Small-Scale Abiotic Factors Influencing the Spatial Distribution of Phytophthora cinnamomi under Declining Quercus ilex Trees

2020

Monographie

40001294

Phytophthora root rot is considered one of the main factors associated with holm oak (Quercus ilex L.) mortality. The eectiveness and accuracy of soilborne pathogen and management could be influenced by soil spatial heterogeneity. This factor is of special relevance in many aorestation of southwestern Spain, which were carried out without phytosanitary control of the nursery seedlings. We selected a study area located in a 15 year-old aorestation of Q. ilex, known to be infested by Phytophthora cinnamomi Rands. Soil samples (ntotal = 132) were taken systematically from a grid under 4 trees, and analysed to quantify 12 variables, the colony forming units (cfu) of P. cinnamomi plus 11 physical and chemical soil properties. The combined analysis of all variables was performed with linear mixed models (GLMM), and the spatial patterns of cfu were characterised using an aggregation index (Ia) and a clustering index () by SADIE. Cfu values ranged from 0 to 211 cfu g􀀀1, and the GLMM built with the variables silt, P, K and soil moisture explained the cfu distribution to the greatest extent. The spatial analysis showed that 9 of the 12 variables presented spatial aggregation (Ia > 1), and the clustering of local patches (i 1.5) for organic matter, silt, and Ca. The spatial patterns of the P. cinnamomi cfu under planted holm oak trees are related to edaphic variables and canopy cover. Small-scale spatial analysis of microsite variability can predict which areas surrounding trees can
influence lower oomycetes cfu availability.
Keywords: GLMM; holm oak decline; tree mortality; root rot.; plantation; dehesas; montados;
open forests