BYDV tolerant varieties can repel aphids

Winter barley varieties with barley yellow dwarf virus (BYDV) tolerance have a repellent effect against aphids, according to Ben Urquhart, technical manager for hybrid barley at Syngenta. Speaking at the Irish Tillage and Land Use Society’s winter conference last week, he told the crowd that research completed with the University of Nottingham show that aphids are more attracted to non-tolerant varieties. They also do not thrive when in a crop of a BYDV tolerant variety, leading to reduced offspring production.

This research also compared aphids infected with BYDV to those without infection. Aphids without BYDV showed reduced settlement and a reduction in offspring on the BYDV tolerant variety, with similar if not more significant reductions with the infected aphids.

This trial work was carried out with SY Kestrel, a BYDV tolerant hybrid winter barley variety, and a second variety that has very similar genetics, but does not have BYDV tolerance. This allows the researchers to deduce that the difference in behaviour is due to the BYDV tolerance gene.

The next step in this research is to figure out why this happens, and whether it is down to the quality of feed that the aphid consumes from the barley, or if it is their ability to feed on the barley in the first place.

Aphid behaviour

BYDV infection alters the behaviour of aphids, and as the population dynamics of aphids are constantly changing, monitoring is essential.

Ben also noted that BYDV is a persistent virus; once an aphid is infected, they will have the virus and can pass it on for the rest of their lives.

However, research shows that infection is not passed on to the aphid’s offspring, so the offspring must also feed on a plant with BYDV to be infected.

Aphids that feed on a tolerant variety infected with BYDV will still be infected with the virus, and so could pass it on to other crops.

Ben reminded farmers that BYDV symptoms such as yellowing are still likely to be seen on tolerant varieties, especially in a high-pressure situation.

He explained that this means there is still viral replication taking place within the plant, but crop yield should be protected.

With a BYDV resistant variety, Ben says there should be little to no symptoms evident as there should be little to no viral replication within the plants, as has been found in the field through ELIZA testing, which tests plants for the presence of BYDV.

When it comes to advising whether to spray an aphicide on these varieties, Ben noted that there are many factors in play, and farmers should not just be thinking of the yield of a certain field.

“With the tolerant varieties, you’re very much thinking about managing the spread of the vector [the aphids]. You still have a source of the virus in the plants. With resistant varieties, there’s a strong argument to be made for not using an insecticide.”

Responding to a question from the audience relating to whether this tolerance and resistance will break down over time, Ben explained that no reduction in the efficacy of the tolerance genes has been seen so far in any of Syngenta’s barley trials, but it is always a potential risk.

Another virus that Ben spoke about was wheat dwarf virus (WDV). This virus still causes yellowing and dwarfing, but it is spread by leafhoppers rather than aphids.

The typical circular patches of BYDV are not visible with this virus, as the leafhoppers tend to jump further and will infect a plant slightly further away leading to a spread of individual infected plants, whereas aphids will walk to an adjoining plant.

This is also rare in this part of the world, with Ben saying it is mostly confined to Suffolk in England at present.

Research is still ongoing, but Ben reported that SY Kestrel has shown some tolerance to this virus too.

While plant viruses, especially BYDV tolerance and resistance are the main focus of plant breeders at the moment, Ben explained that in the medium term, his company’s breeders will be aiming to find resistance to seed-borne diseases, including bunt and smuts, due to the potential loss of active ingredients and difficult regulatory pressures the sector faces.

This work is currently in pre-breeding, where the desired genes are being bred into parent lines for hybrid varieties.

Ben expects it will be five to 10 years before this resistance begins to be seen in new hybrid varieties coming through.

In the long term, selecting for varieties that are resilient to environmental stresses will be focused on.

Ben explained that the extreme weather events seen over the past couple of years, especially directly after planting, will influence breeders to investigate if new varieties in the future can be bred to withstand these stresses and help farmers to cope with difficult and unpredictable weather patterns.

Gene-editing is another potential tool for plant breeders, especially in the UK where they are slowly relaxing the regulations.

“It’s really exciting. Rather than talking about things we can bring to market in 10 years’ time, there’s a very real possibility of being able to launch a product in two of three years.”

Ben did warn that it is essential that the message is made clear to consumers that this is not genetic modification, it does not introduce genes from other species, but rather helps to speed up the selective breeding process.

With so many potential benefits in the pipeline, Ben added, “Genetics is definitely an exciting and important direction to head in.”