Late Blight Breakthrough

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Sophien Kamoun, research group leader at the Sainsbury Laboratory at the United Kingdom’s Norwich Research Park, is part of a team that identified a gene that enhances resistance against late blight disease in potatoes. Photo: The Sainsbury Laboratory.

[deck]A new major genetic discovery could have great potential for the Canadian potato industry.[/deck]

There may be a new weapon in the fight against one of the world’s most devastating potato diseases — late blight.

Scientists from Wageningen University in the Netherlands and the Sainsbury Laboratory at Norwich Research Park in England say they’ve identified a resistant gene that fights against new strains of the oomycete disease.

The wild potato gene targets elicitin, a pathogen protein that performs an important biological function. This make makes it less likely for the late blight pathogen to evolve and evade resistance.

The scientists found that transferring ELR, the elicitin resistance gene, into cultivated potato made it more resistant to several strains of late blight, opening up new possibilities for breeding a broad and durable resistance into various potato varieties, increasing food security and reducing the use of fungicides.

“This is a new line of defense against potato blight,” says Sophien Kamoun, research group leader at the Sainsbury Laboratory.

Late blight disease is caused by Phytophthora infestans, infamous for triggering the Irish potato famine in the 1800s. This widespread pathogen is still a major threat to crops worldwide and remains one of the biggest headaches for potato producers in Canada.

Caused by a fungus-like oomycete microbe, late blight attacks both tubers and foliage, and is a threat at every stage of production from field to storage. New strains of the late blight pathogen that are resistant to conventional fungicide treatments are emerging, and the disease is spreading into parts of Western Canada that were virtually blight-free until only a few years ago.

The discovery is good news for Benoit Bizimungu, potato breeder and gene resources curator for Agriculture and Agri-Food Canada’s Potato Resource Centre in Fredericton, N.B.

“This study represents a significant breakthrough,” he says. “It may help us make even more progress in the fight against late blight.”

Lengthy Search

This genetic breakthrough has been a long time coming. The international team of scientists began their gene research by focusing on proteins considered essential to P. infestans. According to Wageningen University researcher Vivianne Vleeshouwers, the discovery has its roots in an old theory — the so-called Achilles heel hypothesis.

“A problem of breeding for late blight resistance is that introduced resistance genes get quickly overcome by [the late blight pathogen]. This means that [the pathogen] can adapt by changing the protein that is recognized by the resistance gene in the potato. The Achilles heel theory says that if we target a protein that is essential to the pathogen, then it is less likely that it will adapt,” she says.

“The approach we took is only recently possible, thanks to availability of genome sequencing of phytophthora, and an experimental approach — effectoromics — that we designed to be able to screen individual genes in a high-throughput fashion.”

Scientists found this essential protein in elicitin in the late 1980s, initially due to work done by a research group working at the French National Institute for Agricultural Research. Many years of screening wild potatoes for elicitin resulted in its discovery in Solanum microdontum, a South American wild relative of cultivated potatoes.

I think this new layer of immunity has big potential for control of late blight on a world scale.

– Vivianne Vleeshouwers

ELR encodes a receptor-like protein in S. microdontum. Plants contain many of these cell surface receptors, which act as a first line of immune defence much like an array of radar antennas.

The receptors are tuned to different features of invading pathogens, and in the case of this new type of blight-resistant potato, the simultaneous presence of elicitin and the gene that responds to it triggers cell death at the site of infection. It’s this powerful plant defense mechanism that restricts the progress of the late blight pathogen.

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The sporangia of Phytophthora infestans, the pathogen responsible for late blight disease. Photo: Lawrence Kawchuk, AAFC

“There are two classes of immunity receptors in plants. One class functions inside the plant cell and the other on the surface of the plant cell. In the past, for potato blight, we’ve only known about the receptors that work inside the plant cell. This is the first report of a cell surface type of immune receptor against the blight,” Kamoun says.

“For resistance to be deemed durable, it needs to hold over time, but looking at this research, the new gene is really broad-based. It is expected to offer more durable resistance, in theory,” Bizimungu says. “The knowledge we’re getting at the micro-level through genomics research is having a big impact on how we can combat late blight.”

Canadian research played a role in the discovery. Researchers in England and the Netherlands drew upon the work of Lawrence Kawchuk, an Agriculture and Agri-Food Canada research scientist based in Alberta. In 2001, he isolated one of the first plant disease receptors for verticillium wilt resistance, which helps to prevent early dying in potato plants.

New Layer of Immunity

For potato growers, the late blight breakthrough is significant because it may help circumvent the pathogen’s major strength — its ability to evolve and create new versions of itself that overcome resistance that have been bred into potatoes.

The knowledge we’re getting at the micro-level through genomics research is having a big impact on how we can combat late blight.

– Benoit Bizimungu

“I think this new layer of immunity has big potential for control of late blight on a world scale. The research is still in the experimental phase, [and] is not strong enough yet to apply in practice. We need more research to find out how we can further enhance it, and we need to find more of these genes to combine them together,” Vleeshouwers says.

Kamoun adds that “by combining different types of disease resistance, we maximize our chances to delay the evolution of new races of Phytophthora infestans.”

According to Bizimungu, the discovery holds a lot of potential for research in Canada, as S. microdontum germplasm is accessible to researchers through the U.S. Department of Agriculture gene bank. He notes the elicitin resistance gene could potentially be used to conventionally breed new varieties of potatoes with stronger and long-lasting resistance to the late blight pathogen.

Kamoun believes genetic modification represents the most efficient route for commercializing new blight-resistant varieties developed through elicitin resistance technique.

“At this stage, the shortest route to deploy this resistance in the field is through a GM transgenic approach,” Kamoun says. “It all depends on the acceptance of this technology and the willingness to invest in the cost of deregulation.”

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