12th September 2022

Breeding for disease resistance

For plant breeders Limagrain, developing varieties with robust disease resistance has always been a key focus of the company’s breeding programme. This pathology focus was much increased in the late 1960’s following the dramatic breakdown of the yellow rust resistance of Rothwell Perdix, and continues in breeding programmes today aimed at producing both high yielding and high quality varieties. Paul Fenwick, in house pathologist with Limagrain says, “It’s all about providing a safer product for growers; one that has the genetics to cope with a range of conditions and seasons, and still perform season after season. By looking at all the factors that affect yield and quality, it is clear that developing varieties with resilient disease resistance characteristics is critical and integral to this.”One of a rare breed – there are only two or three breeding companies based in the UK with their own pathologists – Mr Fenwick works closely with the Limagrain cereals breeding teams: “I get varieties to test from the wheat and barley breeding teams when they reach the yield trials stage. These are then grown out in specific disease nurseries where they are exposed to a range of diseases and the disease levels are assessed. These data are then utilised by the breeding teams when deciding which varieties are viable to take forward for commercialisation.”“At Limagrain we focus on the best possible levels of disease resistance and we have to stay one step ahead of disease all the time, so I will screen against all the latest disease races. It’s never as easy as it sounds, as there can be more than one type of resistance, and in the field it’s not possible to say if the visible resistance is down to one or multiple genes. So what we try to do is characterise the resistance within the genetic make-up of the plant where possible using molecular marker technology. ““The development of new molecular markers is key to us having a better understanding of the genetics behind resistance and, therefore, the commercialisation of varieties which are likely to be less at risk from race changes. “ â€œAs breeders we aim to use a use a number of different sources of resistance within our breeding programmes as an insurance against major race changes,” he says. The ‘pyramiding’ of resistance factors within single varieties using marker assisted selection makes it more difficult for the pathogen to adapt and gain the required virulence factors for resistance breakdown. “Mr Fenwick feels strongly that the efforts to produce varieties with new, diverse, potent and potentially durable resistance factors should be recognised  and reflected by the appropriate bodies when varieties come up for recommendation.He also adds that, as breeders, it is important to consider requirements for the future. “After all, it takes at least 8-10 years to bring a variety to market, so we need to be planning now for future goalposts. For example, in the near future, we are likely to face a reduction in the use of some pesticides – this in itself reflects the crucial need to develop varieties with robust disease resistance attributes that are high quality and high yielding. Food security is an increasingly important global issue, and breeding resistant varieties will be an integral part of achieving this.”The changing face of disease It is critical that the industry as a whole works together to monitor disease and threats to varietal disease ratings. Rosemary Bayles, pathologist with NIAB TAG and who heads up the UK Cereal Pathogen Virulence Survey, has seen the emergence of particularly virulent races of rust over the past few years. â€œThe breakdown of Warrior to a new yellow rust race last year was a particularly interesting case, as we saw what looks like the same race being reported for the first time right across NW Europe. This is was highly unusual as more normally in the past we have seen races develop in one region and spread to others over a period of a few years. We are working with pathologists from across Europe to try and establish the significance of this.”“In fact there is increasing global interest in understanding and finding ways to understand the rapid appearance of new rust races– to the point that vast amounts of money are being invested in research into these diseases. “The University of Aarhus in Denmark houses the Global Reference Centre for Rust, headed up by Professor Mogens Hovmoller. “The impact of yellow rust across the globe is becoming increasingly significant, particularly in relation to a new aggressive strain in North America that has adapted to warmer temperatures. The significance of this disease threat to cereal production is reflected in the fact that we have just received substantial funding for a five year project – Rustfight  – which will allow us to develop a stronger link between fundamental and applied rust disease research.”“We have established a range of projects looking at developing early warning systems for yellow and stem rust epidemics, providing training to deal with these and also assist with resistance breeding. We also monitor and survey developing rust epidemics across Europe and work closely with bodies such as the UK CPVS. “

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