Spearmint 513
same bacteria. Likewise, Torres et al. (1996) reported the antimicrobial activity of
spearmint oil against Staphylococus aureus and E. coli.
31.7.2 Insecticidal and genotoxic activities
The essential oils (EOs) extracted from mint species, M. spicata and M. pulegium,
together with their main constituents, carvone, pulegone and menthone, were tested
for insecticidal and genotoxic activities on Drosophila melanogaster (Franzios et al.,
1977). The EOs of both aromatic plants showed strong insecticidal activity, while
only the oil of M. spicata exhibited a mutagenic one. Among the constituents studied
by these authors, the most effective insecticide was found to be pulegone while the
most effective for genotoxic activity was menthone. Data revealed that both toxic
and genotoxic activities of the EOs of the two studied mint plants are not in accordance
with those of their main constituents, pulegone, menthone and carvone. Whereas
pulagone is significantly more effective (¥ 9) as an insecticide, menthone and carvone
are less effective (¥ 6 and ¥ 2, respectively) insecticides when used in their authentic
forms.
31.7.3 Nematicidal activities
Walker and Melin (1996) investigated the nematicidal activities of six spearmint and
six peppermint accessions. They inoculated the accessions with Meloidogyne incognita
race 3 and M. arenaria race-2 under greenhouse conditions. No nematode galls
formed on roots of any of the plants inoculated with 1,800 eggs/pot. Fewer than two
galls per root system formed on three accessions of peppermint inoculated with M.
incognita at 5,400 eggs/pot. Only one peppermint accession developed galls when
inoculated with M. arenaria, whereas none of the spearmint accessions was susceptible
to this species. Plant dry weight was in general unaffected by infection with root-
nematodes at these densities. Growing spearmint and peppermint accessions for
eight or 12 weeks in M. arenaria-infested soil before tomato cultivation resulted in
a 90% reduction in root galls compared with tomato following tomato.
31.7.4 Fungicidal activities
Working with several essential oil bearing plants including M. spicata, Yegen et al.
(1992) reported the remarkable fungicidal activities of their essential oils and oil
constituents. These authors investigated the fungitoxicity of these essential oils against
four phytopathogenic fungi. The essential oils were more toxic against Phytopathogenic
capsici than the fungicide carbendazen and pentachlor nitro benzene. The investigations
with thin-layer chromatography implicated carvacrol of M. spicata as one active
compound having significant fungicidal property.
Adam et al. (1998) reported the significant antifungal properties of the essential
oils of various aromatic plants including M. spicata against human pathogens,
Malassezia furfur, Trichophyton rubrum and Trichosporon beigelii. Their results
demonstrated that among the main components of the essential oils, carvacrol of M.
spicata and Thymol of the other plants exhibited the highest levels of antifungal
activity. Furthermore, the studied essential oils when tested with the Ames test did
not exihibit any mutagenic (carcinogenic) activity.