Santos Gerardo Leyva-Mir

Occurrence of Asian grapevine leaf rust disease caused by Phakopsora meliosmae-myrianthae in Mexico

During the falls of 2015 and 2016, rust symptoms were observed on grapevine leaves in a backyard garden located in Tlaxiaco, Oaxaca, Mexico. Based on morphology, analysis of the variable D1/D2 region of the large subunit rDNA, and the fulfilment of Koch’s postulates on grapevine leaves, the causal agent was identified as Phakopsora meliosmae-myrianthae. This is the first report of Asian grapevine leaf rust disease caused by Phakopsora meliosmae-myrianthae in Mexico.

Evaluación de Trampas y Atrayentes para el Monitoreo de Rhagoletis pomonella1 en Tejocote (Crataegus mexicana) en México

Resumen. El Tejocote (Crataegus spp.) es un árbol originario de México, de alto valor alimenticio ya que su fruta tiene un alto contenido de pectina que se consume en México y los EUA durante las celebraciones culturales y religiosas de fin de año. Una de sus principales plagas es la mosca de la fruta Rhagoletis pomonella, comúnmente conocida como mosca de la manzana, que puede infectar hasta 100% de sus frutos. El objetivo del estudio fue evaluar la eficacia de dos trampas con cuatro colores y dos atrayentes alimenticios para el monitoreo de la mosca de la fruta en plantaciones de Tejocote. Trampas pegajosas en forma de esfera y panel de color: amarillo, naranja, blanco y rojo, cebadas unas con Winner 360® y otras con GF-120® fueron evaluadas en tres plantaciones de Tejocote. Los datos de capturas fueron sometidos a un análisis multifactorial de varianza y a una separación de medias de Tukey para determinar que combinación de trampa es mejor para capturar adultos de R. pomonella. La mejor trampa para capturas de R. pomonella en Tejocote en el centro de México con fines de monitoreo, fue la tipo panel de color amarillo con atrayente proteína hidrolizada Winner 360® o GF-120®, con más capturas que las demás combinaciones.

First Report of Golovinomyces biocellatus Causing Powdery Mildew on Spearmint (Mentha spicata) in Mexico

Spearmint (Mentha spicata L.: Lamiaceae) is an aromatic plant that has medicinal properties. It is native to southeastern Europe and distributed around the world. During the spring of 2017, typical symptoms of powdery mildew were observed on spearmint plants in a nursery located in Texcoco, Estado de Mexico, Mexico. Symptoms appeared as white powdery masses on leaves, including petioles, and stems. The preliminary identification of fungus was performed by examination of morphological characters. Mycelium was amphigenous, rarely in thin patches, mostly effuse. Hyphal appressoria were nipple-shaped. Conidiophores were hyaline, erect, 58 to 91 μm long, and terminal on the surface of mother cells. Foot cells were almost cylindrical, 45.7 to 73.4 x 10.5 to 13.4 μm (n=30), followed by 1-3 shorter cells. Conidia produced in chains were hyaline, doliiform to ellipsoid-ovoid, 26.7 to 38.6 x 16.9 to 23.3 μm (n=100), fibrosin bodies were absent, and the germ tube was terminal. Chasmothecia were not observed. The mor...

Regional differences in the composition of Fusarium Head Blight pathogens and mycotoxins associated with wheat in Mexico

Fusarium Head Blight (FHB) is a destructive disease of small grain cereals and a major food safety concern. Epidemics result in substantial yield losses, reduction in crop quality, and contamination of grains with trichothecenes and other mycotoxins. A number of different fusaria can cause FHB, and there are significant regional differences in the occurrence and prevalence of FHB pathogen species and their associated mycotoxins. Information on FHB pathogen and mycotoxin diversity in Mexico has been extremely limited, but is needed to improve disease and mycotoxin control efforts. To address this, we used a combination of DNA sequence-based methods and in-vitro toxin analyses to characterize FHB isolates collected from symptomatic wheat in Mexico during the 2013 and 2014 growing seasons. Among 116 Fusarium isolates, we identified five species complexes including nine named Fusarium species and 30 isolates representing unnamed or potentially novel species. Significant regional differences (P < 0.001) in pathogen composition were observed, with F. boothii accounting for >90% of isolates from the Mixteca region in southern Mexico, whereas F. avenaceum and related members of the F. tricinctum species complex (FTSC) accounted for nearly 75% of isolates from the Highlands region in Central Mexico. F. graminearum, which is the dominant FHB pathogen in other parts of North America, was not present among the isolates from Mexico. F. boothii isolates had the 15-acetyldeoxynivalenol toxin type, and some of the minor FHB species produced trichothecenes, such as nivalenol, T-2 toxin and diacetoxyscirpenol. None of the FTSC isolates tested was able to produce trichothecenes, but many produced chlamydosporol and enniatin B.

First Report of Neofusicoccum algeriense Causing Dieback of Red Raspberry in Mexico

During 2014 and 2015, severe symptoms of dieback were observed in a commercial orchard of red raspberry (Rubus idaeus L.) cv. Heritage in Tangancicuaro, Michoacan, Mexico. Symptoms consisted of brown cankers and dieback on canes, accompanied by reddening and wilting of foliage, at an incidence of 5%. Internal symptoms included a brown discoloration of vascular tissues. A total of 30 stem pieces (approximately 20 cm in length) were collected from 15 diseased plants. Sixty colonies grown on potato dextrose agar (PDA) at 25oC developed a white, aerial mycelium that became olivaceous gray at the surface after 5 days. Pycnidia were produced after 2-3 weeks on autoclaved pine needles placed on water agar and were solitary or aggregated, dark brown to black, uniloculate, of 320 to 417 μm in diameter. Conidiophores were hyaline, cylindrical, smooth, thin walled, and septate. Conidia were hyaline, fusiform, base subtruncate to bluntly rounded, smooth, thin walled, aseptate, of (13-) 16 to 19 (-21) x (4-) 4.5 to 5....

CARACTERIZACIÓN DE ESPECIES DEFusariumCAUSANTES DE PUDRICIÓN DE RAÍZ DEL TRIGO EN EL BAJÍO, MÉXICO

The objectives of this study were to identify Fusarium species causing root rot in wheat produced in the Bajío of Mexico, and to determine the response of 28 wheat varieties to this disease. Fusarium spp. isolates were obtained from samples with root rot symptoms in 2014 and 2015. The fungal isolates were identified by morphological characterization and sequence analysis of ITS and TEF-1α, and also using specific primers for the detection of Fusarium species. Pathogenicity of a representative isolate of each Fusarium species was verified by immersion of seeds of 28 wheat varieties in a conidial suspension. The results of the morphological characterization, sequence analysis, and pathogenicity Recibido: 12 agosto 2016. Aceptado: 28 Febrero 2017. ISSN 0719-3882 print ISSN 0719-3890 online

Pomegranate fruit rot caused by Pilidiella granati in Mexico

During the spring of 2015, fruit rot symptoms were observed on pomegranate fruit in an orchard located in Oaxaca, Mexico. Characteristic lesions were collected and a fungus was isolated from these lesions. Based on morphological characteristics, analysis of rDNA-ITS sequences, and pathogenicity tests on pomegranate fruits, the causal agent was identified as Pilidiella granati. This is the first report of P. granati causing pomegranate fruit rot in Mexico.

FIRST REPORT OF TOBACCO ROOT ROT CAUSED BY PHYTOPHTHORA NICOTIANAE IN MEXICO

During 2014 and 2015, symptoms of root rot were observed in tobacco fields located in Veracruz, Mexico. Phytophthora colonies developing rosaceous pattern were consistently isolated on potato dextrose agar (PDA) and V8 juice agar media. Sporangia were papillate, noncaducous, measuring 40 to 49 x 33 to 37 μm, and with short pedicels. The sporangial shape was ovoid or ellipsoid. Chlamydospores were mostly solitary, intercalary, or terminal, measuring 29-33 μm in diameter. The oomycete was identified as Phytophthora nicotianae based on descriptions of Gallegly and Hong (2008). To confirm the identification, genomic DNA from a representative isolate was extracted, and the internal transcribed spacer (ITS) region was amplified by PCR and sequenced using the primers ITS5 and ITS4 (White et al., 1990). The resulting 896 bp sequence was deposited as GenBank Accession No. KR906059. BLASTn analysis showed a 97% similarity with those of P. nicotianae (GenBank Accession No. AB688370). Pathogenicity tests were performed twice on 20 healthy tobacco plants by immersion of roots in a zoospore suspension adjusted to 1 x 104 zoospores ml-1. Ten tobacco plants inoculated with sterile distilled water served as controls. Inoculated plants developed root rot symptoms after 10 days, whereas no symptoms were observed on the control plants. The oomycete present on inoculated plants was morphologically identical to that originally observed on diseased plants, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of tobacco root rot caused by Phytophthora nicotianae in Mexico.

Caracterización morfológica y molecular de aislados de Macrophomina phaseolina asociados a caña de azúcar en México

Charcoal rot caused by Macrophomina phaseolina is an important disease of sugarcane in Mexico. This study was carried out to characterize isolates of M. phaseolina obtained from sugarcane by the combination of morphological and molecular analyses. The morphological characterization of 10 isolates was performed using scanning electron microscopy and light microscopy. To confirm the morphological identification, rDNA from two representative isolates was extracted, and the internal transcribed spacer (ITS) region was amplified by polymerase chain reaction and sequenced using specific primers MpKF1 and MpKR1. Based on their morphological characteristics, all isolates were identified as M. phaseolina. Moreover, the analysis of two ITS sequences showed 100% similarity with the M. phaseolina sequences deposited in the GenBank. To our knowledge, this is the first study in the world aimed at characterizing isolates of M. phaseolina obtained from sugarcane.

First report of powdery mildew caused by Erysiphe alphitoides on Quercus rugosa in Mexico.

During September to November of 2013 and 2014, typical symptoms of powdery mildew were detected on the leaves of netleaf oak (Quercus rugosa) trees growing in the Distrito Federal (Mexico). Symptoms appeared as irregular necrotic lesions with greyish powdery masses on both sides of the leaves. The preliminary identification of fungus was done based on of morphological characters. Mycelium was amphigenous, persistent, greyish, in dense patches or effuse. Hyphal appressoria were lobed and solitary. Conidiophores were hyaline, erect, straight, length up to about 86 μm. Foot cells were cylindrical, straight, followed by 1-3 shorter cells, and forming conidia singly. Conidia were hyaline, obovoid-doliiform, 27-37x16-24 μm, with germ tubes terminal to subterminal. Conidial appressoria were lobed. Chasmothecia were not observed. The morphological characters were consistent with those of the anamorphic state of Erysiphe alphitoides (Braun and Cook, 2012). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4 and ITS5, and sequenced directly. The resulting 647 bp sequence was deposited in GenBank (accession No. KR269919). A GenBank BLASTn search of this sequence revealed 99% similarity with three ITS sequences of E. alphitoides (AB292699, AB292702 and AB292704). Based on the morphological data and ITS sequence analysis, the fungus was identified as E. alphitoides. To our knowledge, this is the first report of E. alphitoides causing powdery mildew on netleaf oak in Mexico.