• 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.

• 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

• 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

x10-4 ns/s/yr

plum pox virus 90y 1.4

Oz potyviruses 75y 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

x10-4 ns/s/yrplum pox virus 90y 1.4 Oz potyviruses 75y 1.173cowpea aphid-borne mosaic virus 500y 1.397papaya ringspot virus 300y 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

• aroids (dasheen, taro, yam)• cucurbits (cucumber, melon, squashes)• legumes (beans, cowpea, soybean)• orchids (vanilla) • passifloras

• Why > 2000YBP?

• - humans crossed the Wallace line and arrived in Greater Australia 30-40,000ya

• - climate stable after ice age ended 14-9,000ya

• - Australia and P-NG separated 6,000ya

• - Europeans arrived 400ya Macassarese 200ya

• - 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

• 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)

• 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)

• 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.

• So what?• 20 potyviruses entered Australia in <200 yrs• 3 potyviruses entered UK during 1970-2004

• = 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