Population dynamics of Fusarium oxysporum f. sp radicis-lycopersici in relation to the onset of Fusarium crown and root rot of tomato

Fusarium oxysporum f. sp. radicis-lycopersici the causal agent of crown and root rot in tomato comprises two overlapping separate phases: monocyclic a nd polycyclic. Oversummering inoculum is the source of primary infection (t he monocyclic phase) and the spread from plant to plant via root-to-root co ntact is the source of the secondary infection (the polycyclic phase). In t he present work, relationships between initial inoculum density, population dynamics of the pathogen in the root zone of diseased plants, and disease onset were studied. For the monocyclic phase, 55.1% of the variance of dise ase onset was attributed to the rate of pathogen proliferation in the root zone of plants, and only 12.8% of the variance was attributed to the amount of initial inoculum density. For the polycyclic phase, disease onset was n ot related to either initial inoculum density or the rate of pathogen proli feration in the root zone. At disease onset, the inoculum density of the pa thogen in the root zone of plants infected from oversummering inoculum reac hed an average of 4.08 log cfu g soil(-1). The inoculum density of the path ogen in the root zone of plants infected by their diseased neighbors was 3. 23 log cfu g soil(-1). A large variation in pathogen proliferation rate in the root zone was found among individual plants, suggesting that difference s in the level of soil suppressiveness may occur not only between fields, b ut even in the same field over short distances.