Correlation Between Populations of Xanthomonas Axonopodis Pv. Vignicola Builds Up In Vivo and Symptoms Manifestation in Infected Cowpea Plant.

Abstract

From the perspective of plant disease epidemiology, pathogen spread and multiplication is important in assessing the likelihood of disease outbreaks. Many plant pathogenic bacteria multiply quite successfully in association with susceptible tissues without causing lesions. In this paper we aimed to understand the dynamics of Xanthomonas axonopodis pv. vignicola population sizes in regard to symptom development on cowpea plant. Seven cowpea genotypes were use for the investigation. The seed lots were obtained from seed companies, research institute and open markets within Zaria environment. These were so selected to reflect the various ways farmers usually obtain their seeds. The seed samples were grouped into treated and inoculated and non-treated inoculated seed lots. The treated seed lots were treated with three different types of fungicides (Apron star, Dress force, and Team fungicides) before inoculation with bacteria suspension. Since Xanthomonas axonopodis pv. vignicola is a seed-borne pathogen, the inherent bacteria were estimated from which the population builds up were determined. The seeds were inoculated with bacteria suspension adjusted ca. 4.7 x 10⁷ cfu/ml and were also spray inoculated at 14 days after sowing. The result shows that there were no correlation between bacteria disease incidence, severity and population with respect to foliar lesion development.  The usual practice of taking disease incidence and severity should be discouraged. I would recommend pathogen population assessment should be undertaken in conjunction with disease incidence not disease severity.  Fungicides used had no significant effect on the pathogen’s growth and pathogenicity. Although, seed treatment has been adjudged to be the best method of control soil and seed-borne diseases, seed treatment chemical must be pest specific.

Keywords; correlation, population, pathogenicity, symptom.