Reduced Stomatal Density Wheat: New Prospects for Drought and Pathogen Resistance

Lead Research Organisation: National Inst of Agricultural Botany
Department Name: Genetics and Breeding


Stomata are microscopic pores on the surface of leaves that allow gas exchange between plants and the atmosphere. They are crucial for photosynthesis, but water vapour is lost through stomata, and they provide an entry point for damaging diseases. When water is limiting, the stomatal pores adjust to prevent water loss but they can never completely close. We have shown with the test plant Arabidopsis that reducing the number of stomata can improve plant drought resistance by reducing water loss through transpiration. Because of rising carbon dioxide levels these plants showed little or no reduction in photosynthesis. We would like to apply this strategy to wheat so that we can test whether reducing stomatal numbers could improve crop drought tolerance, a major limitation to yield in many parts of the world. We have already generated wheat plants with genetically reduced stomatal numbers, and propose to test whether growing these under drought conditions can improve the total yield of grain harvested. We will check that the alterations we have made in stomatal number and water loss have not had a detrimental effect on the uptake of important minerals, such as phosphate and nitrate by the roots. In addition, we will analyze the wheat grain to ensure that the level of nutrients important for the human diet have not been affected.
Stomata are the only entry point for several important fungal diseases that cause major losses of wheat crops in the UK. We have shown that in addition to being more drought resistant, our Arabidopsis test plants with reduced stomatal number, have the added benefit of reduced entry of disease causing microbes. Therefore an important part of this project will be to test whether the wheat plants that we have identified with reduced stomatal number have enhanced resistance to these fungal diseases. If so, this trait has the potential to protect crop yields, and could be transferred to many crops which are infected by diseases entering through stomata. The experiments to look plant disease tolerance will be carried out by the National Institute of Agricultural Botany (NIAB) in Cambridge.
In Sheffield we have excellent facilities for growing plants under different environmental conditions. We will be able to test whether our wheat continue to perform as well when grown at the raised carbon dioxide levels predicted to occur in the near future. These experiments will be performed on genetically modified (GM) plants but we also propose to isolate wheat variants in genes that are known to be involved in stomatal development through a non-GM technique, so that we can include these in our studies and test them for drought and pathogen resistance.
We hope that one of the commercial members of the Sustainable Agriculture Research & Innovation Club (SARIC) will want to support our work through to commercialising a new drought tolerant wheat variety.

Technical Summary

This project builds on our discovery of a genetic trait that regulates the level of stomatal formation on plant leaves. Our proposal is further underpinned by recent findings from a BBSRC-funded project grant and a DTP studentship, demonstrating that plants with fewer stomata have greatly enhanced water use efficiency and may be better optimised for growth at future atmospheric CO2 levels. We also propose to exploit our recent unpublished work showing that plants with reduced stomatal density have significant tolerance to pathogens that enter through stomata.

In collaboration with NIAB, using BBSRC-BBR funding, we have already introduced this trait into wheat. We are now keen to test the hypothesis in this important crop that 'plants with fewer stomata have enhanced drought tolerance, water use efficiency and pathogen tolerance, particularly at future CO2 levels, without detrimental effect on grain yield, nutrients or quality'. We have initiated a screen to identify non-GM wheat carrying the same genetic trait and already have several good candidates. We expect to identify more in the course of this project and be able to make germplasm available for plant breeding purposes. We will carry out experiments on wheat plants grown with restricted water availability and at elevated CO2. Growth, grain yield, nutrient and quality analysis will be carried out. Pathogen tolerance testing will include three important cereal pathogens; Septoria, brown rust and mildew.

Planned Impact

This project aims to improve drought and pathogen tolerance in wheat, an important food crop both in the UK and around the world. To achieve this we have reduced the number of stomata that develop on wheat leaves. As these are the major routes for water loss from the plant, and entry of several pathogens into the plant, we expect these plants to have enhanced drought and pathogen tolerance. To test this we will use genetically modified plants but part of our project is aimed at identifying non-GM wheat with the same traits. Drought or pathogen tolerant wheat would have an important economic impact for seed companies and farmers, in the UK and in drought prone areas of the world, and could help prevent fluctuations of prices on world markets and improve food security.

In addition to being a major UK crop, wheat is globally the third largest cereal crop, and is grown on the largest area of land of any crop. It is also generally regarded as both the most important cereal for direct human consumption (rather than for livestock feed) and the most significant global source of vegetable protein. Drought tolerance and water use efficiency are key crop traits which are becoming increasingly significant as water resources are limited and the human population continues to rise. Cereal crop losses due to drought in the UK in 2011 and the US grain belt in 2013, caused notable increases in food prices. Septoria tritici blotch and brown rust are major pathogens of UK wheat crops, and resistance is required by breeders for new varieties to be included on HGCA recommended list. 70% of EU spending on fungicides is targeted on combatting Septoria but fungicide resistance is widespread. The occurrence and impact of drought and pathogens on crop yields are predicted to become more severe under future climate change. Our strategy of reducing stomatal density without affecting yield could offer major economic benefits to UK wheat farmers and breeders. Reduced stomatal density is a trait that could be bred into wheat strains that currently have low resistance to fungal disease but have other desirable traits. Furthermore, this strategy could be applied to pathogens in other crops which enter via stomata, such as Cercospora in cereals, coffee, sugar beet and soybean.

This project will build new links between the plant science research group at the University of Sheffield and crop scientists at the National Institute for Agricultural Botany (NIAB) in Cambridge, and the John Innes Institute (JIC) in Norwich. It will therefore provide new routes for Arabidopsis-to-crop translational research, and through the SARIC programme, new links to companies with the ability to commercialise our findings.

The postdoctoral researcher and technician carrying out the research will gain advanced skills in plant physiology and crop science, important for meeting the challenge of global food security, an RCUK cross-council priority area. If funding is awarded, the university will also provide a PhD student and a Masters student to work on related projects thus further expanding the number of trained scientists in these acknowledged areas of skills shortage.They will help to design and deliver a school practical class on crop genetics and will be encouraged to participate in further science communication events at local schools and museums via our active Science Brainwaves group. The researcher will have access to the Faculty of Science 'Think Ahead' training programme; winner of the 2014 THES Outstanding Support for Early Career Researchers prize.


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Description Initial methodologies for quantitative characterisation of effects of stomatal density on disease infection in wheat. These are now being used on modified material to test the effects of reduced density on disease development. Reduced density lines had significant less brown rust (Puccinia triticina) than normal density lines, but the level of powdery mildew was unaffected. This was as expected, since brown rust enters only through stomata, and powdery mildew enters through junction points between epidermal cells.Repeat tests with brown rust of wheat and barley on seedlings of reduced density lines of Fielder and Golden Promise respectively showed that the reduced density trait resulted in fewer pustules per unit area of leaf. Experiments with adult plants showed a smaller effect of reduced density, potentally due to the smaller magnitude of the trait in mature plants. Nevertheless, the effect of reduced density would lead to fewer pustules, and spores, being produced in an epidemic, whih could lead to rate reduction in the field. As expected, there was no effect of reduced stomatal density on mildew, but surprisingly, no effect was seen on the development of Zymoseptoria tritici which does enter through plant stomata. The lack of effect was consistent over repeat experiments, There was however a reduction in yellow rust development in barley. This disease was added at the end of project, and unexpectedly there was a reduced disease development. Yellow rust hs a systemic growth habit within a leaf, with one infection point giving rise to many pustules, so reducing stomatal density was thought unlikley to have an effect on eventual pustule number. This was not the case, and it appears that reducing stomatal density could have a significant effect on both of the main UK cereal rusts.
Exploitation Route Potential use of reduced stomatal density characters in wheat breeding programmes. Though the reduced density lines used in these experiments were acheived by transfrmation, natural variation in stomatal density does occur and could be selected for in breeding programmes.The combination of reduced disease and increased drought tolerance (investigated by lead partner), without compromising yield potential, could be a valuable combination in elite material. Currently, one major breeder is exploring reduced stomatal density.traits.
Sectors Agriculture, Food and Drink

Description Poster presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A poster presentation at International Congress of Plant pathology, Boston 2018. Not a formal scientific publication, but attended by a large number of plant pathologists, students, postgrads, Pis
Year(s) Of Engagement Activity 2018