Activity of papaya seeds (Carica papaya) against Meloidogyne incognita as a soil biofumigant

Seeds of papaya fruit (Carica papaya) are usually unused for the industry, but they have been previously reported to be anthelmintic. However, the effects and mechanisms involved in papaya seeds against root-knot nematodes (RKN) are poorly studied in soil incorporation. Here, we investigated soil biofumigation with papaya seeds against the RKN Meloidogyne incognita and the effect of their volatile organic compounds (VOCs) separately from non-VOCs. Soil biofumigation reduced the number of galls and eggs of RKN about 100% in tomato roots, by using seeds macerates at 4.0 g 100 mL−1, which is a feasible amount for field applications. The VOCs emitted by the seeds killed 80% of M. incognita second-stage juveniles after a few hours of exposure. Furthermore, the whole volatilome of the papaya seed was identified by gas chromatography. Some of the compounds have already been studied against RKN. Therefore, we examined the efficacy of all nonstudied compounds against M. incognita. The most promising compounds were vinyl acetate, phenylacetaldehyde and benzylacetonitrile with lethal concentrations (LC50) of 61.5, 101.3 and 14.4 μg mL−1, respectively. When vinyl acetate and phenylacetaldehyde were applied to the soil at the recommended commercial nematicide dose (396 μg mL−1), the effect on M. incognita was better than the commercial nematicide (Carbofuran), reducing 70% of the number of galls and eggs. However, benzylacetonitrile reduced galls and eggs only by 25%. These results provide evidence for biofumigation with papaya seeds as a sustainable approach to control RKN and the potential use of their VOCs as nematicidal compounds.