Plant-parasitic nematodes represent a significant threat to agriculture, causing substantial economic losses worldwide. Among the biological alternatives for their control, the genus Trichoderma has emerged as a promising solution for suppressing various nematode species. This article reviews key studies on the interaction between Trichoderma spp. and plant-parasitic nematodes, highlighting the most studied species such as Trichoderma harzianum, Trichoderma longibrachiatum, Trichoderma virens, and Trichoderma viride, mainly against the genera Meloidogyne, Pratylenchus, Globodera, and Heterodera. Trichoderma spp. act through mechanisms such as mycoparasitism, antibiosis, competition for space in the rhizosphere, production of lytic enzymes, and modulation of plant defense responses. They also produce metabolites that affect nematode mobility, reproduction, and survival, such as gliotoxin, viridin and cyclosporine A. In addition, they secrete enzymes such as chitinases, proteases, lipases, and glucanases, which degrade the cuticle of nematodes and their eggs. Furthermore, Trichoderma spp. induce systemic resistance in plants through modulation of phytohormones such as jasmonic acid, ethylene, salicylic acid and auxins. The use of Trichoderma in integrated nematode management enables its application in combination with crop rotation, organic amendments, plant extracts, and resistant varieties, thereby reducing the reliance on synthetic nematicides and promoting more sustainable and climate-resilient agriculture.

Sorghum (Sorghum bicolor) leaf sheath blight was observed for the first time in Sinaloa, Mexico in the summer of 2020. Fungal isolates were obtained from symptomatic tissue in potato dextrose agar. Fusarium spp. were associated with symptomatic plants in 10 sampling sites under field conditions. No root and stalk rot was observed during the sampling period. Analysis of fragments of the translation elongation factor alpha and RNA polymerase II second largest subunit genes indicated that all isolates belong to the Fusarium fujikuroi species complex (FFSC). Five groups were delineated from this complex: F. thapsinum, F. verticillioides, Fusarium sp. (four isolates), Fusarium sp. 4 (Fus4), and Fusarium sp. (Fus16), which is closely related to Fusarium madaense. The morphological characteristics (colony color and morphometry of conidia) of isolates with sequence similarities to those of F. thapsinum and F. verticillioides were in the expected range for these species. The morphology of isolates Fus7a, Fus7b, Fus11, and Fus17, as well as Fus4 and Fus16, were similar to those of the FFSC, specially to F. andiyazi and F. madaense. Inoculations of sorghum with representative isolates of F. thapsinum, F. verticillioides and the unidentified Fusarium species resulted in reddish brown lesions similar to those observed under field conditions; the original isolates inoculated were reisolated fulfilling the Koch’s postulates. Although leaf sheaths on sorghum plants were heavily damaged, root and stalk rot were not observed in the greenhouse inoculations or under field conditions. Future research should focus on determining the identity of the unknown Fusarium spp. to design control measures for the disease. This is the first report of Fusarium spp. causing sorghum leaf sheath blight 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.

El objetivode este trabajo fue determinar la relación entre el colordel pigmento producido por aislamientos de F. verticillioidesy la virulencia en plántulas de maíz. Las mazorcas de maízsintomáticas y asintomáticas se colectaron en el Estado deVeracruz, México durante el ciclo agrícola primavera-verano2008. El experimento se analizó siguiendo un diseño experimentalen parcelas con doble división y se realizó en condicionesde invernadero en dos ciclos; otoño- invierno 2008y primavera-verano 2009, en el Colegio de PostgraduadosCampus Montecillo, Estado de México. La pigmentaciónde los aislamientos obtenidos de semillas sintomáticas conmicelio morado, fue más intensa y con micelio blanco mostraronun color más homogéneo, mientras que los de semillasasintomáticas tuvieron coloraciones de micelio violeta tenuey de blanco a crema. Los aislamientos obtenidos de semillassintomáticas y asintomáticas fueron patogénicos, el de colormorado de semillas sintomáticas fue más virulento que elblanco, caso contrario en semillas asintomáticas, donde elblanco fue más virulento.

Wild blackberry species (Rubus spp. L.; Rosaceae) represents an invaluable source of genes for the generation of new varieties, but also serve as a primary source of disease inoculum. During April of 2020, symptoms of powdery mildew were observed on four populations of wild blackberry species located in the states of Chiapas (16°59'11"N, 92°59'07"W; 16°47'08"N, 92°31'05"W) and Michoacán (19°37'17"N, 100°08'59"W; 19°29'25"N, 101°32'54"W), Mexico. Signs of the pathogen were white powdery masses mainly on the top of new shoots. Symptoms included yellowing, necrosis, and early defoliation of the plants. Hyphae were tin-walled, hyaline, smooth, and 4.0-9.0 mm wide. Appressoria were indistinct -to- nipple-shaped. Conidiophores (n=30, 75-225 × 10.5-13.5 μm) were straight, and unbranched with cylindrical foot cells (n=30, 31.5-158 × 8-13.5 μm), straight, somewhat widening upwards, followed by 1-3 shorter cells. Conidia (n=100; 25.5-38.5 × 9.5-22.5 μm) were catenulate, ellipsoid-ovoid -to- doliiform, containing fibrosin bodies (in 3% KOH). Germ tubes (n=30, 13.5-40.5 × 4.5 μm) emerged laterally, and were unbranched with slightly swollen tips. Chasmothecia were not found. Morphological characters of the fungus in all samples corresponded to the previous descriptions of Podosphaera aphanis by Braun and Cook (2012) and Stevanovi´c et al. (2020). Voucher specimens were deposited in the Department of Agricultural Parasitology Herbarium at the Chapingo Autonomous University under accessions UACH421, UACH423, UACH425, UACH426. To confirm the species identification, the internal transcribed spacer (ITS) of one sample was amplified using the primers ITS5 (White et al. 1990) and P3 (Kusaba and Tsuge, 1995) and sequenced. The sequence was deposited in GenBank (accession number MW988591). A phylogenetic analysis using Bayesian inference and maximum likelihood was performed (Hernández-Restrepo et al. 2018) and included other Podosphaera species (Takamatsu et al. 2010). The sequence from the isolate UACH426 clustered with the strain MUMH1871 of P. aphanis forming a definite clade and remained as a sister taxon of P. pannosa. Pathogenicity was verified through inoculation by gently dusting conidia from one powdery mildew patch onto leaves of five healthy blackberry plants of each specie. The same number of noninoculated plants served as controls. All plants were maintained in a greenhouse at 25-30°C with 75% relative humidity. All inoculated plants developed powdery mildew symptoms after 12 days, whereas no symptoms were observed on noninoculated plants. The fungus recovered from the inoculated plants was morphologically identical to that originally observed on diseased blackberry plants, demonstrating the pathogenicity of the fungus. Based on morphological data and phylogenetic analysis, the fungus was identified as P. aphanis. This fungus has been reported to cause powdery mildew on blackberry plants in Serbia (Stevanovi´c et al. 2020). This is the first report of P. aphanis causing powdery mildew on wild backberry species in Mexico according to Farr and Rossman (2021). The primary source of inoculum of powdery mildew for commercial plantings is wild blackberry plants from noncultivated areas and may warrant control of wild populations.