Antagonistic Evaluation of Some Fungal Isolates on Knot-Producing Nematode (Meloidogyne javanica) of Cucumber in Vitro and Greenhouse Conditions

Plant parasitic nematodes cause important economic losses in agricultural crops. Knot-producing nematode, Meloidogyne javanica is the most destructive of many crops in the world. In order to control plant nematodes as one of the important plant pathogens, various methods such as, fallow and crop rotation, cultivation of resistant cultivars, biological control and chemical methods are used. Today, due to the excessive use of agricultural pesticides, the health of the consumer community and the environment are endangered. Because of the chitin and protein are as dominant compositions in middle layer of the eggshell, using of the chitinases and proteases produced as degrading enzymes in a wide range of the fungi is a good strategy for biological control of the on knot-producing nematode. The disintegration of nematode eggs can only be caused by enzymatic action. Activity of the fungal egg-parasites leads to immobility and death of the embryo and results in a reduction of nematode population density. Many natural enemies of plant parasitic nematodes occur that may be useful for biological control. These include pathogens, predators, competitors and antagonists of which 76% are fungi. The fungal antagonists have been most extensively studied and are considered the most applicable for biological control of nematodes. The use of biological agents to control of plant-parasitic nematodes is less effective compared with chemical method, but positive result of fungal agents has been encouraging. In this study has tried to be examined considerable ability of the various antagonistic fungi to control of M. javanica in vitro and greenhouse conditions.

In this study has tried to be examined antagonistic ability of seven isolates of five fungal genus including: Fusarium solani, Fusarium oxysporum, Fusarium equiseti, Paecilomyces sp., Trichoderma atroviridae, Ulocladium dauci and Alternaria alternata on knot-producing nematode in vitro and greenhouse conditions. The ability of the protease enzyme production of fungal isolates was also evaluated. The protease specific activity assay in 7 isolates of various species of fungi obtained from infected knot-producing nematode over 5 days of fungal growth (24, 48, 72, 96 and 120 h) was measured. Also evaluation was performed in vitro by calculating the percentage of parasitized eggs and larvae in water-agar and also in the greenhouse by examining the growth factors of cucumber under the antagonistic effect of fungal isolates on nematodes. The ability of antagonistic activity of the fungi on the eggs was evaluated in water-agar medium with evaluation of the interaction between fungi and eggs. The numbers of healthy and parasitized (dead) larvaes and eggs were calculated after two weeks. The ability of the antagonistic fungi under greenhouse conditions was done. To provide of fungal inoculum, 20g of soaked wheat seed were cast in bags with autoclave capability. Per every gram of casted seed, 2 ml distilled water were added and during 24 hours they autoclaved 3 times. Then to every of bag number of 4 fungi disk with 5 mm diameter from selected isolates was added in 3 repetitions and was kept in 25ºC and dark conditions. To colonization all of the seeds and to avoid of hang of them, every 48 hours interval the seeds in bags were mixed. After three weeks all of the seeds were infected with fungal isolates. The ability of the antagonistic fungi under greenhouse conditions was done by adding fungal inoculum and the numbers of 2000 eggs to each pot and evaluation of performance traits of cucumber in pot after 90 days. In every two conditions, data analysis ANOVA (Analysis of variance) was conducted using of the SAS software version 9.4 in completely randomized design (CRD) with three replicates.

Analysis of variance of evaluation results in vitro and greenhouse conditions showed significant difference among isolates in 1% level. Results showed there is direct relation between increase in plant yield and add fungal isolates to the pot. The results of antagonistic ability of fungal isolates in vitro and greenhouse showed there is good correlation between two conditions. So the results showed a positive effect of the fungal isolates in reducing nematode damages.

Finally, based on all of the evaluations F. equiseti isolate was reported as the most effective isolate an F. oxysporum isolate as the least effective antagonist fungus.