Abstract:
The present study was conducted to evaluate the efficacy of essential oils from leaf
and bark of cinnamon, Cinnamomum zeylanicum in controlling Meloidogyne graminicola
and their effects on rice seedlings and young rice plants. This study was done; to determine
the LC50 of essential oils of the extracts of cinnamon leaf and bark to kill 50% of second
stage juveniles (J2) of Meloidogyne graminicola in rice root galls; to determine the efficacy
of essential oils of cinnamon; in controlling J2 in rice seedlings and young rice plants; and
on the growth of rice plants.
Cinnamon bark oil sample used in the current study contained about 72%
cinnamaldehyde and the leaf sample contained about 86% eugenol. LC50 for cinnamon leaf
oil and cinnamon bark oil for killing 50% of juveniles of M. graminicola in rice root galls
after three days of the treatment was 0.326 ppm and 0.454 ppm respectively. Number of
galls in the root system of nematode infested rice seedlings was significantly reduced when
they were treated with 0.9 ppm of cinnamon leaf oil and bark oil compared to untreated
controls. However, the nematicidal activity between the cinnamon leaf oil and bark oil was
not significantly different. The root gall index of infested young rice plants was
significantly lowered when they were treated with either cinnamon leaf oil or bark oil
compared to untreated controls. It was revealed that the mean plant height and the mean
number of roots of essential oil treated plants were positively correlated with the number
of root galls whereas, the number of dead plants and the mean percentage chlorosis were
negatively correlated. Nevertheless, the mean root length did not show any significant
correlation with number of root galls. This study concludes that essential oils of cinnamon
leaf which contained 86% eugenol and bark which contained 72% cinnamaldehyde are
similarly effective in suppression of M. graminicola in rice seedlings and young rice
plants. According to the rates of application of essential oils of cinnamon leaf and bark,
none of them have significant negative effect on the plant growth. Hence, they can be used
as an alternative nematicide against the rice root knot nematode, M. graminicola in early
stage of rice plants.
