Mechanical transmissibility and pathogenic effect of a mosaic disease of <i>Commelina benghalensis</i> L. in Cowpea, <i>Vigna unguiculata</i> (L) Walp

Abstract

Experiments were conducted using potted plants on the mechanical transmissibility or otherwise and the eventual pathogenic effect, of a viral isolate from naturally infected Commelina benghalensis L. (a broad-leaved weed) on three widely grown cowpea, Vigna unguiculata L. Walp cultivars- Vita 5 (white), IT84S2246-D (Brown) and Ife Brown. The results showed that the virus was mechanically transmitted to cowpea through the sap extract from infected weed leaves. All the cultivars exhibited symptoms of infection, which started as leaf mottle and gradually developed into well pronounced dark green to pale green mosaic pattern that had been observed on the natural weed host. The degree of susceptibility was observed to vary with the cultivars in terms of time of appearance of symptoms and the subsequent growth and yield response. Inter cultivar comparison showed that cv Vita 5 (white) was the most susceptible; having manifested symptoms at least 5 days earlier than others and subsequently having in absolute as well as in percentage terms the lowest number and size of leaf, least plant height, delayed flowering and lesser number and weight of pods as well as grains. IT84S2246D was the most tolerant of the 3 cultivars. It had highest absolute growth and yield parameters compared to other cultivars and intracultivar comparison showed that the infected plants performed just a little lower than the healthy ones Keywords: Mechanical transmission, viral isolate, cowpea cv Vita 5, cv IT84S2246D, and cv Ife Brown, Commelina sp.JARD Vol. 4 (2) 2005: pp. 148-158