First report of Irpex rosettiformis causing white root rot in avocado trees in Michoacán, México

In México, avocado production is an important economic source. In the last season it generated $ 3. 27 billion USD of foreign currency in the country. Irpex spp. are wood decay fungi. In the period 2019-2022, in the state of Michoacán (19°13' N; 101°55' W), México, basidiomes of Irpex sp. were observed on the base of trunks and crowns of 5-years-old and older avocado (Persea americana) trees. The trees exhibited disease symptoms that included white root rot, leaf yellowing, small leaves, branch diebacks, generalized defoliation, apical flaccidity, abundant but small sun burnt fruits due to the lack of foliage, and after 2-4 years of first disease appearance, the infected trees died. In the place where fungus was established, abundant white and cottony mycelium was formed, which caused trees decay. The incidence of the disease in the sampled orchards was estimated to be 30% per ha with 350 - 400 trees, which was determined through a simple sampling design focused on trees with signs and symptoms of the disease due to the phytopathogen. Samples of infected tissue (roots and stems) and fungal basidiomes were collected from 90 trees (5-6 per orchard). The symptomatic avocado trees studied were randomly selected from 17 orchards. For the fungal macroscopic characterization, the synoptic keys described by Gilbertson and Ryvarden (1986) and by Largent (1973) were used. The samples showed typical structures corresponding to Irpex sp., including rosettes, annual basidiomes, a system of monomitic hyphae, and subglobose basidiospores. In vitro fungal isolation from basidiomes and infected tree tissues was done according to the protocol of Agrios (2004). The fungal strains were maintained on PDA at 28 °C. At 16 days of incubation the colonies were opaque, whitish with fluffy and corky mycelium. Microscopic analysis of the fungus showed typical yellowish spores, with an ellipsoid shape of 3-4 x 4-5.5 µm (50 accounted structures per isolate [N=19]) and basidia of 20-25 x 4.5-5.5 µm (n=20 basidiomes). For molecular characterization, two molecular markers were used, the internal transcribed spacer rDNA-ITS1 5.8 rDNA-ITS2 (ITS; White et al. 1990) and the large ribosomal subunit (LSU; Vilgalys and Hester 1990). The PCR reaction was performed as described by Martínez-González et al. (2017). The consensus sequences were compared with those deposited in the NCBI-GenBank, using the BLASTN 2.2.19 tool (Zhang et al. 2000), the samples showed 99% match with the species, Irpex rosettiformis. GenBank accession numbers of the submitted isolates are summarized in supplementary Table 4. To test Koch's postulates, 3-months old avocado plants grown in greenhouse conditions were inoculated (n = 10 per each isolate [N= 19]) on the roots with 3 g of I. rosettiformis mycelium. The experiment was done twice with 20 non-inoculated plants as control. After 67 days, basidiomes (50 x 70 x 1.5 mm in average) were observed where the disease incidence was >77%, with subsequent tree decline. The pathogen was re-isolated in vitro in PDA and its identity was confirmed by morphological characteristics of mycelium. This work shows that I. rosettiformis is not only a wood decay fungus, but also a phytopathogen, the causative agent of white root rot disease in P. americana var. drymifolia, cultivar 'Hass', which establishes a precedent for monitoring and preventing its proliferation to other regions in the American continent and the world where nursery avocado seedlings are exported.

Broadening the Knowledge of Mexican Boletes: Addition of a New Genus, Seven New Species, and Three New Combinations

Boletes are one of the most common groups of fungi in temperate, subtropical, and tropical ecosystems. In Mexico, the northern region has mainly been explored in terms of bolete diversity. This study describes a new genus and seven new species based on macromorphological, micromorphological, molecular, phylogenetic, and ecological data. Garcileccinum gen. nov. is typified with G. salmonicolor based on multigene phylogenetic analysis of nrLSU, RPB2, and TEF1, and it is closely related to Leccinum and Leccinellum. Garcileccinum viscosum and G. violaceotinctum are new combinations. Boletellus minimatenebris (ITS, nrLSU, and RPB2), Cacaoporus mexicanus (RPB2 and ATP6), Leccinum oaxacanum, Leccinum juarenzense (nrLSU, RPB2, and TEF1), Tylopilus pseudoleucomycelinus (nrLSU and RPB2), and Xerocomus hygrophanus (ITS, nrLSU, and RPB2) are described as new species. Boletus neoregius is reclassified as Pulchroboletus neoregius comb. nov. based on morphological and multigene phylogenetic analysis (ITS and nrLSU), and its geographic distribution is extended to Central Mexico, since the species was only known from Costa Rica. Furthermore, T. leucomycelinus is a new record from Mexico. This study contributes to increasing our knowledge of boletes and expands the diversity found in Mexican forests.

Five New Species of Aureoboletus and Chalciporus (Boletaceae, Boletales) and Their Ethnomycological Aspects

Among Boletales, the family Boletaceae has the highest diversity worldwide. Additionally, this fungal group has great ecological relevance because it not only includes mainly ectomycorrhizal but also saprotrophic species. Furthermore, some species are used as food and have sociocultural and economic importance worldwide. In Mexico, the Boletaceae family boasts a substantial number of species, yet our understanding of these species remains far from comprehensive. In this work, by using macro- and micromorphological and phylogenetic analyses of DNA sequences from multi-gene analyses based on ITS, nrLSU, rpb1, rpb2, and tef1, we report five new species belonging to the genera Aureoboletus and Chalciporus: A. ayuukii and A. elvirae from a Quercus scytophylla forest, A. readii from a mixed forest, C. perezsilvae from cloud forest, and C. piedracanteadensis from both a mixed coniferous forest and a Quercus-Pinus forest. In Mexico, four species of Aureoboletus are used as a food source, and in this work, we add another one, A. readii, which is traditionally consumed by members of the Tlahuica-Pjiekakjoo culture, who are located in the central part of the country. This work contributes to our knowledge of two genera of Boletaceae in a geographical area that is scarcely studied, and thus, our understanding of its biocultural relevance is enriched.

New Ascomycetes from the Mexican Tropical Montane Cloud Forest

The tropical montane cloud forest is the most diverse and threatened vegetation type in Mexico. In the last decade, the number of described Ascomycetes species has notably increased, reaching more than 1300 species. This study describes six new species based on their molecular and morphological characteristics. Our results suggest that Mexico has the highest number of described species in the Neotropics. However, many other Mexican lineages still need to be described.

Novelties in Macrofungi of the Tropical Montane Cloud Forest in Mexico

The tropical montane cloud forest in Mexico is the most diverse and threatened ecosystem. Mexican macrofungi numbers more than 1408 species. This study described four new species of Agaricomycetes (Bondarzewia, Gymnopilus, Serpula, Sparassis) based on molecular and morphological characteristics. Our results support that Mexico is among the most biodiverse countries in terms of macrofungi in the Neotropics.

Elaphomyces castilloi (Elaphomycetaceae, Ascomycota) and Entoloma secotioides (Entolomataceae, Basidiomycota), two new sequestrate fungi from tropical montane cloud forest from south Mexico

Two new species of sequestrate fungi are described from south Mexico based on morphological and molecular evidences. Here we describe Elaphomyces castilloi characterized by the yellowish mycelial mat, dull blue gleba and ascospores of 9.7–11.5 µm; Entoloma secotioides is characterized by the secotioid basidiomata, sulcate, pale cream pileus, and basidiospores of 7–13 × 5–9 µm. Both species grow in montane cloud forest under Quercus sp. in the state of Chiapas, Mexico. Descriptions, photographs, and multilocus phylogeny for both species are presented.

A novel coconut-malt extract medium increases growth rate of morels in pure culture

Morels are gourmet wild edible mushrooms that can grow on several substrates with significant growth rate variations. Such variations have hindered the development of a standardized culture media to promote morel’s sustainable production. The aim of this study is developing a novel culture media that takes advantage of coconut water as a complementary component of culture media. Coconut water has been extensively used as a growth-promoting component for plant tissue cultures; however, its application as component of fungi cultivation medium has not been fully developed. This study confirms that coconut water can be efficiently used as culture media component for morels using a kinetic characterization. Morchella sp. kinetic growth is evaluated in different cultures: agar, malt extract agar (MEA), lactose, coconut water (15%) and combinations of them. Kinetic growth parameters (lag phase, λ and maximum specific growth rate, µ_max) are estimated using primary modeling methods. Among the selected models, the best fit is achieved using Baranyi’s model. A significant increase from 15.8% to 43.4% of the µ_max values was observed when culture media (agar, lactose, MEA) is supplemented with coconut water. The largest values of µ_max are obtained in MEA-coconut cultures (21.13 ± 0.43–22.57 ± 0.35). Micro-sclerotia and late sclerotia are observed in all cultures containing coconut water justifying the development of a feasible and cost-effective way of culturing morels. The results demonstrate that coconut water can be used for formulation of standard media for morel cultivation leading to a cheap alternative to produce dense mycelium and promote sclerotia formation.

Three new species of Rhytidhysteron (Dothideomycetes, Ascomycota) from Mexico

The genus Rhytidhysteron is characterised by forming navicular to apothecial hysterothecia, exposing the green, yellow, orange, red, vinaceous or black colours of the hymenium which generally releases pigments in the presence of KOH. The exciple is smooth or striated, the asci bitunicate and ascospores have 1–5 transverse septa. To date, twenty-six Rhytidhysteron species have been described from the Tropics. The present study aims to describe three new species in the Neotropics of Mexico based on molecular methods and morphological features. Illustrations and a taxonomic key are provided for all known species of this genus. Rhytidhysteroncozumelense from the Isla Cozumel Biosphere Reserve, R.esperanzae from the Sierra Juárez, Oaxaca and R.mesophilum from the Sierra Madre Oriental, Hidalgo are described as new species. With the present study, the number of species of Rhytidhysteron known from Mexico is now increased to eight.

A novel sequestrate species from Mexico: Aroramyces guanajuatensis sp. nov. (Hysterangiaceae, Hysterangiales)

Knowledge of sequestrate Hysterangiaceae fungi in Mexico is very limited. In the present study, a new member of the family, Aroramyces guanajuatensis sp. nov., is described. This speciesis closely related to A. balanosporus, but differs from the latter in possessing a tomentose peridium 165-240 µm thick, with occasional large terminal hyphae up to 170 µm, a variable mesocutis (isodiametric to angular), and distinct bright yellowish subcutis. In contrast, A. balanosporus possesses a fibrillose peridial surface with shorter hyphae, a peridium 200-450 µm thick, and a mainly hyaline isodiametric mesocutis with a slightly wider subcutis. The phylogenetic analysis of the LSU gene separated A. guanajuatensis from A. balanosporus with a Bayesian posterior probability (PP) = 1. This is the third Aroramyces species described for the American continent.

Improved method for genomic DNA extraction for Opuntia Mill. (Cactaceae)

BACKGROUND

Genomic DNA extracted from species of Cactaceae is often contaminated with significant amounts of mucilage and pectin. Pectin is one of the main components of cellular walls, whereas mucilage is a complex polysaccharide with a ramified structure. Thus, pectin- and mucilage-free extraction of DNA is a key step for further downstream PCR-based analyses.

RESULTS

We tested our DNA extraction method on cladode tissue (juvenile, adult, and herbaria exemplars) of 17 species of Opuntia Mill., which are characterized by a large quantity of pectin and mucilage.

CONCLUSION

We developed a method for the extraction of gDNA free of inhibitory compounds common in species of Opuntia Mill., such as pectin and mucilage. Compared to previously extraction protocols, our method produced higher yields of high-quality genomic DNA.