(Singh and McIntosh, 1986a) (Plate 3-6)
Synonym
Sr8 (Knott and Anderson, 1956).
Low Infection Type
2- to 3.
Environmental Variability
Low (Roelfs and McVey, 1979).
Origin
Common wheat. This gene was first described in Red Egyptian (Knott and Anderson, 1956) but subsequent work demonstrated its presence in many European and Mexican lines. It probably became widespread in modern spring wheats through the use of Italian lines and their derivatives in South America and elsewhere.
Pathogenic Variability
P. graminis populations in most geographic regions are polymorphic for pathogenicity on seedlings with Sr8a (Luig, 1983; Huerta-Espino 1992).
Reference Stocks
i: ISr8-Ra C.I.14176 (Loegering and Harmon, 1969); Red Egyptian/10*Marquis (Knott, 1965); Sr8a/9*LMPG (Knott, 1990).
s: Chinese Spring*5/Red Egyptian 6A (Sears et al., 1957).
v: Mentana (Luig and Watson, 1965). Red Egyptian Sr6 Sr9a (Knott and Anderson, 1956).
Source Stocks
Sr8a is a very common gene. Examples from lists in Luig (1983), McIntosh (1988a) and elsewhere include the following.
Australia: Jacup. Songlen Sr2 Sr5 Sr6 Sr36. Hartog = Pavon ‘S’ Sr2 Sr12 Sr30 (Brennan, 1983). Warigal Sr5 Sr9b Sr15. Condor Sr5 Sr12. Egret Sr9b Sr12.
China: An-Hewi II Sr5.
CIMMYT: Nuri 70 Sr2 Sr5 Sr6. Penjamo 62 Sr5 Sr6 Sr9b. Inia 66 Sr9a Sr11.
Europe: Victor 1 Sr5 Sr6. Golden Valley Sr7b; Roussalka Sr7b.
South America: Frontana Sr9b.
USA: Geneva. Arthur Sr2 Sr5 Sr36. Centurk Sr5 Sr6 Sr9a Sr17. Era Sr5 Sr6 Sr17. Chris Sr5 Sr7a Sr8a Sr9g Sr12. Butte Sr6 Sr9g. Olaf Sr9b Sr12. Benhur Sr10.
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Use in Agriculture
Despite its high frequency in wheat cultivars, Sr8a probably has limited effects on field responses to stem rust. Wheats with Sr8a may become susceptible even with avirulent pathotypes.