The nematicidal effect of camellia seed cake on root-knot nematode Meloidogyne javanica of banana

Abstract

Suppression of root-knot nematodes is crucially important for maintaining the worldwide development of the banana industry. Growing concerns about human and environmental safety have led to the withdrawal of commonly used nematicides and soil fumigants, thus motivating the development of alternative nematode management strategies. In this study, Meloidogyne javanica was isolated, and the nematicidal effect of Camellia seed cake on this pest was investigated. The results showed that in dish experiments, Camellia seed cake extracts under low concentration (2 g/L) showed a strong nematicidal effect. After treatment for 72 h, the eggs of M. javanica were gradually dissolved, and the intestine of the juveniles gradually became indistinct. Nematicidal compounds, including saponins identified by HPLC-ESI-MS and 8 types of volatile compounds identified by GC-MS, exhibited effective nematicidal activities, especially 4-methylphenol. The pot experiments demonstrated that the application of Camellia seed cake suppressed M. javanica, and promoted the banana plant growth. This study explored an effective nematicidal agent for application in soil and revealed its potential mechanism of nematode suppression.

Fig 1. Molecular identification of M. javanica detected by primers Fjav/Rjav and M. incognita by Finc/Rinc (A); the female perineal pattern of M. javanica showing two obvious lateral lines (B); the hyaline tail observed in J2 of M. javanica (C); the infection of J2s from C11 of M. javanica in banana roots (D); phylogenetic tree of the sequence of nematode C11 (E).

Bars: B, C 10 μm; D 100 μm.

Fig 2. Effects of different concentrations of Camellia seed cake extract on the corrected mortality of M. javanica J2s (A); and the corrected hatching ratio of eggs (B).

Fig 3. Morphological variations of M. javanica J2s (the whole body (A), anterior part of the body (B), tail region (C), junction region of esophagus and intestine (D) and intestine (E)) after treatment with 5 g/L Camellia seed cake extract for different times.

Bars: 10 μm.

Fig 4. Morphological variations of M. javanica eggs after treatment with 5 g/L Camellia seed cake extract.

The egg treated with 5 g/L extract at 72 h (A) and the egg treated with water control (B). Bars: 10 μm.

Fig 5. The effects of the re-dissolved extracts on the number of M. javanica J2s (A) and saponin detected by HPLC-MS (include HPLC profile (B), total ion chromatogram (C) and ESI-MS identification (D)).

DAD: Diode-Array Detector; BPC: Base Peak Chromatogram.

Fig 6. Effects of volatile components (VOCs) from Camellia seed cake extract on the M. javanica J2s (A) and the GC profiles for VOCs produced by the Camellia seed cake (B).

The compounds corresponding to the retention times 0.83, 2.16, 3.12, 3.22, 3.59, 3.7, 3.91, 4.31, 5.29, 5.33, 5.39, 5.48, 5.65, 6.72, 6.99, 7.96, 8.19, 8.64 were designated as products A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q and R, respectively.