In this study, the effects of medicinal plant extracts on the development of mycelium in the following phytopathogenic fungi were evaluated: Phytophthora capsici, Rhizoctonia solani, Fusarium solani, Colletotrichum gloeosprorioides, and Botrytis cinera. Of the 26 medicinal plants tested, six plant extracts showed antifungal activity against phytopathogenic fungi. The highest antifungal activity was exerted against R. solani by the n-hexane fraction of a Cinnamon (Cinnamomum cassia Blume) solvent extract. Therefore, the antifungal compound fractions I and II were purified from the n-hexane fraction by TLC on silica gel plates. When treated with solutions containing compound fractions I or II at a concentration of 2%, the mycelia growth rate of R. solani was reduced to 0.19 and 0.18, respectively. In addition, microscopic observation of the hyphal morphology of R. solani following treatment with compound fraction I revealed the presence of severely damaged hyphae. Specifically, the hyphal tips became swollen, collapsed or were completely destroyed in response to treatment with solution containing compound fraction I at concentration of 1%.

Two extracellular chitinases were purified from Paecilomyces variotii DG-3, a chitinase producer and a nematode egg-parasitic fungus, to homogeneity by DEAE Sephadex A-50 and Sephadex G-100 chromatography. The purified enzymes were a monomer with an apparent molecular mass of 32 kDa (Chi32) and 46 kDa (Chi46), respectively, and showed chitinase activity bands with 0.01% glycol chitin as a substrate after SDS-PAGE. The first 20 and 15 N-terminal amino acid sequences of Chi32 and Chi46 were determined to be Asp-Pro-Typ-Gln-Thr-Asn-Val-Val-Tyr-Thr-Gly-Gln-Asp-Phe-Val-Ser-Pro-Asp-Leu-Phe and Asp-Ala-X-X-Tyr-Arg-Ser-Val-Ala-Tyr-Phe-Val-Asn-Trp-Ala, respectively. Optimal temperature and pH of the Chi32 and Chi46 were found to be both 60 degrees C, and 2.5 and 3.0, respectively. Chi32 was almost inhibited by metal ions Ag(+) and Hg(2+) while Chi46 by Hg(2+) and Pb(2+) at a 10 mM concentration but both enzymes were enhanced by 1 mM concentration of Co(2+). On analyzing the hydrolyzates of chitin oligomers [(GlcNAc)( n ), n = 2-6)], it was considered that Chi32 degraded chitin oligomers as an exo-type chitinase while Chi46 as an endo-type chitinase.

The nematicidal activity of Terminalia nigrovenulosa bark (TNB) and its purified compound were assayed against Meloidogyne incognita in vitro. The nematicidal compound was isolated from TNB using silica gel column and Sephadex LH-20 chromatography combined with thin-layer chromatography and high performance liquid chromatography. Structural identification of the nematicidal compound was conducted using 1H-nuclear magnetic resonance (NMR), 13C-NMR and liquid chromatography-tandem mass spectrometry. We found that the nematicidal compound purified from TNB was gallic acid (GA) or 3,4,5-trihydroxy benzoic acid. Nematicidal activity bioassays revealed that GA treatment resulted in 20.3, 37.5, 73.3, 88.3 and 95.8% hatch inhibition at 0, 0.25, 0.5, 1.0 and 2.0 mg ml−1 after 3 days, respectively, of incubation. Eggshells appeared to be deformed and destroyed at 2 and 3 days after incubation with a GA concentration of 1.0 mg ml−1, respectively. Additionally, after treatment with a GA concentration of 1.0 mg ml−1, mortality of second-stage juveniles of M. incognita was 65.0, 75.0, 96.7 and 100% at 3, 6, 9 and 12 h incubation, respectively.

To investigate in vitro nematicidal activity against the pine wood nematode, Bursaphelenchus xylophilus, plant methanolic extracts were obtained from 26 medicinal plants and herbs in Vietnam. Of the plant extracts tested, a 10 mg ml −1 concentration of Cinnamomum cassia bark extract showed the highest level of nematicidal activity against juvenile and adult B. xylophilus after treatment for 7 h. The remainder of the plant extracts had little or no effect on juveniles or adults. Four solvents, n-hexane, chloroform, ethyl acetate and n-butanol, were used initially to partition the compounds obtained from C. cassia extracts. The compound (5 mg ml −1 ) in the n-hexane fraction showed the highest nematicidal activity at 60 min after treatment. Compounds III and IV were then separated from the n-hexane fraction using silica gel plates. These compounds showed very similar activity against the pine wood nematode. However, treatment with different concentrations of these compounds resulted in a significant difference in their effects on the mortality of the pine wood nematode, with greater concentrations leading to increased mortality after the same exposure time. Overall, treatment with 3 mg ml −1 of compounds III and IV resulted in greater than 95% mortality against juvenile and adult B. xylophilus at 50 min after treatment.

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