Disease Suppressive Soils In the Rhizosphere of Olea Europaea.

We know that a soil is considered suppressive when in spite of favorable conditions for disease to occur a pathogen either cannot become established, establishes but produces no disease, or establishes and produces disease for a short time and then declines. Suppressiveness is linked to the types and numbers of soil organisms, fertility level and nature of the soil itself. The mechanisms by which disease organisms are suppressed in these soils include induced resistance, direct parasitism, nutrient competition, and direct inhibition through antibiotics secreted by bene?cial organisms. Additionally, the response of plants growing in the soil contributes to suppressiveness. This is known as induced resistance and occurs when the rhizosphere is inoculated with a weakly virulent pathogen. Olive plantations (Olea europaea) in Argentine cover about 87000 hectares mainly located in Catamarca, La Rioja and San Juan areas. Following several reports of decline symptoms, a disease survey was conducted during the spring 2005 in 30 olive plantations ranging from 300 to 4000 ha. The main of this study was to obtain bacterial from olive trees rhizospheric soil with pesticide capacity against Phytophthora spp. A total of 452 bacteria were obtained using culture-dependent methods. All of them were tested about the suppressive capability against the pathogen growth in vitro. The pathogen was consistently isolated from rotted rootlets on selective V8 medium . Actually we are examining the identification of the bacterial isolates using 16 S rDNA. On the other hand, PCR amplicons generated from Phytophthora using primers ITS 6 and ITS 4 will be used to confirm the morphological diagnosis using data mining. We believe firmly that biological alternatives capables to control disease of plants are friendly strategies to minimize the disruption of soil environment. This study will continue with the selection of the best bacterial strain obtained in the previous step and testing in vivo experience.