Effect of Soil Water Content and Soil Texture on

Phytophthora cinnamomi is an important soil borne plant pathogen, associated to decline of cork and holm oak stands in Iberian Peninsula. This decline results from a complex of biotic and abiotic interactions culminating in root infection. Field observations in cork and holm oak sites suggested an enhancement of soil moisture and texture in decline processes. Greenhouse assays were developed to evaluate the impact of soil moisture and texture on the severity of root infection on both species. Seedlings were potted in P. cinnamomi infested soils with different textures (loamy-sand, clay and silty- loam) combined with different watering regimes (flooding, normal irrigation, and irrigation till wilting and field capacity). The impact of P. cinnamomi infection was assessed through plant biomass, water consumption and root severity. The infection caused either losses of plant biomass (root and shoot) as plants water consumption, in both species, depending on soil moisture and texture. Holm oak plants were more susceptible to P. cinnamomi infection than cork oak, with higher mortality and root degradation. To minimize the risk of infection, watering managing appeared to be an essential condition to optimize plant growth and survival taking also into account the texture and moisture of the soil