C.A. Scoble{ XE "Scoble, C.A." }A,B, E.C. DonaldA, K.M. PlummerB and I.J. PorterA
A
Department of Primary Industries, 621 Burwood Hwy, Knoxfield, Victoria, 3180
B
Botany Department, La Trobe University, Bundoora, Victoria, 3086
INTRODUCTION
Soilborne plant pathogens including Pythium spp, Fusarium spp,
and Rhizoctonia spp, can cause important diseases such as root
rot and damping off, resulting in heavy crop losses in vegetables
farms. Control of these diseases is problematic because these
pathogens have a wide host range and survive in soil as
oospores, chlamydospores and melanised hyphae, respectively,
for long periods. Compounds derived from plant extracts have
been proposed as potential control treatments for soilborne
pathogens due to their antimicrobial activity in laboratory
studies (1). For instance, essential oils can contain phenolic and
terpenoid compounds which have antimicrobial properties (2).
The antimicrobial activity of thyme oil has been shown to cause
hyphal collapse by membrane disruption (1). In Australia, very
few studies have investigated the effects of antimicrobial volatile
compounds in essential oils on survival of soilborne pathogens.
Our work is therefore investigating the antimicrobial activity of
compounds derived from a range of essential oils and other
plant extracts against key soilborne pathogens isolated from
vegetable crops. Preliminary results from in vitro experiments
are reported here.
MATERIALS AND METHODS
A series of in vitro experiments were conducted to investigate
the effects of plant extracts on mycelial growth of soilborne
pathogen isolates. Treatments tested included the active
constituents (eugenol, thymol, carvacrol and geraniol) of some
essential oils as well as 14 essential oils (thyme, clove bud,
peppermint, geranium, eucalyptus, tea tree, origanum,
rosemary, orange sweet, cardamon, sweet fennel, pine, black
pepper and basil). The pathogenic isolates tested included
Pythium sulcatum, P. aphanidermatum, P. irregulare, Fusarium
oxysporum and a Rhizoctonia sp. Solutions of the actives and the
oils were added to sterile suitable selective media at
concentrations of 500, 1000, and 2500 ppm. A 5 mm mycelial
plug was then plated onto the amended media. Plates with Pythium were incubated at 20ºC and those with Fusarium and Rhizoctonia at room temperature. Mycelial growth, expressed as
colony diameter, was measured until mycelium in unamended
plates reached the edge of the plate. After this, plugs that did
not grow were transferred to fresh unamended media to
determine whether the treatments were fungistatic or
fungicidal. Examples of results are given for some of the isolates
tested to illustrate the suppressive and biocidal effects of some
of the oil treatments tested.
RESULTS
All concentrations of the four plant actives significantly (p<0.001)
inhibited mycelial growth of all isolates tested. Mycelial plugs of
these isolates did not regrow once transferred to fresh media.
Treatments containing the essential oils thyme, origanum and
clove bud also significantly inhibited mycelium (p<0.001) at all
concentrations and mycelium did not regrow on fresh media.
However, other oil treatments varied, with some only
suppressing mycelial growth at higher concentrations. For
instance, 2500 ppm geranium, peppermint and pine oils
significantly (p<0.001) reduced mycelial growth of F. oxysporum
and Rhizoctonia sp., compared to unamended controls (Table 1).
This effect was also observed for P. aphanidermatum, P. sulcatum and P. irregulare. Geranium oil completely inhibited
growth of F. oxysporum and Rhizoctonia sp. at 1000 and 2500
ppm (Table 1), and growth did not resume on fresh media. Pine
oil completely inhibited Rhizoctonia sp. at 1000 ppm and 2500
ppm (Table 1), but mycelial growth resumed at 1000 ppm. Basil,
cardamon, sweet fennel and tea tree oils only suppressed
growth at the highest concentration tested, and mycelial growth
resumed on fresh media. Rosemary, eucalyptus, orange sweet
and black pepper oils did not inhibit mycelial growth compared
to the unamended plates.
Table 1. Effects of three oil treatments on mycelial growth in vitro.
Oil/Pathogen % inhibition of mycelial growth 1
500 ppm 1000 ppm 2500 ppm Pine oil F. oxysporum 26.4 79.3 1002 Rhizoctonia sp. 69.7 100 1002 Peppermint oil F. oxysporum 20.3 35 65.3 Rhizoctonia sp. 0 45.3 94.12 Geranium oil F. oxysporum Rhizoctonia sp. 55.9 43.5 1002 1002 1002 1002 1 % inhibition compared to unamended controls at 10 days. 2 No mycelial growth resumed after transfer to fresh media. DISCUSSION
Preliminary in vitro results indicate that four plant extract actives
and three essential oils were biocidal to mycelium of some
isolates of soilborne pathogens from vegetable crops. Other oil
treatments only delayed mycelial growth but did not affect
mycelium viability, or had no effect on mycelial growth at all.
The biocidal activity observed by origanum, clove bud and thyme
oils against Pythium spp, Fusarium oxysporum and Rhizoctonia
sp. is likely to be due to specific chemical compounds contained
in these oils. For instance, carvacrol and thymol, also found to
have biocidal effects, are major components of origanum and
thyme oils respectively (2). Future experiments will determine
which compounds and dosages are the most effective at killing
mycelium and other resting structures of pathogens. The
mechanisms by which these compounds affect inoculum viability
will be investigated to better understand their mode of action so
they can be developed further for disease control.
ACKNOWLEDGEMENTS
This work has been funded by the Department of Primary
Industries Victoria and Horticulture Australia Ltd (HAL) using the
vegetable levy and matched funds from the Australian
government.
REFERENCES
1. Zambonelli, A., D Zechini D’Aulerio, A., Bianchi, A., Albasini, A. (1996) J. of Phytopathology 144, 491–494.
2. Sun Og Lee, Gyung Ja Choi, Kyuong Soo Jang, He Kyoung Lim, Kwang Yun Cho and Jin‐Cheol Kim (2007). J. of Plant Pathology 23 (2), 97–102
Keynote
address
Use of grid weather forecast data to predict rice blast development in Korea
Wee Soo Kang1, Kyu Rang Kim2, and Eun Woo Park{ XE "Park, E.W." }11
Department of Agricultural Biotechnology, Seoul National University, Seoul 151‐921, Korea
2
Applied Meteorological Research Lab., National Institute of Meteorological Research, Korea Meteorological Administration, Seoul
156‐720, Korea
Timely warnings on plant disease development are useful
information for farmers to determine when to spray fungicides
to control plant diseases. Real‐time weather data monitored by
automated weather stations are often used to generate disease
forecast information. However, when observed weather data are
used, the time window for effective fungicide sprays after the
disease warnings could be too short and farmers may fail to
control the disease in time even though accurate disease
forecast is available. In order to minimise the time limitations
associated with real‐time disease forecasting, the weather
forecast data need to be used for disease forecasting. At every
3 hours, the Korea Meteorological Administration (KMA)
releases 48‐hour weather forecasts at 3‐hour intervals on air
temperature, relative humidity, and probability of precipitation
and at 12‐hour intervals on precipitation based on the outputs
from numerical weather prediction models. The spatial
resolution of weather forecasts is 5 km. Using the grid weather
forecasts, rice blast disease forecasting was conducted. The grid
forecast data at 3 hour intervals are interpolated to produce
hourly data. Hourly wetness period was estimated from a simple
relative humidity model and a CART model using temperature,
relative humidity, precipitation, and wind speed. Based on the
hourly weather data, daily risk levels of rice blast infection were
determined at the spatial resolution of 5 km in the map image.
The results suggested that estimation of hourly leaf wetness
needs to be improved to enhance the accuracy in forecasting
infection periods.