(McIntosh and Luig, 1973 b) (Plate 3-24)
Chromosome Location
2BS (RA McIntosh, unpublished 1978). This gene is completely associated with Lr16. It was initially believed to be located in chromosome 4B, but a Rescue monosomic series was used to establish the location and Rescue carries a 2B-4B reciprocal translocation relative to Chinese Spring (RA McIntosh, unpublished 1980; EDP Whelan, pers. comm. 1982). Sr23/Lr16 are genetically independent of, and presumably distal to, Sr36 (RA McIntosh, unpublished 1980).
Low Infection Type
l++N to 3+CN.
Environmental Variability
Sr23 is expressed only under conditions of high temperature and high light intensity (Luig, 1983). The low infection type is often characterised only by necrosis surrounding some of the otherwise fully compatible uredinia. Roelfs and McVey (1979) observed slight increases in sporulating area with increasing temperature.
Origin
Sr23 was first noted and characterised in common wheat cultivars Selkirk, Exchange and Warden.
Pathogenic Variability
A necrotic response and low infection type with the old Australian pathotype 126-5, 6, 7, 11 is characteristic of plants with this gene. With other pathotypes some necrosis is expressed in otherwise large ‘compatible’ uredinia under high light and temperature conditions. Huerta-Espino (1992) used Exchange as the host tester for Sr23 but it apparently also carries the uncatalogued gene SrMcN. Despite the statement that “all isolates were virulent to ...Sr23 and SrMcN” (Huerta-Espino, 1992), three cultures, one each from Burundi, Turkey and Nepal, were recorded as producing ITs 2C to 23C on seedlings of Exchange. These responses seemed to be too high to be conferred by SrMcN (2-; Roelfs and McVey, 1979), but could be associated with Sr23.
Reference Stocks
v: Exchange (McIntosh and Luig, 1973b). Selkirk Sr2 Sr7b Sr9d Sr17 (McIntosh and Luig, 1973b).
Source Stocks
Warden (McIntosh and Luig, 1973b). Etoile de Choisy Sr29 (McIntosh and Luig, 1973b). All stocks carrying Lr16 are assumed to carry Sr23 (see Lr16).
Use in Agriculture
None. Sr23 is not expected to provide significant levels of protection when deployed in susceptible backgrounds (McIntosh and Luig, 1973b).