Screening Cowpea Genotypes for High Biological Nitrogen Fixation and Grain Yield under Drought Conditions

Abstract

Core Ideas Cowpea nodule biomass was more sensitive to water stress compared to shoot biomass. Rainfed conditions resulted in 57% decrease in N2 fixation compared to well‐watered. Inter‐seasonal variability in rainfall accounted for 58% difference in cowpea grain yield. Future increase in drought and heat stress will challenge legume productivity in many regions. In Sub‐Saharan Africa, legumes are earmarked as an integral component in building resilience to climate change and food security in smallholder farming systems. Hence, the need for continuous screening of drought tolerant legume genotypes for sustained productivity. A 2‐yr field study was conducted to identify superior cowpea genotypes with high biological nitrogen fixation (BNF), grain yield, and drought tolerance. Four genotypes, selected from a pool of 91, were grown under four moisture levels ranging from well‐watered (WW) to severe water stress (SS). Grain yield, shoot biomass, nodule mass, and BNF were determined. There was significant effect of water stress on the measured parameters. Nodule mass and BNF were more sensitive to water stress compared to shoot biomass across genotypes. Water stress resulted in 80% reduction in nodule biomass between WW and SS. As a result, cowpea genotypes grown under SS conditions fixed 57% less N2 compared to those under WW. The study also revealed significant genotypic variation in shoot biomass, grain yield, and BNF. Genotype TVu4607 was low in grain yield but performed better for BNF (71 kg N ha−1 under WW and 30 kg N ha−1 under SS). Genotype IT00K‐1263, proved to be our superior genotype with a good balance of biomass, BNF and grain yield. Our findings suggest that future water stress may significantly affect cowpea productivity, mostly its capacity to fix nitrogen. Consequently, adaptation strategies to improve drought resistance in cowpea are needed, particularly improvement of BNF under water stress.

Stomatal Behavior of Cowpea Genotypes Grown Under Varying Moisture Levels

“…The results suggest that TV2 probably has the capacity to establish an efficient rooting system very early in the season. In a separate study, TV2 was found to have significantly higher root biomass compared to the other genotypes [19].…”

The effect of drought stress on nodulation, plant growth, and nitrogen fixation in soybean during early plant growth

“…In general, drought significantly affects SNF in legumes, and we also found a reduction in total shoot nitrogen fixed in soybean under moderate drought stress conditions. Reduction in SNF under drought was also reported in common bean (Polania et al, 2016), pea (Ladrera et al, 2007), cowpea (Munjonji et al, 2018), lentil (Parvin et al, 2019), and peanut (Wang et al, 2022). Several factors have been related to the inhibition of N 2 fixation under drought, including a reduction in carbon flux to nodules, reduced oxygen availability, the decline in nodule sucrose synthase activity, and an increase in ureides and free amino acids (González et al, 2015;King & Purcell, 2005).…”

Ability of nitrogen-fixing bacteria to alleviate drought stress in cowpea varies depending on the origin of the inoculated strain

“…Cowpea production in Brazil is primarily concentrated in the semi-arid regions of the northeast. Although cowpeas are considered drought-tolerant, water de cits during the early vegetative stages can negatively affect their morphological and physiological traits, ultimately affecting biological nitrogen xation (BNF) and grain yield (Munjonji et al 2018;Ayalew and Yoseph 2022;Lumactud et al 2022).…”

“…Cowpea production in Brazil is primarily concentrated in the semi-arid regions of the northeast. Although cowpeas are considered drought-tolerant, water de cits during the early vegetative stages can negatively affect their morphological and physiological traits, ultimately affecting biological nitrogen xation (BNF) and grain yield (Munjonji et al 2018;Ayalew and Yoseph 2022;Lumactud et al 2022).Plant growth-promoting rhizobacteria (PGPR) offer a promising biotechnological approach for mitigating the effects of abiotic stress on various crops (Bittencourt et al 2023;Cao et al 2023). Microbial communities sourced from speci c environments, such as semi-arid regions, adapted to drought conditions, may exhibit enhanced effectiveness in assisting plants to cope with water de cits (Shirinbayan et al 2019;Shet and Garg 2022;Braga et al 2022).…”

“…N 2 xation is the best example of the successful ecological services offered by PGPR to crops(Alves et al 2003;Telles et al 2023). However, drought stress impairs rhizobial survival in soil or rhizobial inoculants applied to the soil, constraining the process of nodulation and negatively affecting BNF(Munjonji et al 2018;Lumactud et al 2022). …”