PhD investigates the ‘hare’ (wheat) and the ‘tortoise’ (black-grass)

An AHDB PhD student is exposing black-grass’ hidden tricks to help cereals compete with this major arable weed.

Based at the University of Leeds, student Jed Clark has designed experiments to examine what gives some crops the power to fight back against black-grass.

In this battlefield, roots are in charge – something that is difficult to assess in commercial field crops. Jed has devised an experimental system that allows him to use containers to pit crop against weed.

The approach also allows the environment to be controlled and, via the use of permeable and non-permeable barriers in the containers, permits the assessment of physical and chemical interactions.

In addition to clear physical interactions, Jed’s work shows that chemicals play an important role. He found that chemicals released from roots (exudates) – whether from wheat or black-grass – can travel to other plants and affect their growth. In the case of wheat, these chemicals tend to slow down growth. In the case of black-grass, however, chemicals have a neutral or a positive effect on growth. Jed believes that this may help explain the high black-grass densities often observed on arable land.

In another experiment, Jed simulated field conditions and observed a ‘hare-and-tortoise’ response. Over the simulated winter black-grass grew slowly, yet consistently. However, wheat appeared to race away – above the ground, at least.

Hydroponic systems were used to reveal root-growth differences. Black-grass achieved much higher root densities, with wheat investing more in shoot biomass. In fact, final black-grass root biomass was almost double than that for wheat. Black-grass roots also represented a much larger proportion of total plant biomass – 40% compared with 17% for wheat.

Black-grass’ investment in a dense root system gives it a competitive advantage over winter wheat in the spring, when demand for nutrients and water increases. These results also help explain why spring-sown wheat competes better against black-grass. Weed control prior to drilling spring crops kills any black-grass, levelling the playing field. The results may also explain why winter barley – known for its vigorous root growth – is not affected as much by black-grass.

Over the remaining two years of his PhD, Jed plans to screen winter wheat varieties for differences in their ability to compete with black-grass. He also wants to improve in-field assessment approaches, by adopting a ‘shovelomics’ approach – which involves digging up and washing roots prior to their examination. Finally, Jed wants to further investigate the root chemicals behind the growth responses observed in his earlier experiments.