Abstract:
Stem rust, caused by (Puccinia graminis f.sp. lritici) is a catastrophic disease because of its ability to cause complete annihilation of barley and wheat crops over wide areas. Previously rpgl, sr31, sr24 and sr36 genes for resistance were incorporated in genotypes of barley and wheat grown in Kenya kept it at bay. In 2001 a new race Ug99 with virulence to previously resistant genotypes was detected in Kenya. Most of the wheat varieties are susceptible to the disease hence the need to seek for alternative sources of resistance. Barley is one of the genotypes affected by stem rust, but limited work has been done to evaluate the gerrnplasm. There was need to search for new materials that are resistant to the new physiological race of stem rust and estimate the actual yield loss caused by it. The performance of 20 barley genotypes from Kenya and CIMMYT/ICARDA were evaluated under controlled greenhouse and field in stem rust prone environments. At seedling stage, infection levels in most genotypes, ranged fiom 0 to 2, except CBSS99MOO349T-F-3M-IY-IM-OM and CBSW98WOOO54S-BY-2M- IY-2M-IY-OM that showed infection type 3 and 3,4 respectively. Among the 20 genotypes that were evaluated for adult plant resistance CBSS99MOO39IT-H-IM-IY-IM-IY-OM, Nguzo and Karne were moderately resistant while the rest were susceptible or moderately susceptible. The new line 1512-5 showed the highest severity of (93%) in season 1, Sabini had the highest severity of 30% in the season 2. Nguzo had the lowest (16% and 5%) disease severity in season 1 and 2 respectively. In the field, FDS on susceptible cultivars was highly positively correlated with Area Under the Disease Progress Curve (AUDPC). The highest yield loss of 53.8% was attained in CBSSOOYOO236T-E-OY-OM-2Y- OM while the lowest loss of 6.9% was obtained in CBSW98WOOO54S-BY-2M-IY-2M-IY-OM in season 1. In season 2, the highest (32.1%) loss was noted on 1385-13, a Kenyan line from malting. Generally, in the experiment most Kenyan cultivars were susceptible to the new race of stern rust. Race Ug99 of stem rust had highly negative impact in limiting grain production potential of most of the commercially popular Kenyan barley cultivars. Resistance due to ‘slow rusting’ genes appears to be useful especially under high disease pressure with some cultivars posting very high resistance to PgtUg99. The study demonstrated the pathogenicity of Ug99 to barley despite the fact that it poses a great threat to wheat production. The information in this study is beneficial to both researchers, barley and wheat producers in confronting a pathogen that is devastating.
