Crucifer Diseases: Xanthomonas Leaf Spot
Xanthomonas campestris pv. Armoraciae
Xanthomonas leaf spot occurs on all cultivated crucifers and several wild crucifers. The major symptom is leaf spotting, but lesions can also occur on cotyledons, flower stalks, and fruit. Small leaf spots occur scattered over the leaf surface as a result of invasion of bacterium through pores.
Individual lesions begin as water-soaked flecks that enlarge to form lesions about 3 mm (occasionally 5 mm) in diameter that are surrounded by a narrow chlorotic zone that is most evident when leaves are viewed with back lighting. Lesions tend to be more numerous near large leaf veins where they may coalesce to form necrotic streak along the sides of the veins. Dry, dead tissue may fall out of the lesions giving the leaves a shot-hole or tattered appearance. Leaf spots can be so numerous at times that the entire leaf will collapse.