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Plant domestication decreases both constitutive and induced chemical defences by direct selection against defensive traits.

ABSTRACT: Studies reporting domestication effects on plant defences have focused on constitutive, but not on induced defences. However, theory predicts a trade-off between constitutive (CD) and induced defences (ID), which intrinsically links both defensive strategies and argues for their joint consideration in plant domestications studies. We measured constitutive and induced glucosinolates in wild cabbage (Brassica oleracea ssp. oleracea) and two domesticated varieties (B. oleracea var. acephala and B. oleracea var. capitata) in which the leaves have been selected to grow larger. We also estimated leaf area (proxy of leaf size) to assess size-defence trade-offs and whether domestication effects on defences are indirect via selection for larger leaves. Both CD and ID were lower in domesticated than in wild cabbage and they were negatively correlated (i.e. traded off) in all of the cabbage lines studied. Reductions in CD were similar in magnitude for leaves and stems, and CD and leaf size were uncorrelated. We conclude that domestication of cabbage has reduced levels not only constitutive defences but also their inducibility, and that reductions in CD may span organs not targeted by breeding. This reduction in defences in domesticated cabbage is presumably the result of direct selection rather than indirect effects via trade-offs between size and defences.

SUBMITTER: Moreira X

PROVIDER: S-EPMC6107632 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Plant domestication decreases both constitutive and induced chemical defences by direct selection against defensive traits.

Moreira Xoaquín X Abdala-Roberts Luis L Gols Rieta R Francisco Marta M

Scientific reports 20180823 1

Studies reporting domestication effects on plant defences have focused on constitutive, but not on induced defences. However, theory predicts a trade-off between constitutive (CD) and induced defences (ID), which intrinsically links both defensive strategies and argues for their joint consideration in plant domestications studies. We measured constitutive and induced glucosinolates in wild cabbage (Brassica oleracea ssp. oleracea) and two domesticated varieties (B. oleracea var. acephala and B. ...[more]

PMID: 30140028

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Project description:Background and aimsMost crops have been dramatically altered from their wild ancestors with the primary goal of increasing harvestable yield. A long-held hypothesis is that increased allocation to yield has reduced plant investment in defence and resulted in crops that are highly susceptible to pests. However, clear demonstrations of these trade-offs have been elusive due to the many selective pressures that occur concurrently during crop domestication.MethodsTo provide a robust test of whether increased allocation to yield can alter plant investment in defence, this study examined fruit chemical defence traits and herbivore resistance across 52 wild and 56 domesticated genotypes of apples that vary >26-fold in fruit size. Ninety-six phenolic metabolites were quantified in apple skin, pulp and seeds, and resistance to the codling moth was assessed with a series of bioassays.Key resultsThe results show that wild apples have higher total phenolic concentrations and a higher diversity of metabolites than domesticated apples in skin, pulp and seeds. A negative phenotypic relationship between fruit size and phenolics indicates that this pattern is driven in part by allocation-based trade-offs between yield and defence. There were no clear differences in codling moth performance between wild and domesticated apples and no overall effects of total phenolic concentration on codling moth performance, but the results did show that codling moth resistance was increased in apples with higher phenolic diversity. The concentrations of a few individual compounds (primarily flavan-3-ols) also correlated with increased resistance, primarily driven by a reduction in pupal mass of female moths.ConclusionsThe negative phenotypic relationship between fruit size and phenolic content, observed across a large number of wild and domesticated genotypes, supports the hypothesis of yield-defence trade-offs in crops. However, the limited effects of phenolics on codling moth highlight the complexity of consequences that domestication has for plant-herbivore interactions. Continued studies of crop domestication can further our understanding of the multiple trade-offs involved in plant defence, while simultaneously leading to novel discoveries that can improve the sustainability of crop production.

Project description:Summary Chemical signals mediate major ecological interactions in insects. However, using bioassays only, it is difficult to quantify the bioactivity of complex mixtures, such as volatile defensive secretions emitted by prey insects, and to assess the impact of single compounds on the repellence of the entire mixture. To represent chemical data in a different perceptive mode, we used a process of sonification by parameter mapping of single molecules, which translated chemical signals into acoustic signals. These sounds were then mixed at dB levels reflecting the relative concentrations of the molecules within species-specific secretions. Repellence of single volatiles, as well as mixtures of volatiles, against predators were significantly correlated with the repulsiveness of their respective auditory translates against humans, who mainly reacted to sound pressure. Furthermore, sound pressure and predator response were associated with the number of different molecules in a secretion. Our transmodal approach, from olfactory to auditory perception, offers further prospects for chemo-ecological research and data representation. Highlights • The defensive secretion emitted by insects is often a mixture of volatiles• Volatiles were translated into sounds by sonification using parameter mapping• Chemical signals were repulsive for predators, as were the sounds for humans The bigger picture Insects are often defended against predators by emitting volatile secretions that act as a repellent. Chemical analyses of a secretion provide a list of compounds and their concentrations, but it then remains challenging to study their single and combined bioactivities. Here, we provide a first approach in understanding the bioactivity of single volatiles and volatile mixtures by developing a process of sonification (parameter mapping) to model chemical signals into auditory ones. Our study reveals via bioassays that foraging predators are repelled by volatiles as are human volunteers upon hearing "sonified volatiles". In these audio clips, we could also identify one sound attribute, their maximal loudness, that correlates well with the human response in the modeled world and hence with the predator response in the real world. These findings may help in exploring and understanding the seemingly overabundant diversity of deleterious chemicals present in insects and other organisms. A methodology is described to predict and compare the interspecific repellence of defensive secretions from insects that typically emit volatiles as complex mixtures. Sonification by parameter mapping allowed us to hear single molecules, then their mixtures. Bioassays used insect predators tested against the two sets of stimuli, single and mixed volatiles, as well as humans hearing the corresponding auditory translates. The model based on gathered chemical data can serve as a proxy but quantitative indicator of repellent bioactivities.

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Plant domestication decreases both constitutive and induced chemical defences by direct selection against defensive traits.

Publications

Plant domestication decreases both constitutive and induced chemical defences by direct selection against defensive traits.

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