Damping-off disease caused by Rhizoctonia solani AG-4 is a serious disease of cabbage, especially in seedlings grown in culture medium. The treatment of peat moss medium, BVB No.4, infested by the pathogen with 0, 0.25, 0.5, 0.75, and 1 % (w/v) of clove was significantly effective in reducing the disease incidence of seedling damping-off. It showed markedly 52-60% reduction in the disease incidence at the rate of 0.5% (w/v) compared to non-treatment as a control. The similar results were also confirmed in three time large-scale experiments in the greenhouse. The powders of clove flower buds were extracted with methanol for three times. The combination of extractives was partitioned with n-hexane and ethyl acetate. Finally, the rest was extracted with water. The extractives from different solvents were tested for their bioactivity on mycelial growth of the pathogen. The n-hexane extractives showed significant effect on suppression of mycelial growth of R. solani AG-4. The n-hexane-soluble extractive was subjected to systemic separation and purification by column chromatography and thin layer chromatography. One major compound and two minor compounds were obtained and used to test their bioactivity. The mycelial growth of the pathogen was completely inhibited by 2500-fold dilution of the major compound of n-hexane-soluble extractive. In advance, this major compound was characterized by 1H NMR spectrum as eugenol. For fumigation effect of clove powder solution on mycelial growth of the pathogen, the inhibition of mycelial growth by clove-fumigant was increased with increasing the concentrations of clove in water solution. Observations under light microscope and scanning electron microscope indicated that the hyphae or hyphal tips of R. solani AG-4 swelled, plasma seeped around the hyphae, plasma leaked out, cell wall distorted, branched abnormal or fused with main hypha, hyphal tips warped or looped, and surface of hyphae wrinkled were caused by clove-fumigant treatment for 24hr. The clove-fumigant was also identified as eugenol by bioassay method and thin layer chromatography. The results suggest that the major component of clove inhibiting damping-off of cabbage seedlings is eugenol.
|Original language||Traditional Chinese|
|Number of pages||10|
|Publication status||Published - 2002|