Occurrence of Xanthomonas campestris pv. campestris in wild radish (Raphanus raphanistrum L.) in Brazil
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Wild radish (Raphanus raphanistrum L.) is considered an important weed in agricultural fields, because it competes with crops for water, nutrients and light, apart from acting as a host for pathogens and pests. Herbicide resistant populations have hampered the management of this weed (Heap, 2017), contributing to survival of pathogens in fields of cultivation during the off season. Wild radish plants naturally infected with Xanthomonas campestris pv. campestris (Xcc), causal agent of brassicas black rot, were reported in the USA (Schaad and Dianese 1981). In Brazil, this weed is common in fields cultivated with Brassica spp. with black rot occurrence. It has not been described, however, as Xcc host so far. During 2016, wild radish plants with symptoms of yellowing and leaf marginal necrosis were collected in a broccoli (Brassica oleracea var. italica) producing property with a black rot history, located in Pardinho, São Paulo state, Brazil. Bacterial isolation was performed on nutrient sucrose agar (NSA) followed by incubation at 28 °C for 48 h. The presence of yellow colonies, mucoid and shiny, characteristic of Xanthomonas genus were observed. The strain obtained (Nab3175) hydrolyzed starch, was pathogenic to cauliflower plants (cultivar ‘Teresopolis’) and showed positive PCR result using the specific primers HrcCF2 and HrcCR2, that amplified a 519 bp fragment (Zaccardelli et al. 2007). The 16S rDNA gene region of the Nab3175 strain was amplified by PCR using primers FD1 and RD1 (Weisburg et al. 1991) and sequenced, being identified by the degree similarity with GenBank (NCBI). Nab3175 strain (Accession N° MG993191) showed a 100% nucleotide similarity with Xcc strain ATCC 33913 (NR_074936.1), originally isolated from brussels sprout (Brassica oleracea var. gemmifera) in 1957, United Kingdom. To our knowledge this the first report of the natural occurrence of Xcc in wild radish in Brazil.
The first author thanks the São Paulo Research Foundation (FAPESP) for granting the doctoral scholarship and for the financial support (FAPESP process number: 2017/13822-0).
- Heap I (2017) The International Survey of Herbicide Resistant Weeds. Available at: http://www.weedscience.org/. Accessed 29 October 2017