Influence of Seedling Age at Inoculation and Cultivar on the Pathogenicity of a Virus Causing Yellow Mosaic Disease of Commelina Benghalensis L. on Cowpea

A screenhouse experiment was conducted to evaluate the influence of seedling age at inoculation and cultivar on pathogenicity of the virus causing yellow mosaic disease of Commelina benghalensis L, a broad leaf weed, on cowpea. Three cowpea varieties namely Vita 5, IT84S2246D and Ife Brown were grown in pots and inoculated with sap extracted from leaves of C. benghalensis infected with yellow mosaic disease at 7, 14, and 21 days after germination (DAG). It was found that inoculation of cowpea seedlings at 7 DAG subsequently led to the most severe symptoms, which were manifested by mosaic and yellowing of leaves and eventual poor growth and yield attributes. On the other hand, plant growth and yield attributes that were comparable to those of the healthy control plants were recorded for plants inoculated at 21 DAG. Specifically, in regards to the interaction effects, cv. Vita 5 that were sap-inoculated at 7 DAG had the lowest yield attributes, while cv. IT84S2246D inoculated at 21 DAG had the highest yield attributes. The results put together showed that although the yellow mosaic virus of C. benghalensis was sap-transmissible and pathogenic to cowpea causing characteristic yellow mosaic disease symptoms and reduction in yield attributes, severity of the disease is less if infection occurs at older stage of cowpea growth.