(The, 1973a) (Plate 3-22)

Chromosome Location

2A (The, 1973a); 2AL (The et al., 1979). Sr21 mapped 2 cM from the centromere and 48 cM from Pm4.

Low Infection Type

; to 23-. The low infection type becomes higher with increasing levels of ploidy (The, 1973a).

Environmental Variability

Low (Roelfs and McVey, 1979).


T. monococcum accessions, including Einkorn C.I.2433 which was adopted by Stakman et al. (1962) as a pathotype differential (The, 1973a). A gene with identical specificity in chromosome 1D of T. tauschii (McIntosh, 1981) is sometimes referred to as SrX (D The, unpublished 1992).

Pathogenic Variability

Polymorphism occurs in most geographic areas. The frequencies of virulence in North America (Roelfs and McVey, 1979) and South America (Huerta-Espino, 1992) are very high compared to other regions. Virulent mutants have been detected in Australian field surveys but none has become established as a common field pathotype (Zwer et al., 1992).

Reference Stocks

i: Sr21/8*LMPG (Knott, 1990).

v: W3586 = Glossy Huguenot/Einkorn//unknown hexaploid (The, 1973a); R.L.5406 = Tetra Canthatch/T. tauschii R.L.5289 (McIntosh, 1981).

dv: Einkorn C.I.2433.

Source Stocks

i: Sr21/5*Aroona; Sr21/5*Condor; Sr21/5*Egret; Sr21/5*Halberd; Sr21/5*Lance; Sr21/5*Oxley; Sr21/5*Teal(The et al., 1988).

v: Hexaploid derivatives of T. monococcum produced by The (1973b). Hexaploid derivatives of T. tauschii possessing SrX (see Origin).

tv: Tetraploid derivatives of T. monococcum (The, 1973b).

dv: T. monococcum accessions (The, 1973a, 1973b). T. tauschii accessions including R.L.5289 (McIntosh, 1981; RA McIntosh, unpublished 1991).


Seedling leaves of (L to R): Einkorn (T. monococcum), W3586 (Glossy Huguenot/Einkorn//unknown hexaploid), R.L.5406 (Tetra Canthatch/T. tauschii R.L.5289) and Steinwedel; infected with A. pt. 194-2 [P21] and B. pt. 17-1, 2, 3, 7 [p21] and incubated at 20°C. Note the similarity in response of Einkorn and its derivative with the T. tauschii derivative.


Use in Agriculture

This gene has potential for limited use in areas with low frequencies of virulence if deployed together with other genes. If used alone, rapid increases in the frequency of virulent pathotypes can be anticipated. In addition, current lines with Sr21 are not adequately resistant to avirulent pathotypes as adult plants. The et al. (1988) showed that, in the absence of disease, a number of backcross-derived lines possessing Sr21 gave significantly lower yields than near-isogenic counterparts that did not carry the gene.