Pressing the wheat-breeding accelerator
To date, genetic improvements have increased potential wheat yields by 20% since the early 1980s, says James Melichar, cereals R&D crop operations lead at Syngenta.
But now the industry has the ability to accelerate commercial breeding programmes, by increasing throughput and applying greater selection pressure at each stage of the process. The yield breakthrough cereal producers have been waiting for is fairly imminent, he predicts.
“Of course, everyone is only too aware that the on-farm reality has been different to the genetic potential – wheat yields have stalled and the UK average stands at just over 8t/ha,” he reveals. “So there’s definitely room for improvement.”
However, the top growers often get 12t/ha with the same varieties and the world record for an on-farm wheat yield is 15.64t/ha, while the maximum theoretical yield is 19.2t/ha, he notes. “These figures give us a glimpse of what is possible with the genetic material we already have.”
Agronomy package
He believes that for a very high yield to be achieved, the right agronomy is essential. “The growing conditions also have a role, and we’re never going to be able to guarantee perfect weather. But good agronomy, based on targeted inputs, makes a significant difference.”
Tailored agronomy programmes, ideally for each individual variety, are the way forward for the time being, suggests Dr Melichar. “There’s been a great deal of effort put into crop solutions in the past three or four years and that will continue. It’s all about protecting genetic potential through the best use of inputs.”
He believes cell biology techniques – some of which are already being used very successfully – will evolve and become more sophisticated. That will increase the scale of breeding operations, resulting in a huge number of new lines at the front end of any programme, so improving the chances of selecting a superior line.
“Doubled haploid breeding has already reduced the time it takes to bring a new variety to market by three or four years,” he reports. “It has allowed us to bring out better varieties at a faster rate, while reducing the variation between plants.”
But current techniques employed are labour intensive, he acknowledges. “That’s why the numbers of new lines produced are limited at the moment, especially in wheat. We need to be able to routinely develop doubled haploid embryos from pollen grains, in order for this increase in scale to happen.”
Of course, producing a greater quantity of new material creates a new set of challenges for breeders, he remarks. “We don’t want to increase the amount that goes out into the field for selection. This is where marker technology comes in and will be very valuable.”
Markers have two roles, he explains. “They can perform a logistical function, by helping us discard a great deal of material before it gets to the field selection stage, and they can be used to bring new sources of genetics into material and increase its diversity.”
Dr Melichar points out that marker technology is developing at a rapid pace, giving the potential for greater exploitation of natural variation. “With markers, we could be looking at whole genome selection in five years instead of just selecting a small number of major traits as now.”
Currently, markers are used for simple genes that determine a major trait, such as fusarium head blight resistance, he explains. “In the future, they could be used to dissect more complex traits such as water-use efficiency or nitrogen-use efficiency, where dozens of genes across a genome express the trait. That can’t be done routinely at the moment.”
New phenotyping technology is also helping to improve breeder selection. “It’s always been done manually, but now we are starting to use imaging and remote sensing to help with this, as well as automation. It means we can take more measurements, operate round the clock and record the effects of microclimate on crop performance.”
Having breeders out in the field, with a critical farmer’s eye, will always be important, he maintains. “But we can send them out with hand-held devices and automated recording systems, to make their jobs easier and quicker. Their expert interpretation will always be essential, but the technology can help, especially with increasing throughput.”
Bioinformatics
Other specialist skills that may have a role in future breeding work include bioinformatics and predictive breeding, notes Dr Melichar.
“Bioinformatics comes in as the amount of data we collect increases; we need highly trained staff who can do all the number crunching, look for trends and filter out unnecessary information – leaving the breeders with the relevant data.”
Predictive breeding uses a combination of marker and phenotyping data, produced over a range of environmental conditions, to predict the likely outcome of a cross or the field performance of a new variety. “It’s a form of crop modelling and could be used as part of a breeding programme. But it will never replace the need for a knowledge-based breeder.”
But hybrid wheat holds the most promise for the future, he believes. “This could be the game changer. Growers would benefit from the resulting heterosis (hybrid vigour) and would experience greater yield increases than we’ve been able to achieve with conventional varieties.”
As well as an improvement in yield, hybrid wheat offers better environmental stability of lines, he explains. “This is seen in consistency of performance in the field – something that growers will place more value on with our increasingly unpredictable weather.”
Hybrid wheat could be in the marketplace by the 2020s, he predicts. “It will be different to the hybrid wheat that is around at the moment, as there will be a new production method that can increase the scale of the operation.”
The technical expertise to deliver hybrid wheat already exists, he stresses. “We have hybrid barley now, but wheat has a more complex genetic nature. There are still certain challenges to overcome with wheat, but when it arrives, it will be the breakthrough growers have been waiting for.”
Synthetic wheats
Novel sources of genetic diversity are on offer from NIAB TAGs synthetic hexaploid wheats, which are being produced for use in commercial breeding programmes.
Although the first varieties to come from this work arent likely to be on the market before 2022, the project aims to increase the genetic diversity in wheat by introducing new genes from the crops wild ancestors, using conventional plant breeding methods.
The technique employed by NIAB recreates the rare hybridisation event that took place many years ago between an ancient wheat and wild grass species. This time, goat grasses are being crossed with two UK varieties.
When synthetic wheats first came to everyones attention in 2012, it was with a headline promise of a 30% yield boost. But that claim is only partially correct, explains Phil Howell, NIABs senior plant breeder, as the resulting yield should be compared with that of the parent used in the cross.
Our early field trials have been very promising, he says. But any yield benefit has to be measured against the potential of the parent used, not the current highest-yielding UK variety.
There are other benefits to be had from the use of synthetic wheats, he continues. Its important to appreciate that its not only about yield. Improvements in drought tolerance, disease resistance and input use efficiency are also on offer.
Synthetic wheats arent new, he explains, but they havent been exploited in Europe in the same way they have in other parts of the world. Breeders working in drought-prone, lower-yielding, more extensive production systems have made good use of them, with very successful results, as they are fully crossable with current varieties.
They give us a very useful bridge for transferring genetic diversity into modern wheats, says Dr Howell. Thats important because weve lost diversity over the passage of time and our germplasm is now limited.
Synthetic hexaploid wheats are developed in the greenhouse, by crossing a durum wheat with wild goat-grass, effectively mimicking the natural event that took place over 10,000 years ago in the Middle East, from which todays wheat varieties developed.
This gives researchers access to traits from ancestral wheats, many of which have been lost over time, and some of which could have value in todays market.
Once seeds begin to form, the embryos are removed from the wheat plant and germinated in a petri dish, before being chemically treated to double their chromosome number. These are then grown on in pots to produce plants, the seed from which can then be crossed with a modern wheat.
To date, NIABs involvement has been to look at their use in high-input cropping systems and develop large-scale research, close to that of a commercial breeding programme. As a result, the organisation has produced and evaluated 5,600 lines, taking 1,000 forward to yield testing.
Partnership agreements are in place with wheat breeding companies, so they can make use of this development in their own breeding programmes.
