Variable Expression of the Candidate Gene NCED1 Among Cowpea Accessions under Different Drought Stress Conditions

Drought significantly reduces cowpea productivity. Information on genetic variation for differential expression of candidate genes for drought tolerance among cowpea genotypes, from which improvement plan could be drawn is limited in Nigeria. Variability of expression of the candidate gene NCED1 in cowpea was analyzed under different drought stress conditions. Primers based on NCED1 and P-Actin (used as an internal control) successfully amplified products from both stressed and unstressed accessions of cowpea. Contradictory responses were observed among drought-tolerant (mean STI > 0.57) and susceptible accessions (mean STI ˂ 0.57). NCED1 was significantly repressed by drought stress in all accessions, except in AC10, AC11, AC13 (tolerant accessions), and AC12 (susceptible accession). The results from stressed and unstressed conditions confirmed that the gene is expressed in both conditions. Biplot divided the accessions into four major groups, with most of the tolerant accessions in groups I and II, while most of the susceptible accessions occupied III and IV. Tolerant accessions such as AC22, AC15, AC23, AC13, AC10, AC11, and AC21 that combined higher plant height and dry root weight under drought stress with stress tolerance indices (STIs) possessed higher gene expression under both control and drought stress conditions. Therefore, positive correlations between the expression of the gene in both conditions and plant height under stress, on one hand, dry root weight under stress on the other hand, and the STIs confirm that its expression may be involved in drought tolerance of cowpea. Hence, the selection of cowpea based on higher levels of gene expression among accessions under both conditions may be effective for breeding drought-tolerant cowpea.