Wheat is one of the world's most important food staples, but with climate change, threats to the crop are increasing. The fungal disease stem rust can quickly turn entire wheat fields into rotting stalks and unusable grains. Preparedness for fungal attacks is unfortunately low, according to researchers at SLU. But with the help of plant breeding, they hope to make wheat resistant to future outbreaks.
Historically, stem rust has caused major crop losses, leading to famine and economic crises.
“Ancient farmers were aware of this threat and sacrificed animals and worshipped the god Robigus to protect their wheat fields,” says Mahboobeh Yazdani, PhD student at the Department of Plant Breeding, SLU.
In many parts of the world, such as North America, Australia and Ethiopia, stem rust has caused widespread epidemics in the past. By the beginning of the 20th century, the disease was almost eradicated. This was thanks to the development of resistant wheat varieties and the removal of barberry bushes, which serve as an alternative host for the fungus.
Mahboobeh Yazdani says that for the past three decades, stem rust has been considered a forgotten enemy. But in 1999, the aggressive Ug99 race was discovered in Uganda, overcoming all previous resistance genes. Since then, the fungus has spread to East Africa, the Middle East and other parts of the world. Outbreaks have also occurred in Europe.
“Over 80% of the world's wheat varieties are susceptible to this race.”
A larger outbreak occurred in Sicily in 2016, affecting thousands of hectares of durum and bread wheat, leading to crop losses of up to 40%. The stem rust race that caused this outbreak is known as Sicily.
The cold Swedish climate has so far protected wheat crops from rust, but the situation may change with a warmer climate. In 2021, a Sicilian race of stem rust was detected for the first time in southern Sweden. A study, in which two hundred different wheat varieties were tested, showed that none of these varieties had resistance to the Sicilian race.
“Sweden is unprepared for a major stem rust outbreak, especially organic farms that do not use chemical pesticides and are therefore extra vulnerable.”
The world's food supply is already under severe pressure from the Russia-Ukraine war, rising food prices and the threat of famine in many parts of the world.
“A major outbreak of stem rust could have catastrophic consequences for millions of people who depend on wheat for their survival.“
Resistant wheat varieties are needed to protect wheat from attack. Mahboobeh Yazdani and her colleagues are working hard to identify new resistance genes that can resist stem rust. The researchers are transferring resistant genes into wheat varieties to develop new varieties with good resistance. The aim is to make these varieties available in seed banks, so that farmers and breeders worldwide can benefit from them.
"We have developed new resistant varieties that have been tested and approved; they will soon be released in seed banks," says Mahboobeh Yazdani.