Genetic and environmental interactions determine plant defences against herbivores

Abstract

Summary1. Plants express multiple defensive traits, but little is known about the genetic stability and phenotypic plasticity of these traits in nature. To investigate sources of variation and their potential ecological consequences for herbivores, we combined field observations of cyanogenic lima bean with laboratory experiments. 2. Field studies in South Mexico revealed a distinct variability of cyanogenic traits within and among wild lima bean populations. To differentiate among genetic variation and the impact of ambient conditions on plant phenotypes, we used seed-grown plants as well as clones propagated from high-(HC) and low-cyanogenic (LC) wild type plants. 3. In growth chamber experiments, we cultivated plants under three intensities each of drought and salt stress, nutrient supply, and light availability. We consecutively quantified cyanogenesis and total phenolics as chemical defences, soluble proteins as measure of leaf quality, and leaf mass per area and tissue hydration as physical defence-associated traits. 4. Plant traits were genetically stable, as clones propagated from the HC-and LC-mother plants maintained their cyanogenic features and also showed constancy of other leaf parameters tested. 5. In contrast to genetically heterogeneous seed-grown plants, cyanogenesis and soluble protein concentration in clonal plants showed significant variation in response to reduced water supply, increased soil salinity, and fertilization. The other leaf traits, however, showed no significant phenotypic plasticity depending on treatment. 6. Among all traits analysed, genetic and phenotypic variation in cyanogenesis proved the best predictor of herbivore behaviour and development, as LC-plants were preferred by adult Mexican bean beetles and allowed for faster larval development. 7. Synthesis. We demonstrate that (i) functional analyses of plant responses to abiotic factors require methodical separation of genotypic variability and phenotypic plasticity, (ii) different abiotic parameters quantitatively affect the plants' chemical phenotype and that (iii) changes of plant phenotype can have strong impacts on natural herbivores. Our results suggest that genetic variability and phenotypic plasticity of plant anti-herbivore defences allow plant populations to rapidly respond to changing environmental conditions.

Genotype by Environment Interaction Unravels Influence on Secondary Metabolite Quality in Cassava Infested by Bemisia tabaci

“…The possibility of selecting genotypes that are stable within a wide range of environments is due to genomes rapidly responding by selectively regulating the expression of specific genes (Okoth, Rose, Sila, & Viljoen, 2017) in response to environmental changes (Hasanuzzaman et al, 2009). The results agree with Ballhorn et al (2011), where similar selections were made in lima bean studied for biochemical (protein, HCN) responses infested with bean beetle under altered abiotic factors.…”

“…The interaction effects implied that B. tabaci and secondary metabolite concentrations depended on climatic conditions in different locations, in particular seasonal temperature and rainfall variations (Table 1). According to Ballhorn et al (2011), growing conditions influence the genotypes producing metabolite variations due to differing function and expression of genes regulating the traits. Similarly, temperature and rainfall variations were reported to affect plant response to whitefly (Bemisia tabaci) and plant secondary metabolites across environments in aspen juvenile trees (Jamieson et al, 2017).…”

“…However, the changes in metabolite concentration do not always occur in predictable ways (Moore, Andrew, Külheim, & Foley, 2014). Little is known about the phenotypic plasticity of these biochemicals in nature (Ballhorn et al, 2011) and the effect on plant insect interactions (Bohorquez, Tohme, Parsa, & López-lavalle, 2001), suggesting that a consideration of environmental factors as well as plant insect herbivory over a substantial period of time is vital in understanding plant insect resistance.…”

“…The effects of rapidly accelerating environmental changes on local and global scales (Ballhorn et al, 2011) affect plant insect interactions (Jamieson et al, 2017). The simultaneous occurrence of pests and other environmental stresses can either impose a negative (susceptibility) or positive (tolerance) effect on plants depending on the stress, pathogen (Rejeb, Pastor, & Mauch-Mani, 2014), crop and duration of each stress affecting the plant (Ramegowda & Senthil-Kumar, 2015).…”

Exotic Plant Invasion in the Context of Plant Defense against Herbivores

“…Herbivores in native and introduced ranges may influence plant performance to varying degrees but empirical evidence on the impact of specialist and generalist herbivores on the biogeographic differences in the production of chemicals is lacking. Since plant defense against herbivores is influenced by genetic and environmental interaction (Ballhorn et al, 2011), biogeographic comparisons of resource allocation to plant defense and competition traits would help us to better understand the influence of plant defense against herbivores in exotic plant invasion (Fig. 1).…”