TOBY BRUCE THE CALL OF THE WILD - tracking an indirect defence trait in maize TOBY BRUCE Rothamsted...
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THE CALL OF THE WILD - tracking an indirect defence trait in maize
TOBY BRUCE
Rothamsted Research, UK
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Domesticated from Zea mays ssp. parviglumis 8,700 years ago
Photo by Nicolle Rager Fuller, NSF
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High yielding varieties (HYVs) bred from landraces
Nature Genetics 44, 808–811 (2012)
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African smallholders mostly grow LANDRACES not HYVs
Why?
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HYPOTHESIS: Landraces are MORE RESISTANT TO STRESSES such as stemborer attack…
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are parasitoids more attracted to HIPVs from landraces?
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±
24h
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Bioassay of response to volatiles from plants WITH and WITHOUT eggs
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Tamiru et al. (2011) Ecology Letters 14: 1075
Parasitoid response - landraces
ATTRACTED to plants with eggs
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Volatile profiles - landraces
(a) (E)-ocimene, (b) (R)-linalool, (c) (E)-4,8-dimethyl-1,3,7, nonatriene (DMNT), (d) methyl salicylate, (e) decanal, (f) methyleugenol, (g) (E)-(1R,9S)-caryophyllene, (h) (E)-β-farnesene, (i) (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT).
Tamiru et al. (2011) Ecology Letters 14: 1075
INDUCTION with plants with eggs
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Commercial hybrid lines
Tamiru et al. (2011) Ecology Letters 14: 1075
Parasitoid response – commercial hybrids
NOT attracted to plants with eggs
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Volatile profiles – standard commercial hybrids
(a) (E)-ocimene, (b) (R)-linalool, (c) (E)-4,8-dimethyl-1,3,7, nonatriene (DMNT), (d) methyl salicylate, (e) decanal, (f) methyleugenol, (g) (E)-(1R,9S)-caryophyllene, (h) (E)-β-farnesene, (i) (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT).
Tamiru et al. (2011) Ecology Letters 14: 1075
NO induction with plants with eggs
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Ethanol extract of elicitor
Tamiru et al. (2011) Ecology Letters 14: 1075
Effect is systemic + ELICITOR involved
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African landraces
a = 2-heptanol (stereochemistry undefined), b = decane, c = (R)-limonene, d = methyl benzoate, e = (R)-linalool, f = (E)-4,8-dimethyl-1,3,7-nonatriene, g = cis-p-mentha-2,8-dien-3-ol*, h = methyl salicylate, i = decanal, j = 2,3-dimethylacetophenone*, k = neryl acetate, l = eugenol, m = copaene*, n = germacrene D*
Tamiru et al. (2012) J. Chem. Ecol. 38: 213
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New Project: markers for the trait
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Egg induced HIPV emission trait only found in
2 out of 44 commercial hybrid maize lines tested so far
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LandracesH
ybridsReference genome (B-73 maize lines)
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Why is this indirect defence trait so rare in HYV lines ?
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Could it be the legacy of selecting for yield and quality in a pesticide treated background?
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Identifying linked molecular markers using GWAS (genome-wide association study)
maize
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Quantile-quantile (QQ) –plot of P-values for both parasitoid attraction to the volatiles induced and volatiles induction in response to exposure to the parasitoids. The Y-axis is the observed negative base 10 logarithm of the P-values, and the X-axis is the expected observed negative base 10 logarithm of the P- values under the assumption that the P-values follow a uniform [0,1] distribution. The dotted lines show the 95% confidence interval for the QQ-plot under the null hypothesis of no association between the SNP and the trait.
Parasitoid attraction
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Associated SNPs forParasitoid attraction
Manhattan plot generated using 137940 SNPs in preliminary GWAS analysis for both the trait parasitoid attraction and volatile induction. The X-axis is the genomic position of the SNPs in the genome, and the Y- axis is the negative log base 10 of the P-values. Each chromosome is colored differently. SNPs with stronger associations (based on bonferronoi correction) with the trait will have a larger Y-coordinate value denoted by parallel in light green color
Associated SNPs forVolatile induction
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Conclusion
We are developing molecular markers for a valuable indirect defence trait to facilitate breeding via MAS (marker assisted selection) of maize that has BOTH this trait and higher yield…
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