(Sheen and Snyder, 1964) (Plate 3-15)
Sr12 was first used in conjunction with Sr11 to designate complementary genes thought to be present in Gabo, Lee and Timstein (Knott and Anderson, 1956). Luig (1960) and Sears and Loegering (1961) showed that a single gene (Sr11) was involved and that abnormal gametic transmission rates were responsible for the disturbed genetic ratios originally observed by Knott and Anderson (1956). Sheen and Snyder (1964) then used Sr12 to designate a gene in a Thatcher derivative.
3B (Sheen and Snyder, 1964; Knott, 1984); 3BS (McIntosh et al., 1980).
Low Infection Type
;, 2, X to 3.
Most effective at temperatures below 20°C.
Sr12 is derived from T. turgidum var. durum cv. Iumillo and was transferred to Marquillo and, eventually, Thatcher as part of the transference of rust resistance from Iumillo to bread wheat (Hayes et al., 1920).
Virulence is reported to be common. However, RA McIntosh believes this gene is more effective than reported in the literature. Sr12 also shows interactions with other genes, especially the Sr9 alleles, Sr9b and Sr9g.
s: Chinese Spring*7/Marquis 3B (Sheen and Snyder, 1964). Chinese Spring*5/Thatcher 3B Sr16 (Sheen and Snyder, 1964).
v: Thatcher Sr5 Sr9g Sr16 (Luig, 1983). Marquillo Sr9g (Knott, 1984).
Africa: Kenya Plume Sr2 Sr5 Sr6 Sr7a Sr8a Sr9b Sr17 (Singh and McIntosh, 1986b).
Australia: Tincurrin; Windebri. Celebration Sr9g Sr16 (RA McIntosh, unpublished 1980). Tentative results based on multi-pathotype surveys in Australia indicate that Sr12 may be relatively common. Unfortunately, Sr12 is often difficult to distinguish from Sr6 with Australian P. graminis pathotypes and appropriate genetic studies have not been pursued.
North America: Chris Sr5 Sr8a Sr9g (Singh and McIntosh, 1987). Olaf Sr8a Sr9b. Sr12 is likely to occur in Thatcher derivatives.
tv: Yavaros 79 Sr9e (Singh et al., 1992). Other durums (Singh et al., 1992).
Use in Agriculture
Sr12 was highly effective against pre-1950 Australian pathotypes. After 1950 the effectiveness of this gene in wheats such as Windebri and Celebration was reduced but not completely overcome. In wheats combining Sr12 with Sr9b or Sr9g the presence of Sr12 can be recognised through its effects on the expression of the Sr9 alleles in seedlings inoculated with avirulent pathotypes. These interactions also appear to occur in adult plants. One pathotype in the University of Sydney collection is known to be unusually virulent on seedlings of Iumillo durum. This culture (pt. 21-7, 9 ) is potentially virulent on wheats known to carry Sr12. Both the seedling and adult plant resistances of Marquillo are more effective than those of Thatcher and its derivatives. The reasons for this are not fully undetstood but Sr12 appears to be involved (RA McIntosh, unpublished 1980; see also Knott, 1984).
In North America Sr12 was very effective in conferring resistance to race 56. Race 15B is virulent.