Neoerysiphe sechii (Ascomycota: Erysiphales): A new species of powdery mildew found on Sechium edule and Sechium mexicanum (Cucurbitaceae) in Mexico

A novel species of powdery mildew, Neoerysiphe sechii sp. nov., has been proposed based on host, morphological characteristics, and gene sequences. The new species was found on chayote (Sechium edule) and a wild species, chayotillo (S. mexicanum), in Veracruz, Mexico. This novel species was identified as a member of Neoerysiphe, based on the morphological characteristics of the anamorph: catenescent conidia, lobed appressoria, and Striatoidium-type conidia. No teleomorph was observed. Neoerysiphe sechii is distinguished by foot cells that are frequently cylindrical with a slight widening at the base, a feature not observed previously in other species in the genus. An Erysiphales-specific primer was designed for the 5′ end of the ITS region of the nuclear rDNA. Independent and concatenated phylogenetic analyses with our rDNA sequences and sequences available in GenBank for Neoerysiphe spp. confirmed that the powdery mildew specimens found in Sechium spp. form an independent and strongly supported lineage. This is the first report of a Neoerysiphe species causing powdery mildew on members of Cucurbitaceae, and it is the second species reported from Mexico after N. cumminsiana. Neoerysiphe sechii is found on cultivated and endemic hosts in Mexico, suggesting that the fungus itself may be endemic.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Uso de Trichoderma asperellum y lombricomposta para el control de secadera en Physalis ixocarpa Brot

The wilt disease caused by the fungal complex can cause losses of 50% in Physalis ixocarpa. The objective of this work was to determine the effectiveness of Trichoderma asperellum and vermicompost as a biocontrol strategy in in vitro and greenhouse conditions. The antagonism evaluation was carried out of which the strain with the highest degree of inhibition was obtained, inoculating 5 g of each of the pathogens; the antagonist was inoculated five days later, with a concentration of 1x106 microconidia mL-1, when using a vermicompost substrate for cattle, sheep, and alluvial soil. Evaluating different agronomic variables, a completely randomized design with factorial arrangement with a significance level of p<0.005 was used. T. asperellum inhibited pathogens with 83% compared to 100%; the treatment of vermicompost of sheep + alluvial soil + T. asperellum was the best substrate

Powdery mildew on common bean (Phaseolus vulgaris L.) in Northern Sinaloa, Mexico

Powdery mildew of beans is a disease in Northern Sinaloa state in Mexico, however, the identity of the causal agent, which is an obligate parasite, has not yet been elucidated due to lacking formation on its teleomorph. The objective of this study was to identify the causal agent of the disease through morphometric studies of the anamorph, and molecular techniques based on the ITS (internal transcribed spacers) region of the ribosomal DNA. We collected ten samples of different bean varieties that exhibited symptoms of the disease in the Fuerte Valley during the 2006-2007 fall/winter growing season. Morphological characteristics of the anamorph and the molecular phylogenetic analysis revealed that the causal fungus belongs to the mitosporic genus Oidium subgenus Pseudoidium. All samples had conidiophores of the Pseudoidium type, whose conidia were mainly cylindrical, and when partially collapsed, their walls showed longitudinal wrinkling, except on their ends, where the wall appeared almost smooth. Phylogenetic analysis of the ITS1-5.8S-ITS2 rDNA region revealed that our collections of powdery mildew of beans are closely related to specimens of Erysiphe diffusa associated with soybeans and to an Erysiphe sp. associated with Phaseolus vulgaris

Halo-spot and external stem necrosis of tomato caused by Pseudomonas syringae in Sinaloa, Mexico

Pseudomonas syringae pv. tomato has been observed in the fields in Sinaloa causing typical symptoms of bacterial speck. During the 2004–2005 growing seasons atypical symptoms were observed in tomato varieties grown in Sinaloa, consisting of external necrosis of stems, petioles, peduncles and fruit calyxes. Although the disease affected 80–90% of the foliage, there were no speck symptoms on fruit. The objectives of this study were to: (a) identify the causal agent of the disease, (b) determine the sensitivity of the pathogen to various antibiotics in vitro and (c) test their efficacy for controlling the disease in tomato plants under greenhouse conditions. The results of the present study indicate that biochemical and physiological characteristics as well as the molecular studies of bacterial isolates associated with the yellow halo spot and external necrosis of the stem of tomato are closely related to P. syringae pv. tomato, although whether these isolates indeed belong to pathovar tomato needs further assessment. The efficacy of gentamicin sulfate and oxytetracycline chlorhydrate in vitro, and in planta under greenhouse conditions, represents a possible option for the chemical control of the disease under field conditions. The results also indicate a reduced sensitivity of the characterized isolates to copper hydroxide as compared with the above mentioned antibiotics in northern Sinaloa

First Report of Powdery Mildew (Pseudoidium anacardii) of Mango Trees in Sinaloa, Mexico

Powdery mildew of mango is an important disease in Mexico's northern Sinaloa state. Identification of the causal fungal agent has been hindered by the absence of information regarding its teleomorph, as well as a detailed morphometric analysis of the anamorph and molecular characterization. The first symptoms of the disease appear in mango inflorescences of early February, and it subsequently affects young fruits. The disease progresses during March and early April, causing significant fruit abortion and a scabby appearance in a high percentage of fruits that remain attached to the trees. We observed the disease on inflorescences but not in leaves during our sampling period. Powdery mildew specimens were collected during 2011 and 2012 and included Kent and Keith varieties from commercial orchards, and creole materials from backyards of private residences in the Ahome and Fuerte Counties of northern Sinaloa, Mexico. Symptomatic inflorescences were analyzed morphologically. Conidiophores and conidia were prepared by touching the whitish lesions with clear adhesive tape, which was then placed over microscope slides with a drop of distilled water and observed under a compound microscope. The anamorph structures of the pathogen were measured. The mycelium was septate and ramified on the surface of the host, forming a dense coat of branching hyphae. The mycelium had a diameter of 2.5 to 8.7 μm; conidiophores (Pseudoidium type) emerged from the superficial mycelium, were unbranched, and consisted of 1 to 3 cells with conidia forming singly from the apex. The length of the conidiophores varied from 30.0 to 77.5 μm; the foot cell of the conidiophores was straight, 10.0 to 47.5 μm long and with a diameter of 5.0 to 15.5 μm across its midpoint. Conidia without fibrosin bodies were borne singly, and were ellipsoid/ovoid, 22.5 to 46.2 μm long and 15.0 to 27.5 μm wide. Eighty percent of the germ tubes were forked (lobed); the rest were simple, emerged from the end, and were occasionally on the side of the conidia. Germ tubes ranged from 2.0 to 7.2 μm at the midpoint. The surface of the conidia appeared smooth under the scanning electron microscope, and elliptical conidia appeared constricted at their ends; this, however, was not observed in the ovoid conidia. In both cases, the terminal end of the conidia was smooth. The teleomorph was not found. Molecular and phylogenetic analysis of the ITS rDNA (2) region showed that samples are closely related to specimens of Pseudoidium anacardii (1) (teleomorph: Erysiphe quercicola [4]) collected from mango trees in diverse countries. Measurements of somatic and asexual structures are in agreement with descriptions of P. anachardii (formerly known as Oidium mangiferae) from India (3). The nucleotide sequences derived from this research were deposited in GenBank (Accession Nos. JX893951 to JX893957). To our knowledge, this is the first report of P. anacardii associated to mango inflorescences in Sinaloa, Mexico. Due to the economic importance of powdery mildew of mango trees in Sinaloa, future research directions should focus on finding the teleomorph of the fungus to support its identity