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Tylenchulus semipenetrans is a highly damaging obligate plant parasitic nematode (PPN) that poses a significant threat to citrus crops. the use of chemical nematicides has proven effective in reducing T. semipenetrans populations, but their repeated use can have negative environmental impacts, necessitating the adoption of more ecological strategies. The current study aimed to evaluate the nematicidal effect of Rosemary (Rosmarinus officinalis) against Tylenchulus semipenetrans under greenhouse and laboratory conditions.
T. semipenetrans eggs and juveniles were subjected to varying concentrations of aqueous extracts (1%, 4%, 8%, and 10%) for different durations (48, 96, and 144 hours for eggs; 24, 48, and 96 hours for J2), with distilled water serving as a control. Citrus Volkameriana plants, artificially infested with the citrus nematode Tylenchulus semipenetrans, were selected for a greenhouse biological control experiment involving the soil application of a 10% Rosemary aqueous extract at a rate of 20 ml/tree. Results showed that the Rosemary extract exhibited high toxicity against T. semipenetrans, with juvenile J2 mortality ranging between 9.52% and 75.17%, compared to 1.0 to 13.6% in the distilled water treatment, and egg hatch inhibition varying between 0% and 38%, compared to 73 to 95% in the distilled water treatment. Toxicity increased with increasing Rosemary aqueous extract concentration and incubation period, reaching 75% mortality after 96 hours and complete egg hatch inhibition after 144 hours of incubation at an aqueous extract concentration of 10%. In the greenhouse experiment, the aqueous extract of Rosmarinus officinalis significantly reduced the population density of T. semipenetrans J2 in the rhizosphere of Citrus volcameriana compared to the control treatment, with nematode populations ranging from 500 J2/100g of soil and 122 nematodes/10g of roots, compared to populations of 99.33 nematodes/100g of soil and 185 nematodes/10g of roots in the control treatment. As a result, it was concluded that the aqueous extract of R. officinalis can be used as an effective and healthy nematicidal product against T. semipenetrans.
Keywords: Tylenchulus semipenetrans, Rosmarinus officinalis, Citrus, Nematicidal activity
