[Study the influence of the fungus Trichoderma on the growth of the fungus Phytophthora citrophthora]

The gummosis is a dangerous disease on citrus trees which causes large economic losses. Due to pesticides side effects, biocontrol methods were studied as an alternative. This research was conducted to study the effects of fungus Trichoderma on controlling the fungus Phytophthora citrophthora and to compare them with the effects of the most common chemical pesticides on controlling this pathogen. P. citrophthora was identified by morphological aspects of its colony, and tested Trichoderma isolates were identified through colony characteristics, microscopic inspection and references, it was noticed that the isolates T1 and T3 were nearer to fungus T. harzianum, while the isolate T5 was nearer to fungus T. viride. The growth rate of P. citrophthora was studied on different media.The results showed that the rate was higher on V8 and PDA media compared to malt medium, with no significant difference between V8 and PDA media. The effects of several concentrations of the fungicides Metalaxyl and Fosetyl-al on the growth of P. citrophthora in-vitro were investigated. Moreover, 3 local isolates T5, T3 and T1 and two commercial isolates (Tbio and T2) of biological control Trichoderma spp. were tested. The growth inhibition rates were 60, 47.5, 60, 55, 54.17% respectively for the isolates T1, T2, T3, T5 and Tbio, while they were 100 and 23.92% for the fungicides Metalaxyl and Fosetyl-al respectively when used at a concentration of 1000 ppm. For the two fungicides, at a concentration of 5000 ppm, the inhibition rate was 100%. The effects of different Trichodema isolates filtrates on the growth of were studied. It was found that these filtrates had no effect on the growth compared to Metalaxyl which inhibited it. This means that Trichderma doesnt excrete antibiotics or any other inhibition compounds, which implies that its activity on the pathogen was due to direct parasitism. In-vivo, the effects of Metalaxyl and Fosetyl-al as well as the isolates T1, T2 and T3 on P. citrophthora were investigated. The results showed very high activity of the fungicides with less activity of Trichoderma. The gummosis stopped completely in the chemically treated trees, but when Trichoderma was used variations were found in the results of the three isolates even in the replications. The isolate T3 was more active than the other two isolates tested in the field. In non treated treas as a control, the gummosis was clearly continued.