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Title: First report of xanthomonas vasicola causing bacterial leaf streak on corn in the United States

Author
item KORUS, K - University Of Nebraska
item LANG, J.M. - Colorad0 State University
item ADESEMOYE, A.O. - University Of Nebraska
item Block, Charles
item Pal, Narinder
item LEACH, J.E. - Colorad0 State University
item JACKSON-ZIEMS, T.A. - University Of Nebraska

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2016
Publication Date: 6/1/2017
Citation: Korus, K., Lang, J., Adesemoye, A., Block, C.C., Pal, N., Leach, J., Jackson-Ziems, T. 2017. First report of xanthomonas vasicola causing bacterial leaf streak on corn in the United States. Plant Disease. 101(6):1030.

Interpretive Summary: In 2014 and 2015, Zea mays samples (field, seed, and popcorn) were submitted to the Plant and Pest Diagnostic Clinic at the University of Nebraska – Lincoln displaying long, dark, yellow to brown, water-soaked, linear lesions confined to the interveinal spaces of the leaves. Initial symptoms appeared as small water-soaked flecks that expanded between veins to form irregular lesions. In some cases, the disease progressed to cover 40 to 50% of the leaf area. The disease was confirmed by symptom expression and bacterial streaming in 41 counties in Nebraska as well as Yuma Co., Colorado, and Phillips Co., Kansas, both contiguous to Nebraska. No fungal sporulation was observed and excised leaf sections exhibited significant bacterial streaming. Mucoid bacteria were isolated from symptomatic leaf tissue, and their pathogenicity was confirmed when subsequent inoculations produced identical symptoms to those observed in the field. The causal bacterium is rod-shaped, gram-negative, motile, nonfluorescing, and nonfermentative. Based on DNA sequence analysis, the bacterium is similar to X. campestris pv. vasculorum, also called X. vasicola. X. vasicola from corn and sugarcane has also been called X. v. pv. vasculorum and X. campestris pv. zeae), though both of these names are invalid. This organism has been only reported to occur on corn in South Africa, causing bacterial leaf streak). Based on these results, we conclude that X. vasciola is the causal agent of bacterial leaf streak on corn in the United States. To our knowledge, this is the first report of X. vasicola occurring on corn in the United States.

Technical Abstract: In 2014 and 2015, Zea mays samples (field, seed, and popcorn) were submitted to the Plant and Pest Diagnostic Clinic at the University of Nebraska – Lincoln displaying long, dark, yellow to brown, water-soaked, linear lesions confined to the interveinal spaces of the leaves. Initial symptoms appeared as small water-soaked flecks that expanded between veins to form irregular lesions. In some cases, the disease progressed to cover 40 to 50% of the leaf area. The disease was confirmed by symptom expression and bacterial streaming in 41 counties in Nebraska as well as Yuma Co., Colorado, and Phillips Co., Kansas, both contiguous to Nebraska. Tape mounts taken from the abaxial and adaxial sides of the leaf revealed no fungal sporulation. However, excised leaf sections exhibited significant bacterial streaming. Yellow, mucoid bacteria were isolated on nutrient broth yeast extract agar (NBY) from symptomatic leaf tissue. Pathogenicity of the isolates was confirmed by spray-inoculation of Z. mays hybrid DKC 61-88 with a bacterial suspension of 108 to 109 CFU/ml followed by covering the plants with a clear plastic bag for 24 h. Two isolates (201500744 and 201500181) produced identical symptoms to those observed in the field. Corn plants inoculated with all other isolates and control corn (sprayed with water only) were asymptomatic. Isolates 201500744 and 201500181 are pathogenic on greenhouse-inoculated sorghum (Sorghum bicolor cv. Richardson 11043) and sugarcane (Saccharum officinarum cv. L99-266). The causal bacterium is rod-shaped, gram-negative, motile, nonfluorescing, and nonfermentative. Based on multilocus sequence analysis (MLSA) of partial 16S rDNA, rpoD, dnaK, and gyrB gene sequences using MEGA6 (Tamura et al. 2013; Young et al. 2008), 201500744 and 201500181 are most similar to X. campestris pv. vasculorum, also called X. vasicola (Vauterin et al. 1995; Wasukira et al. 2014; Young et al. 2008). In fact, the genes analyzed in MLSA were identical among isolates 201500744 and 201500181 and X. vasicola isolated from corn and sugarcane. However, the two strains are distinct from X. campestris pv. musacearum (Xanthomonas wilt of banana), X. v. pv. holcicola (bacterial streak of sorghum), and X. axonopodis pv. vasculorum type A (sugarcane) (Vauterin et al. 1995). X. vasicola has been reported as a pathogen of palms and broom bamboo in addition to corn (Qhobela et al. 1990). X. vasicola from corn and sugarcane has also been called X. v. pv. vasculorum and X. campestris pv. zeae (Qhobela et al. 1990; Wasukira et al. 2014), though both of these names are invalid. This organism has been only reported to occur on corn in South Africa, causing bacterial leaf streak (Qhobela et al. 1990). Based on these results, we conclude that X. vasciola is the causal agent of bacterial leaf streak on corn in the United States. To our knowledge, this is the first report of X. vasicola occurring on corn in the United States.