Abstract:
Physalis peruviana, known locally as uvilla but internationally as goldenberry or Cape gooseberry, is the fourth most important exotic fruit for export in Ecuador, after Mangifera spp. (mango), Cereus spp. (pitahaya), and Passiflora spp. (maracuya and granadilla). Ecuador is the second world exporter of this solanaceous fruit after Colombia. This crop is produced in four provinces located in the center and north of the Andean region. In 2013, Ecuador exported 91 tons of P. peruviana (ProEcuador 2014). Between October 2016 and March 2017, P. peruviana production fields (provinces of Tungurahua, Cotopaxi, Pichincha, and Imbabura) were scouted for diseases. Wilting plants were found in the 14 fields visited. One hundred ten stem samples were collected from 55 symptomatic plants. The symptoms observed were yellowing and wilting of leaves and necrosis and dry rot of the stem (Estupiñán-Rodríguez and Ossa-Canencio 2007). Fungi with Fusarium sp. morphology (Leslie and Summerell 2006) were isolated from stem samples and grown on potato dextrose agar (PDA) medium and then cultured on Czapek solution agar. Single-spore isolates presented the appearance of cottony mycelia in hues of purple and pink to white on the top of solid medium, whereas on the reverse side they presented white and pink hues. The mycelia produced abundant microconidia, few macroconidia, and chlamydospores. The microconidia were ovoid with one or two divisions. The macroconidia were straight to slightly curved, slender, with acute and curved ends and pointed basal cells. To type these fungi to species, the translation elongation factor 1-alpha gene (TEF) was amplified and sequenced using primers ef1 and ef2 (Geiser et al. 2004). DNA sequences of nine isolates were submitted to GenBank. Isolates were identified to species by comparing the DNA sequences generated using BLAST against sequences in GenBank’s nucleotide database and Fusarium-ID. All the sequences yielded 100% identity with Fusarium oxysporum sequences. TEF sequence MK631989 had 100% identity with GenBank accession KP964857. Koch’s postulates were satisfied by inoculating 4-week-old P. peruviana, Colombiano ecotype, seedlings by immersing the roots in a conidial suspension (approximately 1 × 10⁶ conidia/ml), with four replicates per isolate (Urrea et al. 2011). Negative control seedlings were treated with sterile water. Seedlings were incubated under greenhouse conditions for 3 weeks, at 22°C (±2) and 12-h photoperiod. The characteristic symptoms of the disease were observed in all the inoculated seedlings but not in the negative controls. Pathogenic isolates were recovered on PDA from the inoculated seedlings. These were morphologically and molecularly characterized to species. The TEF sequences obtained confirmed the isolates recovered were the same that were used to inoculate the seedlings, successfully completing Koch’s postulates. This is the first report of Fusarium wilt of P. peruviana caused by F. oxysporum in Ecuador. Propagative materials and produce traded between Ecuador and Colombia have the potential to carry inoculum of plant pathogenic fungi, which may represent a phytosanitary threat to P. peruviana production in Ecuador. Although F. oxysporum has been reported in Colombia as a limiting factor for the production of P. peruviana (Urrea et al. 2011), with up to 50% crop losses, the incidence of Fusarium diseases of this crop outside of Colombia was previously unknown, and its range of distribution remains to be determined.