Studying the effects of two species of bacteria of Bacillus and dry powder of red barberry and peppermint, on the pathogenicity and damage of root-knot nematode in cucumber

Root-knot nematodes (Meloidogyne spp.) are important pathogens that cause damage to cucumber. Although the use of chemical compounds is an effective method for controlling these nematodes, they impose high costs on producers and cause irreparable damage to the environment. Therefore, biological control can be a good alternative to chemical compounds.. To investigate the effect of biological control agents on cucumber root-knot nematode, red barberry (Berberis vulgaris) and peppermint (Mentha piperita), and the bacteria Bacillus subtilis and B. cereus were used. In the laboratory, the effect of different concentrations of aqueous and alcoholic extracts of the plants and different populations of the bacteria on egg hatching was evaluated. In the greenhouse, the effect of dry powder of the above plants and bacteria on the growth indices of healthy and nematode-infected cucumbers and the root knot nematode population indices was investigated. The results of laboratory studies showed an inhibitory effect of plant extracts and biocontrol bacteria on egg hatching compared to the control. After 24 hours, highest inhibition of egg hatching was observed in 10,000 mg/L of red barberry aqueous extract. Although increasing the concentration of the extracts reduced egg hatching, in the case of peppermint aqueous extract, increasing the concentration from 5000 to 10000 mg/L increased egg hatching. The 10⁷ cfu/ml concentration of B. cereus also reduced the percentage of egg hatching more than the other used concentrations after 24 hours. The results of the greenhouse study three months after nematode inoculation showed a significant effect of the application of the studied factors in increasing a number of cucumber growth indices and change of root-knot nematode population indices. Although the application of red barberry dry powder significantly increased the length and fresh weight of the stem in healthy and infected plants, but the difference in the rate of increase between the two groups was not significant. The bacteria studied also had no significant effect on growth indices. The application of biological control agents caused significant changes in a number of nematode population indices. The lowest average number of galls, egg mass, and egg mass per gram of root were observed in the B. subtilis and peppermint dry powder treatments, and the lowest reproductive factor and number of larvae per 100 grams of soil were observed in the peppermint dry powder and red barberry treatments.