What is senescence and why do we want wheat that stays green for longer?

Faced by climate change, and our ever-increasing agricultural demands, what can we do to improve crops being grown?

We sat down with Liz Chapman,who has recently completed her PhD, working on improving wheat yields by investigating the length of time the crops stay green. Here’s Liz to tell us how;

“I’m working in collaboration with KWS-UK, an international plant breeding company, to study regulation of wheat senescence, focusing on ‘staygreen’ phenotypes.

As modern agriculture becomes increasingly intensive and weather patterns become increasingly unstable and unpredictable, we need to develop more resilient crops which also require fewer inputs to ensure sustainable agriculture.

‘Staygreen’ phenotypes are associated with tolerance to heat, drought and low nitrogen conditions; all of which are important traits to consider in the generation of wheat germplasm.

Senescence is the final stage in wheat development and the point when nutrients become remobilised from the plant into the developing grain. Theoretically, delaying senescence, or ‘staygreen’ traits, are associated with extending photosynthetic duration, potentially to increasing availability of resources for grain filling.

However, wheat ears are determinate structures, with grain number; a key yield component, determined at growth stage 31, around mid-April in the UK. After this point yield increases rely on making the most of the grains you have, and this is where ‘staygreen’ traits come in.

We have identified an association between delayed senescence and extended grain fill duration, proportional to the extremity of the respective ‘staygreen’ phenotype. Under certain conditions these ‘staygreen’ traits positively affect grain size, and thus overall grain yield, through maintenance of grain fill under semi-stressful environmental conditions.

Working with KWS-UK has been great because it has provided me the opportunity to conduct wheat trials across multiple locations, including Norwich, Cambridge, France and Germany.

Through the successful collaboration I have also gained insights into the commercial world of wheat and cereal breeding, learned just how efficiently they run their operations, and gained invaluable practical experience and expertise.

Sometimes when considering things in a purely academic environment you can lose sight of the context in which your work sits, because you are focussing on the intricacies, but not the breadth.

My PhD has combined both fundamental and applied bioscience beautifully, identifying genes combined with considering agronomic potential of the germplasm under investigation, and appropriate environments.

In breeding it is important to understand agronomic constraints, or potential penalties we may introduce. For example, ‘staygreen’ wheat may be associated with increased grain yield, but are these traits usable in the field? If plants display an extreme ‘staygreen’ trait, and remain green at harvest time, this causes practical concerns, and is not attractive to farmers.

This exact scenario occurred during the project, with some lines staying green for a very long time, and even after harvest when processing dried plant samples leaf material still remained green. Theoretically this is interesting, but it isn’t useful. You want plants to ‘staygreen’ for a couple of days, up to maybe a week longer, but you don’t want it to be so extreme as to disrupt harvest.

Each year we have trialled the same germplasm to different effect, delivering interesting results, and new genetic x environment interactions to decipher. We have to make the most of the genetic resources we have and identify, interpret and maximise potential benefits. It is my job to interpret all of this, which is an aspect I find most exciting.

Longer term such interactions are likely to become more challenging as the climate changes, altering selection pressures and demands change. In addition, multiple countries are introducing environmental limits regarding nitrogen application, for example, meaning greater adaptability is going to be required during crop breeding.

The great thing about plant science is its diversity, covering multiple different aspects of science, from microscopy, cell and developmental biology and genetics, through to bioinformatics. It’s all encompassing nature allows you to specialise but also explore lots of different areas within it, including highly applied research areas.

When I saw the PhD project at the John Innes Centre, I thought ‘that sounds perfect’. Working on wheat, is both useful and applied, plus the direct link-up with industry provided an invaluable opportunity to gain an understanding into what it is like to work both in industry and in academia.

I recently submitted my thesis and passed my viva. Before I came to the John Innes Centre for my PhD, I studied for a BSc in Biological Sciences at the University of Birmingham.

As part of my degree I did a placement year within the Conservation and Research Department at the National Botanic Garden of Wales. That was a great experience and taught me that I really enjoy doing research, and am capable. As such, I was encouraged to consider applying for a PhD, which previously I have never considered. When I returned to university for my final year I chose to specialise in plant science and genetics, because it combined my interests, and I found it really interesting.

In future I wish to continue with scientific research, particularly with an eye to maintaining my links with both academia and industry, as being able to exchange research ideas in different contexts is so rewarding.

I am currently preparing to embark on a Postdoc position in Canada, with a view to remaining able to conduct field trials and crop research.”

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