Xanthomonas spp. (bacterium)
Bacterial plant pathogens that enter plants through wounds or natural openings, such as stomata (breathing pores) or hydathodes. Once the bacterium’s cells enter the plant, they can move systemically, causing severe leaf blight. Initial symptoms appear as small, water-soaked, circular lesions with irregular borders near the leaf margin.
The water-soaked leaf areas can be readily observed by examining the underside of the leaves. After 7–14 days of initial symptoms, lesions enlarge, coalesce, and typically cover large portions of the leaf area. Eventually, the lesions turn brown with greenish-yellow borders, resulting in premature senescence and leaf drop.
Symptoms of most bacterial blights first appear on leaves as small, watersoaked spots and/or light green areas. These spots enlarge and the tissue in the centers dies and turns brown.
These irregularly shaped spots are bordered by a lemon yellow ring, which is a diagnostic symptom of common blight. These spots or lesions can develop on the edges or in interveinal areas of leaves. The spots may grow together, resulting in the death of the entire leaf and defoliation of the plant. Infected pods will first show small, watersoaked spots that develop into large, dark red irregular spots. Under favorable conditions, these spots may show a yellow slimy ooze (pod symptoms of common and halo blight diseases are virtually indistinguishable). Seed in infected pods can become infected; white-colored seed may show butter yellow spots when infected. Heavily infected seed may be shriveled and germinate poorly.