RELATIVE TOLERANCE OF SOME COWPEA (VIGNA UNGUICULATA L. WALP.) CULTIVARS TO BLACKEYE COWPEA MOSAIC AND COWPEA MOTTLE VIRUSES

Abstract

Twenty five cowpea cultivars were evaluated for tolerance to Blackeye cowpea mosaic virus (BICMV) and Cowpea mottle virus (CPMoV) under field conditions at Mokwa, Southern Guinea agro-ecological zone of Nigeria in the 2017 wet season. The trial was laid out using randomized complete block design with three replications. Each of the twenty five cultivars was inoculated singly with BICMV or CPMoV at ten days after sowing (DAS) while for the mixed virus inoculation: each of the twenty five cultivars was inoculated with BICMV or CPMoV at 17 DAS. Parameters recorded include plant height, number of leaves, pods and seeds per pod. Symptom expression such as bright yellowing, mosaic and mottling started one week after inoculation (WAI) from both treatments. At 2 WAI, 85 - 100 % infection was observed among the viruses and cowpea cultivars. The plants showed typical symptoms of both viruses but at varying levels. The rating done on a scale of 1 - 5 with respect to symptomatology indicated that the viruses had significant (p < 0.05) severe effects on the crops. The severity of the viruses on symptom rating indicated that BICMV caused the highest severity effects in Ife Brown, IT99K – 316 – 2 and IT07K – 211 – 1 - 8 which rated 4.3, 4.3, and 4.3 at 5 WAI respectively and CPMoV elicited the highest severity effects in Ife Brown, IT99K – 316 – 2 and IT06K – 137 – 1 with ratings of 4.6, 4.6 and 4.6 at 5 WAI respectively. However, BICMV disease severity was significantly lowest (1.9) in IT06K – 137 – 1 while cultivars IT04K – 321 – 2 and IT07K – 211 -1 – 8 exhibited significantly low of 1.7 each disease on CPMoV infection. Cultivars IT06K – 137 – 1 (BICMV) and IT04K – 321 – 2 and IT07K – 211 -1 – 8 which elicited the lowest severity scores also had significantly (p < 0.05) highest number (11) of pods per plant. The present results indicated the potentials of cultivars IT06K – 137 – 1 (BICMV) and IT04K – 321 – 2 and IT07K – 211 -1 – 8 (CPMoV) as sources of resistance gene (s) based on low disease severity for breeding cowpea against BICMV and CPMoV disease to enhance productivity and food security.