology in SSA for crop improvement has had mixed results, particularly when attempting to transfer technologies developed under controlled conditions to diverse on-farm settings. The challenges of transferring genetic technologies from controlled US environments to the variable and stressful environments of SSA emphasize the importance of on-farm testing and participatory approaches involving farmers in technology development. Previous work demonstrated the potential yield benefits of FNP hybrids, but this was largely limited to high-yield trials conducted under optimal growing conditions in the US. Therefore, there was a significant gap in understanding the potential of this technology in real-world African farming systems.

This study evaluated the yield performance of FNP hybrids across diverse on-farm conditions in Kenya, South Africa, and Zimbabwe from 2016 to 2019. Multiple hybrid pairs (FNP and pollen-producing (PP) controls) were grown in both on-station trials (OST) and on-farm field trials (OFT) across 112 locations, encompassing a range of environments (optimal, low-N, heat, and drought-stressed). The dominant male-sterile allele *Ms44* was introgressed into five inbred maize lines, resulting in 18 unique single-cross hybrid pairs and eight three-way cross hybrids. OSTs were conducted using a randomized complete block design with split plots. OFTs involved smallholder farmers, who were instructed to follow appropriate pest and weed management but not to use nitrogen fertilizer. Data on grain yield, yield components, plant height, ear height, tassel traits, and kernel characteristics were collected. Ear images were analyzed to estimate kernel number, 100-kernel weight, and ear length. Farmer participatory evaluations were conducted in Kenya in 2017 and 2018 involving 2697 farmers, assessing their perceptions and preferences for FNP hybrids compared to PP controls. Statistical analysis was conducted using ASREML. The economic impact was assessed using net present value (NPV), internal rate of return (IRR), and benefit-cost ratio (BCR) under different adoption scenarios.

FNP hybrids consistently outperformed PP hybrids across a wide range of environments and yield levels. The FNP trait resulted in a 202 kg/ha yield advantage on average, with consistent yield improvements observed across diverse hybrid backgrounds and locations. The absolute yield improvement remained consistent across different yield levels, with a predicted 192 kg/ha improvement in low-potential environments and 229 kg/ha in high-potential environments. Analysis of yield components revealed a 5.9% increase in the number of kernels per plant and a small increase in 100-kernel weight in FNP hybrids. Farmer participatory evaluations showed that while initially farmers noticed differences in tassel and pollen formation, they consistently preferred FNP hybrids due to superior ear size and yield. Economic analysis indicated that even under a conservative adoption scenario (10% of the current hybrid maize area), the technology would increase maize production by 244,204 tonnes per year, with benefits outweighing costs by a factor of 6:1. Under an optimistic scenario (25% adoption), the economic benefits would be significantly higher. The benefits to seed companies include reduced detasseling costs, improved seed purity, and potentially increased seed production yields. The additional benefits stemming from the replacement of older hybrids with newer, higher-yielding ones further enhance the overall impact.

This study demonstrates the significant yield benefits of incorporating the *Ms44*-based FNP trait into hybrid maize under low-input, smallholder farming conditions in SSA. The consistent yield advantage across diverse environments and hybrid backgrounds underscores the broad applicability of this technology. The observed yield increase surpasses the rate of genetic gain typically observed under drought or low-nitrogen conditions, representing a substantial advance in maize breeding. The reduction in tassel size and pollen production in FNP hybrids leads to more efficient resource allocation toward grain production, thereby improving nitrogen use efficiency. The high farmer acceptance observed in this study suggests strong potential for rapid adoption, particularly due to improved yield and ear size. The economic analysis demonstrates significant benefits to both farmers and seed companies, making this technology a promising solution to enhance maize productivity and food security in SSA.

The results of this study demonstrate that incorporating the *Ms44* dominant male sterility gene into hybrid maize significantly increases yield in resource-limited environments typical of SSA smallholder farms. This technology offers a promising approach to improve maize productivity with benefits for both farmers and seed companies. Future research could focus on further optimizing the technology for various agro-ecological zones, exploring the interaction with other agronomic practices such as fertilizer management, and evaluating the long-term sustainability of the FNP system.

The study primarily focused on Kenya, South Africa, and Zimbabwe. While this provided a good representation of diverse conditions across SSA, further testing in other countries would strengthen the generalizability of the findings. The economic analysis relied on projections and certain assumptions regarding adoption rates, which are subject to market dynamics. Long-term effects on soil health and biodiversity warrant further investigation. More detailed analysis of the impact of the Ms44 gene on other agronomic traits under various conditions is also needed.