Stripe rust adapting to Aus heat

Speaking at the Borlaug Summit in Mexico, former Australian agricultural economist and University of Minnesota Department of Applied Economics professor Phil Pardey said there were signs the disease was undergoing genetic change that was allowing it to spread its footprint.

He said historically stripe rust had been considered a cooler climate disease than stem rust but its climate suitability appeared to be shifting.

“One notion is that the disease has become more aggressive and can generate a lot more spores,” he said.

“It also may be becoming more heat tolerant and may be able to move into areas and infect the wheat crop at slightly higher temperature regimes than in the past.”

Professor Pardey said work by the university and worldwide collaborators, including the CSIRO and USDA Cereals Disease Lab, had identified the temperature and moisture thresholds that drove the location and climate suitability of stripe rust.

“We now have a measured view of where the disease is climate suitable and persists,” he said.

“In some places the disease occurs year round and in other places it dies out and regenerates through wind or human-induced transmission.”

Professor Pardey said by overlaying the areas where the disease was likely to occur on a map of the world’s wheat growing regions, scientists had identified those regions where the disease posed the greatest threat.

“Our estimates are that half the world’s wheat crop is growing in areas where the disease is suited, so that means those crops are susceptible to the disease,” he said.

“About one-third of the wheat area in Australia is climate-suitable for stripe rust.

“In just under 10pc of that wheat area, if the rust got there it would establish itself and persist from season to season.

“However, in North America, more than 40pc of the wheat area is suitable for rust but in less than 1pc would the disease persist.

“The Australian area is not as encompassing in terms of suitability as the US, but it is more encompassing in terms of persistence which possibly exposes Australian wheat growers to a higher risk from stripe rust than their brethren in the US.”

Professor Pardey said stripe rust was currently active in Australia and there had been outbreaks of stem rust in the past.

“But the new Ug99 variants of stem rust that are now popping up in Uganda have moved into Kenya, Ethiopia, Yemen and down into South Africa,” he said.

“The stem rust outbreaks in Australia in the past have been traced to the occurrence of the disease in South Africa. The spores move over thousands of kilometres across the ocean.

“There are questions of whether stripe rust moves that far because the spores drift into the upper atmosphere where they are exposed to UV radiation.

“Stem rust is resistant to UV radiation but stripe rust is not as resistant, so there are questions about whether it can move over such long distances.

“There is a suspicion that it is more likely introduced through accidental human transmission.”

Professor Pardey said stripe rust was estimated to cause average yield losses of 1.5 per cent across the US wheat crop every year.

“If the pattern of loss in the US was to be applied globally, we have come up with estimates that $700 to $800 million a year is being lost to stripe rust,” he said.

“We estimate $28 to $30 million a year in R&D research on this one disease would be economically justified.

“It is an ongoing fight year-in, year-out. Globally we are spending less than half of what the economics suggests should be spent.”

Neil Lyon travelled to Mexico with the assistance of the Crawford Fund and the Department of Foreign Affairs and Trade’s Council on Australia Latin America Relations.