Over the years, breeders’ concentration on increasing wheat varieties’ harvest index may unwittingly have made the crop more susceptible to black-grass competition.
That is according to researcher Jed Clark, who is halfway through a four-year AHDB-funded PhD study.
He is currently conducting research to identify wheat varieties that are more competitive against black-grass.
He says: “Previously, certain above ground traits have been described as conveying competitiveness against black-grass, but very little is known regarding below-ground interactions.
“Our aim is to identify certain traits in wheat, with a focus on roots, which convey a competitive advantage over black-grass and then screen and identify possible competitive lines to be added to the Recommended List for combating the weed.”
The research mainly consists of growing plants in the laboratory under controlled glasshouse conditions and in the field and outdoor containers at ADAS Boxworth.
Six winter wheat varieties and one hybrid barley are being examined (see panel, left).
Comparisons “We grow plants individually to allow comparisons over time between different lines,” explains Mr Clark.
“And we grow different plants together, for example wheat and black-grass, to compare the competitive effects they have on one another under different conditions.
“Over their lifespan we assess growth stages, tiller numbers and biomass to allow us to create a workable dataset for statistical analysis.”
In the laboratory the plants are grown in pots of soil as well as hydroponically in water and in rhizoboxes, the latter two options allowing root growths to be seen and measured.
Barriers through which chemicals can pass without the roots touching are also used to see how neighbouring plants detect and interact with each other.
Chemical signalling and growth inhibition are clearly involved.
Both wheat and black-grass grow better alone than when growing side by side in containers with the barriers, says Mr Clark.
“We have a container trial underway which consists of 92 x 20-litre pots containing different crop lines with theoretically different root traits, in competition with different black-grass densities.
“This trial is looked after by staff at ADAS and I have visited several times throughout the year to aid in key data collection.
“We’ll continue to work with ADAS, with container and field trials due to commence in the next winter growing season.”
Mr Clark outlines some key findings to date.
Barley grows better roots than elite wheats and so is less affected by black-grass.
Competition Root growth in black-grass is better than in wheat.
“The question is, does this difference in root growth result in a crop winning or losing in competition with black-grass? “Black-grass gains its competitive advantage over wheat due to its faster growth in winter conditions, increased ‘investment’ in its root system and a prolonged period in which to build its root system.
These allow it to dominate the underground space and resources by spring.
“The weed doesn’t have the same advantages in spring sowings.
“We hope that by identifying traits and lines that are more competitive we’ll be able to give growers another factor to consider when choosing which varieties to sow,” says Mr Clark.
He also hopes that the results may influence the direction of crop breeding, with an emphasis on root traits for multiple benefits.
“Overall, we want to help reduce the impact of black-grass.”