Eco-friendly management of damping-off of tomato caused by Pythium aphanidermatum with abiotic stress-tolerant native antagonistic rhizosphere bacteria

Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops cultivated in Oman. High soil salinity, high temperature, drought, pests and diseases are the major constraints to tomato production in Oman. Damping-off disease, incited by the oomycete Pythium aphanidermatum is one of the most important diseases of tomato causing high mortality of seedlings in the nursery as well as in the main field. P. aphanidermatum is a soil-borne pathogen and hence it is difficult to manage. Currently, there are no commercial tomato cultivars showing resistance/tolerance to damping-off disease. Though a few phenylamide fungicides are effective in the control of Pythium spp., fungicides application in the soil may cause undesirable effects on the environment and may lead to development of fungicide resistance in Pythium spp. A few non-chemical methods like soil solarization, biofumigation and top-soil replacement are employed to control damping-off of green-house grown tomato; but each method has its own shortcomings. Biological control method, by using naturally occurring antagonistic fungi or bacteria has been considered as an effective, environmentally safe and sustainable alternative to synthetic chemical fungicides for the management of soil-borne diseases including damping-off. A few biofungicides based on Streptomyces griseoviridis and Trichoderma harzianum are available in the international market for the control of P. aphanidermatum-induced damping-off of tomato and other crops. However, the performance of introduced biocontrol agents (BCAs) largely depends on prevailing environmental conditions in the fields. The hot and dry climate, high sub-surface soil temperature, and salinity in Oman may affect the growth and activity of the ?exotic? BCAs when used. Furthermore, ?-tomatine, an antimicrobial steroidal glycoalkaloid, secreted by tomato roots may interfere with the growth and establishment of BCAs in the soil. Under these conditions, native antagonistic microorganisms that can maintain threshold populations in the rhizosphere of tomato may be ideal to be used as BCAs. The primary aim of the proposed work is to isolate abiotic stress-tolerant native antagonistic bacteria from the rhizosphere of tomato for ecofriendly management of damping-off of tomato.