History is littered with examples of seemingly robust varieties that succumbed to new disease races. A few years ago Torch quickly broke down to a new yellow rust pathogen, while last December Reflection saw its AHDB resistance rating halved. Stigg met a similar fate when it was overcome by a new strain of brown rust.
This all comes at a time of increasing need for strong varietal resistance to multiple diseases to help overcome the loss of effective chemistry, whether from tightening regulations or the development of fungicide-resistant pathogens.
We cannot prevent the natural evolution of plant pathogens, but understanding why it happens will help us all – farmers, advisers, breeders and agchem suppliers – minimise the threat to crops.
Breeders and researchers are working hard to produce new varieties that combine the traits farmers need, from yield and quality to long-lasting, all-round disease resistance. But it takes around nine years to develop a new variety from the first cross to joining the Recommended List, so we cannot expect any quick fix.
Broad-spectrum fungicides remain central to the disease control armoury and are pivotal to supporting varietal resistance, which we know can sometimes be quickly overcome by new races. We also need broad-spectrum fungicides to control new diseases. For example, control of Ramularia leaf spot of barley depended on fungicides for the first 15 years.
If regulations make it harder to register azole chemistry in future we may have to look to new actives or revisit old chemistry such as morpholines to top-up defences as new diseases or strains develop.
Powdery mildew control in winter wheat is a classic example of how breeders can build durable disease resistance into varieties and we need the same level of durability for septoria and rust resistance in future. New digital sensor technology will hopefully speedup the selection process and enable breeders to bring new, robust varieties to market faster, thereby helping growers stay ahead of constantly evolving disease threats.
Crop Breeding sessions sponsored by Bayer
Professor James Brown is a crop genetics researcher. He will speak in the Crop Breeding Seminars at The CropTec Show about why resistance breaks down, what growers can do to avoid it and how new breeding techniques working with new chemistry might provide the answer.
The session will be chaired by the progressive, Twitter vocal, Cambridgeshire Nuffield Scholar farmer, Russell McKenzie, this session will also cover:
- Reading between the lines of the latest variety recommendations
- Jock Willmott from Strutt & Parker will explore how to select varieties based on financial performance achieved under local conditions.