Exploiting the immune system to tackle emerging filamentous diseases in tomato

The world's population is expected to increase by 1.6 billion in the next 40 years, which challenges humanity to increase food production by 70%. Despite current control measures, weeds, pests and pathogens claim up to 40% of our major crop yields after use of effective control. Filamentous pathogens (e.g. mildews, molds and late blight) are exceptionally problematic to control as their evolutionary capacity makes them highly proficient on overcoming the resistance offered by genes or chemical pesticides. In the past century, there has been an increasing number of virulent emerging pathogenic fungi. Agricultural systems are extremely vulnerable to emergence and epidemics of filamentous disease due to food mobility and climate change. Moreover, crop cultivation under controlled environment, even when it provides advantages in terms of increased production, it represents a clear disadvantage in controlling the spread of filamentous diseases. Current methods of control depend largely on the use of fungicides, which are under strict European regulation due to its toxicity to human health and the environment. Therefore, it is urgent to develop alternative strategies to control diseases.
Plants are equipped to defend themselves against harmful microbes through constitutive and inducible defence strategies. Alternatively, plants have evolved the capacity to prepare their immune system to respond faster and stronger against attackers. This so-called priming of defence can be triggered by a variety of signals that warn of an upcoming attack, including treatments with priming agents such as b-amino butyric acid (BABA). BABA has been shown to provide protection against a wide spectrum of filamentous diseases. The reason for this outstanding performance is due to its priming activity at different defence signalling pathways that are used by plants to fight diseases with different lifestyles. BABA has been shown to be effective in inducing resistance against a broad-spectrum of diseases in crops such as tomato. Filamentous pathogens are particularly problematic in this crop as they are responsible for yield loses pre- and post-harvest. Therefore, emerging filamentous diseases are a serious threat to the tomato market.
Tomato is a model plant for research in Solanaceae as its genome has been sequenced and crosses with their wild relatives allow the study of the genetics behind different processes. However, only one study in Arabidopsis has investigated genetic variation in the induced resistance response. This project will investigate genetic variation in induced resistance trigger by BABA in tomato with the overarching aim to identify advantageous traits which could potentially maximise the inducible resistance capacity of commercial varieties.
To achieve this aim, I will test BABA-induced resistance against the devastating pathogen Phytophthora infestans (late blight) in a Recombinant Inbred Line (RIL) population from the cross between a commercial tomato cultivar, and an accession of the wild relative. Induced resistance quantification will be done by using a sophisticated phenotyping scanner that can image and analyse different disease parameters in a high-throughput manner. The induced resistance traits (IR-traits) will be identified by sequencing of the significant quantitative trait loci (QTLs) and the molecular mechanisms behind the response will be investigated. The last part of the project will test the hypothesis that multi-directional resistance as a result of the IR-traits offers effective protection against newly identified strains of filamentous pathogens with a high risk of emergence, such as strains of late blight or Fusarium wilt (caused by the multi-host pathogen Fusarium oxysporum).
The results coming from this work will identify the genetic traits to exploit the tomato immune system for enhanced defence against a broad-spectrum of diseases, including emerging pathogens that can have a huge devastation potential.

Agricultural systems are highly exposed to devastating attacks by emerging filamentous pathogens. Current methods of disease control depend on pesticides, increasingly regarded as unsuitable. Research that exploits the plant immune system against these biological threats provides a potential source for future disease control strategies. In addition to the innate immune system, plants have evolved the ability to adapt to hostile conditions by priming their defence mechanisms in response to hostile signals. Priming is triggered by signals that indicate an up-coming attack, including chemical priming agents such as b-amino butyric acid (BABA). BABA-induced resistance is an attractive concept for sustainable agriculture because it provides broad-spectrum resistance in a wide range of plant species, including tomato. The reason for its performance results from it priming multiple defence signalling pathways. Tomato is a host for pests and diseases that limit yield. Genetic variation in the induced resistance response has only been studied before in Arabidopsis. The overall aim of the project is to identify the induced-resistance traits (IR-traits) that maximise the induced resistance capacity of tomato to provide broad-spectrum protection against emerging filamentous diseases. I will use state-of-the-art facilities to quantitatively phenotype BABA-IR in a recombinant inbred line population against the devastating oomycete pathogen Phytophthora infestans. I will then identify and characterise the genetic and molecular mechanisms responsible for the IR-traits. Finally, I will test the hypothesis that multi-directional resistance provided by the IR-traits offers effective protection against new virulent strains of P. infestans and Fusarium oxysporum with highly emerging potential. This work will provide a revolutionary steps-ahead strategy against biological threats by exploiting the immune system to prepare for the fight against rapidly-evolved emerging pathogens.

The project described in my proposal ultimately aims to find solutions to reduce the amount of pesticides in the tomato fields, thus enhancing the highly pursued agricultural sustainability. The main beneficiaries of my research are:

- Global agri-tech community:

Plant breeders. Due to their increasing unsuitability, the use of pesticides in agricultural fields has been highly legislated. In the next few years, practices need to dramatically change in order to implement new strategies that incur in lower costs for the health and environment. Upon project completion, plant breeders will benefit from having new tomato varieties available that enhance the capacity of plants to defend themselves better against emerging diseases.

Farmers. The proposed work develops technology to be implemented into Integrated Pest and Disease Management (IPM). The results will provide new strategies to reduce pesticides in greenhouse-grown tomatoes, therefore, farmers will be offered opportunities to change several agricultural practices that comply with new European regulation. The use of priming agents to boost the immune capacity of the plant will be implemented by the introduction of optimised treatments into the automatic irrigation system under greenhouse growth.

- Distributors and consumers: These two sectors will benefit from the development of new IPM strategies that will lower chemical pesticides residues and the risks of spreading emerging diseases.

- Policy makers. New cultivars and IPM strategies will ultimately provide solutions to secure food production in a sustainable manner. The use of pesticides that are under strict legislation. Therefore, the implications arising from the work described in this proposal will serve policy makers to identify and prioritise the new challenges in food security and safety.

- Global population. UK and global population directly benefit from this work as results will provide alternatives to the use of pesticides, increasingly looked down upon socially. Agriculture and food security is one of BBSRC's strategic priorities and my work will benefit from inspiring the next generations of scientists to pursue careers in plant science and agronomy, thus securing the UK intellectual investment in translational research to provide food security.