Future projections suggest that warmer drier summers will be more common in the UK sugar beet growing area so losses due to drought will be more frequent (Evans, 2017). Irrigation is not a feasible option as many growers do not have access to irrigation, or where they do it is reserved for higher value crops such as potatoes. Even when beet is irrigated the return on irrigation is only beneficial the very driest years (Hess, BBRO project 16-02). The alternative to irrigation is the use of varieties which yield well both under optimal and dry conditions.
It is important varieties yield well across a range of moisture deficits because the UK climate is still unpredictable and even with the warmer drier summers forecast there will be years where rainfall is sufficient for the crop to maximise yield. To ensure the UK sugar beet crop can produce a stable yield across years with varying rainfall it is imperative that varieties which have a high drought tolerance, without penalty to overall yield potential are available for UK growers. This is especially important as so many sugar beet fields consist of sandy soils that are prone to drought.
We already know through Ober (2004, 2005) that genotypic differences in drought tolerance are evident in sugar beet breeding lines and commercial varieties developed for the UK market. Additionally, Ober (2005) also identified that drought tolerance was not related to overall yield potential. This is important because it shows that it is possible to have varieties which have a high yield potential but are also drought tolerant. Even more promising is that the work of Ober (2005) and Pidgeon (2006) identified that the commercial variety Roberta showed a greater drought tolerance than the other commercial varieties examined. This suggests that there will be variation in drought tolerance in the current RL varieties which is why examining them is worthwhile.
The comprehensive work undertaken at Brooms Barn and during the BBROs infancy provide a solid framework for this work to be undertaken and means that much of the work on developing protocols is not required which saves time and money. We just need to take this approach and apply it to the commercial varieties available to UK growers to ensure optimal variety selection for yield stability.
Virus yellows is undoubtedly responsible for much of the yield reduction in the crop this season with research showing that BYV can reduce sugar yields up to 47% whilst BYMV can lead to a 29% reduction (Smith & Hallsworth, 1990). However drought has been shown to reduce sugar yield by up to 43% in some trials (Clover et al., 1999) which does not interact with the affect of virus. This is because as virus tends to reduce green canopy area, light interception and thus yield early in the season later whilst drought tends to have an affect mid to late season (Clover et al., 1999).
For this reason it is important to study the effect of drought on the crop and not to focus solely on the immediate threat of virus yellows.