Search

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. [ABSTRACT FROM AUTHOR]

The wilt or damping-off of husk tomato is a disease caused by fungi originating in the soil, among which Fusarium oxysporum, Macrophomina phaseolina, and Rhizoctonia solani stand out, causing losses due to the lack of resistant varieties. This study aimed to determine the response of husk tomato (Physalis ixocarpa Brot.), Dalí, Siqueiros, and Tamayo hybrids, as well as cv. Gabriela, Puebla, San Miguel, and Tecozautla, to pathogenic isolates of F. oxysporum, M. phaseolina, and R. solani. The study was conducted under greenhouse conditions; sterilized substrate of river sand + peat (1:3 v/v) was placed in pots and then inoculated with three isolates of F. oxysporum 1.6x105 CFU, two of M. phaseolina, and three of R. solani (8 g of infested sorghum seed/pot, of each fungus). Five seeds of the corresponding husk tomato cultivar were deposited in each pot, then covered with the same substrate and incubated for 30 days. A completely randomized design was used, with three repetitions (pots). In the control treatment, the seeds were sown on soil without fungus. The emergence of seedlings was estimated nine days after sowing (das), and the severity of infection for each of the pathogens (scale of 0-5) at 30 das. Data were analyzed using nonparametric statistics. The seven cultivars tested were susceptible to the species F. oxysporum, M. phaseolina, and R. solani; some of the isolates tested exerted a significant differential effect of virulence on some of the varieties studied. [ABSTRACT FROM AUTHOR]

Soursop (Annona muricata L: Annonaceae) is a small tropical fruit tree native to South America (Pinto, 2005). The flesh of its fruits is widely used as a main ingredient of pastries, even young fruits are used as a vegetable. In June 2022, leaf spots symptoms were observed on fifty soursop plants in a commercial nursery located in Juan José Ríos (25°45'20"N 108°50'21"W), Ahome, Sinaloa State. The incidence of the disease was 75%, while the severity was 12%. Symptoms were round, small black necrotic spots, that grew up to 6 mm in diameter with brown or gray color at the center. Fungal isolation was done on potato dextrose agar (PDA) and Colletotrichum-like colonies were obtained. Five isolates were recovered and purified by single spore culture and only a single morphotype was observed. One random isolate was selected for pathogenicity tests, morphological and molecular characterization. The isolate was deposited in the Culture Collection of Phytopathogenic Fungi of the Biotic Products Development Center at the National Polytechnic Institute under accession no. IPN 13.0102. Colonies in PDA at 25°C grow at a rate of 9.0-14.0 mm/d. After 14 days, the colony was olive to gray with orange conidial masses, and conidia (n =100) were hyaline, aseptate, cylindrical, and straight with rounded ends, measuring 11.5 to 18.5 and 3.5 to 5.5 μm. Appressoria were melanized and circular or oval in shape, measuring 6.0 to 4.0 μm (n=20). According to the morphological characteristics observed, the isolate was placed tentatively within the Colletotrichum gloeosporioides species complex (Weir et al. 2012). For molecular confirmation, genomic DNA was extracted, and the internal transcribed spacer (ITS) region (White et al. 1990), partial sequences of actin (ACT) (Weir et al. 2012) and span style="font-family:'Times New Roman'">glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were amplified and sequenced. Sequences were deposited in GenBank under the accession numbers: ITS, OQ606966; ACT, OQ617292 and GAPDH, OQ617293. A phylogenetic tree including published sequences of the C. gloeosporiodes species complex was constructed according to Talhinhas and Baroncelli (2021) and the isolate IPN 13.0102 was grouped in a clade with the ex-type culture of C. siamense (ICMP18578) and C. pandanicola. However, C. pandanicola was recorded only as an epiphytic fungus occurring on leaves of Pandanus sp. (Pandanaceae) (Tibpromma et al. 2018) and there are no additional reports of this fungus as a plant pathogen on Pandanus or any other plant. Therefore, the isolate IPN 13.0102 corresponds to C. siamense. Pathogenicity was demonstrated by spraying a conidial suspension (1 × 105 conidia/ml) onto four healthy soursop plants, while two control plants were sprayed using sterile distilled water. All plants were kept in a wet chamber for 48 h at 28  2°C and 85% RH. The characteristic symptoms of the disease were observed 14 days after inoculation, while control plants remained healthy. The pathogenicity test was repeated twice obtaining the same results. The morphology of the recovered fungus was consistently identical to that originally isolated from diseased leaves, fulfilling Koch's postulates. Colletotrichum siamense has been previously reported on Anona spp. in Brazil (Costa et al. 2019). To our knowledge, this is the first report of Colletotrichum siamense causing leaf spots on Annona muricata in Mexico. Further studies for monitoring and control strategies of leaf spots on soursop are required.

Peppermint (Lamiaceae) is an aromatic herb with culinary, medicinal, and industrial properties. In June 2022, symptoms and signs of foliar rust were observed in four commercial fields of peppermint (Mentha × piperita) in San Buenaventura Tecalzingo, San Martín Texmelucan, Puebla, Mexico (19°14'34.0"N 98°27'25.4"W; 19°14'16.7"N 98°27'21.4"W; 19°14'37.0"N 98°27'07.7"W; 19°15'00.6"N 98°26'54.7"W). Two diseased plants were collected at each site. The disease was present in 50% of the plants and the damaged foliar tissue was under 17%. Initial symptoms included small chlorotic spots on the adaxial surface of the leaves, which later spread to form a necrotic area surrounded by a broad chlorotic halo. Necrosis developed only in the presence of abundant reddish-brown pustules on the abaxial surface of the leaf, while smaller pustules were observed on the adaxial surface. The signs were detected as numerous reddish-brown pustules on the abaxial surface of the leaves. The infected leaves of all samples showed subepidermal uredinia, erumpent, with hyaline and cylindrical paraphyses. Urediniospores (n = 50) were hyaline to light brown, echinulate, with two germinative pores, obovoid (16.5-26.5 × 11.5-25.5 μm, mean ± SD = 22 ± 1.6 × 19 ± 0.4 μm and 0.6 μm of wall thickness), individually supported on pedicels. Morphological characteristics aligned most closely with the description of Puccinia menthae by Kabaktepe et al. (2017) and Solano-Báez et al. (2022). A voucher specimen was deposited in the Herbarium of the Department of Plant-Insect Interactions at the Biotic Products Development Center of the National Polytechnic Institute under accession no. IPN 10.0115. From one sample, genomic DNA was extracted, and the 28S gene region of rDNA was amplified by a nested PCR using the primer sets Rust2inv (Aime, 2006) and LR6 (Vilgalys and Hester, 1990), and Rust28SF (Aime et al., 2018), and LR5 (Vilgalys and Hester, 1990) for the first and second reactions, respectively. The obtained sequence (GenBank accession No. OQ552847) showed 100% homology (902/1304bp) with the type-specimen sequence of P. menthae (DQ354513) from Cunila origanoides from USA (Aime, 2006). A phylogenetic analysis using Maximum Likelihood including a published 28S dataset for Puccinia species was executed and the isolate IPN 10.0115 was grouped into a clade of P. menthae with bootstrap support value of 100%. Pathogenicity was assessed by spraying a suspension of urediniospores (1×104 spores/ml) of the isolate IPN 10.0115 onto six healthy peppermint plants (Mentha × piperita) that were 30 days old, while six other plants were sprayed with sterile distilled water. All plants were kept in a wet chamber for 48 h at temperatures from 28±2°C and relative humidity of 95%, after which the plastic bag was removed. All inoculated plants developed disease symptoms after 15 days, whereas the control plants remained symptomless. The pathogenicity assay was conducted twice with similar results. The morphology of the pathogen recovered from the pustules of the inoculated plants was identical to that originally recollected, thus fulfilling Koch'postulates. To our knowledge, this is the first report of Puccinia menthae causing leaf rust on Mentha × piperita in Mexico. This species has been previously identified using morphological characteristics in Brazil, Canada, Poland, and USA on Mentha × piperita (Farr and Rossman, 2023). Since the disease defoliates peppermint plants reducing yield, further information on disease management is needed.

Guar ( Cyamopsis tetragonoloba ), is an annual legume belonging to the Fabaceae family and it is grown mainly for industrial purposes and also as an ingredient for animal feed. In September 2021, anthracnose symptoms were observed on guar fields distributed in Guasave, Sinaloa, Mexico. Disease incidence was estimated up to 15%. Diseased plants exhibited symptoms on leaves and pods. On leaves, lesions were irregular, necrotic, and often surrounded by a dark brown halo. On pods, necrotic and sunken lesions were developed. Colletotrichum -like colonies were consistently isolated on PDA medium and five monoconidial isolates were obtained. One isolate was selected as representative for morphological characterization, multilocus phylogenetic analysis, and pathogenicity tests. The isolate was deposited in the Culture Collection of Phytopathogenic Fungi of the Faculty of Agriculture of Fuerte Valley at the Sinaloa Autonomous University under the accession number FAVF642. Colony on PDA was flat with an entire margin, dense, initially grayish white, then became dark gray with black microsclerotia and setae. Conidia ( n = 50) were curved, hyaline, aseptate, with granular content, and measuring 20.4 to 25.8 × 2.8 to 3.9 μm. Setae were dark brown, straight, and septate. Morphological features matched those of Colletotrichum truncatum (Damm et al. 2009). For morphological identification, total DNA was extracted, and the internal transcribed spacer (ITS) region (White et al. 1990), and partial sequences of actin (ACT), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were amplified by PCR (Weir et al. 2012), and sequenced. The resulting sequences were deposited in GenBank under the accession nos. OM616022 (ITS), OM630461 (ACT), and OM630462 (GAPDH). BLASTn searches in GenBank showed 100%, 99.49%, and 99.15% identity to MT583079 (ITS), MG198003 (ACT), and MG703491 (GAPDH) of C. truncatum , respectively. A phylogenetic tree based on maximum Likelihood method and including published ITS, ACT, and GAPDH sequence data for Colletotrichum truncatum species complex was generated (Talhinhas and Baroncelli 2021). In the phylogenetic tree, the isolate FAVF642 was placed in the same clade of C. truncatum . Pathogenicity of the isolate FAVF642 was verified on 10 guar seedlings (15-day-old) by spraying a conidial suspension (1 × 10 6 spores/mL) onto leaves until runoff. Five plants noninoculated served as controls. All plants were kept in a moist chamber for 2 days, and subsequently transferred to a shade house where the temperature ranged from 20 to 30°C. The experiment was conducted twice with similar results. All inoculated leaves developed irregular and necrotic lesions 8 days after inoculation, whereas no symptoms were observed on the control leaves. The fungus was consistently re-isolated from the diseased leaves, fulfilling Koch´s postulates. Colletotrichum truncatum has been previously reported to cause guar anthracnose in India (Farr and Rossman 2022). To our knowledge, this is the first report of C. truncatum causing guar anthracnose in Mexico. This disease is an emerging problem in guar fields in Sinaloa, therefore further studies are required to understand its occurrence and impact in Mexico.

Leucophyllum frutescens (Scrophulariaceae family), commonly known as Texas sage or cenizo, is an evergreen shrub native to southwestern United States and northern Mexico. This plant is commercially sold as a native, drought-tolerant ornamental. During the spring of 2019 and 2020, typical symptoms of powdery mildew were found on cenizo plants growing as ornamentals in urban areas in the municipality of Ahome, Sinaloa, Mexico. Disease incidence was 95% from a sampled population of 120 plants. Initial symptoms of powdery mildew developed as irregular white colonies on upper leaf surfaces which expanded as infections progressed. In severe infections, leaves became distorted, exhibiting premature defoliation. Microscopic examination showed nipple-shaped appressoria. Conidiophores ( n = 30) were hyaline, cylindrical, erect, 89.4 to 134.2 μm long, and forming catenescent conidia. Foot-cells were cylindrical, 35.7 to 65.3 × 10.2 to 13.5 μm, followed by 1-3 shorter cells. Conidia ( n = 100) were hyaline, ellipsoid to ovoid, 27.9 to 40.5 × 13.8 to 18.9 μm, containing distinct fibrosin bodies. Germ tubes were simple to forked and laterally produced from the middle of conidia. Chasmothecia were not found during the sampling period on the infected leaves. Based on morphological characteristics, the fungus was identified as Podosphaera xanthii (Braun and Cook 2012). A voucher specimen (accession no. FAVF219) was deposited in the Herbarium of the Faculty of Agronomy of El Fuerte Valley at the Autonomous University of Sinaloa (Juan Jose Rios, Sinaloa, Mexico). To further confirm the identification, total DNA was extracted, and the internal transcribed spacer (ITS) region was amplified by PCR using the primers ITS5/ITS4 (White et al. 1990) and sequenced. The resulting 503 bp sequence (GenBank accession no. MT624793) had 100% coverage and 100% identity to those of P. xanthii (MT568609-MT568611, MT472035, MT309699, MT250855, MT242593). A phylogenetic tree using the maximum parsimony (MP) and maximum likelihood (ML) methods and including published ITS sequences for Podosphaera species was obtained. Phylogenetic analyses revealed that ITS sequence from FAVF219 isolate was grouped into a clade with P. xanthii . Pathogenicity was demonstrated by gently dusting conidia from infected leaves onto 50 leaves of five healthy plants. Five non-inoculated plants served as controls. All plants were covered with polyethylene bags for 48 h to maintain high humidity and were maintained in a greenhouse at temperatures ranging from 20 to 35ºC. All inoculated plants developed similar symptoms to the original observations after 19 days, whereas no symptoms of powdery mildew were observed on control plants. The fungus present on the inoculated plants was morphologically identical to that originally observed on diseased plants, fulfilling Koch's postulates. This fungus has been reported infecting members of the Cucurbitaceae in Mexico (Félix-Gastélum et al. 2017; Farr and Rossman 2020). However, to our knowledge, this is the first report of P. xanthii causing powdery mildew on a member of Scrophulariaceae, specifically L. frutescens in Mexico and worldwide. Further studies for monitoring and control strategies of powdery mildew on Texas sage are required.

Citrus anthracnose, caused by Colletotrichum spp., is a major disease in many citrus-growing regions of the world. During the spring of 2019, symptoms of petal necrosis and necrotic lesions on fruits were detected on Mexican lime ( Citrus aurantifolia ), sweet orange ( Citrus sinensis ), and grapefruit ( Citrus paradisi ) trees in three commercial orchards distributed in northern Sinaloa (El Fuerte and Ahome municipalities), Mexico. Colletotrichum -like colonies were consistently isolated on potato dextrose agar (PDA) medium from symptomatic petals and fruits, and 30 monoconidial isolates (10 per orchard) were obtained. Five isolates were selected as representative for morphological characterization, multilocus phylogenetic analysis, and pathogenicity tests. The isolates were designated as FAVF355-FAVF359 and were deposited in the Culture Collection of Phytopathogenic Fungi of the Faculty of Agronomy of El Fuerte Valley at the Autonomous University of Sinaloa (Mexico). Colonies grown on PDA at 25ºC were cottony, dense, with grayish white aerial mycelium and with pink conidial masses. Conidia ( n = 100) were cylindrical, hyaline, aseptate, 13.7 to 18.8 × 4.3 to 5.8 μm, with both ends rounded. Based on morphological features, the five isolates were tentatively identified in the Colletotrichum gloeosporioides species complex (Weir et al. 2012). For molecular identification, total DNA was extracted, and the internal transcribed spacer (ITS) region (White et al. 1990), and partial sequences of actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and β-tubulin (TUB2) genes were amplified by PCR (Weir et al. 2012), and sequenced. A phylogenetic tree based on Bayesian inference for species belonging to the C. gloeosporioides species complex was constructed. The multilocus phylogenetic analysis distinguished the isolates FAVF355-FAVF357 as C. gloeosporioides sensu stricto and the isolates FAVF358-FAVF359 as C. siamense . The sequences were deposited in GenBank (accession numbers ITS: MT850050-MT850054; ACT: MT834528-MT834532; GAPDH: MT855979-MT855982; TUB2: MT834533-MT834536). Pathogenicity of the five isolates was verified on healthy fruits of their original host species. Five fruits per isolate were inoculated using the colonized agar plug method. Fruits were wounded with a sterile toothpick and mycelial plugs (5 mm in diameter) removed from the margin of a 6-days-old culture were placed onto three wound sites in each fruit. Non-colonized agar plugs were placed on the wounds of 10 fruits used as the control. The fruits were kept in a moist chamber at 25°C for 8 days. The experiment was repeated twice. All inoculated fruits developed circular and necrotic lesions 6 days after inoculation, whereas the control fruits remained symptomless. The fungi were consistently re-isolated from the diseased fruits and were morphologically identical to that originally inoculated, fulfilling Koch´s postulates. To date, only C. gloeosporioides sensu lato and C. acutatum sensu lato has been associated with sweet orange and Mexican lime in Mexico (Farr and Rossman 2020), whereas C. gloeosporioides sensu stricto has been recently recorded in a different area (Iguala, Guerrero) of Mexico (Cruz-Lagunas et al. 2020). To our knowledge, this is the first report of C. gloeosporioides sensu stricto causing anthracnose on sweet orange, and of C. siamense on Mexican lime in Mexico, as well as C. gloeosporioides s. s. causing disease on grapefruit in Sinaloa, Mexico.