(McIntosh et al., 1976) (Plate 3-26)
7D (Sharma and Knott, 1966). 7DL (McIntosh et al., 1976; Dvorak and Knott, 1977); 7AL (Eizenga, 1987); 7Ag (Sears, 1973). In most stocks Sr25 is associated with Lr19.
Low Infection Type
1- to 23. Low infection types recorded by Knott (1980, 1990) were generally lower than those obtained in Australia.
Low (Roelfs and McVey, 1979), but probably inadequately researched (Luig, 1983). Gough and Merkle (1971) suggested that lines with Sr25 may become more susceptible at high temperatures.
Luig (1983) mentioned an Israeli isolate with putative virulence. Huerta-Espino (1992) identified one virulent culture from Ethiopia and two virulent cultures from Nepal.
i: Sr25/9*LMPG (Knott, 1990). Sears’ independently derived 7D/Ag translocation stocks (Sears, 1973) can be considered near-isogenic to Chinese Spring. Agatha Sr5 Sr9g Sr12 Sr16 = T4 (Sharma and Knott, 1966) is near-isogenic to Thatcher.
su: Chinese Spring 7Ag(7D) (Sears, 1973). Agrus, a 7Ag(7D) stock (Sharma and Knott, 1966).
Because of its close association with Lr19 (McIntosh et al., 1976), Sr25 should be present in Oasis F86, Indis and Sunnan (see Lr19).
Use in Agriculture
Lines of Chinese Spring with Lr19/Sr25 can become moderately rusted with avirulent cultures in breeding nurseries and losses may occur (McIntosh et al., 1976; Roelfs and McVey, 1979). The use of this gene in breeding can be justified by its linkage with Lr1 9. However, lines with Sr25/Lr19 from Agatha and Sears’ translocations are characterised by high levels of yellow pigment in the endosperm. Knott (1980) obtained two mutants of Agatha with reduced levels of yellow pigment in the flour. One of these mutants lacked Sr25. Marais (1992a) reported that a gene very similar to Sr25, and designated Sr25d, was present in the Inia 66 x Th. distichum derivative, Indis. Marais (1992a, 1992b) also obtained mutants with reduced yellow pigment in Indis derivatives and some of these lacked Sr25d.