鈥淭he disease produces billions of very minute spores, known as urediniospores,鈥 says Dr Bhavani. 鈥淎nd because they are so light, these spores can easily be carried by strong wind currents to susceptible geographies thousands of kilometers away.鈥
听
This put many of the world鈥檚 largest wheat-growing regions at risk, as the pathogen鈥檚 wind migration pathways pointed towards Asia鈥檚 most powerful wheat producers. 鈥淎t that point, we were not prepared for the consequences of the disease鈥檚 migration,鈥 says Dr Bhavani. 鈥淛ust 10 percent susceptibility of the global wheat area to wheat stem rust could have led to billions of dollars of losses鈥攏ot 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.鈥
听
And it wasn鈥檛 just a matter of migration, it was also the degree of devastation. While leaf rust and yellow rust incur yield losses of 60鈥70 percent at most, a severe invasion of wheat stem rust can destroy an entire crop, leaving farmers with nothing at all to harvest.
听
What can be done?
With a villain as virulent as Ug99, there are many ways to fight back鈥攁nd for this pathogen in particular, it takes every available tool to gain the upper hand.
听
Fungicides are the simplest, most obvious solution鈥攁nd they are effective against rust diseases鈥攂ut they often aren鈥檛 always an option in the regions that need them most. 鈥淚n the majority of the developing countries that grow wheat, small-scale farmers cannot afford to use fungicides鈥攅specially in most parts of Africa,鈥 explains Dr Bhavani. 鈥淭hese farmers would be the biggest losers to this disease if their varieties were susceptible.鈥
听
Even in developed countries, farmers can鈥檛 rely solely on fungicides, as the pathogen develops a natural resistance over time.
听
Dr Bhavani notes that, 鈥淓urope 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.鈥
听
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鈥攁nd then providing the world with new, more resilient wheat varieties that continue to grow and thrive.
听
The first step involves identifying genes that can provide resistance to Ug99. 鈥淲hen Ug99 was first detected, we had over 50 genes that were characterized to be resistant for stem rust鈥攂ut 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.鈥
鈥淭he disease produces billions of very minute spores, known as urediniospores,鈥 says Dr Bhavani. 鈥淎nd because they are so light, these spores can easily be carried by strong wind currents to susceptible geographies thousands of kilometers away.鈥
听
This put many of the world鈥檚 largest wheat-growing regions at risk, as the pathogen鈥檚 wind migration pathways pointed towards Asia鈥檚 most powerful wheat producers. 鈥淎t that point, we were not prepared for the consequences of the disease鈥檚 migration,鈥 says Dr Bhavani. 鈥淛ust 10 percent susceptibility of the global wheat area to wheat stem rust could have led to billions of dollars of losses鈥攏ot 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.鈥
听
And it wasn鈥檛 just a matter of migration, it was also the degree of devastation. While leaf rust and yellow rust incur yield losses of 60鈥70 percent at most, a severe invasion of wheat stem rust can destroy an entire crop, leaving farmers with nothing at all to harvest.
听
What can be done?
With a villain as virulent as Ug99, there are many ways to fight back鈥攁nd for this pathogen in particular, it takes every available tool to gain the upper hand.
听
Fungicides are the simplest, most obvious solution鈥攁nd they are effective against rust diseases鈥攂ut they often aren鈥檛 always an option in the regions that need them most. 鈥淚n the majority of the developing countries that grow wheat, small-scale farmers cannot afford to use fungicides鈥攅specially in most parts of Africa,鈥 explains Dr Bhavani. 鈥淭hese farmers would be the biggest losers to this disease if their varieties were susceptible.鈥
听
Even in developed countries, farmers can鈥檛 rely solely on fungicides, as the pathogen develops a natural resistance over time.
听
Dr Bhavani notes that, 鈥淓urope 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.鈥
听
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鈥攁nd then providing the world with new, more resilient wheat varieties that continue to grow and thrive.
听
The first step involves identifying genes that can provide resistance to Ug99. 鈥淲hen Ug99 was first detected, we had over 50 genes that were characterized to be resistant for stem rust鈥攂ut 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.鈥
