Figure 2. Photographs of mycelia of P. oryzae taken through scanning electron microscope (arrows)
a. Control (mycelia without extract treatment). b. Mycelia with extract treatment. Bars = 5 m.
Observation through SEM showed that the size of hypae and spore were smaller when compared to
control because of lysis of the cells. Several mode of actions may happened resulted from antifungal substances
from plants such as the alteration of cell permeability, degradation of cell wall, inhibition of enzymatic activities
in the fungal cells that in turn affected the cell membrane permeability (Semangun, 2006). This phenomenon
occurred on the leaf extract of Piper beltle that contain essensial oil where 55% of them is phenol. This
substance actively precipitated the protein which resulted in disintegration of fungal cell membrane. The surface
tension of cell membrane is reduced and resulted in cell lysis. As a consequence, the growth of a fungus is
suppressed (Rachmawati and Korlina, 2009). Present study revealed that the leaf extract of P. caninum showed
a remarkable antifungal activity against P. oryzae through lysis of mycelial cells of P. oryzae, suggested that this
extract potenally can be used as an alternative agent to control rice blast disease. The field research is needed to
evaluate the effectiveness of the extract of P. caninum to control rice blast disease. Which of substances
responsible for the antifungal activity against P. oryzae is still unclear. A further study to purify and indentify
substances responsible for the antifungal activity is necessary to be done.
4. Conclusion
The leaf extract of P. caninum showed a very strong antifungal activity against P. oryzae, the cause rice blas
disease under in vitro condition on PDA medium. The mínimum inhibitory concentration (MIC) of this extract
was 0.5% (w/v). This extract significantly inhibited the growth of colony, spore density and biomass formation
of P. oryzae. The growth inhibition resulted from this extract is due to the lysis of fungal cells indicated by the
size of mycelia treated with extract was obviously smaller than that of control. It is necessary to purify and
identify the substances in the leaf extract of P. caninum that responsible the most for the antifungal activity
against P. oryzae.
Acknowledgement
Authors would like to express our great appreciation to Khamdan Khalimi of the Laboratory of Biopesticide,
Faculty of Agriculture Udayana University for technical assistance during the study.