Experts are investigating yield stability once more following the recent HGCA report on why crops yields have plateaued and a season marked by yield variability and inconsistent harvest performance.

It’s been the focus of recent work by RAGT’s wheat breeders. However, during the past four years, many wheat varieties have been consistent within 1-2% of their expected performance, with only a few significantly underperforming, claims the company.

Not surprisingly, the biggest differences between two consecutive years have been observed in 2011 and 2012, says Celia Bequain (pictured), RAGT’s UK wheat breeder. “That’s because 2011 favoured the later, high-tillering varieties, which survived the spring drought and then maximised the benefit of the long grain fill period.

“In contrast, although 2012 generated high tiller numbers, it was limited by dull weather and low light levels. Grains failed to fill well, giving low TGW and thin grains.”

As a result, varieties with fewer tillers and less grain gave better results in 2012, she reports, as these were able to fill relatively well.

Across the past four seasons, varieties that have been most stable and consistent in yield terms include Crusoe, Warrior and Scout in the lower-yielding, quality sector, while high-yielding types JB Diego, Torch, KWS Santiago and Horatio have been the most consistent in their category.

This consistency comes from a variety’s ability to buffer against extremes in conditions, explains Ms Bequain. “This is especially important at key development stages such as stem extension, flowering and grain fill.

“Varieties with mid maturity, medium height, intermediate speed of development and good tiller numbers are able to cope better with more extreme conditions.

“Similarly, those that accumulate more soluble stem carbohydrates can use these reserves to continue grain fill, even if the plant is stressed and canopy survival and activity is poor. The soluble stem carbohydrates act as a buffer to any drought.”

Looking ahead, she predicts yield stability across seasons will become more valuable. “It applies to disease control, too. We are seeing regional extremes for particular diseases, rather than the same levels of the major diseases across the country.”

Plant breeders can select for yield stability by ensuring stiff straw and good disease resistance in their programmes, as well as testing in more extreme environments, she believes.

“At RAGT, we conduct trials across twenty sites and eight countries in Europe. It means we have results from sixty locations by the time varieties enter the RL trialling system.”

Increasingly variable climatic conditions will make reliability more important, she says. “It’s the best way to deliver the combination of yield and quality that growers and the end market require.”