THE CALL OF THE WILD - tracking an indirect defence trait in maize

TOBY BRUCE

Rothamsted Research, UK

Domesticated from Zea mays ssp. parviglumis 8,700 years ago

Photo by Nicolle Rager Fuller, NSF

High yielding varieties (HYVs) bred from landraces

Nature Genetics 44, 808–811 (2012)

African smallholders mostly grow LANDRACES not HYVs

Why?

HYPOTHESIS: Landraces are MORE RESISTANT TO STRESSES such as stemborer attack…

are parasitoids more attracted to HIPVs from landraces?

±

24h

Bioassay of response to volatiles from plants WITH and WITHOUT eggs

Tamiru et al. (2011) Ecology Letters 14: 1075

Parasitoid response - landraces

ATTRACTED to plants with eggs

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

Commercial hybrid lines

Tamiru et al. (2011) Ecology Letters 14: 1075

Parasitoid response – commercial hybrids

NOT attracted to plants with eggs

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

Ethanol extract of elicitor

Tamiru et al. (2011) Ecology Letters 14: 1075

Effect is systemic + ELICITOR involved

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

New Project: markers for the trait

Egg induced HIPV emission trait only found in

2 out of 44 commercial hybrid maize lines tested so far

LandracesH

ybridsReference genome (B-73 maize lines)

Why is this indirect defence trait so rare in HYV lines ?

Could it be the legacy of selecting for yield and quality in a pesticide treated background?

Identifying linked molecular markers using GWAS (genome-wide association study)

maize

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

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

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…