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Wild radish flowers
Photo: J.K. Scott, CSIRO
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Wild radish flowers showing the range of flower colours
in Western Australia
Photo: J.K. Scott CSIRO
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Background
Wild radish (Raphanus raphanistrum L.) (Brassicaceae)
is one of the most important weeds of crops in southern Australia.
Control of this weed is usually by a combination of herbicide,
crop and pasture rotation and management. One result of the
current shift to minimum till cropping systems has been a
rise in herbicide resistance in wild radish. Some populations
of this weed have developed multiple resistance to herbicide
groups B, C and F. To widen the management options we are
examining the potential to apply inundative or classical biological
control to wild radish.
The Project
Two research directions are being investigated. The region
of origin of wild radish, the circum-Mediterranean countries
are being searched for potential biological control agents
that could be safe to release in Australia. The second approach
is to investigate the biological control potential of pathogens
already in Australia.
Biological control
Classical biological control
Classical biological control of wild radish is a difficult
objective. The main issue is the safety of biological control
because of the shared evolution between wild radish and some
important crop species such as canola and edible radish. The
potential for classical biological control of this exotic
weed in Australia is being investigated in the weed's original
distribution, southern Europe and the circum-Mediterranean
region. Surveys for insects and pathogens were undertaken
in southern parts of Portugal, France, Greece, Spain and northern
Tunisia. Canola crops were also examined when found in association
with wild radish.
About 50 species of phytophagous insects and 15 species of
pathogens were found associated with wild radish. One of the
species being studied is the flower gall midge, Gephyraulus
raphanistri. So far none of the insects or pathogens assessed
appear sufficiently safe for introduction into Australia.
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Galls caused by Gephyraulus raphanistri on wild
radish Tunisia.
Photo: J.K. Scott, CSIRO
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Wild radish affected by Albugo candida (left)
and
healthy flowering stem (right). This pathogen has a
wide host range and was rejected as a potential agent.
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A mycoherbicide from a local pathogen?
The family Brassicaceae contains many of the world's
important weeds, including wild radish. The host range of
pathogens found on Brassicaceae often includes a suite of
related species opening the possibilities of developing mycoherbicides
useful against a range of related weeds. As part of the work
of the CRC for Australian Weed Management, we are examining
the potential for the use of mycoherbicides for the control
of weeds from the family Brassicaceae in Australia, in particular
wild radish. The use of such mycoherbicides would need to
be managed to avoid causing problems in Brassicaceae crops
such as canola.
Initially, a survey for pathogens of wild radish in south-western
Australia was conducted in order to identify gaps in the pathogen
profile that could be filled via classical introductions,
and to determine whether fungi suitable for development into
a mycoherbicide were present. Disease symptoms, incidence
and severity on wild radish were rated at 75 locations throughout
the grain-growing region of south-western Australia and pathogens
isolated and identified.
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Wild radish infestation,
Western Australia.
Photo: J.K. Scott, CSIRO
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White flowers of wild radish showing
through a wheat field, Western Australia
Photo: J.K. Scott, CSIRO
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Ten disease symptoms were recorded on wild radish and were
associated with 11 pathogenic fungal taxa. Alternaria infectoria,
Leptosphaeria maculans and Peronospora parasitica
were most commonly associated with severe disease. Based on
their morphological identity, most of the important fungal
pathogens of wild radish known from elsewhere are present
in south-western Australia. However, the taxonomy of some
of these species, including P. parasitica is under
debate and molecular data is required to clarify the status
of species within these genera. Research is currently being
conducted to compare the molecular taxonomy and host range
of Alternaria and Peronospora pathogens of Brassica
species. This information will enable a decision to be made
on whether a classical or inundative strategy for the biological
control of wild radish, is most promising.
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Peronospora on a wild radish fruit (silique)
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Leptosphaeria causing a leaf lesion
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Alternaria causing necrotic spots on a silique
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Photos: A. Maxwell, CSIRO
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Key People
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Western Australia
Dr John K. Scott
CSIRO Entomology
Researcher in Charge
Ph: +61 8 9333 6647
Fax: +61 8 9333 6646
Email: john.k.scott@csiro.au
Dr Aaron Maxwell
CSIRO Entomology
Ph: +61 8 9333 6159
Fax: +61 8 9333 6646
Email: aaron.maxwell@csiro.au
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France
Janine Vitou
CSIRO European Laboratory, France
Ph: +33 4 67 59 31 00
Fax: +33 4 67 59 90 40
Email: janine.vitou@csiro.au
Mireille Jourdan
CSIRO European Laboratory, France
Ph: +33 4 67 59 31 00
Fax: +33 4 67 59 90 40
Email: mireille.jourdan@csiro.au
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Collaborators
CRC Australian Weed
Management
Publications
Scott, J.K., Vitou, J. and Jourdan, M. (2002). Review of
the potential for biological control of wild radish (Raphanus
raphanistrum) based on surveys in the Mediterranean region.
Proceedings of the 13th Australian Weeds Conference,
eds H. Spafford Jacob, J. Dodd and J.H. Moore, pp. 377-80
(Plant Protection Society of Western Australia, Perth).
Maxwell, A. and Scott, J.K. (2004). The potential for using
mycoherbicides to control weeds from the family Brassicaceae
in Australia. Proceedings of the 14th Australian Weeds
Conference (in press).
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