Sr6

(Knott and Anderson, 1956) (Plate 3-3)

Synonym

SrKa1 (Athwal and Watson, 1954).

Chromosome Location

2D (Sears, 1954; Wiggin, 1955; Sears et al., 1957); 2DS (McIntosh and Baker, 1968). Sr6 showed close linkage with Lr2 and Lr15 and linkage of 19-40 cM with gene C for compact spike (McIntosh, 1988a).

Low Infection Type

0; through X to 3+, varying with pathogen culture and temperature. Sr6 may be dominant or recessive depending on pathogen culture, temperature and genetic background.

Environmental Variability

Most effective at temperatures less than 20°C. Becomes ineffective at 24-27°C (Forsyth, 1956; Watson and Luig, 1968).

Origin

Common wheat. Sr6 was identified in McMurachy, a farmer’s selection from Canada, and Red Egyptian which originated from Ethiopia (Knott and Anderson, 1956). Both are club wheats but are genetically distinct. McMurachy was used as a rust resistant parent in North America and Red Egyptian was used in Kenya to produce a number of wheats that were subsequently widely used as parents, for example Kenya 58 in North America and Kenya W743 in Australia.

Pathogenic Variability

When first exploited Sr6 was very effective in most geographical areas. Now virulence occurs in most areas (Luig, 1983; Huerta-Espino, 1992). Progressive increases in virulence for Sr6 were documented by Watson and Luig (1968). Some cultures with intermediate pathogenicities would be classified as virulent in regular surveys.

Reference Stocks

i: ISr6-Ra C.I.14163 (Loegering and Harmon, 1969); Kenya 58/6*Marquis (Green et al., 1960); Kenya 58/10*Marquis (Knott, 1965); Sr6/9*LMPG (Knott, 1990).

s: Chinese Spring*5/Red Egyptian 2D (Sears et al., 1957).

v: McMurachy (Knott and Anderson, 1956; Watson and Luig, 1963). Red Egyptian Sr8a Sr9a (Sears et al., 1957).

Source Stocks

Many wheats carry Sr6 (see Luig, 1983; McIntosh, 1988a).

Africa: Bonza 63 Sr8a Sr9b. Many Kenyan lines (Knott, 1962a; Watson and Luig, 1963).

Australia: Eureka; Wongoondy. Songlen Sr2 Sr5 Sr8a Sr36. Gamut Sr5 Sr8a Sr12; Oxley Sr5 Sr8a Sr12. Bayonet Sr8a. See Luig (1983).

North America: Milam; Shield; Trapper; Travis; Twin. Selkirk Sr2 Sr7b Sr9d Sr17 Sr23. Manitou Sr5 Sr7a Sr9g Sr12. Centurk Sr5 Sr8a Sr9a Sr17. Butte Sr8a Sr9g. Colt Sr8a Sr9a Sr17 Sr24. Onas Sr10; White Federation 54 Sr10. Homestead Sr17.

Seedling leaves of (L to R): McMurachy, Eureka, I5r6-Ra, Kenya 58/6*Marquis and Chinese Spring. Upper sets were infected with A. pt. 126-5, 6, 7, 11 [P6] and B. pt. 126-1, 5, 6, 7, 11 [p6] and incubated at 21°C. tower sets were inoculated with pt. 34-2 [P6\ and incubated at C. 21°C and D. 28°C. The upper sets demonstrate specificity between culture and host gene, whereas the lower sets demonstrate temperature sensitivity.

 

Use in Agriculture

Sr6 was a very effective source of resistance when first used in Australia (Eureka) and Canada (Selkirk). Sr6 continues to be present in a range of modern cultivars; however, virulence is now widely distributed in most geographic areas (Luig, 1983).

Knott and Anderson (1956) found that Sr6 was dominant when segregating populations were tested with race 56 but was recessive when they were tested with race 15B.