Tomato is the second most cultivated vegetable crop both worldwide and in Australia. Processing tomatoes grown in the field in Victoria suffer a 10% yield loss due to soil-borne pathogens, with Fusarium oxysporum and Pythium spp. being the most aggressive. Biocontrol is a promising disease management practice with high sustainability, target specialization and cost-efficiency. This research focused on identifying potential biocontrol microorganisms, examining their antagonism against F. oxysporum and Pythium spp., testing their beneficial effects on plant growth and development, and evaluating their effectiveness in controlling root disease in processing tomatoes using both in vitro media incubation tests and glasshouse pot trials.
In in vitro media incubation tests, a local Pythium oligandrum strain UM202001 colonized root tissue of tomato seedlings without causing symptoms and led to the improved root branching and lateral root growth as well as changes in the composition of the carbohydrate exudates from the colonized plants, which probably provided the oomycete with a nutritional source. In glasshouse pot trials, the application of UM202001 both before and after inoculation with Fusarium and Pythium resulted in reduced level of root necrosis in tomato plants and increased shoot and root dry weight compared with the uninoculated controls. Further glasshouse trials showed that application of up to 10% v/v of UM202001 inoculum did not impact the growth or development of tomato plants. Therefore, UM202001 was considered to have tomato growth promoting and biocontrol potential, which should be investigated in further field experiments.