Efecto de Trichoderma y Bacillus en la dinámica poblacional de Fusarium spp. en agave tequilero (Agave tequilana Weber. var. Azul) en Jalisco.

La marchitez es uno de los problemas fitosanitario más importantes en el agave tequilero Agave tequilana Weber var. Azul, enfermedad que esta asociada con varios microorganismos y que principalmente se presenta en plantaciones de más de 2 años de edad. Entre los posibles agentes causales de esta enfermedad se reportan a varias especies de Fusarium spp., así como a Thielaviopsis paradoxa. En el presente trabajo se planteó el de inocular con organismos benéficos plantas de agave tequilero que se usan como material propagativo en vivero para nuevas plantaciones, como parte de un manejo preventivo e integrado del cultivo. En este trabajo se estudió en vivero (Rancho El Indio, Tequila, Jalisco) y en campo, en plantaciones comerciales de agave en las localidades de Ahualulco y Tecalitlán, Jalisco, el establecimiento y desarrollo de aislados nativos de especies de Trichoderma harzianum, T. virens y T. aureoviride y la presentación comercial de la bacteria Bacillus subtilis, aislados que se inocularon en plantas de agave en vivero. También se estudió el posible efecto de los organismos benéficos sobre la dinámica poblacional de propágulos de Fusarium spp., en plantas de agave a nivel de vivero y en campo, determinando en campo la flora microbiana nativa previo a los ensayos. En ambos casos, en vivero y en campo, se registraron las variables siguientes: unidades formadoras de colonias (UFC) de los organismos citados por gramo de suelo y características agronómicas de las plantas de agave como altura, cobertura y contenido de clorofila. Las plantas tratadas desde vivero tuvieron una menor densidad de UFC de Fusarium spp., y un buen establecimiento en vivero de T. harzianum, T. aureoviride y B. subtilis, así como la mezcla de los últimos. Sin embargo en campo, su comportamiento y desarrollo de estos organismos benéficos se ve influenciado por las condiciones climáticas y características propias de cada nicho ecológico que se encuentra en la rizosfera que comparte la planta con flora microbiana nativa y condiciones físicas de suelo. En campo se encontró que B. subtilis tolera temperatura de 32 a 34oC y periodos de sequia con humedad relativa por debajo del 40%; mientras que Trichoderma si se ve afectado y disminuido en estos periodos críticos. Por el contrario, en áreas con temperaturas similares pero mayor humedad relativa cercana al 60%, Trichoderma se adapta fácilmente, no obstante que ya existen cepas nativas bien establecidas, las cuales desplazaran poco a poco a las introducidas debido a que han coevolucionado con el ambiente y el hospedante. Con ambos organismos y en las localidades de estudio, Fusarium spp., se mantuvo con densidades menores a las de los organismos benéficos. _______________ EFFECT OF TRICHODERMA AND BACILLUS ON THE POPULATION DYNAMICS OF Fusarium spp:, ON AGAVE TEQUILERO Agave tequilana Weber var. AZUL IN JALISCO. ABSTRACT: The agave wilt is one of the most important plant pathology problems of the agave tequliero Agave tequilana Weber var. Azul, disease that has been associated with several plant pathogens such as Fusarium spp., and Thielaviopsis paradoxa, and this disease is present mainly on crops of 2 o more years old. In the present study agave tequilero plants that are used as propagative plant material were inoculated with beneficial organisms, and as a part of a preventive and integrated crop management strategy. Experiments were established in a greenhouse (Rancho el Indio, Tequila, Jalisco) condition and on two commercial agave crops, in the localities of Ahualulco and Tecalitlán, Jalisco, in order to study the possible establishment and later development of native isolate of Trichoderma harzianum, T. virens y T. aureoviride, and the commercial formulation of the bacteria Bacillus subtilis. These isolates were inoculated in the agave plants grown in the greenhouse. The possible effect of beneficial organisms on the population dynamics of Fusarium spp., present on agave plants growing on the greenhouse and the commercial agave plantations was also studied, where the microbial compositions was determined before the experiments were established. In both cases, at the greenhouse and the commercial agave plantation, the following variables were recorded: precursor units of colonies (PUC) of the beneficial organisms form the soil, content of chlorophyll, height and width of the agave plants were recorded. Treated agave plants had less PUC densities of Fusarium spp., and had a good establishment of T. harzianum, T. aureoviride and B. subtilis at the greenhouse, as well as with the mixture of the last ones. However, at the commercial plantation, the behavior and development of these beneficial organisms were affected by characteristic weather conditions of each ecological niche that is present at the rhizosphere, where the plant has an association with the native microbiological flora and the physical properties of the soil. At the commercial agave plantations B. subtilis may tolerate temperatures between 32 to 34ºC and wet extended conditions, with 40% relative humidity, while Trichoderma has been affected and reduced for such weather conditions. However, in regions with similar temperatures but with high relative humidity around 60%, Trichoderma could adapt very easily, regardless if native strains already existed, which may displace in some times the introduced ones; this is because they had co-evolved with the weather and the host. Fusarium spp., were maintained at low levels compared to the introduced beneficial organisms at both experimental sites.Tesis (Doctorado en Ciencias, especialista en Fitopatología).- Colegio de Postgraduados, 2013.Consejo Nacional de Ciencia y Tecnología (CONACYT)

HONGOS CAUSANTES DE ENFERMEDADES POSTCOSECHA EN CHAYOTE (Sechium edule (Jacq.) SW.) Y SU CONTROL IN VITRO

El fruto de chayote (Sechium edule (Jaqc.) Sw.) es una hortaliza de exportación de importancia para México y Costa Rica. El proceso comercial exige cumplir con estándares de calidad, que implican frutos sanos y libres de defectos. Sin embargo, debido a las condiciones de alta humedad que se desarrollan en los frutos empacados en películas plásticas, se han presentado rechazos en el mercado de exportación, por la presencia de enfermedades fungosas. El objetivo de este trabajo fue identificar morfológica (microscopía óptica y electrónica de barrido) y molecularmente (PCR: Polimerase Chain Reaction) las especies de hongos causales de las principales enfermedades postcosecha de chayote en frutos infectados procedentes de huertas comerciales para exportación, así como probar in vitro la efectividad de diversos productos comerciales en la inhibición del crecimiento de dichos hongos. Los resultados mostraron a Didymella bryoniae como el causante de “gomosis de las cucurbitáceas” y a Fusarium oxysporum y F. solani como causales de fusariosis o ahogamiento de guías; estos patógenos dañan la parte basal y media de frutos comerciales, además de Chaetomium globosum, un asociado al proceso infeccioso de Fusarium sp., como saprófito no patógeno. La inoculación con Bacillus subtilis presentó una inhibición efectiva (0,01 mg.l-1 i.a) en las pruebas in vitro contra Didymella bryoniae, Fusarium oxysporum y F. solani; el fungicida más efectivo contra los 2 primeros fue Tebuconazole-trifloxystrobin, con una DL50 de 0,0116 y 0,0106 mg.l-1 respectivamente; no así contra F. solani, cuyo mayor control fue registrado con procloraz, con DL50 de 0,0042 mg.l-1. Estos resultados contribuyen al reconocimiento de las enfermedades fungosas más importantes en chayote y su perspectiva de control durante el manejo postcosecha de frutos para exportación

Efficacy of Biorational Products for Managing Diseases of Tomato in Greenhouse Production

Gray mold (Botrytis cinerea), late blight (Phytophthora infestans), powdery mildew (Leveillula taurica), pith necrosis (Pseudomonas corrugata), and bacterial canker (Clavibacter michiganensis) are major diseases that affect tomato (Solanum lycopersicum L.) in greenhouse production in Mexico. Management of these diseases depends heavily on chemical control, with up to 24 fungicide applications required in a single season to control fungal diseases, thus ensuring a harvestable crop. While disease chemical control is a mainstay practice in the region, its frequent use increases the production costs, likelihood of pathogen-resistance development, and negative environmental impact. Due to this, there is a need for alternative practices that minimize such effects and increase profits for tomato growers. The aim of this study is to evaluate the effect of biorational products in the control of these diseases in greenhouse production. Four different treatments, including soil application of Bacillus spp. or B. subtilis and foliar application of Reynoutria sachalinensis, Melaleuca alternifolia, harpin αβ proteins, or bee honey were evaluated and compared to a conventional foliar management program (control) in a commercial production greenhouse in Central Mexico in 2016 and 2017. Disease incidence was measured at periodic intervals for six months and used to calculate the area under the disease progress curve (AUDPC). Overall, the analysis of the AUDPC showed that all treatments were more effective than the conventional program in controlling most of the examined diseases. The tested products were effective in reducing the intensity of powdery mildew and gray mold, but not that of bacterial canker, late blight, and pith necrosis. Application of these products constitutes a disease management alternative that represents cost-saving to tomato growers of about 2500 U.S. dollars per production cycle ha−1, in addition to having less negative impact on the environment. The products tested in this study have the potential to be incorporated in an integrated program for management of the examined diseases in tomato in this region

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

La pudrición carbonosa, causada por Macrophomina phaseolina, es una enfermedad importante de la caña de azúcar en México. Este estudio se realizó con el objetivo de caracterizar aislados de M. phaseolina obtenidos de caña de azúcar mediante análisis morfológicos y moleculares. La caracterización morfológica de 10 aislados se llevó a cabo con el uso de microscopia electrónica de barrido y microscopia de luz. Para confirmar la identificación, se extrajo el ADNr de 2 aislados representativos, y la región del espaciador interno transcrito (ITS) se amplificó mediante la reacción en cadena de la polimerasa y se secuenció usando los iniciadores específicos MpKF1 y MpKR1. Los aislados se identificaron como M. phaseolina con base en la morfología. El análisis de secuencias ITS mostró 100 % de similitud con las secuencias de M. phaseolina depositadas en el GenBank. Para nuestro conocimiento, este es el primer estudio del mundo enfocado a caracterizar aislados de M. phaseolina obtenidos de caña de azúcar

Ocurrencia de hongos y etiología de la secadera de la fresa con diferentes sistemas de manejo agronómico

In México, strawberry dry wilt (Fragaria x ananassa) has been associated with a fungus complex in which only the implication of Fusarium oxysporum (Fox) is evident. Therefore, in the present study the association of fungi and pseudofungi with the disease was determined in different systems of agronomical management, and pathogenicity was verified. Two samplings were made in the 2002/03 season and three in 2003/04 in 16 localities of the Valley of Zamora, Michoacán, México, where 2640 sections of roots and 365 of necrotic crowns were sown, along with 400 sections of asymptomatic tissue in potato-dextrose-agar (PDA) culture medium and a selective medium with antibiotics and PCNB (PARPH) fungicide. Fox, F. solani (Fso), Cylindrocarpon sp. (Cyl), Pythium aphanidermatum (Pyt), Phytophthora sp. (Phy), Rhizoctonia fragariae (Rhi), Verticillium albo-atrum (Ver) and Colletotrichum sp. (Col) were associated with the dry wilt. Fox was the most frequent species (p=0.05) and the only one that showed an increase from flowering to fructification of 47 to 62% in root and 77 to 83% in crown. In plantations with plastic mulch and drip irrigation (A + G), Fox decreased by 18% with respect to unmulched soil with gravity irrigation, whereas Cyl increased by 15% in A + G (p=0.05). The clay and clay loam soil contrasted in the detection of Fox (46.8 and 12.4%) and Rhi (9.1 and 43.7%). Symptoms of wilting with necrosis in root and crown and general death were reproduced with individual inoculations of Fox (100%), Pyt (100%), Phy (100%), Rhi (60%) and combinations of Fox with Rhi (100%), Pyt (100%) and Cyl (100%). This is the first report that implies Phytophthora sp., P. aphanidermatum and R. fragariae as causal pathogens of dry wilt in México. The morphological identification of Fox and Rhi was confirmed by sequencing of the intergenic region of the rDNA

Agentes asociados y su papel en la declinación y muerte de encinos (quercus, fagaceae) en el centro-oeste de México

ABSTRACT This study was carried out to identify biotic and abiotic agents and to determine their role in oak decline and death in five states of the Mexican Republic: Aguascalientes, Colima, Guanajuato, Jalisco and Nayarit. Two 0.1-ha permanent plots were established at the most representative forested areas with tree death, dieback and bleeding cankers in these states and sampled during 2003, 2004 and 2005 (10 plots in total). Field observations were made, and foliage, branch, trunk and soil samples were collected to identify the associated agents in each plot. Isolates from bleeding cankers were made in situ. The most commonly found biotic agents were: Phytophthora cinnamomi, Pythium sp., Hypoxylon antropunctatum, Ganoderma spp., Armillaria sp., Apiognomonia quercina, the dwarf mistletoe (Phoradendron villosum), bark borers, insect defoliators and livestock overgrazing. Among the abiotic stress factors commonly found were the effects due to low temperature-lack of water and fire. Based on their incidence, P. cinnamomi, H. antropunctatum and low temperature-lack of water were considered the most important contributors to the decline and death of the oaks. P. cinnamomi was identified in four of the 10 plots, mainly in Colima and Jalisco; H. antropunctatum was detected in six plots, particularly in Nayarit and Aguascalientes. Stem cankers (cracks) due to low temperature-lack of water were observed in four plots, damaging 52% of the trees in Aguascalientes and 24% in Guanajuato. It was concluded that P. cinnamomi is killing some oak species, H. antropunctatum is colonizing weakened trees, and low temperature-lack of water is causing stress and in some cases death in oaks.RESUMEN Este estudio tuvo como objetivo identificar y determinar el papel tanto de los factores bióticos como de los abióticos asociados a la declinación y muerte del encino en cinco estados de la República mexicana: Aguascalientes, Colima, Guanajuato, Jalisco y Nayarit. Para esto, se establecieron dos sitios permanentes de 0.1 ha en cada una de las áreas más representativas (con arbolado muerto, con muerte regresiva y cancros con exudado) de los estados mencionados (10 sitios en total), los cuales fueron muestreados durante 2003, 2004 y 2005. Se hicieron observaciones y colectas en campo de follaje, ramas, tronco y suelo, para identificar a los diferentes agentes de daño en cada sitio. Se realizaron aislamientos in situ de cancros con exudado en medios específicos. Los agentes bióticos más comunes fueron: Phytophthora cinnamomi, Pythium sp., Hypoxylon antropunctatum, Ganoderma sp., Armillaria sp., Apiognomonia quercina, el muérdago enano (Phoradendron villosum), barrenadores, defoliadores y sobrepastoreo. Entre los abióticos causantes de estrés y muerte, destacaron los daños ocasionados por las bajas temperaturas-falta de agua y fuego. Con base en su incidencia, P. cinnamomi, H. antropunctatum y las bajas temperaturas-falta de agua son considerados los factores de mayor importancia en la declinación y muerte del encino. P. cinnamomi fue identificado en cuatro de los diez sitios, particularmente de Colima y Jalisco; H. antropunctatum fué detectado en seis de diez, principalmente en los rodales de Nayarit y Aguascalientes. Los cancros de troncos (rajaduras), debido a las bajas temperaturas-falta de agua, se observaron en cuatro sitios, afectando al 52% de los árboles en Aguascalientes y 24% en Guanajuato. Se concluye que P. cinnamomi está ocasionando la muerte de algunas especies de encino, H. antropunctatum está coloni-zando árboles debilitados y las bajas temperaturas-falta de agua están participando como agentes causantes de estrés y muerte en algunos casos

The Need and Opportunity to Update the Inventory of Plant Pathogenic Fungi and Oomycetes 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