SEED INFECTION ROUTS OF COWPEA BACTERIAL BLIGHT INDUCED BY Xanthomonas axonopodis pv. vignicola (BURKHOLDER) DYE.

Abstract

The significant role played by seed-borne infection calls for more studies on seed infection routes of cowpea bacterial blight, since epidemics have been reported on newly opened areas; suggesting seed transmission rather than infected plant debris or soil contamination. Although it is understood that cowpea bacterial blight is seed transmitted, and that seed-borne inoculum play a significant role in the disease epidemiology, the mechanism of transmission from seed to emerging seedling has not been fully elucidated. The objective of the studies was to study seed infection routes of cowpea bacterial blight (Xanthomonas axonopodis pv. vignicola). Direct systemic infection of seed by the pathogen was investigated using artificial inoculation and spray-inoculated at vegetative state (25 days after sowing) method while indirect systemic infection was determined by at spray-inoculated at flowering, flat pod and mature pod stages with bacteria suspension adjusted to ca. 4.7 x 107cfu ml-1 while one seed lot soaked in/spray with sterile distilled water was used as control. Harvested pods were sorted into symptom categories using scale 1-9 and threshed accordingly. Hundred seeds each of the harvested seeds were plated on YDCA media and planted in the screen house to examine the presence of Xav and percentage infected seedlings were calculated. While the population of Xav in/on was determined by seed destruction assays. The study indicated that the bacterium was able to transmit systemically from inoculated seeds to harvested seeds and epiphytically from inoculated vegetative parts into the harvested seeds.