Talaromyces variabilis interferes with Pythium aphanidermatum growth and suppresses Pythium-induced damping-off of cucumbers and tomatoes.

Pythium-induced damping-off disease is a major disease limiting cucumber and tomato production in different parts of the world. The current study investigated the efficiency of Talaromyces variabilis and its bioactive metabolites in suppressing Pythium-induced damping-off of cucumbers and tomatoes. T. variabilis inhibited the in vitro growth of P. aphanidermatum in solid and liquid media. In addition, abnormalities in P. aphanidermatum hyphae were observed as a result of T. variabilis. Extracts from T. variabilis induced cellular leakage and suppressed oospore production of P. aphanidermatum. Biochemical analyses of T. variabilis metabolites showed that T. variabilis produces glucanase, cellulase and siderophores, suggesting the contribution of these metabolites in the inhibition of P. aphandermatum growth and in hyphal abnormalities. Treating cucumber seeds with spore and mycelial suspension of T. variabilis isolates led to a significant improvement in the seedling survival of P. aphanidermatum-inoculated seedlings from 18 to 52% (improvement by 34%) for isolate 48 P and from 30-66% (improvement by 36%) for isolate 28 R. Similarly, treating tomato seeds with spore and mycelial suspension of T. variabilis isolates led to a significant improvement in the seedling survival of P. aphanidermatum-inoculated seedlings from 7 to 36% (improvement by 29%) for isolate 28 R and from 20 to 64% (improvement by 44%) for isolate 48 P. Differences in the percent improvement in seedling survival between experiments may be related to difference in the efficacy of the two different isolates or their interaction with the hosts and pathogen. The use of T. variabilis in the biocontrol of Pythium-induced diseases may offer alternatives to the currently used chemical control.