Sr5

(Ausemus et al., 1946) (Plate 3-2)

Synonym

Srrl 1 (Rondon et al., 1966).

Chromosome Location

6D (Sears et al., 1957); 6DS (RA McIntosh, unpublished 1984).

Low Infection Type

Usually 0 to ;. Sr5 is often cited as the ‘immunity’ gene from wheat stem rust research. The low infection type is usually very low but can be significantly higher (IT X) when Sr5 is transferred to a highly susceptible genetic background (Luig and Rajaram, 1972).

Environmental Variability

Low (Luig and Rajaram, 1972).

Origin

Common wheat. Sr5 is present in the Stakman et al. (1962) differential, Reliance C.I.7370, having been inherited from Kanred, a Crimean introduction to the USA.

Pathogenic Variability

Virulence occurs in all geographic areas (Luig, 1983; Huerta-Espino, 1992).

Reference Stocks

i: ISr5-Ra C.I.14159 (Loegering and Harmon, 1969); ISr5-Rb C.I.14161 (Loegering and Harmon, 1969); Line B = W2691*7/Reliance (Luig, 1983); Sr5/7*LMPG (Knott, 1990); Thatcher/10*Marquis (Knott, 1965). Although Marquis is susceptible to many pathotypes of economic significance, lines near-isogenic to Marquis may carry the genes Sr7b, Sr18, Sr19 and Sr20, which are present in this cultivar.

s: Chinese Spring*6/Thatcher 6D (Sears et al., 1957); Chinese Spring*7/Marquis 6D (Sheen and Snyder, 1964). The ‘Marquis’ line used by Sheen and Snyder was probably Thatcher or a closely related derivative.

v: Kanred (Sears et al., 1957). Thatcher Sr9g Sr12 Sr16 (Luig, 1983). Reliance Sr16 Sr18 Sr20 (Luig, 1983).

Source Stocks

Many wheats possess Sr5 (see Luig, 1983; McIntosh, 1988a).

Australia: Zenith. Catcher Sr2 Sr6 Sr8a Sr9g Sr12. Bindawarra Sr6 Sr9b Sr15. Aroona Sr8a Sr9b Sr15. Avocet Sr26; Hybrid Titan Sr26.

China: Dong-Fang-Hong 2; Ke-Fang 1. Dong-Xie 3 Sr31.

Europe: Panis; Primus. Hochzücht Sr9g Sr12. Orlando Sr31.

Indian Subcontinent: NP789 Sr11.

North America: Cheyenne; Chisholm; Justin; Winoka. Arthur Sr2 Sr8a Sr36. Fortuna Sr6 Sr7a Sr17. Era Sr6 Sr8a Sr17. Centurk Sr6 Sr8a Sr9a Sr17. Chris Sr7a Sr8a Sr9g Sr12. Oasis Sr8a Sr36. Apex Sr9g Sr12; Kitt Sr9g Sr12. Thatcher Sr9g Sr12 Sr16. Agatha Sr9g Sr12 Sr16 Sr25.

Seedlings of (L to R): Reliance, Zenith, ISr5-Ra, Line B (W2691*7/Reliance) and Chinese Spring; infected with A. pt. 194-2 [P5] and B. pt. 34-2 [p5]. With the avirulent culture, ISr5-Ra (genetic background of Chinese Spring) sometimes gives small necrotic pustules but in the W2691 background, Sr5 confers IT X. With the virulent culture, Reliance usually develops slightly smaller pustules than the other lines. This slightly retarded rusting has been attributed to Sr16.

 

Use in Agriculture

At various times Sr5 has been a useful and very effective source of resistance. However, resistance proved transient in all geographic areas because of selection and rapid increase of virulent pathotypes. The dominance of Thatcher and its derivatives in the northern Great Plains of North America undoubtedly influenced the increase in pathotypes virulent for Sr5.