Cowpea viruses: Quantitative and qualitative effects of single and mixed viral infections

Abstract

Multiple viral infections have been reported on cultivated commercial cowpeas (Vigna unguiculata) in Nigeria. In this study, the effect of inoculating two commercial cultivars (cvs) (“Oloyin” and “Olo II’) and two lines from IITA (Ife Brown and TVu-76) with buffer, Cowpea aphid-borne mosaic (CABMV), Cowpea mottle (CMeV) and Southern bean mosaic (SBMV) viruses individually as well as in mixtures (CABMV+ CMeV, CABMV+ SBMV, CMeV+SBMV, and CABMV+ CMeV+SBMV) at 10 and 28 days after planting (DAP) on the growth, yield and nutritive content of seeds from infected plants were evaluated. The age of the plants at time of infection and the different viral treatments significantly affected the different parameters assessed. The average height of plants inoculated 10 DAP were significantly shorter than those of plants inoculated 28 DAP. Inoculating with single, double and triple viruses (10 DAP) resulted in 19-34%, 31-46% and 42-53% reductions in plant height, respectively. Viral infections also resulted in significant reductions in the number of pods and seeds produced. Plants inoculated with the three viruses 10 DAP produced the least number of pods and seed. Viral treatments resulted in the production of seeds with a lower protein content of 24.8-28.9% compared with the 28.5-30.4% protein in seeds from the control plants. Plants inoculated 10 DAP with the triple viruses produced the seeds with the least protein content (24.8-27.1%). The carbohydrate, fat and moisture contents of seeds from virus infected plants were however slightly higher than those of the control plants while the ash contents were lower. Generally, the commercial cowpea cvs were more severely affected by the viral treatments. These results indicate that infection at an early age and by multiple viruses can have devastating effects on the growth, yield and the nutritional quality of cowpea.