Although the number of oilseed rape varieties on the AHDB oilseed rape Recommended List (RL) remains high, the different types are well spread across hybrids and specialist varieties such as Clearfield and semi-dwarf.

However, conventional varieties are in ‘a bit of a crisis, says Dr Paul Gosling, head of the RL.

The number of conventionals on the RL since 2010 has fluctuated, now sitting at just six.

And with 30-40% of planted oilseed rape being conventional varieties, the figure is not representative of what growers are looking for.

Difference Dr Gosling says: Next year we only have one conventional candidate.

Varieties just arent coming through on the green list, so we need to tweak things to make sure we still have the varieties growers want to grow.

The recommendation process has now been updated so conventional varieties will only be compared to other conventionals on the list, rather than all varieties, as they have been previously.

Thats because we know conventional varieties can usually yield pretty well, but theres a lag in getting new traits into the varieties compared to the hybrids.

If were still struggling to get varieties on the list, we might have to tweak the process again, Dr Gosling adds.

Being able to pick a variety based on its ability to cope with flea beetle may be high on growers wish lists, but creating a metric for this is not without its challenges.

AHDB has been exploring how to measure whether certain varieties are less susceptible to the pest following the suggestion some are able to tolerate larval feeding better than others.

Dr Gosling says: Some varieties may be less susceptible to damage so larvae dont thrive in those varieties, or it may be some varieties can compensate more and therefore suffer less yield impact.

AHDB introduced a protocol for assessing damage in 2020 which appeared to show some statistically significant results.

Dr Gosling says: Varieties were put on a one to nine scale based on level of damage and in 2020 we found small but statistical differences in between varieties.

Difference However, when the 2021 and 2020 data was combined there were no statistical difference between varieties.

Were not sure if this doesnt reveal the difference or that there just isnt a meaningful difference between varieties.

Spring assessments were done this year, but Dr Gosling says even if a protocol that works is found, cabbage stem flea beetle tolerance ratings are unlikely to be published until at least 2023/24.

AHDB is also exploring how the term ‘vigour - well-loved by marketeers - can be measured.

Dr Gosling says: Everyone comes back with a different answer when you ask for the definition.

It could be size, green area index (GAI), speed of development or other factors.

In 2020, AHDB asked trials operators to time how long it took for different varieties to reach key growth stages and then take biomass samples and plant population readings.

However, our trials officers found it too difficult and onerous and we didnt get good data, he says.

The following year, the protocol was flipped and they were asked to look at the development stage of the crop at specific points in time after drilling.

Dr Gosling says: Looking at three trials sites in Fife, Lincolnshire and Herefordshire, it does look as though weve got some differences in autumn vigour measure.

However, some varieties had high GAI in one location and very low in another.

As part of the next step, AHDB will review the protocol with its trials operators and, depending on the outcome, continue the work into next autumn.

However, a vigour rating will not appear on the RL before 2024/25.