The Threat of a New Wheat Stem Rust to the World's Food Supply

Over 635 million tons of wheat is produced from 215 million ha worldwide under diverse environments. It provides about 20% of the food calories and protein to more than 4.5 billion people in 94 developing countries. Numerous diseases and pests and abiotic stresses such as drought and heat cause significant reduction in yields annually. Stem, or black, rust caused by the fungus Puccinia graminis tritici was a serious disease of wheat since biblical time until 1960s causing periodic famines and starvation in epidemic years. Stem rust became insignificant worldwide due to the spread of high-yielding, rust resistant varieties during the “Green Revolution” era in late 1960s and thereafter. However, Ug99 race group, first detected in Uganda in 1998 and seven biotypes belonging to the same lineage identified since then, have spread to various wheat-growing countries in the eastern African highlands, as well as Zimbabwe, South Africa, Sudan, Yemen, and Iran. Because of the susceptibility of 90% of the wheat varieties grown worldwide at present, the Ug99 group of races is recognized as a major threat to wheat production and food security. Its spread, either wind-mediated or human-aided, to other countries in Africa, Asia, and beyond is evident. Recognizing the urgency, Nobel Peace Laureate Dr. Norman E. Borlaug raised the alarm in 2005 that lead to the initiation of Ug99 surveillance and various other research and development activities to reduce the Ug99 risk worldwide through financial supports from various donors. Over 200,000 wheat materials were screened in Kenya and Ethiopia since 2005 and a low frequency of resistant varieties and breeding materials identified. CIMMYT in collaboration with KARI (Kenyan Agricultural Research Institute) initiated a two crop-season per year shuttle breeding between field sites in Mexico and Kenya in 2006 and successfully developed high-yielding, durably resistant wheat varieties that are under performance trials in various countries. Identification and transfer of new sources of race-specific resistance from various wheat relatives is underway in the US, Canada and Australia to enhance the diversity of resistance.  Although new Ug99-resistant varieties that yield 5-10% more than current popular varieties are being released and promoted, major efforts are required to displace current Ug99 susceptible varieties with varieties that have diverse race-specific or durable resistance and mitigate the Ug99 threat and enhance productivity.