AGENTES ASOCIADOS Y SU PAPEL EN LA DECLINACIÓN Y MUERTE DE ENCINOS (QUERCUS, FAGACEAE) EN EL CENTRO-OESTE DE MÉXICO

This study was carried out to identify bioticand abiotic agents and to determine theirrole in oak decline and death in five statesof the Mexican Republic: Aguascalientes,Colima, Guanajuato, Jalisco and Nayarit.Two 0.1-ha permanent plots wereestablished at the most representativeforested areas with tree death, diebackand bleeding cankers in these statesand sampled during 2003, 2004 and 2005(10 plots in total). Field observations weremade, and foliage, branch, trunk and soilsamples were collected to identify theassociated agents in each plot. Isolates frombleeding cankers were made in situ. Themost commonly found biotic agents were:Phytophthora cinnamomi, Pythium sp.,Hypoxylon antropunctatum, Ganodermaspp., Armillaria sp., Apiognomoniaquercina, the dwarf mistletoe(Phoradendron villosum), bark borers,insect defoliators and livestock overgrazing.Among the abiotic stress factors commonlyfound were the effects due to lowtemperature-lack of water and fire. Basedon their incidence, P. cinnamomi, H.antropunctatum and low temperature-lackof water were considered the most importantcontributors to the decline and death of theoaks. P. cinnamomi was identified in four ofthe 10 plots, mainly in Colima and Jalisco;H. antropunctatum was detected in sixplots, particularly in Nayarit andAguascalientes. Stem cankers (cracks) dueto low temperature-lack of water wereobserved in four plots, damaging 52% of the trees in Aguascalientes and 24% inGuanajuato. It was concluded that P.cinnamomi is killing some oak species, H.antropunctatum is colonizing weakenedtrees, and low temperature-lack of water iscausing stress and in some cases death inoaks.Este estudio tuvo como objetivo identificary determinar el papel tanto de los factoresbióticos como de los abióticos asociados ala declinación y muerte del encino en cincoestados de la República mexicana: Aguascalientes, Colima, Guanajuato, Jalisco yNayarit. Para esto, se establecieron dossitios permanentes de 0.1 ha en cada una delas áreas más representativas (con arboladomuerto, con muerte regresiva y cancros conexudado) de los estados mencionados (10sitios en total), los cuales fueron muestreados durante 2003, 2004 y 2005. Sehicieron observaciones y colectas en campode follaje, ramas, tronco y suelo, paraidentificar a los diferentes agentes de dañoen cada sitio. Se realizaron aislamientosin situ de cancros con exudado en mediosespecíficos. Los agentes bióticos máscomunes fueron: Phytophthora cinnamomi,Pythium sp., Hypoxylon antropunctatum,Ganoderma sp., Armillaria sp.,Apiognomonia quercina, el muérdagoenano (Phoradendron villosum), barrenadores, defoliadores y sobrepastoreo. Entre los abióticos causantes de estrés ymuerte, destacaron los daños ocasionadospor las bajas temperaturas-falta de aguay fuego. Con base en su incidencia, P.cinnamomi, H. antropunctatum y las bajastemperaturas-falta de agua son considerados los factores de mayor importanciaen la declinación y muerte del encino. P.cinnamomi fue identificado en cuatro delos diez sitios, particularmente de Colimay Jalisco; H. antropunctatum fué detectadoen seis de diez, principalmente en losrodales de Nayarit y Aguascalientes. Loscancros de troncos (rajaduras), debido a lasbajas temperaturas-falta de agua, seobservaron en cuatro sitios, afectando al52% de los árboles en Aguascalientes y24% en Guanajuato. Se concluye que P.cinnamomi está ocasionando la muertede algunas especies de encino, H.antropunctatum está coloni-zando árbolesdebilitados y las bajas temperaturas-faltade agua están participando como agentescausantes de estrés y muerte en algunoscasos

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

Fungi associated to bark lesions of Eucalyptus globulus stems in plantations from Uruguay Fungos asociados as lesões da casca do caule de Eucalyptus globulus em plantações no uruguai

Trees with stem bark lesions are frequently observed in Eucalyptus globulus Labill. plantations, particularly in the central west region of Uruguay. These lesions constitute a problem for trunk decortications at harvest and they also facilitate the access of fungi that could cause wood decay. Seven, three and oneyear-old plantations, located at three sites in close proximity were selected. Four types of trunk lesions were present in trees regardless the age of plantation and more than one type was found in each plantation. The aim of this study was to investigate the fungal composition associated with these lesions and compare them to healthy tissues and try to find out the origin of these symptoms. Another purpose was to elucidate the real role of the fungi considered pathogens by means of experimental inoculations. Segments from lesions and healthy tissues yielded 897 fungal isolates belonging to 32 taxa, 681 isolates from bark lesions and 216 from healthy tissues. Both healthy and symptomatic tissues showed similar fungal species composition, but with differences in frequencies of colonization. Cytospora eucalypticola Van der Westhuizen, Botryosphaeria spp., Pestalotiopsis guepinii (Desm.) Stey. and Penicillium spp. were the dominant species isolated. As symptoms were not reproduced after experimental inoculation with Botryosphaeria ribis Grossenb. & Duggar and B. eucalyptorum Crous, & M.J. Wingf, it could be suggested that these lesions were originated by unfavorable environmental conditions. The frost that occurred for several days out of season and flooding may have been involved in the development of bark lesion.<br>As lesões na casca de Eucalyptus globulus Labill. são frequentemente observadas nas plantações da Região Centro-Oeste do Uruguai. Constituem problema para o descortiçamento na colheita e, além disso, facilita a penetraçao de fungos apodrecedores da madeira. Selecionaram-se plantações com 1, 3 e 7 anos de idade, em três localidades próximas, para serem estudadas. Quatro tipos de lesões em caule foram encontrados nas árvores, independentemente da idade destas. Numa mesma plantaçao, havia mais de um tipo de lesão. Os objetivos deste estudo foram identificar a composição da micobiota associada a cada tipo de lesão da casca, compará-la com a dos tecidos sadios e investigar a origem desses sintomas. Outro objetivo foi verificar o papel de alguns colonizadores considerados patógenos, através de inoculações experimentais. Obtiveram-se 897 isolamentos correspondentes, a 32 taxa, 681 de casca lesionada e 216 dos tecidos sadios. Tanto os tecidos lesionados quanto os sadios mostraram composição micobiota específica similar, mas diferentes na frequência de colonização. Cytospora eucalyptica Van der Westhuizen, Botryosphaeria spp., Pestalotiopsis guepinii (Desm.) Stey. e Penicillum spp. foram as espécies dominantes isoladas. Devido à não reprodução dos sintomas depois da inoculação experimental com Botryosphaeria ribis Grossenb. & Duggar e B. eucalyptorum Crous & Wingf, foi sugerido que as lesões aqui estudadas fossem originadas de condições ambientais desfavoráveis. A ocorrência de geadas fora de estação associada à inundação pode ter influenciado o desenvolvimento dessas lesões na casca