The effect of separately inoculating cowpea cultivars, ‘Ife brown” (IF) and “Owode” (OW) with Cowpea aphid-borne mosaic virus (CABMV), Cowpea yellow mosaic virus (CYMV) and Rhizobium IRc 284(RH-284) on nodulation was investigated. Also, the effect of inoculating the cowpea cultivars with RH-284 on the severity of infection caused by the viruses was studied. The interactive effects of inoculating cowpea with RH- 284 and each of CABMV, CYMV, Southern bean mosaic virus (SBMV) and Blackeye cowpea mosaic virus (BICMV) on nodulation, growth and yield of IF and OW were also investigated. The results showed that infection by CYMV and CABMV significantly reduced nodulation by about 20-30% and 40-45% in IF and OW, respectively. Inoculating with RH-284 alone significantly increased nodulation by about 20% in both cowpea cultivars. In the interactive study involving virus-RH 284 inocula, slight but non-significant increases of 22, 2 and 9% in nodule number were observed in IF inoculated with RH-284 and SBMV, CYMV and CABMV, respectively. The differences observed in the nodule, shoot and seed weights were not significantly different from those of the control. There was a negative correlation between nodule number and severity of symptom. BICMV caused the most severe effect on the two cowpea cultivars. It reduced the number of nodules by 55-66% with or without RH-284. It also caused significant reductions of over 80% in nodule and seed weights of OW. In conclusion, increase in nodulation reduced viral disease severity, the slight but non-significant increases observed in the growth and yield parameters suggest that improved nodulation can be advantageous to cowpea.
Key words: Blackeye cowpea mosaic virus, cowpea aphid-borne mosaic virus, cowpea yellow mosaic virus, southern bean mosaic virus.
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