What is 'relative risk'? Complete ‘agronomic package’ revealed by variety’s ‘relative risk’ rating
United Kingdom
December 18, 2015
The 2015 Agronomists’ Conference was the first activity conducted by AHDB Cereals & Oilseeds under its ‘Risk, resilience, reward’ communication theme.
Taking place on 8 December, Dr Simon Oxley, Senior Research & Knowledge Transfer Manager AHDB Cereals & Oilseeds, explained how the ‘relative risk’ of varieties is now assessed as part of the AHDB Recommended Lists for cereals and oilseeds (RL) trials.
It is hoped that the new assessment will play a key role in the development and selection of varieties with an exceptionally strong positive balance of features which perform reasonably well under variable conditions.
The concept of ‘relative risk’ was first introduced at the RL 2016/17 launch on 30 November 2015.
Using feed wheat varieties as a case study, the concept of selecting varieties for inclusion on the RL based on their relative risk was explored further at the conference.
Dr Oxley first explained that many quality and agronomic criteria are already used to assess the performance of a potential new RL variety.
By adding a criterion for relative risk, based on agronomic merit and untreated yield, Dr Oxley said ‘it can help identify varieties that stand the best chance of performing relatively well in an extreme year’.
He added that product withdrawals, a lack of new chemistry, changing pathogen populations and challenging weather mean that ‘varieties increasingly need to be able to stand up for themselves in the fight against disease and lodging’.
What is ‘agronomic merit’?
Delegates were informed of how an agronomic merit rating is first calculated for each variety.
This rating takes account of resistance to all key diseases (instead of looking at individual diseases in isolation) and standing power.
The rating also considers the relative importance of each disease, for example septoria tritici is higher risk compared with yellow rust ‘as control options are more limited’.
The agronomic merit rating produced provides a single measure of the underpinning genetic resistance of a variety. ‘The higher the rating the better, overall, the agronomics of the varieties.’
Calculating ‘relative risk’
Once the agronomic merit rating is established, a chart can then be prepared with additional untreated yield trial data as ‘this allows the risk of yield loss to be factored in’.
Above: The ‘relative risk’ concept. Varieties can be mapped on the chart above to reveal how likely they are to perform well under variable conditions. The cross wires (red dashes) represent the average untreated yield and agronomic merit rating of all the varieties.
Selecting a new feed variety
Using the approach, Dr Oxley presented a map of relative risk for group 4 feed varieties and made comparisons between new and established varieties. This showed varieties in a completely different light.
For example, KWS Santiago ‘which performs well when treated does not perform so well when things go wrong with fungicide application and timing choices’. However, some of the newer varieties, for example Graham and KWS Siskin, were shown to have ‘a better agronomic package, performing well in untreated situations’. These varieties were considered to have a lower relative risk.
Dr Oxley explained that a challenge with newer varieties is that there is less seasonal data, less market confidence and less grower experience. All of which ‘can reduce the uptake of newer varieties with low relative risk’.
It is early days for the approach but, it is hoped, over the longer term, it will play a key role in the development of varieties with an exceptionally strong positive balance of features that perform reasonably well under variable conditions.
Additional topics
Dr Oxley’s presentation also included information on variation of seasonal yields, regional yields, milling wheat protein content and sterility in wheat.
Some of the main genetic challenges facing barley breeders were also discussed and the risks to growers looking to grow spring malting barley for the first time.
Topics
Species
