First Report of Blackleg of Potato Caused by Dickeya solani in Brazil

In May 2013, unusual high incidence of blackleg symptoms, attributed to a contaminated lot of imported seed tubers, was observed in potato (Solanum tuberosum cv. Taurus) in a commercial field in Minas Gerais, Brazil. Diseased plants displayed typical blackleg symptoms and yielded soft rotted tubers. Bacterial isolates were obtained on Kado 523 medium and four isolates (CL139-IBSBF 3229, CL140-IBSBF 3230, CL141-IBSBF 3231, CL142-IBSBF 3232) from symptomatic plants were determined as member of genus Dickeya based on biochemical and molecular tests. They were Gram negative rods, facultative anaerobes, oxidase negative, sensitive to erythromycin (15 μg/disk), grew at 37°C, and negative for acid production from α-methylglucoside (Sławiak et al. 2009a). PCR using ADE1 (5′-GATCAGAAAGCCCGCAGCCAGAT-3′)/ADE2 (5′-CTGTGGCCGATCAGGATGGTTTTGTCGTGC-3′) primers, corresponding topelgenes, as described by Nassar et al. (1996), confirmed the genus. In addition, the 16S rDNA and dna X genes were amplified by PCR using primers Y1 (5′-TGGCTCAGAACG AACGCTGGCGGC-3′)/Y3 (5′-TACCTTGTTACGACTTCACCCCAGCT-3′) (Young et al. 1991) and dnaXf (5′-TATCAGGTYCTTGCCCGTAAGTGG-3′)/dnaXr (5′-TCGACATCCARCGCYTTGAGATG-3′) (Sławiak et al. 2009b), respectively, and sequenced. BLASTn analyses of 16S rDNA anddnaXsequences showed similarity to several species of Dickeya, with 99 and 100% nucleotide similarity to strains NCPPB 4575 (KF639914.1) and IPO2222 (JN663794.1) of D. solani, respectively. Potato tubers (cv. Ágata) were inoculated by injecting 20 μl of bacterial suspension (108CFU/ml) at the stolon end with a 200-μl tip. Tubers inoculated with distilled sterile water were included as negative controls (six tubers by treatment). After 5 days at 28°C, typical soft rot symptoms developed on tubers inoculated with the bacteria, while the negative controls remained symptomless. The bacteria were reisolated from lesions in King’s B medium, and had identical morphological, biochemical, and molecular characters of the inoculated isolates. Recently, Brazilian government agencies have expressed concern since D. solanihas emerged as a major threat to potato production in Europe, from where most of the seed potatoes are imported. To our knowledge, this is the first report of potato blackleg caused byD. solaniin Brazil. The inclusion of this pathogen in the list of pests tested in the certification programs is advisable to avoid further spread and high economic impact, an estimate over 20% of stocks and field production due to downgrading and rejection. GenBank accession numbers:dnaX gene: CL139 (KX118324), CL140 (KX118325), CL141 (KX118326), CL142 (KX118327); 16S rDNA: CL139 (KX247286), CL140 (KX247287), CL141 (KX247288), CL142 (KX247289). © The American Phytopathological Society.