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First Report of a Member of the Fusarium oxysporum Species Complex Causing Cladode Rot in Nopalea cochenillifera in Brazil
- Santiago, M. F., Santos, A. M. G., Inácio, C. P., Neves, R. P., Andrade, D. E. G. T., Santos, D. C., Assis, T. C., Doyle, V. P., Vieira, W. A. S., Veloso, J. S., Câmara, M. P. S., Laranjeira, D.
- Plant disease 2018 v.102 no.12 pp. 2652
- Fusarium oxysporum, Opuntia ficus-indica, agar, alcohols, cladodes, conidia, culture media, databases, death, feeds, growth chambers, humidity, hyphae, leaves, loci, mycelium, pathogenicity, pathogens, peptide elongation factors, phenotype, photoperiod, phylogeny, semiarid zones, sodium hypochlorite, statistical analysis, Brazil
- Nopalea cochenillifera is economically important in Brazil owing to its use for animal feed in semiarid areas. A disease-causing cladode rot and prickly pear cactus death was observed in April 2015 in Surubim in northeast Brazil. Disease symptoms on the cladodes initially consisted of softened areas that subsequently wilted and fell off the plant after a few days, becoming dark with the internal woody tissue exposed. Fragments of symptomatic tissue were removed from the lesion transition area, surface disinfected (30 s in 70% alcohol, 1 min in 1% NaOCl, and rinsed with sterile water), plated on potato dextrose agar (PDA), and incubated at 25°C for 7 days. Most of the isolates were similar in colony morphology to Fusarium and were transferred to PDA and preserved. The pathogenicity of five isolates was tested by inoculating cladodes of N. cochenillifera ‘Miúda’. Isolates were inoculated at four locations in each cladode (four replicates) with PDA mycelial plugs after wounding. Cladodes inoculated with sterile PDA plugs represented the negative control. The experiment was conducted three times. Inoculated plants, including the negative control, were kept in a growth chamber at 25°C, 85% humidity, and 12-h photoperiod. The same cladode rot symptoms seen in April 2015 were observed on inoculated cladodes 7 days after inoculation, and the pathogen was reisolated from diseased tissue. These isolates were similar in morphology to those used to inoculate the cladodes, thus fulfilling Koch’s postulates. Symptoms were not observed on control plants. Fusarium colonies on PDA produced hyphae that were appressed to the medium and varied from white to pink. Macroconidia on clove leaf agar were three to five septate and 11.7 to 42.7 μm in length × 1.7 to 4.6 μm in width. Microconidia were oval to cylindrical, 3.2 to 9.04 μm in length × 3.04 to 5.93 μm in width, and borne on false heads. Phenotypic characters were similar to Fusarium oxysporum (Leslie and Summerell 2006). A representative isolate, URM7638 (GenBank accession no. MG029526), was partially sequenced at the elongation factor-1α (EF-1α) locus to compare with other species of Fusarium. A query of our sequence against the Fusarium-ID database (Geiser et al. 2004) showed 99.27% similarity (e value = 0) to NRRL40180, a member of the F. oxysporum species complex (FOSC). A maximum likelihood phylogenetic analysis, including previously published sequences of closely related species, placed the isolate in the F. oxysporum clade with 100% bootstrap support. A member of the FOSC was previously described causing rot in cladodes of Opuntia ficus-indica in Brazil (Souza et al. 2010); however, this is the first report of a member of the FOSC in association with N. cochenillifera in Brazil and worldwide. Further research is needed to establish management strategies to control the pathogen because the disease symptoms are severe and can compromise prickly pear cactus production in Brazil.