Speed of development ratings will be a new feature of the 2008/9 HGCA Recommended Lists, helping UK wheat growers to plan variety choice, crop monitoring and agronomy more precisely.

The latest list (to be launched next week) will, for the first time, show how quickly varieties reach GS31 – first node detectable.

The information will cover, separately, early September, early October and early November sowings to account for drilling date’s impact on development.

“Winter wheat varieties are wellknown to differ quite markedly in their speed of development,” says RL manager, Jim McVittie. “Equally, growers have long appreciated the value of slower developing varieties for early sowing, and faster developing ones for later sowing.

“But until recently almost all our understanding of wheat development was based on work before the arrival of the semi-dwarfs. It was almost entirely derived from mid-October sowings, too, which we haven’t always found helpful in selecting varieties for early drilling.”

The new ratings indicate the number of days earlier (negative) or later (positive) than average taken for all established varieties to reach GS31 from sowing.

They are derived from detailed plant dissection at trial sites in Essex and Yorkshire averaged over up to five years, depending on how long the varieties have been tested.

Dr McVittie admits there is still a lot of “noise“in the data, so individual figures should be interpreted with care. But he is confident the ratings are reliable enough to be commercially valuable.

From early September sowing, they show a range of a good two weeks –from Soissons (-8) at one extreme to Riband (+7) at the other –although the particularly mild season produced a four-week range in Essex last year.

In most cases varieties that develop more slowly from early sowing also do so from later sowing and viceversa. Butsome seem to behave quite differently.

While Xi19 is one of the fastest (-6) from early sowing it is also one of the slowest (+3) from later sowing.

Variety development

By contrast Battalion is one of the slowest from early sowing (+4) and somewhat speedier (-1) sown later.

“Knowing how fast varieties are likely to develop from a particular sowing time can be extremely valuable in guiding spring observations to get fungicide timing spot on,” says Dr McVittie.

“It can also be useful in variety selection to spread the peak of spring workloads and, given the general correlation with earliness of ripening, harvesting.

“The greatest value of our new ratings, though, almost certainly lies in selecting varieties for early drilling.”

Although the HGCA runs useful late sown trials, logistics rule out similar early sown evaluations, making speed of development a more valuable indicator, he says.

“I’d certainly be prioritising a relatively slow developer for early–September sowing.

“Of course, for this slot I’d also be looking for good lodging resistance, good disease resistance (especially eyespot) and the sort of all-round strength indicated by a reasonable second wheat performance.”

Exploiting growth potential

At ADAS Boxworth, crop physiologist Roger Sylvester-Bradley welcomes “Speed to GS31“ratings as an objective measure in matching variety to sowing date.

Prof Sylvester-Bradley, who heads a new four-year DEFRA LINK project “Adapting Wheat to Global Warming“, regards them as valuable in optimising wheat performance and managing peak workloads. But they are only a start in better exploiting the development and growth potential of the crop, he stresses.

“With the project we call ERYCC – Earliness and Resilience for Yield in a Changed Climate –we are looking to improve yield and reliability by reducing the crop’s risk to frost on the one hand and drought on the other,” he says.

“In this context, we are exploring how best to shorten the crop’s foundation period (vegetative phase) and lengthen its construction period (reproductive phase).

“Speed of development in the foundation period to GS31 essentially depends on a variety’s responsiveness to temperature, vernalisation and day length.

“HGCA’s ratings are the net result of all three effects. So it’s not surprising that varieties show different speeds of development at different sowing dates. This almost certainly reflects their sensitivity to the three determinants of earliness.“

See next week’s issue for full details of newly recommended cereal and oilseed rape varieties for 2007/08.