10 June 2008
New Varieties Underpin UK Cereal Yield Growth

Around 90% of the increase in national average cereal yields over the past 25 years can be attributed to innovation in plant breeding. That is the interim conclusion of a new study by researchers at NIAB.

Statistical analysis of trial yield data over the past 60 years has found that while UK cereal yield increases prior to 1982 were attributable to a combination of factors, including plant breeding, agronomy and inputs, yield increases in winter wheat, spring barley and winter barley over the past 25 years have been almost exclusively due to improved varieties.

The findings are part of a major new study taking place at NIAB to assess the contribution of plant breeding to improved crop performance in wheat and barley. The research, co-funded and conducted in collaboration with BSPB, updates and extends previous work carried out by Valerie Silvey, former Head of Statistics at NIAB.

Silvey’s analysis, last updated more than 20 years ago, showed that around half of the total increase in yields of wheat, barley and oats between 1947 and 1986 could be attributed directly to the efforts of plant breeders, rather than the contribution of other factors such as fertilisers, pesticides or machinery.

Interim results of the new study, covering the period 1947-2006 and applying more advanced statistical methods and computing power, not only bear out Silvey’s original analysis but suggest that since 1982, around 90% of all yield increases in wheat and barley have been due to the introduction of new varieties.

Dr Ian Mackay, a statistical geneticist at NIAB leading the research, said:
“Winter wheat yields have more than trebled over the past 60 years from around 2.5 tonnes/ha in the mid-1940s to 8 tonnes/ha today.

“Non-varietal factors such as N fertiliser, agrochemicals, plant growth regulators, improved agronomy and machinery have all contributed, and remain an essential component of modern crop production to protect the genetic potential of new varieties.

“But while improved crop varieties have shown consistent genetic yield gain, decade after decade, our analysis suggests that for the past 25 years the yield-enhancing contribution of other, non-genetic factors has remained broadly neutral.

“Even in most recent years when national average wheat yields have been on a plateau, trials data have shown continued genetic yield gain from new varieties.

“It is not clear whether the national picture can be explained by the very variable growing seasons we have experienced recently, whether economic and environmental constraints have forced farmers to cut back on their use of fertilisers and other inputs, or whether there are other reasons why farmers are not realising the full genetic potential of the varieties available.

“But our research clearly indicates that without continued breeding effort and the contribution of new varieties, UK cereal yields would certainly be static, possibly even in decline” said Dr Mackay. BSPB chairman Dr Thomas Jolliffe welcomed the interim findings as a categorical demonstration of the need for continued investment in UK-based plant breeding.

“This updated study confirms that since Valerie Silvey ‘s original analysis, plant breeders have continued to deliver major improvements in genetic yield potential. While other inputs have a crucial role to play in helping farmers realise that potential, this research is quite clear that genetic improvement is now the single most important source of yield increases.

"As environmental and other regulatory influences look set to exert yet more constraints on farmers’ input use, the challenge for breeders is to close the gap between treated and untreated yield by continuing to develop varieties more resilient to the impact of changing climate, disease and pest pressures." said Dr Jolliffe.
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Notes

Background & methodology to interim results
A set of analyses of NL/RL trials to assess the contribution of breeding to the improvement of cereal crops was carried out by Valery Silvey, then Head of Statistics at NIAB, for the period 1947–1977 (Silvey 1978) and subsequently extended to cover more years (Silvey 1981, 1986).Twenty years on, it is timely to update and extend these analyses.

Silvey’s approach, limited by the software and analytical methods available at the time, was to assess genetic contribution by comparing relative yields of recommended list varieties over a running five year interval with actual yields, taken from published statistics. After adjusting for the differential uptake of varieties, assessed from seed certification statistics, the total increase in yield and the proportion attributable to variety improvement could be estimated.

Advances in statistical methods and computing power mean that it is now possible to analyse a whole series of trials over 60 years as a single dataset to derived estimates of relative variety performance. For winter wheat, this encompasses about 53,000 data points from 3,600 trials for over 300 varieties tested in a minimum of three years. Aside from the difference in scale, the analytical methods are the same used to derive recommended lists by analysing three to five year datasets. NIAB have then followed Silvey’s approach in relating trial performance to national yields by using historical records, held by DEFRA, coupled with NIAB seed certification figures (which give an estimate of the national variety mix in any year).

References
Silvey V (1978) The contribution of new varieties to increasing cereal yield in England and Wales. J Natl Inst Agric Bot
Silvey V (1986) The contribution of new varieties to cereal yields in England and Wales between 1947 and 1983. J Natl Inst Agric Bot
SIlvey V (1981) The contribution of new wheat, barley and oat varieties to increasing yield in England and Wales 1947. J Natl Inst Agric Bot

Contacts for further information:

Dr Penny Maplestone, BSPB.
Tel: 1353 653200
E-mail: penny.maplestone@bspb.co.uk

Dr Ian Mackay, NIAB.
Tel:01223 342200
E-mail: ian.mackay@niab.com

Issued by Daniel Pearsall, Front Foot Communications.
Tel: 01487 831425
E-mail: daniel.pearsall@frontfoot.uk.com