The efficacy of Iranian Pythium oligandrum isolates in biocontrol of soil-borne fungal pathogens of tomato

Pythium oligandrum is known as an important biological control agent against fungal plant pathogens. The commercial formulations of this oomycete could reduce the application of the chemical fungicides and lessen the environmental impact of treatments. This study aimed to investigate the antagonistic ability of Iranian isolates of P. oligandrum to select proper and efficient candidates as native biocontrol agents using a previously characterized collection of forty-five isolates from fields of different regions of Iran. The antagonistic effects of native P. oligandrum isolates were evaluated against two soil-borne fungal pathogens, Fusarium oxysporum f. sp. lycopersici and Phytophthora parasitica, causing diseases on tomato. Pythium oligandrum isolates K29, K48, and K87 were recognized as the most effective isolates based also on previously published in vitro antagonistic assays, oligandrin production, and the ability of root colonization. The oospores of the selected candidates were formulated as seed-coating, kaolin dust mixture, and perlite-coating and compared with common fungicides in greenhouse tests. The results of greenhouse studies revealed that all selected P. oligandrum isolates and chemical fungicides significantly reduced disease severity but the efficacy of P. oligandrum isolates varied according to the type of formulation. Seed-coating formulation with oospores exhibited better performance than other formulations. The results showed that the application of formulated P. oligandrum selected isolates had the same performance (40–50% reduction in disease severity) as compared to the chemical fungicide treatments for controlling soil-borne pathogens. These results make it possible to consider in the near future the use of isolates of P. oligandrum as biocontrol agents to protect vegetable crops, in particular tomato, from soil-borne pathogens.