Nematicidal Evaluation and Active Compounds Isolation of <i>Aspergillus japonicus</i> ZW1 against Root-Knot Nematodes <i>Meloidogyne incognita</i>

The root-knot nematode is one of the most damaging plant-parasitic nematodes worldwide, and the ecofriendly alternative approach of biological control has been used to suppress nematode populations. Here the nematicidal activity of <i>Aspergillus japonicus</i> ZW1 fermentation filtrate against <i>Meloidogyne incognita</i> was evaluated in vitro and in greenhouse, and the effects of <i>A. japonicus</i> ZW1 fermentation filtrate on seed germination and the active compound of <i>A. japonicus</i> ZW1 fermentation filtrate were determined. The 2-week fermentation filtrate (2-WF) of <i>A. japonicus</i> ZW1 exhibited markedly inhibitory effects on egg hatching, and 5% 2-WF showed potential nematicidal activities on second-stage juveniles (J2s); the mortality of J2s was 100% after 24 h exposure. The internal contents of nematodes were degraded and remarkable protruded wrinkles were present on the body surface of J2s. The nematicidal activity of the fermentation was stable after boiling and was not affected by storage time. A germination assay revealed that 2-WF did not have a negative effect on the viability and germination of corn, wheat, rice, cowpeas, cucumbers, soybeans, or tomato seeds. The pot-grown study confirmed that a 20% fermentation broth solution significantly reduced root galls and egg numbers on tomatoes, and decreased galls and eggs by 47.3% and 51.8% respectively, over Czapek medium and water controls. The active compound from the <i>A. japonicus</i> ZW1 fermentation filtrate was isolated and identified as 1,5-Dimethyl Citrate hydrochloride ester on the basis of nuclear magnetic resonance (NMR) and LC-MS (liquid chromatograph-mass spectrometer) techniques. Thus, fermentation of <i>A. japonicus</i> ZW1 could be considered a potential new biological nematicide for the control of <i>M. incognita</i>.