Abstract
Wheat is an important staple food crop in sub-Saharan Africa. However, the current wheat consumption of 900 000 tons in Kenya outweighs the wheat production of 350 000 tons given the high population growth and inflation. The stem rust currently poses the greatest threat to wheat production due to the emergence of the virulent race of thePuccinia graminis f. sp tritici, Ug99 (TTKS) and its variants Ug99 + Sr24 (TTKSK) andUg99 + Sr36 (TTKST) leading to about 70 to 100% yield losses. This study aimed at evaluating twenty-five wheat genotypes for both field and seedling resistance to stem rust. The genotypes were grown in an alpha lattice design and in two replicates both in the greenhouse and in the field at Kenya Agricultural Research Institute (KARI), Njoro. The seedling stage infection types were scored based on Stakman et al. (1962) scale. At the adult plant stages, the stem rust disease severity was based on modified Cobb’s scale. The genotypes showed diverse seedling and adult plant resistance responses. The most resistant entries, KSL-2, KSL-3 and KSL-20 also exhibited the pseudo black chaff (PBC) trait implying they contain the Sr2 gene in their background; the basis of breeding for durable resistance to stem rust in wheat. These lines with high stem rust resistance could be backcrossed to the adapted and high yielding but susceptible Kenyan wheat varieties to avert further wheat yield declines. Key words: Stem rust, wheat, Ug99, resistance, disease severity.
Highlights
Wheat is grown on 225 million ha with a total production of 600 000 tons (Singh et al, 2008)
Significant variations were noted for stem rust, plant height, yellow rust and days to 50% flowering among the wheat genotypes tested across the seasons (Table 2)
A diverse field reaction ranging from trace resistance (TR) to moderately susceptible (MS) to susceptible (S) responses was observed
Summary
Wheat is grown on 225 million ha with a total production of 600 000 tons (Singh et al, 2008). Stem rust is considered as the greatest threat to wheat production in the East African region due to the emergence of a virulent race of the P. graminis f. In 1998, wheat varieties carrying the Sr31 gene widely grown in Uganda in 1998 were observed to exhibit high susceptibility to stem rust and a race Ug99 was associated with this virulence. This race was later designated TTKS based on North American stem rust nomenclature (Xu et al, 2009). The Ug99 spores have been spread over vast areas causing epidemics and high yield losses in Kenya and Ethiopia in 2002, Sudan, Iran and Yemen in 2007 with the possible route of stem rust spread been proposed as East Africa - Middle East West Asia - South Asia (Ayliffe et al, 2008; Singh et al, 2008)
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