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Occurrence of bacterial spot (Xanthomonas cucurbitae) in pumpkin fields in the Midwest.
M. BABADOOST (1), A. Ravanlou (1), D. S. Egel (2), D. O’Brien (3). (1) University of Illinois, Urbana, IL, U.S.A.; (2) Purdue University, Vincennes, IN, U.S.A.; (3) Crop Production Services, Hudson, OH, U.S.A.

Bacterial spot, caused by <i>Xanthomonas cucurbitae</i>, was economically an insignificant disease in the Midwest until 2005. But, in the past four years, the disease occurred widely in pumpkin fields in the Midwest. Yield losses up to 90% forced some growers to abandon pumpkin production. A survey was conducted in 2011 to assess the occurrence of bacterial spot in pumpkin fields in Illinois, Indiana, Iowa, Kansas, Missouri, Nebraska, Ohio, and Wisconsin. During three weeks of pumpkin harvest, 111 pumpkin fields were visited and incidence and severity of bacterial spot on fruit were assessed. In each field, 60 fruit in 12 locations (five fruits per location) were examined in an M-shaped walking path. The incidence of <i>X. cucurbitae</i>-infected fruit were observed in 95 fields (86% of fields visited), with overall 26% of fruit infected. Severity of the disease on fruit (percent surface area of the fruit with bacterial lesions) ranged from 1 to 20%. Bacterial spot was observed in both jack-o-lantern and processing pumpkin fields. <i>X. cucurbitae</i> was isolated from infected fruit and the identity of the isolates was confirmed using biochemical tests and molecular methods. Koch’s postulates for representative isolates were carried out on ‘Howden’ pumpkin in greenhouse trials. <i>X. cucurbitae</i> infection was also observed and confirmed on all winter squashes grown near pumpkin fields visited in 2011. In addition, greenhouse studies showed that all cucurbit crops are susceptible to <i>X. cucurbitae</i>.<p><p>Keywords: Bacteria-Phytoplasma-Spiroplasma-Fastidious Prokaryote, Vegetables

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