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RESPONSE OF VEGETABLE COWPEA (Vigna unguiculata L. Walp) TO SOME BIOPESTIDES FOR THE CONTROL OF BACTERIAL LEAF SPOT IN UMUDIKE, SOUTH EAST NIGERIA
Abstract
An experiment trial was conducted in Michael Okpara University of Agriculture, Umudike to assess the efficacy
of some leaf extracts (Vernonia amygdalina, Gongronema latifolium and Ocimum gratissimum) in the control
bacterial leaf spot disease of vegetable cowpea). Also, their effects on disease severity and disease incidence,
growth and yield performance were also investigated during the 2016/2017 and 2017/2018 cropping seasons.
Four varieties of vegetable cowpea were used (Black vegetable cowpea, Brown vegetable cowpea, Ife brown and
Ife-143), were tested to susceptibility by bacterial leaf spot pathogen with a view to identify the most resistant
variety that can be adopted by farmers. The experiment was laid out in a randomized randomized complete block
design (RCBD) with three replicates and plant the plant extracts were applied two weeks after planting. Isolation
and identification were also done by collecting diseased leaf plants from the field to the laboratory by performing
pathogenicity tests both invivo and invitro to confirm the identity of the casual organism. Similarly, some
biochemical tests were conducted (Gram-negative, catalase, oxidase, indole, maltose, xylose and glucose) to
further confirm the identity of the pathogen. Based on these tests conducted, the pathogen was identified as
Xanthomonas axonopodis pv. vignicola. Data obtained from the two years field trials on growth parameters (plant
height, number of branches, number of leaves per plant, stem girth) and on yield performance including thoe of
disease (incidence and severity) were subjected to statistical analysis (Fishers Lsd P≤0.05 ). Results obtained
from the field showed that significant differences (P≤0.05 ) existed among the different varieties on one hand and
among the leaf extracts on the other hand (74-80% success in reduction) for instance lowest percentage disease
incidence on vegetable cowpea was recorded with Vernonia amygdalina treated plants (10%) when compared
with the control (80%). While reduced disease severity score was recorded for the Gongronema latifolium (2.00)
compared with the control (8.90) on Ife-143 plants. These significantly enhanced yield and yield components
(P≤0.05 ).
