Hyphal interaction mechanism between some fungal biocontrol agents and some cucurbitaceous damping-off pathogens

Light microscope was used to dual cultures, containing the tested fungal biocontrol agents: namely; Trichoderma harzianum, T.. viride, T. konningii and Gliocladium roseum and some cucurbitaceous damping-off pathogens: namely; Rhizoctonia solani, Pythium ultimum, Fusarium solani and Alternaria alternata. Microscopic examinations indicated that growth of the mycoparasitic fungal mycelium was characterized by the formation of highly active, thin, dense and well-branched hyphae compared to those of the tested pathogens, where hyphae were thicker and less branched. This behavior was common in most of the tested mycoparasitic isolate/pathogen interactions. After colonization, short infection hyphae were mostly formed by the mycoparasitic isolate, grew toward host hyphae and penetrate them directly with or without the formation of prepenetration structures. However, in most of the examined combinationss, mycoparasitic hyphae grew toward the hyphae of the pathogen, then parallel and in complete contact with them, twisted in most cases around host hyphae for establishment before the formation of penetration structures. Many distinguished structures were formed from tips of the attacking hyphae such as appressorium, foot, pincer, hook or hyphopodium-like structures before penetrating the host hypha. After penetration and lysis of the host hyphae, conidiophores of the mycoparasitic isolat -s were observed protruded from the attacked host hypha. Hyphal interaction between the tested isolates of T. harzianum and G roseum and isolates of R. solani and P. ultimum were also studied using scanning electron microscope. Examinations results were almost similar to those of light microscope. Growth of attacking hyphae toward host hyphae, formation of, appressorium-like structures and direct penetration without the formation of prepenetration structures were also recorded.