Symptomless spread of blight-inducing strains of Xanthomonas campestris pv. campestris on cabbage seedlings in misted seedbeds

Xanthomonas campestris pv. campestris induces two types of symptoms, namely , black rot and blight. Black rot symptoms are V-shaped lesions and black v eins on the leaf, and blight symptoms are sudden collapse of interveinal ti ssues following the lack of veinal necrosis at early stages of infection. T hese two symptoms can occur simultaneously. However, the tendency to induce either symptom type is strain-dependent. Six strains were evaluated for th eir rate and pattern of spread in misted seedbeds by using strain-specific monoclonal antibodies and miniplate enrichment/ELISA. Data on pathogen inci dence was defined as the presence of the pathogen in or on plants rather th an visual symptoms. The results indicated that blight-inducing strains spre ad to more seedlings than black rot-inducing strains. The high incidences o f blight-inducing strains in experimental plots were associated with non-ra ndomness of spatial pattern of pathogen spread, indicating that high incide nce is primarily due to the spread from adjacent plants by leaf contact and water splash. Most ELISA-positive seedlings were symptomless, indicating t hat the sensitivity of the system used in this study was adequate for detec tion of latent or epiphytic spread.