Impact of drought and cucumber mosaic virus infection on the physiological responses and yield of cowpea (Vigna unguiculata L. Walp.)

As climate change continues to negatively influence cropping seasons and patterns especially in Africa, field crops are constantly exposed to simultaneous environmental and biotic stresses. Constraints, such as drought and virus infections, occurring either as individual or combined stresses, limit cowpea production. In this study, we investigated the responses of two cowpea varieties with contrasting cucumber mosaic virus (CMV) susceptibilities, 'Ife-Brown' (highly susceptible) and 'IT97K-1042-3' (moderately susceptible), simultaneously exposed to varying drought regimes and CMV infection. The cowpea plants were mechanically inoculated with CMV nine days after planting and exposed to three levels of water stress (zero, six and 12 days of water stress) at 3 weeks after planting. Data on vegetative and yield parameters, biomass, canopy temperature, chlorophyll and proline contents were collected. The effects of CMV infection alone on cowpea growth and yield parameters were greater than those of drought stress alone, while the combination of CMV and water deficit was more deleterious than the individual treatments. Conversely, six days of water stress improved the growth and yield of both cowpea varieties. Between the two varieties, 'Ife-Brown' outperformed 'IT97K-1042-3' in terms of growth and biomass accumulation. However, the canopy temperature increased with the number of days of water stress although the values were not statistically different from the control plants. Variations in proline accumulation were observed more positively correlated with drought than with CMV infection. A greater proline content was detected in cowpea exposed to severe drought than in plants subjected only to CMV infection. Combined drought and virus stress reduced cowpea yields while 'Ife-Brown' was more tolerant than 'IT97K-1042-3'. Comparing the effects of CMV infection and drought on both cowpea varieties, 'Ife-Brown' had greater vegetative parameters, biomass accumulation and yield than 'IT97K-1042-3'. The effects of drought and virus infection on cowpea plants, within the context of climate change, are discussed.