Evolution mode of deadly cereal rust heightens threat fears

Researchers have solved the mystery of how the Ug99 strain of wheat rust evolved

Weeds, Pests, Diseases
CSIRO group leader Dr Melania Figueroa says research is helping protect the Australian wheat industry against a deadly wheat stem rust fungus. PHOTO CSIRO

CSIRO group leader Dr Melania Figueroa says research is helping protect the Australian wheat industry against a deadly wheat stem rust fungus. PHOTO CSIRO

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CSIRO scientists have discovered crucial information about a wheat stem rust fungus.

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The Agricultural Biotechnology Council of Australia (ABCA) is an industry initiative established to increase public awareness of, and encourage informed debate and decision-making about, gene technology.

Researchers from CSIRO, with colleagues from the USA and South Africa, have solved the mystery of how the devastating Ug99 strain of the wheat stem rust fungus was created, observing that different rust strains simply fused to create a new hybrid strain.

Called somatic hybridisation, this fusion process enables the fungi to merge their cells and exchange genetic material without the complex sexual reproduction cycle.

The study found half of Ug99's genetic material came from a strain that has been in southern Africa for more than a century and occurs in Australia, and that other crop-destroying rust strains could hybridise in other parts of the world. Scientists found evidence of this in their study.

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"Ug99 is considered one of the most threatening of all rusts as it has managed to overcome many of the stem rust resistance genes used in wheat varieties and has evolved many variants," says CSIRO group leader Dr Melania Figueroa.

"While outbreaks of Ug99 have so far been restricted to Africa and the Middle East, it has been estimated that a nationwide outbreak here could cost Australia up to $500 million in lost production and fungicide use in the first year," Dr Figueroa says.

"There is some good news, however, as the more you know your enemy, the more equipped you are to fight against it.

"Knowing how these pathogens come about means we can better predict how they are likely to change in the future and better determine which resistance genes can be bred into wheat varieties to give long-lasting protection."

The findings were published in Nature Communications.

GM REDUCED-LIGNIN LUCERNE: THE US EXPERIENCE

Genetically modified (GM) reduced-lignin alfalfa (lucerne) has been available to growers in the US for four years.

At dairy forage seminars held in conjunction with World Dairy Expo in October, Michigan State University extension forage specialist Kim Cassida detailed what has been learned about the performance of these GM varieties based on published university research and grower experience.

Since lignin is indigestible for ruminants, it impedes cellulose and hemicellulose digestion, reducing fibre digestibility and, ultimately, feed intake. Researchers inhibited one of the pathways for lignin production by turning off a gene.

Lignin is needed in the plant for structural support, plays a role in water movement and acts as a defence against pests and pathogens, so it remains a vital component of the plant.

"I got asked recently why we have to call it 'reduced lignin' instead of 'low lignin'," Dr Cassida says.

"The reason behind that terminology is that it is really not low. Only a small amount of lignin has been taken out, but it is enough to make a difference in how it will perform in cow diets.

"There is also research to suggest that lignin is positively related to yield, probably because of its beneficial attributes.

"The theoretical reduced-lignin advantage is equal annual yield and quality in fewer harvests and with better persistence."

According to Dr Cassida's presentation, results from several university trials comparing a reduced-lignin variety with conventional varieties, some of which were bred for either high forage yield or high quality, "essentially confirmed that the reduced-lignin trait does what it was developed to do - provide higher-quality forage at any given point in time compared to standard varieties, allowing for a delayed harvest to obtain the same quality yet higher yields."

NEW PLANT GENE DEVELOPMENTS PROVIDE DIRECTION FOR FUTURE CROPS

International researchers have released new data on plant evolution and the genetic map of peas in two recent announcements involving researchers from Western Australia.

In September, an international team of researchers, including professors David Edwards and Jacqueline Batley from The University of Western Australia's (UWA) School of Biological Sciences and Institute of Agriculture, announced they had assembled the first field pea genome.

This is a significant development in global nutrition and crop sustainability, because field peas are the second-most-important grain legume in the world, after the common bean. They are an important protein source of food and feed.

"With the field pea genome sequenced, we can now start to understand the basis for the variation which has evolved," Professor Batley says.

This research was supported by GRDC and the Australian Research Council.

Most recently, a global consortium of almost 200 plant scientists mapped the genome sequences of 1100 plants over a nine-year period. Associate Professor Patrick Finnegan, Associate Professor Martha Ludwig and Dr Matthew Nelson from UWA were all part of this international team.

"From this information, key gene sets underlying plant innovations such as living on land, producing seed, flowering, growing tall, occupying challenging environments and interacting harmoniously with beneficial bacteria and fungi can be identified in plants that, among other things, provide us with essential food, fuel and fibre," Associate Professor Finnegan says.

"This will contribute to our understanding of how biochemical pathways such as photosynthesis, stress avoidance and tolerance, and nutrient uptake have been built over evolutionary time.

"We will be able to see commonalities and differences, which will inform future strategies in protecting biodiversity as well as improving crop performance."

TOMATO GENES OFFER DROUGHT-TOLERANCE HOPE

Researchers from the University of Cambridge's Sainsbury Laboratory and Department of Plant Sciences have discovered that drought stress triggers the activity of a family of 'jumping genes' (Rider retrotransposons) previously known to contribute to fruit shape and colour in tomatoes.

Published in the journal PLOS Genetics, the research showed that the Rider gene family is also present and potentially active in other plants, including economically important crops such as canola, beetroot and quinoa.

This highlights their potential as a source of new traits that could help plants better cope with more extreme conditions.

Also looking at genes from the tomato, molecular biologist Simon Ruiz from the University of Talca, Chile, looked to the intense desert regions for plants with traits that could be beneficial in a changing climate.

"Many plant species cannot survive salinity, drought and constant temperature changes. We [are beginning] to test Chilean native plants that can withstand these conditions and produce transgenic seeds," Dr Ruiz says.

The team is working with a tomato variety that grows in the Atacama Desert, which only receives water from Bolivia's winter rains - if they come.

They have isolated 78 genes that confer tolerance to drought, salinity and cold and have developed a GM corn that can go almost two months without water in field trials.

For more information go to the ABCA website

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