Stem Rust (Puccinia graminis f.sp. tritici) Disease Indeces on Barley (Hordeum vulgare L.) Genotypes
K. E. MWANDO, I. M. TABU, O. D. OTAYE, P.N.NJAU

Abstract
Stem rust, caused by (Puccinia graminis f.sp. tritici) is a catastrophic disease because of its ability to cause complete annihilation of barley and wheat crops over wide areas. Previously rpg1 sr31, 24 and 36 genes for resistances were incorporated in genotypes of barley and wheat grown in Kenya. In 1999, a new race Ug99 was detected in Uganda; that has virulence to a number of genes that were initially resistant to stem rust. The new race spread rapidly and in 2001, stem rust monitoring in Kenya detected isolates of Ug99. Most of the work on wheat shows susceptibility and barley being one of the genotypes affected by stem rust limited work has been done to it. There was need to search for new materials that are resistant to the new physiological race of stem rust. In this study 20 barley cultivars locally from Kenya and imported from ICARDA were screened in controlled greenhouse environment and in the field with isolate of Puccinia graminis f.sp. tritici. The infection levels in most genotypes at seedling stage in the greenhouse, ranged from 0 to 2, except in  CBSS99MOO349T-F-3M-IY-IM-OM and CBSW98WOOO54S-BY-2M-IY-2M-IY-OM that showed infection type 3and 3,4 respectively. At adult plant stage only CBSS99MOO39IT-H-IM-IY-IM-IY-OM, Nguzo and Karne were moderately resistant while the rest were susceptible or moderately susceptible. In the field, the new line 1512-5 showed the highest severity of 93% in season 1, with Sabini having the highest severity of 30% in the second season; Nguzo had the lowest disease severity of 16% and 5% in season 1 and 2 respectively. From the results in this experiment most of the Kenyan grown cultivars were susceptible to the new race of stem rust. Race PgtUg99 of stem rust has highly negative impact in limiting grain production potential of most of the commercially popular Kenyan barley cultivars. The study has demonstrated the pathogenicity of PgtUg99 to barley despite the fact that it poses a great threat to wheat production in the world. The information in this study is beneficial to both researchers, barley and wheat producers in confronting a pathogen that is devastating.

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