DETECTION OF XANTHOMONAS AXONOPODIS pv. VESICATORIA IN NATURALLY INFECTED PEPPER SEEDS IN TURKEY

Abstract

Bacterial spot, caused by Xanthomonas axonopodis pv. vesicatoria, is one of the most important diseases of pepper in Turkey, where the disease has been epidemic in the last six years in the eastern Mediterranean region. The incidence and importance of natural infection in pepper seeds produced in the region was investigated in the present study. A total of 29 seed samples were tested by immunofluorescence assay using a commercial specific antibody, semi-selective isolation on medium Tween B, and a seedling screening tests, where plantlets were examined for typical spot symptoms on cotyledons 7-14 days after emergence. Pathogen populations were found to be in the range of 5x10(1)-5x10(4) cells/g seed when using semi-selective medium Tween B. The diseased seeds as determined in the seedling screening ranged from 7 to 36%; these figures agreed with numbers found in the Tween B medium test. The strains isolated on Tween B were identified by PCR using primer designed on the hrp gene specific for Xanthomonas spp., and pathogenicity on pepper plants. Twenty-one out of 29 seed samples were found to be contaminated by Xanthomonas axonopodis pv. vesicatoria. On the basis of these findings, infested seeds must be seen as a major source of inoculum for this disease in the region