First Report of Xanthomonas phaseoli pv. dieffenbachiae Causing Bacterial Leaf Blight on Anthurium andreanum in Mexico

Abstract

Xanthomonas phaseoli pv. dieffenbachiae (= Xanthomonas axonopodis pv. dieffenbachiae) (Xad) was first reported as causing bacterial blight on anthurium (Anthurium andreanum) in New Jersey, U.S.A. (McCulloch and Pirone 1939) and described as Bacterium dieffenbachiae. The bacterium occurs in a broad range of ornamental crops, with most reports coming from anthurium, although there are reports on Syngonium, Dracaena, caladium, Xanthosoma, and Philodendron (Borkar and Yumlembam 2016). In Mexico, there are no reports of the bacteria. In March 2018 and May 2019, anthurium plants grown in a commercial orchard were detected with symptoms of leaf and spadix blight and discoloration on the vascular tissue with an incidence of about 60%. Leaves from 15 plants showing symptoms of a vascular discoloration and water-soaked spots were collected from the township Adolfo Ruiz Cortinez in San Andres Tuxtla, Veracruz (18°26′59″N, 95°12′44″W) and Ocozotepec, Veracruz (18°15′00.0″N, 94°54′00.0″W) and processed for isolation. Leaf tissue was surface disinfected with 1% sodium hypochlorite before being placed in sterile water. The suspension was streaked onto King’s B medium and incubated at 28°C. Yellow, mucoid, and slimy bacterial colonies appeared after 4 days, and strains were purified by selecting single colonies. The bacterium was rod-shaped, motile by a polar flagellum, and gram negative, and was positive for catalase, gelatinase, casein, and starch hydrolysis, eliciting a hypersensitive response in tobacco plants, and acid production from carbohydrates (Chase et al. 1992; Lelliott and Stead 1987). For further confirmation, DNA was extracted from bacterial colonies using PureLink Genomic DNA Kits (Invitrogen Life Technologies, Carlsbad, CA) following the manufacturer’s instructions. Immunoassay analyses were performed by specific antibodies (Bacterial Reagent Set for Xad, Agdia, Elkhart, IN) and processed according to the manufacturer’s instructions. Five-microliter subsamples were subjected to PCR using universal primers 8F and 1492R (Turner et al., 1999) and gyrB genes according to the method of Parkinson et al. (2007, 2009), using primers X. gyrPCR2F and X. gyrrsp1 and corroborated by sequencing (MN394616, MN394617, MN394618, MN394619, and MN402441; and MN402442, MN402443, MN402444, MN402445, and MN402446, respectively). All strains were confirmed by specific primers PXadU and PXadL and nested PCR with NXadU and NXadL primers (Robene-Soustrade et al. 2006). Pathogenicity was tested in 6-week-old plants of A. andreanum; leaves were infiltrated with a suspension at a concentration of 10⁸ CFU/ml into the mesophyll. Plants were then held at a constant 26°C with a 16-h photoperiod. Symptoms appeared 7 days postinoculation as water-soaked spots and leaf blight. The pathogen was reisolated and cultured, and after 4 days samples appeared morphologically to be the same bacterium and were positively identified using the Xad-specific primer set. This is the first report of Xad on anthurium causing bacterial blight in Mexico, and the impact of the disease can be devastating due to the number of hosts present and the favorable climatic conditions for the development of the disease. However, we believe that more studies are needed on the epidemiology and spread of the bacteria.