is a limiting factor for cotton production in Australia. As a soil-borne fungal pathogen, epidemiological, ecological and genetic features of Fov populations are strongly influenced by soil conditions. This includes key fungal life-history traits crucial to managing the disease such as and aggressiveness. The objectives of this project were to provide a better understanding of how Fov copes with different soils in the perspective of aggressiveness, saprophytic ability and evolution.

Soil samples were collected from Moree, Boggabilla, and the Darling Downs regions and disease incidence, Fov density, and soil abiotic conditions were tested. Results showed that Fov density varied among fields and disease incidence was not significantly correlated to Fov density (P=0.1281). However, correlation and stepwise regression analyses found significant relationships between disease incidence and soil conditions like calcium/magnesium (Ca/Mg) ratio, sodium, chloride, and electric conductivity, among which only soil Ca/Mg ratio showed a negative relationship. This observation was confirmed by further studies in soils inoculated with the same level of Fov inoculum, suggesting that lifting soil Ca/Mg ratio could be used as an alternative disease control measure provided the efficacy is verified under field conditions in future studies.

Studies of 17 representative Fov isolates clarified that fast-growing Fov isolates are more aggressive than slow-growing ones and aggressive isolates usually produce few spores than less aggressive ones, suggesting trade-off between spore producing ability and aggressiveness in Fov. Consistently, the trade-off was also detected in the soil when the same Fov population was associated with cotton and wheat, respectively. Compared with cotton soils, Fov density was significantly greater in wheat soils due to enhanced saprophytic ability as a result of the absence of cotton. Furthermore, a significant impact of the interaction between Fov and soil origins on the trade-off was also noticed.

Difference in Fov recovery frequency on diseased plants grown in different soils suggests a strong soil impact on Fov evolution. When the recovery frequencies of a from different soils are compared, it is usually higher in the soil from which it derives than in those so-called alien soils. This suggests that Fov can evolve to become soil- or region-specific due to local adaptation and this should be taken into consideration when a suitable cotton cultivar is chosen for different soils.