“The disease produces billions of very minute spores, known as urediniospores,” says Dr Bhavani. “And because they are so light, these spores can easily be carried by strong wind currents to susceptible geographies thousands of kilometers away.”
This put many of the world’s largest wheat-growing regions at risk, as the pathogen’s wind migration pathways pointed towards Asia’s most powerful wheat producers. “At that point, we were not prepared for the consequences of the disease’s migration,” says Dr Bhavani. “Just 10 percent susceptibility of the global wheat area to wheat stem rust could have led to billions of dollars of losses—not to mention hunger and poverty in those economies that were dependent on wheat and wheat-based farming systems where devastating epidemics could have occurred, as the majority of the varieties were susceptible.”
And it wasn’t just a matter of migration, it was also the degree of devastation. While leaf rust and yellow rust incur yield losses of 60–70 percent at most, a severe invasion of wheat stem rust can destroy an entire crop, leaving farmers with nothing at all to harvest.
What can be done?
With a villain as virulent as Ug99, there are many ways to fight back—and for this pathogen in particular, it takes every available tool to gain the upper hand.
Fungicides are the simplest, most obvious solution—and they are effective against rust diseases—but they often aren’t always an option in the regions that need them most. “In the majority of the developing countries that grow wheat, small-scale farmers cannot afford to use fungicides—especially in most parts of Africa,” explains Dr Bhavani. “These farmers would be the biggest losers to this disease if their varieties were susceptible.”
Even in developed countries, farmers can’t rely solely on fungicides, as the pathogen develops a natural resistance over time.
Dr Bhavani notes that, “Europe is also battling a huge challenge with yellow rust, for example, where multiple applications of fungicides are being advocated, but it is still unable to control rust completely.”
According to Dr Bhavani, the long-term solution for diseases such as Ug99 wheat stem rust lies in introducing genetics less susceptible to the pathogen—and then providing the world with new, more resilient wheat varieties that continue to grow and thrive.
The first step involves identifying genes that can provide resistance to Ug99. “When Ug99 was first detected, we had over 50 genes that were characterized to be resistant for stem rust—but this unique strain was able to overcome more than 50 percent of the genes that were catalogued at the time. In addition to that, Ug99 was able to overcome multiple resistance genes, so the pathogen was mutating and evolving virulence for whatever gene we were trying to deploy.”
“The disease produces billions of very minute spores, known as urediniospores,” says Dr Bhavani. “And because they are so light, these spores can easily be carried by strong wind currents to susceptible geographies thousands of kilometers away.”
This put many of the world’s largest wheat-growing regions at risk, as the pathogen’s wind migration pathways pointed towards Asia’s most powerful wheat producers. “At that point, we were not prepared for the consequences of the disease’s migration,” says Dr Bhavani. “Just 10 percent susceptibility of the global wheat area to wheat stem rust could have led to billions of dollars of losses—not to mention hunger and poverty in those economies that were dependent on wheat and wheat-based farming systems where devastating epidemics could have occurred, as the majority of the varieties were susceptible.”
And it wasn’t just a matter of migration, it was also the degree of devastation. While leaf rust and yellow rust incur yield losses of 60–70 percent at most, a severe invasion of wheat stem rust can destroy an entire crop, leaving farmers with nothing at all to harvest.
What can be done?
With a villain as virulent as Ug99, there are many ways to fight back—and for this pathogen in particular, it takes every available tool to gain the upper hand.
Fungicides are the simplest, most obvious solution—and they are effective against rust diseases—but they often aren’t always an option in the regions that need them most. “In the majority of the developing countries that grow wheat, small-scale farmers cannot afford to use fungicides—especially in most parts of Africa,” explains Dr Bhavani. “These farmers would be the biggest losers to this disease if their varieties were susceptible.”
Even in developed countries, farmers can’t rely solely on fungicides, as the pathogen develops a natural resistance over time.
Dr Bhavani notes that, “Europe is also battling a huge challenge with yellow rust, for example, where multiple applications of fungicides are being advocated, but it is still unable to control rust completely.”
According to Dr Bhavani, the long-term solution for diseases such as Ug99 wheat stem rust lies in introducing genetics less susceptible to the pathogen—and then providing the world with new, more resilient wheat varieties that continue to grow and thrive.
The first step involves identifying genes that can provide resistance to Ug99. “When Ug99 was first detected, we had over 50 genes that were characterized to be resistant for stem rust—but this unique strain was able to overcome more than 50 percent of the genes that were catalogued at the time. In addition to that, Ug99 was able to overcome multiple resistance genes, so the pathogen was mutating and evolving virulence for whatever gene we were trying to deploy.”
