• Over past two decades
• many more gene sequences
• many more methods
• World Wide Web
• >> answers to more subtle questions
• “The hypothesis is proposed that all
plant viruses in Australia were
introduced since European settlement
of the Australia continent towards the
end of the eighteenth century”
• N.H.White 1973.
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Potyviruses
genus Potyvirus in Potyviridae
150+ species
15%+ of all named plant virus species
infect all types of plants, worldwide
transmitted by aphids while probing
many transmitted by seed
flexuous filamentous particles (RNA 10kb)
many potyviruses in Australia
• 5500 potyvirus sequences in Genbank
• 100+ potyviruses recorded in Australia
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coat protein gene sequences of
40+ Australian potyvirus species
Why are there so many potyviruses?
Where did the Australian potyviruses
come from?
Hibbertia virus Y
Hibbertia virus Y
• Australian potyviruses > two groups
• Australia and overseas (17) - mostly in crops
• - twigs of world population (0.2-4.2% varn)
• - close to overseas populations (1.1-7.5%)
• - represent 13 different lineages
• Australia only (18) – mostly in wild and weeds
• - branches of word popn (0.7-15.9% varn)
• - distant from nearest (11-26%)
• - 14/18 are from the BCMV lineage
plum pox virus
Oz potyviruses
90y
75y
x10-4 ns/s/yr
1.4
1.173
• 250,000 species of flowering plants
• 1,800 species ‘domesticated’ (+/-)
• 100 species important
• Before 1492 only two of these species
found in both Old World and New World
• coconut and calabash gourd
plum pox virus
90y
Oz potyviruses
75y
cowpea aphid-borne mosaic virus500y
papaya ringspot virus
300y
x10-4 ns/s/yr
1.4
1.173
1.397
1.25
1.15x10-4 ns/s/yr
radiation 6,600 YBP
assuming lineage-specific rates
(‘relaxed clock’)
• potyviruses radiated 6,600 years ago
when agriculture was spreading fast
especially in Eurasia
• - agriculture provided large populations
of genetically uniform host plants
• - agriculture thereby fostered aphidines
and potyviruses
• Why are most Australian endemic potyviruses
from the BCMV lineage?
• When did they enter Australia?
• How did they enter Australia?
• Hosts of bean common mosaic virus lineage
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aroids (dasheen, taro, yam)
cucurbits (cucumber, melon, squashes)
legumes (beans, cowpea, soybean)
orchids (vanilla)
passifloras
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Why > 2000YBP?
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- humans crossed the Wallace line and arrived in
Greater Australia 30-40,000ya
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- climate stable after ice age ended 14-9,000ya
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- Australia and P-NG separated 6,000ya
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- Europeans arrived 400ya Macassarese 200ya
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- Austronesian expansion from 6,000ya
Austronesians
• - adventurers, fishermen, farmers
• - chickens, pigs, dogs
• - aroids, nuts, fruits, fibres, woods, etc
SUMMARY
• Potyviruses radiated 6,600 years ago when
agriculture was spreading in Eurasia
• Australian potyviruses came in two waves:
• - some were carried across the Wallace line >2000ya, probably
in Austronesian crops, then spread by aphids and in seed
• - others arrived in plant materials imported during the past 200
years by the Europeans from all regions of the world
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The potyviruses of Australia.
Archives of Virology DOI 10.1007/s00705-008-0134-6
Gibbs, A. J., Mackenzie, A. M., Wei, K.-J. and Gibbs, M. J. (2008)
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The Prehistory of Potyviruses: Their Initial Radiation Was during the Dawn of
Agriculture.
PLoS ONE 3(6): e2523. doi:10.1371/journal.pone.0002523
Gibbs, A.J., Ohshima, K., Phillips, M.J., Gibbs, M.J. (2008)
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The bean common mosaic virus lineage of potyviruses; where did it arise and
when?
Archives of Virology?
Gibbs, A.J., Trueman, J., Gibbs, M.J.
John Armstrong, Carlye Baker, Lute Bos, Mark Clements, Vic Eastop, Denis
Fargette, Mathieu Fourment, Pat Gibbs, Bryan Harrison, Roger Jones, Ramon
Jordan, Terry Macfarlane, Rick Mumford, Denis Persley, Brendan Rodoni, Len
Tessorerio, Anupam Varma, Colin Ward, Les Watson, Josef Vetten.
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So what?
• 20 potyviruses entered Australia in <200 yrs
• 3 potyviruses entered UK during 1970-2004
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= c. one significant potyvirus/decade
• 1970-2004 a total of 234 plant pathogen
species arrived in the UK:
• 157 fungi, 27 oomycetes, 26 viruses, 23 bacteria,
one phytoplasma;
• 53% infect ornamentals, 16% horts, 15% wild, 12% agrics,
2% pasture, 2% trees