The Need and Opportunity to Update the Inventory of Plant Pathogenic Fungi and Oomycetes in Mexico.

Mexico generates specific phytosanitary regulations for each product and origin to prevent the entry of quarantine pests and/or delay their spread within the national territory, including fungi and oomycetes. Phytosanitary regulations are established based on available information on the presence or absence of these pathogens in the country; however, the compilation and precise analysis of reports is a challenging task due to many publications lacking scientific rigor in determining the presence of a taxon of phytosanitary interest in the country. This review evaluated various studies reporting the presence of plant pathogenic fungi and oomycetes in Mexico and concluded that some lists of diseases and phytopathogenic organisms lack technical-scientific basis. Thus, it highlights the need and presents an excellent opportunity to establish a National Collection of Fungal Cultures and a National Herbarium for obligate parasites, as well as to generate a National Database of Phytopathogenic Fungi and Oomycetes present in Mexico, supported by the combination of morphological, molecular, epidemiological, pathogenicity, symptom, and micrograph data. If realized, this would have a direct impact on many future applications related to various topics, including quarantines, risk analysis, biodiversity studies, and monitoring of fungicide resistance, among others.

First report of Nalanthamala vermoesenii causing pink rot of Phoenix canariensis in Mexico.

In Mexico City, the Canary Island date palm (Phoenix canariensis Chabaud) is an important plant forming part of its landscape identity. In February 2022, pink rot disease symptoms were observed on 16 P. canariensis plants in Mexico City (19°25'43.98"N, 99° 9'49.41"W). The incidence was 27%, while the severity 12%. External symptoms included necrotic lesions that advanced from the petiole towards the rachis. Internal symptoms were rotted, dark brown discoloration in bud, petiole, and rachis. Abundant conidial masses were developed on the infected tissues. Pieces of diseased tissues (5-mm cubes) were surface sterilized for 2 min in 3% sodium hypochlorite, rinsed with sterilized distilled water, plated onto potato dextrose agar (PDA), and incubated at 24°C and 12-h photoperiod, 20 pink fungal colonies were developed with sparse aerial mycelia on PDA. Conidiophores were hyaline, dimorphic, penicillate, and Acremonium-like. Conidia were dimorphic, typically with somewhat truncated ends, 4.5 to 5.7 × 1.9 to 2.3 µm (mean 4.99 × 2.15, n = 100), borne in long chains on penicillate conidiophores; on Acremonium-like conidiophores conidia were cylindrical, straight, and slightly curved, 4.55 to 10.1 × 1.2 to 2.35 µm (mean 8.2 × 1.7, n = 100). These morphological characteristics resembled those of Nalanthamala vermoesenii (Biourge) Schroers (Schroers et al. 2005). Genomic DNA was extracted from the mycelia of a representative isolate CP-SP53. The internal transcribed spacer (ITS) region and the large subunit of ribosomal ribonucleic acid (LSU) were amplified and sequenced. The sequences were deposited in GenBank with accession numbers OQ581472 (ITS) and OQ581465 (LSU). Phylogenetic trees based on ITS and LSU sequences of Nalanthamala species were reconstructed using maximum likelihood and Bayesian inference methods. Isolate CP-SP53 was placed in the clade of Nalanthamala vermoesenii. The pathogenicity test was carried out twice with isolate CP-SP53 on five 3-year-old P. canariensis plants. Four petioles per plant were surface disinfected with 75% ethanol, and wounded with a sterilized scalpel (shallow cuts 0.5 cm wide). A mycelial plug (5 mm in diam.) of a 1-week-old PDA culture was placed on each wounded site. Sterile PDA plugs were used for five non-inoculated control plants. All plants were maintained at 22 ± 2°C and a 12-h photoperiod. Twenty-five days after inoculation (dai), wounded petioles showed the same symptoms observed in the field, whereas control plants remained healthy. Forty-five dai, all inoculated plants died. Pink conidial masses developed on symptomatic tissues. To fulfill Koch's postulates, the pathogen was reisolated by placing the pink conidial masses onto PDA. The colony characteristics and morphometric measurements were identical to those of isolate CP-SP53. Nalanthamala vermoesenii has been reported on P. canariensis in Greece and United States (Feather et al. 1979; Ligoxigakis et al. 2013) and Syagrus romanzoffiana in Egypt (Mohamed et al. 2016). To our knowledge, this is the first report of Nalanthamala vermoesenii as the causal agent of pink rot on P. canariensis in Mexico. This plant is the most commonly planted ornamental palm in Mexico City. The spread of N. vermoesenii could be a threat for the estimated 15 thousand palms, therefore dramatically change the urban landscape.