In recent decades, the biological control of the diseases caused by plant pathogens using other microorganisms has attracted the attention of researchers. In the present study, we assessed the biological control of root knot nematode Meloidogyne javanica in cucumber using three isolates of the fungus Trichoderma harzianum under greenhouse condition. The roots of the cucumber seedlings were inoculated with fungal spore suspension and 300 active second-instar larvae of the nematodes. One million spores/mL from the fungus was used for each plant. In this experiment, we assessed the effects of Trichoderma harzianum according to the diameter of the gall, number of the root knots, mean weight of the wet and dry roots and aerial parts, number of the egg masses per each plant, and number of the eggs per each egg mass. The isolates of the fungus reduced the severity of the disease and number of the galls in the roots. Moreover, increasing of the mortality rate in the larvae and decreasing of the hatching rate of the eggs were compared to the control samples. The results showed, the changes in the entire diseased plant which indicated that M. javanica could be controlled in cucumber by Trichoderma harzianum.

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