Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, USA.
Department of Entomology, Cornell University, Ithaca, USA.
Ann Bot. 2019 Jun 24;123(6):1029-1041. doi: 10.1093/aob/mcz010.
Most 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.
To 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.
The 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.
The 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.
大多数农作物与野生祖先相比已经发生了巨大的变化，其主要目标是提高可收获的产量。一个长期存在的假设是，为了提高产量而进行的分配，减少了植物对防御的投资，导致农作物对害虫非常敏感。然而，由于作物驯化过程中同时存在许多选择压力，这些权衡的明确证明一直难以捉摸。
为了提供一个强有力的测试，即增加产量的分配是否可以改变植物对防御的投资，本研究调查了 52 个野生和 56 个驯化的苹果基因型的果实化学防御特性和草食性动物抗性，这些基因型的果实大小差异超过 26 倍。在苹果皮、果肉和种子中定量了 96 种酚类代谢物，并通过一系列生物测定评估了对苹果蠹蛾的抗性。
结果表明，野生苹果的果皮、果肉和种子中的总酚浓度和代谢物多样性均高于驯化苹果。果实大小与酚类物质之间的负表型关系表明，这种模式部分是由产量与防御之间基于分配的权衡所驱动的。野生苹果和驯化苹果之间没有明显的苹果蠹蛾表现差异，也没有总酚浓度对苹果蠹蛾表现的总体影响，但结果确实表明，酚类物质多样性较高的苹果中，苹果蠹蛾的抗性有所提高。少数几种化合物（主要是黄烷-3-醇）的浓度也与抗性的增加有关，这主要是由于雌蛾蛹重的减少。
在大量野生和驯化基因型中观察到的果实大小与酚类物质含量之间的负表型关系，支持了作物产量与防御之间存在权衡的假设。然而，酚类物质对苹果蠹蛾的影响有限，这突出了驯化对植物-草食性动物相互作用的后果的复杂性。对作物驯化的持续研究可以进一步了解植物防御所涉及的多种权衡，同时也可以发现提高作物生产可持续性的新发现。
