First report of Curvularia cactivora causing fruit rot of red dragon fruit ( Selenicereus undatus ) in Ecuador

Red dragon fruit (Selenicereus undatus (Haw.) Britton & Rose) is an emerging high-value crop in Ecuador, particularly in Manabí Province, where its cultivation provides a profitable alternative to traditional crops. Between April 2018 and March 2023, symptomatic fruits were observed in Rocafuerte and Santa Ana cantons, with an incidence ranging from 7 to 11%. Initial symptoms appeared as small, slightly sunken brown spots that enlarged and turned olive to black, developing a superficial powdery mycelium. Lesions expanded rapidly, causing extensive epidermal decay and abundant sporulation. Five symptomatic fruits were collected from each canton. Fungal isolates were obtained from 9 out of 10 surface-sterilized (70% ethanol, 1% NaOCl) tissue fragments from fruit lesions, which were plated on potato dextrose agar (PDA) and incubated at 28°C for 4 days. Colonies were circular, moderately growing, with abundant cottony gray to dark brown aerial mycelium. Conidia were straight, pale brown, 18–30 × 8–12 µm, with 2–6 transverse septa, characteristic of the genus Curvularia (Manamgoda et al. 2012). Morphological identification was confirmed by sequencing the internal transcribed spacer (ITS), of isolates FP180444 and FP230447, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and translation elongation factor 1-alpha (TEF1α) genes of isolate FP180444, using ITS1/ITS4, gpd1/gpd2 and TEF1-983F/TEF1-2218R primers respectively (Ahmadpour et al., 2020). BLAST analysis showed 100% (ITS), 99.7% (TEF1α), and 99.8% (GAPDH) identity with C. cactivora CBS 580.74 (GenBank accession nos. MN688803, MN688857, and LT715853). Sequences were uploaded to GenBank with accession nos. PX485998, PX485999 , PX551765, and PX551766. A multilocus phylogeny based on concatenated ITS, GAPDH, and TEF1α sequences was generated using RAxML v8.2.12 with the GTR+GAMMA model and 100 bootstrap replicates, with Bipolaris sorokiniana CBS 110.14 as the outgroup. The isolates grouped with C. cactivora (Petr.) M.B. Ellis reference strains with a bootstrap support of 100, confirming its identity. To further confirm the identity and explore genomic features, whole-genome sequencing of isolate FP180444 was performed using Illumina NovaSeq. The C.cactivora FP180444 genome is available at NCBI with accession number SAMN52968965. Pathogenicity was confirmed by inoculating five-month-old healthy plants and fruits with 0.5 ml of a 1 × 10⁵ conidia/ml suspension from monoconidial cultures from isolates FP180444 and FP230447, by syringe infiltration. Controls were treated with sterile distilled water. After 15 days at 28°C and 77% relative humidity, inoculated fruits and cladodes developed typical brown to black lesions, while controls remained symptomless. Three plants and three fruits were used per isolate, and the experiment was conducted twice. The fungus reisolated from infected tissues was confirmed as C. cactivora by microscopic observation and ITS sequencing, fulfilling Koch’s postulates. To our knowledge, this is the first report of Curvularia cactivora causing fruit rot of red dragon fruit in Ecuador, and the first genome assembly of a C. cactivora isolate. Given the increasing commercial importance of dragon fruit in the country, the presence of this pathogen may pose a risk to yield, fruit quality, and market access, while the genome resource will facilitate future studies on pathogenicity, host adaptation, and disease management.