Unusually hot ambient temperatures (HAT) can cause preanthesis abortion of flowers in many diverse species, limiting crop production. This limitation is becoming more substantial with climate change. Flower primordia of passion fruit (Passiflora edulis Sims) vines exposed to HAT summers, normally abort. Flower abortion can also be triggered by gibberellin application. We screened for, and identified a genotype capable of reaching anthesis during summer as well as controlled HAT conditions, and also more resistant to gibberellin. Leaves of this genotype contained higher levels of endogenous cytokinin. We investigated a possible connection between higher cytokinin levels and response to gibberellin. Indeed, the effects of gibberellin application were partially suppressed in plants pretreated with cytokinin. Can higher cytokinin levels protect flowers from aborting under HAT conditions? In passion fruit, flowers at a specific stage showed more resistance in response to HAT after cytokinin application. We further tested this hypothesis in Arabidopsis. Transgenic lines with high or low cytokinin levels and cytokinin applications to wild-type plants supported a protective role for cytokinin on developing flowers exposed to HAT. Such findings may have important implications in future breeding programmes as well as field application of growth regulators.

BackgroundHerbivore-induced changes in plant traits can cause indirect interactions between spatially and/or temporally separated herbivores that share the same host plant. Feeding modes of the herbivores is one of the major factors that influence the outcome of such interactions. Here, we tested whether the effects of transient aboveground herbivory for seven days by herbivores of different feeding guilds on tomato plants (Solanum lycopersicum) alters their interaction with spatially as well as temporally separated belowground herbivores.Results The transient aboveground herbivory by both chewing caterpillars (Spodoptera exigua) and sucking aphids (Myzus persicae) had significant impacts on plant traits such as plant growth, resource allocation and phytohormone contents. While the changes in plant traits did not affect the overall performance of the root-knot nematodes (Meloidogyne incognita) in terms of total number of galls, we found that the consequences of aboveground herbivory for the plants can be altered by the subsequent nematode herbivory. For example, plants that had hosted aphids showed compensatory growth when they were later challenged by nematodes, which was not apparent in plants that had hosted only aphids. In contrast, plants that had been fed by S. exigua larvae did not show such compensatory growth even when challenged by nematodes.ConclusionThe results suggest that the earlier aboveground herbivory can modify plant responses to subsequent herbivores, and such modifications may depend upon identity and/or feeding modes of the aboveground herbivores.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-017-0115-2) contains supplementary material, which is available to authorized users.

Herbivory‐induced changes in plant resistance and tolerance traits can mediate the interaction between spatially and temporally separated above‐ and below‐ground herbivores. However, it is unknown how long the impact of transient herbivory events last or if legacy effects can be detected systemically in the plant and across plant generations. Here, we studied the impact of transient above‐ground herbivory by the specialist caterpillar Manduca sexta on the plant traits of wild tobacco Nicotiana attenuata and the consequences for below‐ground root‐knot nematodes Meloidogyne incognita in short‐term, long‐term, and transgenerational experiments. In the short‐ and long‐term experiments, above‐ and below‐ground herbivory had significant, albeit independent, impacts on key plant traits such as plant biomass, nutrient content, and secondary metabolites. In addition, herbivory influenced fitness parameters such as seed yield and quality. In the long‐term and transgenerational experiments, transient above‐ground herbivory had facilitating effects on nematodes, irrespective of any treatments of the parental plants. We found evidence for transgenerational legacy effects of both above‐ and below‐ground herbivory on the resistance of progeny plants against above‐ground herbivores. Additionally, below‐ground herbivory in the parental generation increased the root biomass of progeny plants. Synthesis. Our results suggest that herbivory may have a long‐term impact on plant fitness by improving the performance of progeny plants challenged by above‐ and below‐ground herbivory.

Generalist insects show reduced selectivity when subjected to similar, but not identical, host plant chemical signatures. Here, we produced transgenic Arabidopsis thaliana plants that over-express genes regulating the aliphatic- and indolyl- glucosinolates biosynthetic pathways with either a constitutive (CaMV 35S) or a phloem-specific promoter (AtSUC2). This allowed us to examine how exposure to high levels of aliphatic- or indolyl-glucosinolates in homogenous habitats (leaf cage apparatus containing two wild-type or two transgenic leaves) and heterogeneous habitats (leaf cage apparatus containing one wild-type and one transgenic leaf) affects host selection and performance of Bemsia tabaci, a generalist phloem-feeding insect. Data from homogenous habitats indicated that exposure to A. thaliana plants accumulating high levels of aliphatic- or indolyl-glucosinolates negatively affected the performance of both adult females and nymphs of B. tabaci. Data from heterogeneous habitats indicated that B. tabaci adult females selected for oviposition plants on which their offspring perform better (preference-performance relationship). However, the combinations of wild-type and transgenic plants in heterogeneous habitats increased the period of time until the first choice was made and led to increased movement rate on transgenic plants, and reduced fecundity on wild-type plants. Overall, our findings are consistent with the view that both performance and selectivity of B. tabaci decrease in heterogeneous habitats that contain plants with closely-related chemical signatures.

Plants are challenged by both above- and belowground herbivores which may indirectly interact with each other via herbivore-induced changes in plant traits; however, little is known about how genetic variation of the host plant shapes such interactions. We used two genotypes (M4 and E9) of Solanum dulcamara (Solanaceae) with or without previous experience of aboveground herbivory by Spodoptera exigua (Noctuidae) to quantify its effects on subsequent root herbivory by Agriotes spp. (Elateridae). In the genotype M4, due to the aboveground herbivory, shoot and root biomass was significantly decreased, roots had a lower C/N ratio and contained significantly higher levels of proteins, while the genotype E9 was not affected. However, aboveground herbivory had no effects on weight gain or mortality of the belowground herbivores. Root herbivory by Agriotes increased the nitrogen concentration in the roots of M4 plants leading to a higher weight gain of conspecific larvae. Also, in feeding bioassays, Agriotes larvae tended to prefer roots of M4 over E9, irrespective of the aboveground herbivore treatment. Fourier-Transform Infrared Spectroscopy (FT-IR) documented differences in metabolic profiles of the two plant genotypes and of the roots of M4 plants after aboveground herbivory. Together, these results demonstrate that previous aboveground herbivory can have genotype-specific effects on quantitative and qualitative root traits. This may have consequences for belowground interactions, although generalist root herbivores might not be affected when the root biomass offered is still sufficient for growth and survival.