Black Rot of Cabbage in Hawaii: Inoculum Source and Disease Incidence

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Abstract
Commercial cabbage seed and soil of 9 cabbage-growing areas in Kula, Maui, were assayed for the presence of Xanthomonas campestris to determine the relative importance of each in the annual recurrence of black rot. The pathogen was recovered from only 1 of 20,500 individually tested seeds from commercial lots. Disease-free seedlings planted in areas of high black rot incidence became severly diseased at maturity, whereas in areas with no history of crucifer production, they remained disease-free. The incidence of black rot was influenced by environmental conditions, soil properties and rotation to nonsusceptible crops. Plants on farms located at low elevations (490- 655 m) and in the Keahua soil series had a higher incidence of the disease than did those on the farms located at higher elevations (850-1000 m) and in the Kula soil series. On farms at low elevations where 50-90% disease occurred, soils contained 1.1-2.3% organic C, 1.6-13.5 meq extractable Ca/100 g, and pH was 4.2-4.9. In farms at low and high elevations, where 0-5% disease occurred, soils contained 3.2-6.2% organic C, 15.4-42.2 meq extractable Ca/100 g, and pH was 5.5-6.8.

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