IDENTIFICATION OF THE BACTERIAL LEAF-SPOT PATHOGEN OF LETTUCE, XANTHOMONAS-CAMPESTRIS PV. VITIANS, IN OHIO, AND ASSESSMENT OF CULTIVAR RESISTANCE AND SEED TREATMENT

In 1995, a bacterial leaf spot disease was observed on lettuce plants grown on muck soils in north central Ohio. Characteristic symptoms wer e water-soaked circular, dark brown-or olive-colored spots, approximat ely 1 to 2 mm in diameter, along the margin of leaves; V-shaped lesion s beginning at the leaf margins and advancing along the veins; and ind ividual black spots scattered on the leaf surface. Five bacterial stra ins were isolated from infected leaves of two lettuce cultivars, Darkl and and Go Go Green. These strains were identified as Xanthomonas camp estris pv. vitians based on morphological, physiological, biochemical, and pathogenicity tests, as well as fatty acid methyl ester (FAME) an alyses. One of the five strains tested was resistant to streptomycin s ulfate (100 mu g/ml), and none were resistant to copper sulfate. Eight commercial lettuce cultivars were evaluated for resistance to X. camp estris pv. vitians. Of these cultivars, Redine was highly resistant; F ocus and Crisp and Green were partially resistant; Slobolt, Tiara, and Carmona were susceptible; and Darkland and Go Go Green were highly su sceptible to the pathogen. Surface disinfection with 0.52% sodium hypo chlorite for 5 min nearly eliminated the bacterium from lettuce seed w ithout affecting seed viability.