Elicitor Application in Strawberry Results in Long-Term Increase of Plant Resilience Without Yield Loss.

For a first step integrating elicitor applications into the current IPM strategy increasing plant resilience against pests, we investigated repeated elicitor treatments in a strawberry everbearer nursery and cropping cycle under glass. During nursery methyl-jasmonate (MeJA), testing induction of defenses with plant bioassays was applied every 3 weeks. Thrips damage and reproduction by spider mites, whitefly and aphids were strongly reduced upon elicitor treatment. Subsequently, we applied MeJA every 3 weeks or based on scouting pests during a whole cropping cycle. Thrips leaf bioassays and LC-MS leaf metabolomics were applied to investigate the induction of defenses. Leaf damage by thrips was lower for both MeJA application schemes compared to the control except for the last weeks. While elicitor treatments after scouting also reduced damage, its effect did not last. Thrips damage decreased from vegetative to mature plants during the cropping cycle. At the end of the nursery phase, plants in the elicitor treatment were smaller. Surprisingly, growth during production was not affected by MeJA application, as were fruit yield and quality. LC-MS leaf metabolomics showed strong induction of vegetative plants decreasing during the maturation of plants toward the end of cultivation. Concurrently, no increase in the JA-inducible marker PPO was observed when measured toward the end of cultivation. Mostly flavonoid and phenolic glycosides known as plant defense compounds were induced upon MeJA application. While induced defense decreased with the maturation of plants, constitutive defense increased as measured in the leaf metabolome of control plants. Our data propose that young, relatively small plant stages lack constitutive defense necessitating an active JA defense response. As plants, mature constitutive defense metabolites seem to accumulate, providing a higher level of basal resistance. Our results have important implications for but are not limited to strawberry cultivation. We demonstrated that repeated elicitor application could be deployed as part of an integrated approach for sustainable crop protection by vertical integration with other management tactics and horizontal integration to control multiple pests concurrently. This approach forms a promising potential for long-term crop protection in greenhouses.

Host plant resistance to thrips (Thysanoptera: Thripidae) - current state of art and future research avenues.

Integrated Pest Management (IPM) is endorsed as the future standard for crop protection worldwide. This holistic concept integrates preventative and curative measures amongst which host plant resistance (HPR) plays an essential role. Up to now HPR has been a somewhat under-utilized tool in pest management due to widespread use of pesticides and technological hindrance. Thrips are key pests in agriculture and horticulture worldwide. Here we provide an overview on the current status of research on constitutive and induced HPR including thrips-host relationships and thrips as virus vectors. We stress modulation of plant defense responses by abiotic and biotic elicitors to increase HPR and provide an outlook on the increasing potential of HPR inspired by the fast advancement of -omics techniques.

Cultivar Variation in Tomato Seed Coat Permeability Is an Important Determinant of Jasmonic Acid Elicited Defenses Against Western Flower Thrips.

Induction of defenses is one of the most widely accepted eco-friendly approaches for management of pests and diseases. Seeds are receptive to resistance-inducing chemicals and could offer broad-spectrum protection at the early stages of development. However, seed treatment with elicitors has previously been shown to differentially influence induced defense responses among cultivars and thus, could hamper commercial exploitation. In this context, the objective of the present study was to evaluate the genotype-dependent ability of jasmonic acid (JA) to induce resistance against western flower thrips (WFT) at the seed stage. We examined the variation in inducibility of resistance in eight commercial tomato cultivars. Causal factors accounting for discrepancies in JA-induced responses at the seed stage were phenotypically and biochemically evaluated. Seed receptivity to exogenous JA appeared to be cultivar dependent. Thrips associated silver damage was only reduced in JA seed-treated plants of cultivar Carousel. Enhancement of resistance, was not associated with activation of defense-related traits such as polyphenol oxidase activity (PPO), trichomes or volatiles. Sulfuric acid scarification, prior to JA seed incubation, significantly augmented the embryonic responsiveness to JA in cv. Moneymaker without an adverse effect on growth. Hence, these results support the hypothesis that seed coat permeability is a key factor for successfully inducing JA mediated thrips defenses. The outcome of our study is of translational value as it creates opportunities for the seed industry to perform pre-treatments on non-responsive cultivars as well as for tomato breeding programs to select for genetic traits that affect seed permeability.

Water Dipping of Auxin Coated Chrysanthemum Cuttings Confers Protection against Insect Herbivores.

Auxins are commonly used for commercial propagation of chrysanthemums by stem cuttings. Recent studies imply that these root-promoting hormones also affect plant defense responses. The underlying motive of this study stems from the serendipitous observation that water dipping of auxin-coated cuttings beneficially affected thrips herbivory. Therefore, the primary objective of this investigation was to explore the role of indole-3-butyric acid (IBA) in relation to herbivore susceptibility in chrysanthemum. We observed contrasting findings concerning the physical presence of IBA and it's role in promoting susceptibility of cuttings to thrips, which may in part be explained by the phenotypical variations of cuttings generated from mother plants. Nonetheless, we repeatedly demonstrated considerable protection, in some experiments up to 37%, against thrips and leaf miner upon water dipping of IBA-coated cuttings. Assessment of polyphenol oxidase activity (PPO), 14 days after dipping treatment, suggests that neither direct induction nor priming of plant defenses are involved. Future experiments aimed at understanding the early signaling events may help to explain the underlying mechanisms involved in conferring herbivore protection. We propose a dual role for auxins in early integrated pest management strategies to maximize plant development and minimize herbivory through feasible, cost-effective water dipping treatments.

Thrips advisor: exploiting thrips-induced defences to combat pests on crops.

Plants have developed diverse defence mechanisms to ward off herbivorous pests. However, agriculture still faces estimated crop yield losses ranging from 25% to 40% annually. These losses arise not only because of direct feeding damage, but also because many pests serve as vectors of plant viruses. Herbivorous thrips (Thysanoptera) are important pests of vegetable and ornamental crops worldwide, and encompass virtually all general problems of pests: they are highly polyphagous, hard to control because of their complex lifestyle, and they are vectors of destructive viruses. Currently, control management of thrips mainly relies on the use of chemical pesticides. However, thrips rapidly develop resistance to these pesticides. With the rising demand for more sustainable, safer, and healthier food production systems, we urgently need to pinpoint the gaps in knowledge of plant defences against thrips to enable the future development of novel control methods. In this review, we summarize the current, rather scarce, knowledge of thrips-induced plant responses and the role of phytohormonal signalling and chemical defences in these responses. We describe concrete opportunities for breeding resistance against pests such as thrips as a prototype approach for next-generation resistance breeding.

Towards eco-friendly crop protection: natural deep eutectic solvents and defensive secondary metabolites.

With mounting concerns over health and environmental effects of pesticides, the search for environmentally acceptable substitutes has amplified. Plant secondary metabolites appear in the horizon as an attractive solution for green crop protection. This paper reviews the need for changes in the techniques and compounds that, until recently, have been the mainstay for dealing with pest insects. Here we describe and discuss main strategies for selecting plant-derived metabolites as candidates for sustainable agriculture. The second part surveys ten important insecticidal compounds, with special emphasis on those involved in human health. Many of these insecticidal metabolites, however, are crystalline solids with limited solubility which might potentially hamper commercial formulation. As such, we introduce the concept of natural deep eutectic solvents for enhancing solubility and stability of such compounds. The concept, principles and examples of green pest control discussed here offer a new suite of environmental-friendly tools designed to promote and adopt sustainable agriculture.

Integrated pest management in western flower thrips: past, present and future.

Western flower thrips (WFT) is one of the most economically important pest insects of many crops worldwide. Recent EU legislation has caused a dramatic shift in pest management strategies, pushing for tactics that are less reliable on chemicals. The development of alternative strategies is therefore an issue of increasing urgency. This paper reviews the main control tactics in integrated pest management (IPM) of WFT, with the focus on biological control and host plant resistance as areas of major progress. Knowledge gaps are identified and innovative approaches emphasised, highlighting the advances in 'omics' technologies. Successful programmes are most likely generated when preventive and therapeutic strategies with mutually beneficial, cost-effective and environmentally sound foundations are incorporated. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.