Bacterial spot of pumpkin, incited by X. cucurbitae (ex Bryan) Vauterin et al. (1995) [syn. Xanthomonas campestris (Pammel) Dowson pv. cucurbitae (Bryan) Dye], has become one of the most important diseases of pumpkin [Cucurbita pepo L. and Cucurbita moschata (Duchesne) Duchesne ex Poir] in Illinois and some other pumpkin-growing areas in the United States (Babadoost et al., 2012; Babadoost and Ravanlou, 2012; Babadoost and Zitter, 2009). This disease was first reported as bacterial leaf spot on ‘Hubbard’ squash in New York in 1926 (Bryan, 1930). Subsequently, the disease was identified in other cucurbit-growing areas in Asia, Australia, Europe, and North America on cucumber, pumpkin, squash, and watermelon (Bineeta et al., 1999; Dutta et al., 2013; Lamichhane et al., 2010; Pruvost et al., 2008; Pruvost et al., 2009; Williams and Zitter, 1996).
Xanthomonas cucurbitae infects leaves and fruit of cucurbit crops (Babadoost and Ravanlou, 2012; Saddler and Bradbury, 2005; Williams and Zitter, 1996). Symptoms reported on leaves of gourd, pumpkin, and squash are small (2–4 mm), chlorotic to beige spots (Babadoost and Zitter, 2009; Williams and Zitter, 1996). As lesions coalesce, they may appear more angular and similar to the spots incited by Pseudomonas syringae pv. lachrymans (Williams and Zitter, 1996). On fruit, small, slightly sunken, circular spots, 1–3 mm in diameter, with a beige center and dark brown halo develop. Secondary fungi and bacteria may colonize the spots, resulting in enlarging spots cracking epidermis (Babadoost and Zitter, 2009; Williams and Zitter, 1996).
In the past 7 years, bacterial spot was widely observed in pumpkin and winter squash fields in Illinois, and X. cucurbitae was consistently isolated from lesions (Babadoost and Ravanlou, 2012). In wet conditions, fruit with bacterial spot usually collapses and rots. Therefore, the affected fruit is not accepted for marketing. Yield losses because of bacterial spot in some pumpkin fields in Illinois exceeded 90% (Babadoost and Ravanlou, 2012). At present, management of the bacterial spot is limited to spray applications of copper compounds, which has a limited effect on suppressing the disease. Information on the biology and epidemiology of bacterial spot is not sufficient for developing effective strategies for management of the disease.
Illinois ranks first in pumpkin production in the United States, where more than 90% of processing pumpkins are produced (Babadoost and Islam, 2003; Babadoost and Ravanlou, 2012). This study was conducted to further understand the etiology of bacterial spot in cucurbit corps. The objectives of the study were: 1) monitor development of bacterial spot on pumpkin leaves and fruit in commercial fields during the growing season; 2) define symptoms of the disease on leaves and fruit of various pumpkin cultivars; and 3) assess incidence of pumpkin fruit with bacterial spot at harvest in commercial fields.
Babadoost, M. & Ravanlou, A. 2012 Outbreak of bacterial spot (Xanthomonas cucurbitae) in pumpkin fields in Illinois Plant Dis. 96 1222
Babadoost, M., Ravanlou, A., Egel, D.S. & O’Brien, D. 2012 Occurrence of bacterial spot (Xanthomonas cucurbitae) in pumpkin fields in the Midwest Phytopathology 102 S4.8
Babadoost, M. & Islam, S.Z. 2003 Fungicide seed treatment effects on seedling damping-off of pumpkin caused by Phytophthora capsici Plant Dis. 87 63 68
Barak, J.D., Koike, S.T. & Gilbertson, R.L. 2001 The role of crop debris and weeds in the epidemiology of bacterial leaf spot of lettuce in California Plant Dis. 85 169 178
Bineeta, S.B., Majumder, S. & Kumar, S. 1999 Fungal and bacterial diseases of cucurbits, p. 251–252. In: L.R. Verma and R.C. Sharma (eds.). Diseases of horticultural crops: Vegetables, ornamentals and mushrooms. Indus Publishing, New Delhi, India
Blancard, D., Lecoq, H. & Pitrat, M. 1994 A color atlas of Cucurbit disease: Observation, identification, and control. John Wiley & Sons, New York, NY
Dutta, B., Gitaitis, R.D., Lewis, K.J. & Langston, D.B. 2013 A new report of Xanthomonas cucurbitae causing bacterial leaf spot of watermelon in Georgia, USA Plant Dis. 97 556
Goto, M., Takahashi, T. & Messina, M.A. 1980 A comparative study of the isolates of Xanthomonas campestris pv. citri isolated from citrus canker in Japan and cancrosis B in Argentina Ann. Phytopathol. Soc. Jpn. 46 329 338
Kado, C.I. 2010 Rapid necrotizing diseases, p. 79–84. In: C.I. Kado (ed.). Plant bacteriology. American Phytopathological Society, St. Paul, MN
Koike, S.T., Gladders, P. & Paulus, A.O. 2007 Vegetable diseases, a color handbook. Academic Press, Boston, MA
Lamichhane, J.R., Varvaro, L. & Balestra, G.M. 2010 Bacterial leaf spot caused by Xanthomonas cucurbitae reported on pumpkin in Nepal New Disease Reports 22 20
Lane, D.J. 1991 16S/23S rRNA sequencing, p. 115–175. In: E. Stackebrandt and M. Goodfellow (eds.). Nucleic acid techniques in bacterial systematics. John Wiley & Sons, Chichester, UK
Leite, R.P. Jr, Minsavage, G.V., Bonas, U. & Stall, R.E. 1994 Detection and identification of phytopathogenic Xanthomonas strains by amplification of DNA sequences related to the hrp genes of Xanthomonas campestris pv. vesicatoria Appl. Environ. Microbiol. 60 1068 1077
Lelliott, R.A., Billing, E. & Hayward, A.C. 1966 A determinative scheme for the fluorescent plant pathogenic pseudomonads J. Appl. Bacteriol. 29 470 489
Meng, X.Q., Umesh, K.C., Davis, R.M. & Gilbertson, R.L. 2004 Development of PCR-based assays for detecting Xanthomonas campestris pv. carotae, the carrot bacterial leaf blight pathogen, from different substrates Plant Dis. 88 1226 1234
Mohammadi, M., Mirzaee, M-R. & Rahimian, H. 2001 Physiological and biochemical characteristics of Iranian isolates of Xanthomonas axonopodis pv. citri, the causal agent of citrus bacterial canker disease J. Phytopathol. 149 65 75
Pruvost, O., Robene-Soustrade, I., Ah-You, N., Jouen, E., Boyer, C., Waller, F. & Hostachy, B. 2008 First report of Xanthomonas cucurbitae causing bacterial leaf spot of pumpkin on Reunion Island Plant Dis. 92 1591
Pruvost, O., Robène-Soustrade, I., Ah-You, N., Jouen, E., Boyer, C., Wuster, G., Hostachy, B., Napoles, C. & Dogley, W. 2009 First report of Xanthomonas cucurbitae causing bacterial leaf spot of watermelon in the Seychelles Plant Dis. 93 671
Saddler, G.S. & Bradbury, J.F. 2005 Xanthomonadales, p. 63–121. In: D.J. Brenner, N.R. Krieg, J.T. Staley, and G.M. Garrity (eds.). Bergey’s manual of systematic bacteriology. 2nd ed. Springer, New York, NY
Schaad, N.W., Jones, B.J. & Chun, W. 2001 Laboratory guide for identification of plant pathogenic bacteria. 3rd ed. American Phytopathological Society, St. Paul, MN
Suzuki, A., Togawa, M., Ohta, K. & Takikawa, Y. 2003 Occurrence of white top of pea caused by a new isolate of Pseudomonas syringae pv. pisi Plant Dis. 87 1404 1410
Williams, P.H. & Zitter, T.A. 1996 Bacterial leaf spot, p. 35. In: T.A. Zitter, D.L. Hopkins, and C.E. Thomas (eds.). Compendium of cucurbit diseases. American Phytopathological Society, St. Paul, MN
Winkler, J., Freistetter, B. & Huss, H. 2008 The effect of different varieties on fruit rot incidence during ripening of oilseed pumpkin (Cucurbita pepo var. styriaca) Saatgut Osterreichs 59 137 138
Zhao, Y.F., Damicone, J.P. & Bender, C.L. 2002 Detection, survival, and sources of inoculums for bacterial diseases of leafy crucifers in Oklahoma Plant Dis. 86 883 888