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Helping plants become healthier

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Ionic liquids are highly customisable compounds and can be designed to perform specific functions. Building on this concept, a team of researchers at the Poznan Science and Technology Park, Poland, have developed substances that mimic those that induce a plant’s natural pathogen defence system. The researchers have designed ionic compounds that not only significantly protect plants from harmful pathogens but also increase crop growth and yield. Their novel custom compounds have opened up an effective and sustainable approach to agriculture that could help satisfy the increasing global demand for food.
An increasing human population creates an ever-growing demand for food. As a result, the use of pesticides to control pests and weeds has become a common practice. According to the UN Food and Agricultural Organization, up to 40% of global crops are lost to pests, with plant diseases and invasive insects costing the global economy $220 billion and $70 billion respectively. However, this does not mean we should use these often highly toxic substances without limit to maximise yields. The EU, regarded as the world leader in the legislation on ecological development and natural environment protection, recognised the need for sustainable development many years ago. EU policies include curbing the use of pesticides to reduce their impact on human health and the environment, as well as incentivising alternative approaches and techniques. The desire to reach these goals is expressed in the directives 1107/2009 and 128/2009, which set out legal requirements defining the active substances allowed for use in agricultural practice. As a result, the number of pesticides available for agricultural production has declined. The first to be eliminated were the substances most toxic to the natural environment although they are often the most effective against pathogens. Their elimination has stimulated the search for new and effective methods of plant protection, employing the use of novel active ingredients that satisfy legal requirements, environmental issues, and societal expectations.

Ionic liquids

A research team at the Poznan Science and Technology Park in Poland, led by Associate Professor Marcin Smiglak, set out to address this gap. The research team uses ionic liquids for the synthesis of new chemical substances with desirable biological properties. Ionic liquids are salts which have a melting point below 100ºC, meaning that they are often liquid at room temperature and exhibit drastically different properties than their neutral derivatives (such as an improved solubility in water). The ionic form of a substance has many advantages compared to its neutral form, and a wide range of properties that can be controlled depending on the choice of ions.

“The systemic acquired resistance (SAR) phenomenon is a very attractive option for reducing the use of plant protection products.”

Ionic liquids are comprised of a positively-charged ion (a cation) and a negatively-charged ion (an anion). They constitute a structural platform on which the properties of cationic or anionic components can, in theory, be independently modified. Introduction of such modifications often requires several chemical reactions, and alteration of the functional groups of individual molecules. However, in any chemical design procedure, each step in the synthesis process creates a new molecule, and its new properties must be verified. This stepwise approach allows the custom design of new properties while still retaining certain other characteristics, for example, biological features of the original components. The development of a wide range of new functional ions offers a library of building blocks from which chemists can design new combinations. The resulting molecules can be ‘tuned’ to exhibit desired physical, chemical, or biological properties simply by manipulating the structures of the component ions.

One area of research in Smiglak’s team is the design and development of new chemical substances that offer a sustainable alternative to conventional pesticides. To date, the researchers have synthesised nearly 150 novel chemical substances that can effectively enhance the natural defence mechanisms of plants.

Systemic acquired resistance

The systemic acquired resistance (SAR) phenomenon is a very attractive option for reducing the use of plant protection products/pesticides (PPP). SAR is a natural mechanism triggered in plants as a response to pathogen attack and results in systemic increased resistance to infections caused by fungi, bacteria, or viruses. The plant SAR response can last for an extended length of time, given repeated applications of its inducer, and conveys resistance to a broad spectrum of pathogens. The use of SAR inducers as a plant protection strategy has a number of advantages over the application of PPPs. It overcomes the problem of pathogen resistance, and it endows long-term resistance against a broad spectrum of pathogens which continues even after the application of SAR inducers is terminated; it usually lasts for weeks after the final application as a result of the stimulation action of the inducer on the plant’s natural defence mechanisms. In addition, the pathogens themselves are not a direct target of the SAR inducer. SAR can be induced via a biological stimulus (eg, pathogen attack, or the mechanical introduction of pathogens by insects) or by chemical agents. Salicylic acid has been identified as the main natural signalling substance for SAR induction, yet SAR can also be induced by artificial inducers such as functional analogues of salicylic acid.

A sustainable approach

Due to their mode of action (which is directed at the stimulation of a plant’s natural defence mechanisms and not toward pathogens directly), SAR inducers are used in much lower doses than typical pesticides, especially fungicides. This is also the case for the SAR inducers developed by Smiglak’s team; their effective doses are in the range of 10–50mg per litre of solution, which scales up to 4–20g of active substance applied per hectare of crop. For comparison, a typical fungicide dose for the same area is around 100–500g (eg, doses of tebuconazole-based fungicides are 190–250g per hectare). In 2019, the use of active substances in pesticides in Europe was on average 1.66kg per hectare of crop land.

Reliable research on new active substances for agricultural applications requires not only comprehensive evaluation of their biological activity but also evaluation of their environmental impact. Therefore, the appropriate approach is to compare the values describing environmental hazards of the approved active substances with those under study to avoid an undesirable substitution. However, apart from intrinsic hazard, it should not be forgotten that SAR inducers are designed to be administered in much lower doses than conventional pesticides. Therefore, potential environmental exposure will be lower than that of conventional pesticides, at the concentrations used to maintain effective plant protection and the stimulation of a plant’s defence systems.

Screening tests for the efficacy of active substances carried out on two plant pathogen models, TMV virus and tobacco model.

More than just plant resistance

Preliminary testing of SAR inducers has been conducted for shorter periods, usually between three to four weeks, and largely focused on investigating the mechanisms that induce plant resistance. Smiglak and his team have also had the opportunity to perform experiments in greenhouse and field conditions over longer time periods, encompassing the entire plant vegetation period.

Taking into account the SAR mechanism, the researchers treated the plant with these substances at the beginning of the growing season to stimulate their resistance towards plant diseases. Notably, the results showed that the plant’s response was much broader than just an induction of defence mechanisms. Positive effects were also observed on plant growth and development, resulting in an increase in quantitative and qualitative parameters of crop yields including green biomass, root zone, fruit size, and rate of metabolism. Plants experienced accelerated growth and higher yield, with an increase in the size and weight of crop.

These results indicate that it is possible to combine the stimulation of plant defence mechanisms and stimulation of plant growth and development, which is in contrast to previous reports that have indicated a trade-off between growth and immunity. This phenomenon suggests that the allocation of plant resources towards induction of resistance results in a reduction in yield, which is particularly risky when such substances are used during the growing season when pathogen pressure does not occur. It turns out, however, that by appropriate application, it is possible to avoid the negative impact of these substances on yield, and it is even possible to increase the yield while providing the plant with enhanced resistance. Smiglak explains that ‘It is appropriate to name such substances not only as resistance inducers but as plant growth and development stimulants which also promote plant resistance mechanisms. Therefore, by using SAR inducers, we help plants become healthier.’

“Plant stimulants and plant resistance inducers are a sustainable method of crop production with lower environmental exposure than conventional pesticides.”

The group of best-performing compounds have been tested on various species of horticultural crops, root crops, and cereals. The results exceeded the expectations. In a field experiment conducted on rapeseed, the addition of plant stimulants to the standard protection programme resulted in an increase in biomass by more than 35% and increased the yield by over 15%. In a field experiment conducted on sugar beet, the standard fungicide programme was effectively completely replaced by treatment with plant stimulants. The protection against pathogens as well as sugar yield were comparable for both types of treatments. In a greenhouse experiment on tomatoes with pathogen inoculation, treatment with plant stimulants inhibited infection by more than 80% compared to untreated infected plants, while still increasing the yield by nearly 10%. In a greenhouse experiment on tulips conducted with and without the presence of a pathogen, treatment with plant stimulants resulted in an increase in biomass by over 20% and 100% compared to that of untreated plants, respectively.

The effect of plant stimulant treatment in inhibiting development of powdery mildew fungal disease on tomato plants (right) compared to untreated plant (left).

The research team plans to supply external collaborators with samples of developed plant stimulants for further testing on various crops. With continued success, the researchers predict that responsible agricultural practice will adopt their compounds which stimulate of plants’ natural immunity and improve their health, to strengthen the wellbeing of both the environment and humanity.

Your concept of modifying chemical substances to change their properties in a specific direction has demonstrated very positive results. Does this work have other applications?
Most certainly! We have been working with ionic liquids for many years now, and this is one of the main fields of our research. Thanks to a series of modifications of both ionic liquid molecules and the improvement of the synthetic processes themselves, we have successfully implemented this group of compounds in many practical applications. The most important ones are: a) dissolving, recovering or processing biomass (cellulose, lignin); b) production of epoxy composites and biocomposites, in which ionic liquids act as initiators of resin curing and modifiers of the final material (we have experience in designing many modern epoxy systems); and c) design of new materials for nanoimprint lithography, based on ionic liquids, by polymerisation of unsaturated bonds under the influence of electron beam, UV light, or temperature. In our research, controlled modifications of chemical substances have been used primarily to advance research on new materials.



  • Spychalski, M, et al (2021) Use of new BTH derivative as supplement or substitute of standard fungicidal program in strawberry cultivation. Agronomy, 11(6):1031
  • Markiewicz, M, et al (2021) New bifunctional ionic liquid-based plant systemic acquired resistance (SAR) inducers with an improved environmental hazard profile. Green Chemistry, 23(14), 5138–49.
  • Smiglak, M, et al (2017) Dual functional salts of benzo [1.2.3] thiadiazole-7-carboxylates as a highly efficient weapon against viral plant diseases. ACS Sustainable Chemistry & Engineering, 5 (5), 4197–204.

Research Objectives

Marcin Smiglak designs new substances to improve plant health as a novel approach to effective plant protection and the enhancement of plant productivity.


The ‘New plant resistance inducers and their application as innovative approach to plant protection against pathogens’ project is carried out within the Team-Tech (POIR.04/04.00-00-5BD9/17-00) programme of the Foundation for Polish Science, co-financed by the EU under the European Regional Development Fund.


Professor Marcin Smiglak is involved in the development of the concept of dual-function ionic liquids as a tool to obtain unique substances with a wide range of potential applications. After his PhD studies with Professor Robin Rogers at the University of Alabama, he moved to work for industry. Upon returning to Poland, he set up his research group at the Poznan Science and Technology Park. Professor Henryk Pospieszny has worked on ways of inducing the natural defence mechanism of plants that allow protection against pathogens for many years. Dr Rafał Kukawka, the chemist, currently CTO of Innosil, has been working in this group since the beginning. Maciej Spychalski, the biologist, joined the team as a PhD student in 2019.

Marcin Smiglak


E: [email protected]
Innosil Ltd: [email protected]
T: +48 61 827 9700

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