Abstract
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.
Highlights
Plants are continuously under attack by a variety of pests and pathogens
We addressed the following questions: (i) can tomato seed treatments with jasmonic acid (JA) confer resistance to western flower thrips (WFT)? (ii) if so, are the defense responses against thrips elicited by JA seed soaking cultivar dependent? (iii) what mechanisms underlie this elicitor-mediated resistance? and (iv) can tomato seed scarification, prior to exogenous JA seed treatment, augment thrips resistance in cultivars that are non-responsive?
With the aim to explore whether seed scarification could augment JA receptivity at the seed stage, we evaluated the effect of scarification on JA-induced defenses against WFT, using tomato seeds of one of the non-responsive tomato cultivars
Summary
Plants are continuously under attack by a variety of pests and pathogens. Plants may deploy inducible defenses that are activated in response to an attack. For several decades it is known that activation of the JA signaling pathway is characterized by induction of multiple defensive traits including secondary metabolites (Bennett and Wallsgrove, 1994; War et al, 2012), proteins (Farmer and Ryan, 1990; Thaler et al, 1996), leaf trichomes (Boughton et al, 2005) as well as indirect induction mechanisms such as the production of plant volatiles (Ament et al, 2004; Arimura et al, 2005). Artificial manipulation of these JA-associated defenses by natural or synthetic elicitors has proven to confer enhanced resistance against multiple insects and diseases and is, regarded as a valuable component in pest management programs (Thaler, 1999; Vallad and Goodman, 2004; Walters et al, 2013; Steenbergen et al, 2018)
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