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In 2022, potato plants exhibiting symptoms of stem canker were observed in commercial fields in northern Sinaloa, Mexico. Morphological characterisation of two isolates allowed the identification of Ceratobasidium sp., whereas molecular analysis using sequences of the ITS region and the rpb2 gene distinguished the isolates within the Anastomosis Group A (AG‐A). Both isolates induced symptoms of stem canker on inoculated potato plants and exhibited median EC50 values of 19.46, 5.20, 62.71 and 0.33 μg mL−1 for the fungicides thiophanate methyl, pyraclostrobin, prochloraz and penflufen, respectively. However, the two isolates differed by > 65‐fold in their EC50 value relative to pyraclostrobin. [ABSTRACT FROM AUTHOR]

In August 2023, severe symptoms of crown and root rot were detected on blueberry plants in two commercial fields located in Guasave, Sinaloa, Mexico. Colonies with oomycete morphology were obtained and two isolates were purified. The causal agent was identified as Phytopythium helicoides by a combination of morphological studies, pathogenicity tests, and phylogenetic analysis including data from internal transcribed spacer and large subunit sequences. This is the first report of P. helicoides causing crown and root rot of blueberry worldwide. [ABSTRACT FROM AUTHOR]

Turcicum leaf blight (TLB) of maize is caused by Exserohilum turcicum. The TLB resistance is mainly associated with qualitative race‐specific resistance that is linked to several Ht genes namely Ht1, Ht2, Ht3, HtM, HtN, HtNB and HtP. However, quantitative TLB resistance also occurs, but its mechanisms are poorly understood. In this study, tolerance or insensitivity to chlorosis and necrosis of E. turcicum culture filtrate was associated with quantitative TLB resistance. A novel detached maize seedling assay was developed for E. turcicum culture filtrate using methanol‐treated modified Fries medium. Screening of E. turcicum isolates of races 2, 3, 23, 3 N, 23 N and 123 N against 61 maize inbred lines with diverse levels of resistance to TLB was conducted in the greenhouse by fungal inoculation and the detached seedling culture filtrate assay. Using an isolate of race 123 N, which can overcome all the qualitative resistance genes, a simple linear regression model (R2 = 0.68, p =.90) for the 61 inbred lines was established between disease severity from foliar inoculations and culture filtrate symptom rating of the detached seedling assay. Two maize lines CML474 and CML483 had relatively high culture filtrate symptom ratings but very low disease severity with foliar inoculation indicating that these sources of quantitative TLB resistance may be unrelated to tolerance to E. turcicum culture filtrates, whose effect on seedlings could be due to the toxin known as HT‐toxin or monocerin. [ABSTRACT FROM AUTHOR]

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In September 2022, symptoms of leaf anthracnose were observed on desert rose (Adenium obesum) plants distributed in parks and gardens in Culiacán, Sinaloa, Mexico. Two morphotypes of Colletotrichum isolates were obtained from symptomatic tissues. Based on morphological characterization in combination with multilocus phylogenetic analyses including data from internal transcribed spacer, actin, glyceraldehyde‐3‐phosphate dehydrogenase, and β‐tubulin, and pathogenicity tests, it was confirmed that C. siamense and C. truncatum are the causal agents of the disease. This is the first report of C. siamense and C. truncatum causing leaf anthracnose in desert rose worldwide. [ABSTRACT FROM AUTHOR]

Dieback of mamey sapote (Pouteria sapota) grafts is the most important disease during vegetative propagation in commercial nurseries. In 2008, Lasiodiplodia theobromae identified by cultural, morphological and molecular characterization was associated with this disease in 97 % of necrotic rootstocks and scions samples from a nursery in Guerrero, México. The fungus was inoculated onto the binding site of El Mexicano grafted plants. Dieback symptoms and gradual drying with cracking of the bark from the apex to the base of the scion were observed 30 d after inoculation. Abundant mycelia and pycnidia were found on inoculated scions and graft union areas, in the periderm, and on leaf scars. Transverse sections of inoculated scions tissues showed pycnidia. Parenchyma cells of cortex and phloem collapsed and died. L. theobromae mycelia and red inclusions, probably of phenolic nature, were observed in both xylem vessels and pith parenchyma cells. To our knowledge, this is the first study that provides pathogenicity and histopathological data about a disease caused by L. theobromae during the grafting process. [ABSTRACT FROM AUTHOR]

AbstractChickpea wilt, caused by a complex of soilborne fungi (Fusarium spp. Macrophomina phaseolina, Rhizoctonia solani, Sclerotium rolfsii, and Sclerotinia sclerotiorum), is the most important disease of chickpeas (Cicer arietinum) in Mexico. The aims of this study were to characterize Trichoderma isolates using a combination of phenotypic and molecular approaches and to evaluate their antagonistic activity against soilborne fungi associated with chickpea wilt. A total of 30 Trichoderma isolates were obtained from rhizospheric soil samples collected from chickpea fields in different locations of Sinaloa, Mexico. Dual confrontation assays showed the potential antagonistic effect of Trichoderma isolates against F. languescens, M. phaseolina, R. solani, S. rolfsii, and S. sclerotiorum. Five Trichoderma isolates (FAVF335, FAVF340, FAVF345, FAVF349, and FAVF351) exhibited mycelial growth inhibition of the five pathogens that ranged from 56 to 71%. These isolates were characterized using cultural, morphological, and molecular studies and tested in vivo for their ability to control soilborne pathogens in two chickpea cultivars (Blanco Sinaloa-92 and P2245) under greenhouse conditions. Phylogenetic analysis based on a combined ITS, EF-1α, and rpb2 sequence dataset identified T. afroharzianum (FAVF345, FAVF349, and FAVF351) and T. longibrachiatum (FAVF335 and FAVF340). Coating of chickpea seeds with T. longibrachiatum (FAVF335 and FAVF340) significantly reduced the disease severity and improved the plant growth-promoting attributes. [ABSTRACT FROM AUTHOR]

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., (Copyright © 2014 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.)