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ARS Home » Midwest Area » St. Paul, Minnesota » Cereal Disease Lab » Research » Publications at this Location » Publication #245193
Title: Identification and Evaluation of New Sources of Resistance to Stem Rust Race Ug99 in Wheat

Author
item NJAU, P - Kenya Agricultural Research Institute
item Jin, Yue
item HUERTA-ESPINO, J - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP)
item KELLER, B - University Of Zurich
item SINGH, R - International Maize & Wheat Improvement Center (CIMMYT)

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2009
Publication Date: 4/1/2010
Citation: Njau, P.N., Jin, Y., Huerta-Espino, J., Keller, B., Singh, R. 2010. Identification and evaluation of new sources of resistance to stem rust race Ug99 in wheat. Plant Disease. 94:413-419.

Interpretive Summary: Stem rust race Ug99 or TTKSK, initially identified in Uganda in 1998 and subsequently detected in Yemen and Iran, has caused periodic losses to wheat crop in East Africa. The most effective approach to prevent losses from stem rust is through the deployment of resistant varieties. New sources of resistance need to be identified and incorporated in the existing commercial varieties. Elite and advanced CIMMYT bread wheat lines were evaluated for resistance to Ug99 in Njoro, Kenya for four consecutive seasons (2005-2007). Seedling reactions were determined in the greenhouse. Two race-specific genes, Sr24 and Sr25, were found to confer resistance to Ug99. There were also likely three previously uncharacterized resistance genes, one each originating from synthetic wheat, Chinese germplasm and other genetic backgrounds. Although 30% of the screened lines were susceptible in the seedling stage, these lines displayed various levels of adult plant resistance (APR) phenotypes in the field tests. Presence of the adult plant resistance gene Sr2 was common in wheat lines with APR. The information on the resistance reported here constitutes an important sources for breeding wheat for durable resistance.

Technical Abstract: The race Ug99 of Puccinia graminis f. sp. tritici causing stem rust disease of wheat was initially identified in Uganda in 1998. It was designated as TTKSK based on the North American nomenclature and has caused periodic losses to wheat crop in East Africa. Ug99 has recently moved out of Africa to Yemen and West Asia. The most effective approach to prevent losses from stem rust is through the deployment of resistant varieties. New sources of resistance need to be identified and incorporated in the existing commercial varieties. The first Stem Rust Resistance Screening Nursery (1stSRRSN) developed by CIMMYT consisted of elite and advanced CIMMYT bread wheat lines and were evaluated for resistance to Ug99 in Njoro, Kenya for four consecutive seasons (2005-2007). Seedling reactions were determined in the greenhouse at the of Cereal Disease Laboratory, St. Paul, MN, US. Two race-specific genes, Sr24 and Sr25, were found to confer resistance to Ug99 although Sr24 became ineffective to a mutant race of Ug99, TTSKT, in 2007. There were also likely three previously uncharacterized resistance genes, one each originating from synthetic wheat, Chinese germplasm and other genetic backgrounds. Although thirty percent of the screened lines were susceptible in the seedling stage, these lines displayed various levels of adult plant resistance (APR) phenotypes in the field tests. Presence of the adult plant resistance gene Sr2, identified based on the pseudo-black chaff phenotype on glumes and darkened internode, was common in wheat lines with APR. The information on the resistance identified in the 1stSRRSN constitutes an important sources for breeding wheat for durable resistance.