Virulence evolution in the Russian wheat aphid and its impact on Australia’s preparedness strategy
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Virulence evolution in the Russian wheat aphid Cooperative Research Centre for National Plant Biosecurity Owain Edwards | Group Leader, Invertebrate Genomics & Evolution CSIRO ECOSYSTEM SCIENCES, PERTH, WA
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In 2004 a resistance-breaking strain (virulent biotype) of the Russian wheat aphid (RWA), Diuraphis noxia, appeared in the US, throwing into disarray a breeding program initiated in 1986 after the introduction of this invasive pest. Three years later a virulent biotype was also identified in South Africa, the only other country where resistance against RWA was deployed widely. Virulent biotypes of RWA have since been identified from regions of the world where resistance has never been deployed. In response, the grains industry in Australia realised that any strategy of pre-emptive breeding against RWA must protect against the introduction or evolution of virulent biotypes.
Transcript of Virulence evolution in the Russian wheat aphid and its impact on Australia’s preparedness strategy
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Virulence evolution in the Russian wheat aphid
Cooperative Research Centre for National Plant Biosecurity
Owain Edwards | Group Leader, Invertebrate Genomics & Evolution CSIRO ECOSYSTEM SCIENCES, PERTH, WA
biosecurity built on science
The Problem Through the GRDC, the Australian grains industry is
developing a RWA pre-emptive breeding strategy
History has demonstrated that any widespread deployment of RWA-resistant lines leads to the appearance of resistance-breaking (virulent) biotypes
How can we ensure that resistant lines developed for Australia will be effective against an RWA incursion, and will remain durable?
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Aims
To understand the mechanisms of virulence evolution in RWA, and
To use this information to inform the RWA pre-emptive breeding program to assist in the breeding of RWA-resistant lines
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RWA recent history Evidence for a host shift to cereals in last 10,000
years - all RWA worldwide can be traced back to a single
mitochondrial haplotype (Bo Zhang’s CRCNPB PhD project)
Virulent biotypes are closely related to virulent
biotypes in same area
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RWA damage symptoms
Leaf rolling
Chlorosis
Biomass reduction
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Aphid Feeding
Courtesy of F. Tjallingii
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Aphid salivary genomics
Aphid salivary proteins are somehow evolving faster than their homologues in other insects
Most often achieved through gene duplication and diversifying selection
ACYPI000001 ACYPI006675
ACYPI000734 ACYPI008967 ACYPI001389 ACYPI003280
ACYPI003669
ACYPI001227 ACYPI001092 ACYPI007583 ACYPI002583 ACYPI003165 ACYPI005810 ACYPI010198 ACYPI009427 ACYPI004403
IAGC 2010. PLoS Biology
Carolan et al. 2011. J. Proteom. Res.
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Aphid salivary transcriptomics
High levels of transcript diversity in salivary gland genes
Transcripts all related to the same pea aphid orthologue, suggesting they are alleles of the same gene rather than arising from gene duplicates
Transcriptional infidelity?
Cui et al. 2012. Insect Science
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Virulence phenotypes
SA1 SA20
50
100
150
200
250
300
350
SA1 SA20.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
SA1 SA20
2
4
6
8
10Aphid Numbers Leaf Rolling Chlorosis
Leaf rolling always proportional to aphid population growth Chlorosis can be independent of leaf rolling (and aphid numbers)
Jimoh et al, 2011. Ent Exp Appl
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Mexico HungaryMexico Hungary
Frac
tion
of p
lant
s
0.0
0.2
0.4
0.6
0.8
ResistantSusceptible
Wheat Barley
Mexico HungaryMexico Hungary
Frac
tion
of p
lant
s
0.0
0.2
0.4
0.6
0.8
1.0
ResistantSusceptible
Wheat Barley
Virulence phenotypes Virulence phenotype often varies with host plant “Hypervirulence” phenotype: excessive chlorosis
Leaf rolling Chlorosis
Edwards et al., in prep
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Summary Rapid evolution of salivary gland genes allows RWA to quickly
develop resistance-breaking virulent biotypes
Leaf rolling and chlorosis are independent damage symptoms, and can depend on the host plant o Leaf rolling is adaptive, associated with aphid population
growth o Chlorosis is maladaptive, perhaps a reflection of the novel
host association with cereals
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Ongoing research
RNASeq (transcriptome) comparisons of biotypes o “virulence” comparisons (population growth/leaf rolling) o “hypervirulence” comparisons (chlorosis)
Assisting the Australian and global RWA breeding efforts
o demonstrating the need to measure all symptoms (because they are independent)
o providing access to both “virulent” and “hypervirulent” biotypes at CSIRO’s European Laboratory
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Acknowledgements
Jerry Reeck, John Reese, Mike Smith
Jim Carolan, Tom Wilkinson
Ted Botha
Feng Cui, Le Kang
