Disease suppression and systemic-acquired-resistance-induced in plants by compost-amended potting mixes, compost water extracts and no-tillage soil

cucumber (Cucumis sativus 'Straight Eight') split-root technique was used to demonstrate that systemic acquired resistance (SAR) at least in part explained suppressiveness of compost mixes to Pythium root rot caused by Pythium ultimum and P. aphanidermatum. Root rot severity was reduced on roots in an infested peat mix paired with a compost mix. Anthracnose caused by Colletotrichum orbiculare was less severe in leaves of cucumber plants grown in the compost than in the peat mix. There was no difference in anthracnose severity among 'classic-induced' plants versus those grown in the compost mix. Compost-induced SAR was destroyed by autoclaving, and then restored by inoculation of the autoclaved mix with the natural compost (10%, v/v) or Pantoea agglomerans 278A. Efficacy of Pseudomonas putida 371 varied and Flavobacterium balustinum 299 failed to induce SAR. The foregoing suggests that compost-induced SAR in plants was biological in nature and responsible for suppression of anthracnose and Pythium root rot. Bacterial speck caused by Pseudomonas syringae pv. maculicola ES4326 (Psm) was less severe on Arabidopsis plants (Arabidopsis thaliana ecotype Columbia) grown in the compost than in the peat mix and Psm populations were lower in plants grown in the compost mix. Compost water extracts reduced bacterial speck severity and Psm populations on plants grown in the peat mix but not on those in the compost mix. A spray with salicylic acid (SA) reduced disease severity without affecting Psm populations. Apparently, disease suppression caused by sprays with compost extracts and SA was due to different mechanisms. Activity of compost extracts was heat stable and passed through a 0.2...