ABSTRACT

A pot experiment was conducted in 2018 cropping season in the Research farm of Michael Okpara University of Agriculture, Umudike to assess the efficacy of some leaf extracts of Vernonia amygdalina, Gongronema latifolium, Ocimum gratissimum and the control (sterile water) in the control of bacterial leaf spot disease of vegetable cowpea. Also their effects on disease severity and incidence, sowing date; growth and yield performance were monitored. Four varieties of vegetable cowpea: Black vegetable cowpea, Brown vegetable cowpea, Ife brown and Ife 143, were subjected to infection by bacterial leaf spot pathogen with a view to identifying the most resistant variety that can be used to reduce the disease. The experiment was laid out in a completely randomized design (CRD) with three replicates, the pot size was (15cm), plant materials were washed, air dried, exactly 250g of each milled paste of the leaves were added in 200ml of sterile water for 10minutes in a 500ml beaker to obtain suspension and strained through two layers of cheese-cloth using Whatman No.1 Filter Paper, plant extracts were applied two weeks after planting (2WAP). Isolation was done by collecting diseased leaf part from field to the laboratory, pathogenicity test was also conducted both in vivo and in vitro to confirm the identity of the casual organism in the laboratory. Similarly some biochemical tests were conducted in which Gram, catalase, oxidase, indole, maltose, xylose and glucose all tested positive. Data were collected four weeks after planting (4WAP), for growth characteristics such as plant height (cm), number of branches, number of leaves per plant, stem girth, disease incidence and severity while data on yield performance were taken at maturity for grain yield, number of pods per plant, number of seed per pod, weight of seeds. Data generated from the study were subjected to Statistical analysis. Results obtained from the data analysis showed that significant difference (P≤0.05) existed among the leaf extracts used as treatment. The highest (80 and 74%) and lowest (10%) incidence of bacterial disease on vegetable cowpea were recorded in Vernonia amygdalina and control pot, respectively. Bacterial diseases severity indices of 5.16 and 6.14 were recorded for the Ocimum gratissimum and control pots, respectively. Results of the effect of plant extracts on the various growth component, yield and yield component per plant were significant (P≤0.05). Pots sprayed with plant extract significantly enhanced growth and yield when compared with the control pots. Based on the pathogenicity test conducted result obtained showed that pathogen caused symptoms on the leaves and was identified in the laboratory through some biochemical tests as Xanthomonas axonopodis pv vignicola