Fruit Decay to Diseases: Can Induced Resistance and Priming Help?

Humanity faces the challenge of having to increase food production to feed an exponentially growing world population, while crop diseases reduce yields to levels that we can no longer afford. Besides, a significant amount of waste is produced after fruit harvest. Fruit decay due to diseases at a post-harvest level can claim up to 50% of the total production worldwide. Currently, the most effective means of disease control is the use of pesticides. However, their use post-harvest is extremely limited due to toxicity. The last few decades have witnessed the development of safer methods of disease control post-harvest. They have all been included in programs with the aim of achieving integrated pest (and disease) management (IPM) to reduce pesticide use to a minimum. Unfortunately, these approaches have failed to provide robust solutions. Therefore, it is necessary to develop alternative strategies that would result in effective control. Exploiting the immune capacity of plants has been described as a plausible route to prevent diseases post-harvest. Post-harvest-induced resistance (IR) through the use of safer chemicals from biological origin, biocontrol, and physical means has also been reported. In this review, we summarize the successful activity of these different strategies and explore the mechanisms behind. We further explore the concept of priming, and how its long-lasting and broad-spectrum nature could contribute to fruit resistance.This work was funded by the BBSRC Future Leader Fellowship BB/P00556X/1 to E.L., by Bordeaux University and INRA, Bordeaux Metabolome Facility and MetaboHUB (ANR-11-INBS-0010 project) to P.P., and by the H2020-MSCA-IF-2016-EPILIPIN-746136 to A.L.Peer reviewe

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Defense Priming: An Adaptive Part of Induced Resistance

Priming is an adaptive strategy that improves the defensive capacity of plants. This phenomenon is marked by an enhanced activation of induced defense mechanisms. Stimuli from pathogens, beneficial microbes, or arthropods, as well as chemicals and abiotic cues, can trigger the establishment of priming by acting as warning signals. Upon stimulus perception, changes may occur in the plant at the physiological, transcriptional, metabolic, and epigenetic levels. This phase is called the priming phase. Upon subsequent challenge, the plant effectively mounts a faster and/or stronger defense response that defines the postchallenge primed state and results in increased resistance and/or stress tolerance. Priming can be durable and maintained throughout the plant's life cycle and can even be transmitted to subsequent generations, therefore representing a type of plant immunological memory

Primed plants do not forget

In their struggle for life, plants can employ sophisticated strategies to defend themselves against potentially harmful pathogens and insects. One mechanism by which plants can increase their level of resistance is by intensifying the responsiveness of their immune system upon recognition of selected signals from their environment. This so-called priming of defence can provide long-lasting resistance, which is based on a faster and/or stronger defence reaction upon pathogen or pest attack. Priming can target various layers of induced defence that are active during different stages of the plant–attacker interaction. Recent discoveries have extended our knowledge about the mechanistic basis of defence priming and suggest that a primed defence state can be inherited epi-genetically from defence-expressing plants. In this review, we provide an overview of the latest insights about defence priming, ranging from early responses controlled by adjustments in hormone-dependent signalling pathways and availability of signal transduction proteins, to longer lasting mechanisms that involve possible regulation chromatin modification or DNA methylation

Optimizing chemically induced resistance in tomato against <i>Botrytis cinerea</i>

Resistance-inducing chemicals can offer broad-spectrum disease protection in crops, but can also affect plant growth and interactions with plant-beneficial microbes. We have evaluated different application methods of β-aminobutyric acid (BABA) and jasmonic acid (JA) for long-lasting induced resistance in tomato against Botrytis cinerea. In addition, we have studied nontarget effects on plant growth and root colonization by arbuscular mycorrhizal fungi (AMF). Germinating seeds for 1 week in BABA- or JA-containing solutions promoted seed germination efficiency, did not affect plant growth, and induced resistance in 4-week-old plants. When formulating BABA and JA in carboxymethyl cellulose seed coating, only BABA was able to induce resistance in 4-week-old plants. Root treatment of 1-week-old seedlings with BABA or JA also induced resistance in 4-week-old plants. However, this seedling treatment repressed plant growth at higher concentrations of the chemicals, which was particularly pronounced in hydroponically grown plants after BABA treatment. Both seed coating with BABA, and seedling treatments with BABA or JA, did not affect AMF root colonization in soil-grown tomato. Our study has identified commercially feasible application methods of BABA and JA, which induce durable disease resistance in tomato without concurrent impacts on plant growth or colonization by plant-beneficial AMF. </jats:p

Fine Tuning of Reactive Oxygen Species Homeostasis Regulates Primed Immune Responses in Arabidopsis

Selected stimuli can prime th e plant immune system for a faster and stronger defense reaction to pathogen attack. Pretreatment of Arabidopsis with the chemical agent β - aminobutyric acid (BABA) augmented H 2 O 2 and callose production after induction with the pathogen-associated molecular pattern (PAMP) chitosan, or inoculation with the necrotrophic fungus Plectosphaerella cucumerina. How- ever, BABA failed to prime H 2 O 2 and callose production after challenge with the bacterial PAMP Flg22. Analysis of Arabidopsis mutants in reactive oxygen species (ROS) pro- duction ( rbohD ) or ROS scavenging ( pad2 , vtc1 , and cat2 ) suggested a regulatory role for ROS homeostasis in prim- ing of chitosan- and P. c u c u m e r i n a -inducible callose and ROS. Moreover, rbohD and pad2 were both impaired in BABA-induced resistance against P. cucumerina . Gene ex- pression analysis revealed direct induction of NADPH/res- piratory burst oxidase protein D ( RBOHD ), γ -glutamylcys- teine synthetase 1 ( GSH1 ), and vitamin C defective 1 ( VTC1 ) genes after BABA treatment. Conversely, ascorbate peroxi- dase 1 ( APX1 ) transcription was repressed by BABA after challenge with chitosan or P. cucumerina , probably to pro- vide a more oxidized environment in the cell and facilitate augmented ROS accumulation. Measuring ratios between reduced and oxidized glutathione confirmed that augmented defense expression in primed plants is associated with a more oxidized cellular status. Together, our data indicate that an altered ROS equilibrium is required for augmented defense expression in primed plants