Cariru (Talinum fruticosum) is a non-conventional food plant and a source of vitamins A, B2, B5, and C, calcium, phosphorus, and iron. It is an important crop for producers of the Amazon region and it is used as a leafy green vegetable, similar to spinach, as well as for medicinal purposes. It is cultivated by producers in the states of Pará and Amazonas (Amorim et al. 2014). In February 2020, in gardens of approximately 1.0 and 0.18 ha in the municipality of Ananindeua (01° 34' 12" S - 48° 38' 11" W), Pará, Brazil, we observed approximately 10% of the plants exhibited soft rot symptoms, bacterial oozing, and stem pith disintegration. From cariru infected leaves, the bacteria were selectively isolated using healthy pepper fruit, as described by Moraes et al. (2017). Two strain (UFRADD17 and UFRADD18) were obtained and both showed white, small, "broken glass" colonies on CPG (peptone-casamino acid-glucose) medium when observed in a stereoscope under oblique lighting. Pathogenicity tests were performed on 20-day-old cariru seedlings by depositing 10 ul of the bacterial suspension (106 CFU/ml) onto a wound made on the leaf blade with an entomological pin. After inoculation, seedlings were incubated in a greenhouse for 48 h at 30 ± 2°C and 90 ± 2% RH. Plants treated similarly with sterile distilled water were used as a negative control. Symptoms of soft rot were observed between 12 and 24 h after inoculation. Seedlings used as negative control remained symptomless. Forty-eight hours after inoculation, we reisolated the pathogen and performed rep-PCR (REP, ERIC, and BOX-PCR) analyses (Gama et al. 2018) with the strains used for inoculation and those reisolated from the pathogenicity test to confirm the identity of the strains and to fulfill Koch's postulates. The two re-isolated strains showed the same REP, ERIC, and BOX-PCR profiles as the strains used for inoculation. In addition, there were no differences between the rep-PCR profiles of the isolates UFRADD17 and UFRADD18. These isolates were Gram-negative, grew at 37°C, and were positive for maceration in pepper fruit and potato tubers. Molecular identification of the isolate UFRADD18 was performed from sequencing fragments from the 16S rDNA region and dnaX, fusA, gyrA, and mdH housekeeping genes as previously described (Van der Wolf et al. 2014; Ma et al. 2007). Sequences were deposited in Genbank under accessions OP142347, OP191704, OP191705, OP191706, and OP191707. Blastn analysis showed 96.15% identity with the 16S rDNA region of accession KY231142.1 (400/416 bp), 99.5% identity with dnaX of accession KC844490.1 (396/398 bp), 99.86% identity with fusA of accession CP023467.1 (714/715 bp), 99.74% identity with gyrA of accession KC844598 (387/388 bp), and 99.10% identity with mdH of accession GQ891979.1 (563/560 bp) from the type strain of Dickeya dadantii. A phylogenetic analysis performed by Bayesian inference with the dnaX, fusA, gyrA, and mdH genes grouped the isolate UFRADD18 along with NCPPB898T, with a 1.00 posterior probability. To our knowledge, this is the first report of D. dadantii causing soft rot in cariru in the Brazilian territory. In addition, this report increases understanding of the host range of this bacterium, which is important for adopting management strategies based on the control of alternative hosts.
Keywords: Talinum fruticosum; pectinolytic bacteria; unconventional food plants.