Resumen

ALVARADO-ROSALES, D. et al. AGENTES ASOCIADOS Y SU PAPEL EN LA DECLINACIÓN Y MUERTE DE ENCINOS (QUERCUS, FAGACEAE) EN EL CENTRO-OESTE DE MÉXICO. Polibotánica [online]. 2007, n.23, pp.1-21. ISSN 1405-2768.

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.

Palabras llave : Quercus spp.; oak; decline; P. cinnamomi; H. antropunctatum; low temperature-lack of water.

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