Wheat black stem rust, one of the most damaging diseases of wheat, had largely been under control for more than three decades when, in 1999, a new race of the fungus causing the disease was identified in the fields of Uganda. Named Ug99, to reflect where and when it was first identified, the deadly disease began to spread across East Africa to Yemen and as far as Iran, to the point that it threatened the wheat production of 18 countries and, potentially, global food security. In answer to this, the Joint FAO/IAEA Division, working with national and international research institutes, initiated a multi-country program focused on using induced mutations to increase the genetic diversity of wheat which, in turn, would increase the chances of developing wheat varieties with resistance to the black stem rust. In 2014, the first Ug99-resistant varieties, Eldo Ngano-1 and Eldo Mavuno-1, were ready for Kenya’s wheat fields, and six other countries had new resistant lines in advanced field trials.
Wheat black stem rust can turn a healthy looking crop, only weeks away from harvest, into nothing more than a tangle of black stems and shrivelled grains. It is a highly mobile disease, which can spread rapidly over enormous distances. It spreads mostly through wind, but it can also be spread by accidental human transmission – through clothing or plant material.
Wheat black stem rust had largely been under control since the 1960s, mainly because researchers had developed wheat cultivars resistant to the disease. When Ug99 emerged in 1999, it proved to be a particularly devastating race. In fact, some 80 to 90 per cent of global wheat varieties were susceptible, meaning most farmers in its path had no way to fight back.
As the disease spread from its first sighting in Uganda, 17 other countries were considered at risk. The tolls mounted in each country where it emerged, eventually reaching an annual loss of 8.3 million tonnes of wheat grain production with a value of USD 1.23 billion. This presented a potential threat to global food security as well as the multi-billion dollar wheat market.
In 2009, the Joint FAO/IAEA Division initiated and led an interregional project to help in developing new wheat varieties resistant to wheat black stem rust. This project focused on mutation induction with a goal of increasing the genetic diversity of wheat, increasing the chances of finding varieties with resistance to Ug99 that could then be further developed.
