Statement of authorship: MRL, PAC, and CPO designed the study. MRL generated and analysed data. EGE and RCL performed the PEPC quantifications. MRL, PAC, BSR, GB, and CPO contributed plant material. MRL, CL, PWH, and RPE contributed accession collection locations and isotope data.MRL, PAC, and CPO wrote the paper, with the help of all the authors.

Cowpea is the major source of vegetable protein for rural populations in sub-Saharan Africa and average yields are not keeping pace with population growth. Each day, crop leaves experience many shade events and the speed of photosynthetic adjustment to this dynamic environment strongly affects daily carbon gain. Rubisco activity is particularly important because it depends on the speed and extent of deactivation in shade and recovers slowly on return to sun. Here, direct biochemical measurements showed a much faster rate of Rubisco deactivation in cowpea than prior estimates inferred from dynamics of leaf gas exchange in other species1–3. Shade-induced deactivation was driven by decarbamylation, and half-times for both deactivation in shade and activation in saturating light were shorter than estimates from gas exchange (≤53% and 79%, respectively). Incorporating these half-times into a model of diurnal canopy photosynthesis predicted a 21% diurnal loss of productivity and suggests slowing Rubisco deactivation during shade is an unexploited opportunity for improving crop productivity.

Cowpea (Vigna unguiculata [L.] Walp.) yields within the dry savannahs of Sub-Saharan Africa are low. Given the contribution of cowpea to food security in this region, it is essential that high-yielding varieties are developed to improve crop productivity in a sustainable manner. Identifying morphological or physiological traits that correlate with biomass could assist breeders with rapid screening of diverse germplasm. This study investigated 23 diverse Nigerian cowpea lines in an environmentally controlled greenhouse and 50 diverse lines from a Multiparent Advanced Generation Intercross (MAGIC) population in the field to identify easily measurable traits associated with high above ground biomass. Correlation analyses found that leaf traits were significantly and positively correlated with above ground biomass, and the leaf width of the youngest fully expanded leaf was the best indicator of biomass yield. Analysis of variance identified significant differences among the genotypes for all measured traits, indicating that there is genetic variation among these varieties and opportunity for selection. These results from the greenhouse and the field indicate that the leaf width of the youngest fully expanded leaf can be used to rapidly select cowpea lines with high biomass production potential.

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