Sr38

(Bariana, 1991; Bariana and McIntosh, 1993) (Plate 3-39)

Chromosome Location

2AS. Sr38 is completely linked with Lr37 and Yr17, and is closely linked in repulsion with Lr17 (Bariana and McIntosh, 1993).

Low Infection Type

X, often with very large pustules towards the leaf base.

Environmental Variability

More effective at lower temperatures.

Origin

T. ventricosum.

Pathogenic Variability

Virulence has not been reported, although this gene has not been widely tested.

Reference Stocks

i: Thatcher*8/VPM1, R.L.6081 (PL Dyck, pers. comm. 1991).

v: VPM1 (Doussinault et al., 1981, 1988).

Source Stocks

Australia: Trident (= Spear*4/VPM1). Sunbri Sr5 Sr6 Sr8a Sr36 (Brown et al., 1991). Various backcross-derived lines generated at the PBI, Cobbitty.

UK: Rendezvous (Bariana, 1991).

USA: Hyak (RA McIntosh, unpublished 1990); Madsen (RA McIntosh, unpublished 1990).

 

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Seedling leaves of (L to R): VPM1 leaf tip, VPM1 mid leaf, Tc*8/VPM1, Trident, Chinese Spring and Marne; infected with pt. 34-1, 2, 3, 4, 5, 6, 7 and incubated at A. 20/23°C and B. 23/28°C. Resistance conferred by Sr38 is more effective at lower temperatures. Uredia are often larger, even fully compatible, towards the leaf base.

 

Use in Agriculture

Because of the associated resistances to all three rust diseases, wheats with Sr38, Lr37 and Yr17 will be useful in most parts of the world. VPM1 was initially selected as a breeding parent in Australia because of high levels of resistance to all three rusts. The phenomenon of linkage was noted locally during the backcrossing, following tests on Rendezvous bred in the UK and on Hyak and Madsen bred in the Pacific Northwest of the USA, and was demonstrated formally by Bariana and McIntosh (1993). Rendezvous, Hyak and Madsen were bred primarily for resistance to eyespot or strawbreaker disease (caused by Pseudocercosporella herpotrichoides) controlled by gene Pch in chromosome 7DL. Selection for stripe rust resistance, also practiced by the breeders, presumably led to the leaf rust and stem rust resistances present in these cultivars. The Australian cultivar Sunbri was bred for rust resistance and is assumed not to carry Pch.