In Vitro and Enzymatic Studies of Inhibitory Activities of Three Trichoderma Species against Pythium Aphanidermatum in Infected Sweet Pepper

This study investigated the antifungal activities of Trichoderma species against Pythium aphanidermatum; determined and measured the induction of defense enzymes (such as peroxidase, polyphenol oxidase and phenylalanine ammonia lyase) by Trichoderma species in seedlings inoculated with Pythium aphanidermatum. This was with a view to obtaining the best antagonist among the Trichoderma species. Inhibition percentages of the three Trichoderma species on Pythium aphanidermatum were determined via dual inoculation method and via production of volatile compounds. Fifteen day old seedlings of treated and untreated seeds were inoculated with 5 X 10 5 spores/ml of Pythium aphanidermatum. Extraction of enzymes was carried out at different time interval of 1, 3, 5, 7, 9 and 11 days after pathogenic inoculation and they were assayed. The phenolic content for each of the treatment was also determined. The in vitro results suggested that, Trichoderma harzianum and T. koningii inhibited the growth of Pythium aphanidermatum mainly through their higher competitive abilities for space (on the plate) and nutrients at the expense of P. aphanidermatum, while T. atroviride inhibited the growth of P. aphanidermatum on the third day before occupying the space and absorbing nutrients from the substrates. The peroxidase activities were higher in T. atroviride plus pathogen in comparison with its activities in T. atroviride alone, T. harzianum alone and pathogen alone, while higher accumulation of phenolic contents was recorded in dual inoculations with T. atroviride than with T. harzianum. The study confirmed the ability of T. atroviride to inhibit the infection of P. aphanidermatum through the induction of activities of oxidative enzymes, competition and mycoparasitism, which was found to be high in interactions with the pathogen at all levels.