RESUMO
In Mexico strawberry production has great economic importance for the local and export markets as the country is the main strawberry supplier to the United States (SIAP, 2020). In 2022, strawberry plants with yellowing and wilting leaves, root rot and wilting, necrosis of vascular bundles and small fruits symptoms were observed in different commercial fields in the north-central Mexican state of Sinaloa, causing yield losses of about 10%. Typical Fusarium spp. colonies were recovered from all samples. They produced abundant white aerial mycelium with cream to orange pigment and branched septate hyphae (Fig. 1) (Leslie and Summerell, 2006). A total of 18 monosporic isolates were obtained by serial dilutions. The 18 isolates grown for 10 days on carnation leaf agar (CLA) produced hyaline microconidia with 0-2 septa, measuring 9.2 - 15.4 by 4.5 - 6.5 µm (n = 40) and hyaline macroconidia with three septa that measured 28.4 - 53.5 by 4.5 - 9 µm (n = 40). Chlamydospores were not observed. A fragment of the translation elongation factor 1-alpha (EF1-alpha) gene was amplified by polymerase chain reaction (PCR) using the primer pair EF-1/EF-2 (O'Donnell et al. 1998) from two monosporic isolates. The sequences were registered in the NCBI GenBank under accession numbers OR878541 and OR878543 (FRESIN178 and FRESIN194). BLASTn queries of NCBI GenBank identified the sequences as F. falciforme with 98% and 100% similarity to accession numbers OQ262968 and DQ246941 respectively. Fusarium ID database also identified the sequences as F. falciforme, is a member of the F. solani species complex (FSSC). Phylogenetic analysis revealed the partial EF1 sequences grouped with F. falciforme (Fig. 2). A pathogenicity test was performed on thirty strawberry plants (cv. Cabrillo) grown in sterile vermiculite. The plants were inoculated by immersing roots in 20 mL of a conidial suspension (1 × 105 conidia/mL) of isolate FRESIN194. Twelve uninoculated plants served as the control. All plants were grown for 60 days under greenhouse conditions (28 to 35°C). The assay was repeated twice. After 50 days, symptoms of root rot and wilting leaves like those observed in the field were observed. Uninoculated control plants did not develop symptoms. The fungus was reisolated from necrotic tissues of the inoculated plants and identified as F. falciforme by sequencing the EF1-alpha gene and morphological characteristics, completing Koch's postulates. Fusarium falciforme has been reported as the causal agent of root rot, stem rot, and wilt of tomato, papaya, chickpea, onion, common bean, and maize in Mexico (Díaz-Najera et al. 2021, Douriet-Angulo et al. 2021, Felix et al 2022, Tirado-Ramírez et al 2018, Vega-Gutiérrez et al. 2019a, Vega-Gutiérrez et al. 2019b). To our knowledge this is the first report of F. falciforme causing root rot and wilt on strawberry in Sinaloa, Mexico. This result provides useful information for the development and implementation of disease control strategies to mitigate damage caused by F. falciforme.
RESUMO
Strawberry (Fragaria × ananassa) is a fruit of economic importance for Mexico, occupying the third place in world production, with an approximate production of 861, 337 t (SIAP, 2021). In January 2021, in Culiacan, Sinaloa, Mexico (24°46'46â³N; 107°27'04â³ W), wilting symptoms (stunted growth, leaf yellowing and wilting, necrosis in vascular bundles, root rot and wilting) were observed on commercial strawberry crops, with an incidence of 5 to 10 %. Tissue samples from symptomatic roots were cut and disinfected with alcohol, sodium hypochlorite and sterile water, to later be plated on potato dextrose agar (PDA). Fifteen monosporic isolates were obtained by single-spore culturing (Hansen and Smith, 1932). Typical Fusarium spp. colonies were obtained from all root samples. On PDA the colonies were abundant with white aerial mycelium, hyphae were branched and septate, and light-yellow pigmentation was observed in the center of old cultures (Leslie and Summerell 2006). From 10-day-old cultures grown on carnation leaf agar medium, macroconidia were slightly curved, showing three marked septa, broad central cells, slightly tapered apices, foot-shaped basal cells and measured 59.6 - 73.4 (xÌ = 68.7) x 10.4 - 14.9 µm (xÌ = 13.6) (n = 40). The microconidia (n = 40) were thin-walled, hyaline, ovoid unicellular that measured 19.7 - 32.2 (xÌ = 26.6) x 8.8 - 11.8 µm (xÌ = 10.2). The translation elongation factor 1 alpha (EF1-α) gene (O'Donnell et al. 1998) was amplified by polymerase chain reaction and sequenced. Maximum likelihood analysis was carried out using the EF1-α sequence from the isolate FKTFRESCULSIN (GenBank accession no. OK491929) and other Neocosmospora and Fusarium species. Phylogenetic analysis revealed the isolate was Fusarium keratoplasticum (currently named Neocosmospora keratoplastica) belonging to the Fusarium solani species complex (FSSC). Pathogenicity tests were performed on strawberry plants (cultivar Camarosa) grown on autoclaved sandy loam soil mix. Twenty plants were inoculated by drenching with 20 ml of a conidial suspension (1 × 105 CFU/ml) in an isotonic saline solution of FKTFRESCULSIN grown on PDA. Ten uninoculated plants served as controls. Plants were maintained for 60 days under greenhouse conditions (25 to 30°C). The assay was conducted twice. Root and stem rot similar to that observed on the infected plants in the field was observed. No symptoms were observed on uninoculated control plants after 60 days. The pathogen was reisolated from necrotic tissue from all inoculated plants and identified as F. keratoplasticum by sequencing the partial EF1-α gene and based on its morphological characteristics, thus fulfilling Koch's postulates. To our knowledge, this is the first report of root rot and wilt of strawberry caused by F. keratoplasticum in Mexico; it also contributes knowledge to the scientific community, since there is little information about this pathogen causing damage to plants in the world. Strawberry is an important crop in Mexico, and the occurrence of this disease could threaten strawberry production.
