Utility of root cortical aerenchyma under water limited conditions in tropical maize (Zea mays L.)

•Root cortical aerenchyma (RCA) reduces root metabolic costs.•Maize lines with contrasting RCA were grown under drought in Malawi.•High RCA lines had better growth and yield under drought.•RCA could be used to improve drought tolerance in maize. It has recently been shown that root cortical aerenchyma (RCA) formation substantially reduces the metabolic costs of soil exploration, thereby improving rooting depth, water capture, and plant growth under drought. The objectives of this study were to evaluate phenotypic variation of RCA formation in Malawi maize germplasm and confirm the utility of RCA formation in different agroecologies at field stations and on smallholder farms in Malawi. Forty maize accessions collected across Malawi were grown under rainfed field conditions, and a subset contrasting for RCA were grown under well-watered and water stressed conditions at two research stations and under natural drought on farms across two agroecological zones in Malawi. We found substantial variation for RCA in local germplasm ranging from 0% to 37% of root cross sectional area. Suboptimal water availability increased RCA from 54% to 77% across environments. Under water stress high RCA genotypes had 23% to 29% greater leaf relative water content, 67% to 96% greater shoot biomass 70 days after planting, and 78% to 143% greater grain yield than low RCA genotypes. Our results are consistent with the hypothesis that RCA improves plant growth under drought by reducing the metabolic costs of soil exploration and improving water acquisition. RCA has value as a selection criterion to improve the performance of maize and possibly other cereal crops in water limited environments.