Bacterial wilt of common bean: effect of seedborne inoculum on disease incidence and seedling vigour

Bacterial wilt of common bean caused by Curtobacterium flaccumfaciens pv. flaccumfaciens is a seedborne disease. The seeds of great northern cultivar US 1140 infected by the yellow variant of the pathogen showed symptoms of yellow discolouration on the white seed coat. In this study, the great northern bean seeds, cultivar US 1140, from the dockage of 2001 crops grown in Alberta were sorted into four categories according to the degree of yellow discolouration on the seed coat: apparently healthy or white seeds (0%), slight infection (25-50%), moderate infection (51-75%) and severe infection (76-100% yellow discolouration). Results of testing of these seed samples showed that bacterial population in the seeds, seedling emergence, plant height and incidence and severity of bacterial wilt were significantly (P<0.05) affected by the degree of discolouration of the seed coat. A greater seed coat discolouration was associated with a higher bacterial population of the seed, which resulted in a higher incidence of bacterial wilt and poorer growth of seedlings. Examination of 14-day-old seedlings originating from discolored seeds revealed that the pathogen was systemically distributed throughout the entire seedling if plants showed wilt symptoms. Although some of the 14-day-old seedlings derived from seeds with yellow discolouration remained symptomless, the bacterial pathogen was detectable in such seedlings regardless of differences in the extent of discolouration of seed coat. However, the bacterial pathogen was not detected in the 14-day-old seedlings originating from the seeds with 0% yellow discolouration of the seed coat.