Ecology and biological control of Verticillium dahliae

The dynamics of Verticillium dahliae , the causal agent of wilt disease in many crops including potato, cotton, and olive, were investigated. Its biological control with Talaromyces flavus with or without additional Pseudomonas fluorescens was attempted. Arabidopsis thaliana was selected as a bioassay plant for studying aspects of ecology and biological control of the pathogen because of its short life cycle and high sensitivity to the pathogen. The optimal temperature for production of microsclerotia, the survival structures of the pathogen, both in vitro and on A. thaliana was about 20°C. Microsclerotia incorporated in soil were exposed to a range of conditions of temperature and moisture and quantified on several sampling occasions. One day after incorporation, densities were low, these densities were even lower over the following 1-6 months, but subsequently densities increased. These changes were ascribed to changes in the level of soil mycostasis rather than death and new formation of microsclerotia. After application of T. flavus to fresh organic debris containing microsclerotia followed by a 3-wk incubation aboveground at 15 or 25°C the population density of T. flavus increased in soil, especially at 25°C. T. flavus significantly reduced the density of microsclerotia in soil, especially at 25°C, and delayed the development of senescence of A. thaliana at 15 and 25°C.It is concluded that above-ground application of T. flavus may lead to more consistent effects. The effect of P. fluorescens strain P60, originally isolated from a take-all decline field continuously grown to wheat, on V. dahliae was also studied. Strain P60, and two other isolates of P. fluorescens , inhibited the in vitro mycelial growth of 20 isolates of V. dahliae , reduced formation of microsclerotia both in vitro and on A. thaliana and they retarded senescence of A. thaliana to a rate like that of uninoculated plants