Wheat continues to be threatened by UG99, a strain of stem rust that has moved from Africa into Yemen and is now poised to move into Iran and the subcontinent.
Researchers from around the world are working to find a way to slow, or shut down, the rust’s terrible potential.
So far, it is slow going — little resistance to the rust has been found in available wheat varieties and breeding new varieties isn’t an overnight process. Fears remain that the disease could ruin wheat crops and lead to mass hunger and political instability in developing nations.
In late March, Farm Press spoke with Gene Milus, University of Arkansas professor and wheat pathologist, about UG99’s potential, where it’s now established and when it is expected to reach the U.S. wheat crop. Among his comments:
• On where UG99 is established…
“Based on the latest information, the most prevalent race of the UG99 family now overcomes both the Sr31 and Sr24 resistance genes (the second UG99 race identified).
“This race of stem rust is firmly established in Kenya and Yemen. The reason: they plant wheat year-round. There’s a wheat crop in the field 12 months of the year in Kenya and Yemen. That keeps the rust cycling constantly — there’s never a down time. That’s part of the problem in dealing with this disease.
• On UG99 in Iran…
“UG99 has made it to Iran” where “besides wheat there are Barbary bushes, which are alternate hosts.
“The thing we don’t know about Iran is whether UG99 is actually established there or if it must blow in from somewhere like Yemen every year. That’s a big unknown and, unfortunately, it’s a bit difficult to get good information out of Iran.
“The big concern is that, if it isn’t already, UG99 will eventually be established in Iran. From there, the wind currents will take it everywhere.
“Iran grows a lot of wheat. Plus, the country has Barbary bushes which allow the disease to go through the sexual cycle and become established.”
• On Barbary bushes and UG99…
“The bushes in Iran are very similar to what we once had in the northern Great Plains — Minnesota, Wisconsin, and North Dakota. If Barbary bushes are in the environment, the fungus goes through its complete life cycle and produces the sexual stage on the bushes. In turn, that allows inoculum to be produced early in the spring. So, it can survive over winter up north.
“Without the Barbary bushes, it can’t survive in the north. Every year, it must blow up on winds from the south, where it is warmer during the winter. In our case, it survives in the Gulf Coast of Texas and, maybe, in southern Louisiana and southern Alabama.”
• On past efforts to deal with the bushes…
“There was a big Barbary bush eradication campaign 50 years ago (in the United States). That got rid of 99-plus percent of the Barbary bushes — especially ones close to wheat fields.
“Since those eradication efforts, a few Barbary bushes have been found. Folks are now thinking, ‘well, maybe we need to go back and get the few that are left. That’ll help fight stem rust in the United States.’
“In Iran, I’m not sure how prevalent the Barbary bushes are or where they are in relation to wheat fields. But the fact they’re in the country will help stem rust to establish there. In Iran they don’t grow continuous wheat like they do in Kenya and Yemen.
“Without the Barbary bushes, the rust must stay on a living host. It can’t go dormant in the winter. It can also live on certain grasses, although the grasses aren’t as good of a host as wheat.
• On UG99 reaching the “stans” and the United States…
“The belief is that once UG99 races are established in Iran, it’s an easy hop over to the central-Asian ‘stan’ countries” such as Afghanistan, Kazakhstan, Uzbekistan and Turkmenistan. “Wheat is an important crop in every country ending in ‘stan.’ From Iran, it’s an easy shot to get spores to those countries.
“There’s no reason to be alarmed about UG99 in the United States. It isn’t an imminent problem here. On the other hand, there is a need to remain vigilant and to get prepared. Left to natural means, I’d estimate it’ll take more than 10 years for UG99 to make it to the continental United States.”
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