We are writing a paper on this exact topic at the moment, submitting in August. We will outline knowledge gaps, constraints and opportunities. Hopefully this will be of general interest. Best wishes, Nick Birch.

We have carried out quite some work on induced systemic resistance against plant virus infections, references to which can be found on my page on ResearchGate. Proteins inducing systemic antiviral resistance have been isolated and characterized from (non-host) higher plants, and evidence has been presented that such resistance could be taking effect through suppression of virus replication.

There is perhaps an expanded sense in which induced resistance can contribute to IPM. My research collaborators and I have discovered that (at least) cereal species can respond to systemic virus infection with an enhanced variation in the expression of genetically determined traits. In a subset of individuals these altered traits (including traits of disease resistance) become stably inherited, amounting to an evolution of trait(s) de novo. In settings in which successive generations of the target population are iteratively subjected to the pressures of pests and diseases one may thus EVOLVE descendant populations with enhanced resistance and/or tolerance.

We illustrate a 'narrow', specific example of this in the paper (available on this site) "Epigenetics serves genetics: Fusarium Head Blight (FHB) resistance in elite wheat germplasm" and expand a little more widely on this idea in a book chapter (particulars in attachment).

The use of plant defense mechanisms, particularly the expression and regulation of the resistance associated with the phenomenon spectrum SAR, emerges as a viable alternative to design. Strategies for the control of pathogens. Understanding the mechanisms by which natural plants are able to defend themselves, will produce plants with higher levels of resistance, without it is necessary to make use of foreign genes to the species or strangers. Although there is still much to investigate, based schemes regulation natural mechanisms of response to attack pathogens, represents a more viable and lasting to produce genetically modified plants. in

contrast to the strategies that tend to introduce unique foreign genes and pathogen resistance, whose ability to confer resistance is overcome quickly by pathogens or insect populations.

I very much concur with the sense of the response given by Dr. Gonzalo Galileo Rivas Platero. It is indeed the case that "... Understanding the mechanisms by which natural plants are able to defend themselves, will produce plants with higher levels of resistance, without it [being] necessary to make use of foreign genes to the species or strangers...".

But the (perhaps unexpectedly) good news is that it is possible to make progress toward more robust and stable expressions of resistance -- even without at first understanding the details of the relevant mechanisms -- if one applies continuing, iterative selection within a matrix of continually applied biotic and abiotic stresses. This provides a setting in which one can EVOLVE more effective expression of existing gene alleles, without needing necessarily to introduce or introgress exotic counterparts.

The beauty of an 'evolutionary' approach is that it one can continue to find more optimized solutions without absolutely needing to know how all the internal moving parts work and interact with each other. As more examples are developed, the 'understanding' can 'evolve' as well.

From our recent research it seems that genotype x environment interactions are very important at each trophic level in the system. This makes induced resistance more 'labile' than constitutive resistance - so needs to be within a tailored IPM system that 'cushions' the up and down regulation of plant defence genes. We also found that some combinations of constitutive and induced resistance work better than others and are investigating the mechanisms of these interactions.

May You please explain more about how You can apply this system? I ask this question because plants are naturally bombarded with different kinds of organisms that some either pathogenic or non-pathogenic can induce host resistance reactions. If You want to use chemical inducers, then You will need costly and labor-needing treatments. If You use biological factors from genes to microorganisms You will have continuous expression of defense genes and products, and this means continuous energy and material consumption that will end to lowered yield. Then, I would be very thankful if You let me learn more.

Dear Babak

application of resistance inducers, although costly, can be one of the few ways to mange diseases for which pesticides are not effective, or where there are no possible (allowed) treatments. Effectiveness is never 100%, but if you are able to contain losses it is a good results. Induced resistance usually declines, except for some inducers as BTH, where in some systems (e.g. some cereals) it can be enough an application at the beginning of the season to protect te crop by different diseases at the same time. You should find the best combination (dose/timing/interval) in each pathosystem. In our recent investigations on grapevines, we did not find any yield reduction, both in qualitative and quantitative parameters of production, also with repeated applications.

@ Dear Gianfranco, Thanks very much for your clear explaining.

I would agree, that each crop/pest system needs to be carefuklly optimised for dose, timing, frequency, combinations...even time of day to apply (circadian cycles in plants can affect induced resistance).

I feel that a lot of work is still needed in this field, and we are here also for that!

Yes, I agree. The interactions can be complex, leading to varying efficacies. So more research isdefinitely needed (as I indicated in my last response). We are doing more at both the fundamental (gene expression) and applied (IPM tools + systems at The James Hutton Institute. Take a look at our IPM web pages if you are interested.

Plant genotype (eg tomato cultivars with different types of partial resistances to pests) show different but consistent responses to primers and elicitors in our EU PURE experiments using a range of chemicals to trigger plant responses. On top of that, the environmental conditions that the plant grows in modify the elicitor responses. So for robust application of inducible plant defences in agriculture or horticulture there is a fair bit of fine tuning required to optimise the use of inducible plant defence in IPM strategies.

I conducted experiment on cotton host plant resistance and found cotton lines having maximum concentration of phenols, condensed tannins and gossypol in floral squares, flowers and seeds caused resistance against spotted bollworm, Earias spp. infestation.

Most induced resistance I've seem gives an additional 10-30% protection, under certain environmental conditions. Plants are responding to multiple stressors in a dynamic way, so continuously changing their resources to try to optimise fitness. So I think induced plant defence can 'top up' plant protection in IPM and reduce selection pressure on constitutive R genes but not as a first lines of defence in most situations where pest/disease pressure is high.

I agree with the comment of Nicholas, I think that we have the chance to go also beyond 30% in specific situations (e.g. phytoplasma diseases, or postharvest decay), and this is very useful when alternatives are poor or lacking. When alternatives are available, we can further improve the effectiveness of other means, so it may be useful a combination of resistance inducers and commonly used strategies (e.g. fungicides or other control means). I feel that most of currently applied treatments to protect plants from diseases and pests has an effect (also) on the host, often not deeply investigated, and NGS approach could be useful to elucidate them.

 We found (not yet published) very clear crop genotype x elicitor interactions (in tomato), so choice of optimal crop varieties could be a key feature of future IPM using induced defence systems. What does NGS stand for (sorry for my ignorance)?

Next generation sequencing, as far as I know the most updated system to quantify gene expression