Sr9b

(Green et al., 1960) (Plate 3-9)

Synonym

SrKb1 (Athwal and Watson, 1954).

Low Infection Type

1+ to 3. 2 (DR Knott, pers. comm. 1993).

Environmental Variability

Low (Roelfs and McVey, 1979).

Origin

Common wheat. Sr9b was first found in certain Kenyan wheats (Knott and Anderson, 1956). Its presence in the Brazilian cultivar Frontana must derive from Fronteira whose pedigree is Polysu/Alfredo Chaves 6 (Zeven and Zeven-Hissink, 1976).

Pathogenic Variability

Wheats with Sr9b produce differential responses to P. graminis in most geographic areas (Luig, 1983). In the survey of Huerta-Espino (1992) frequencies of virulence for Sr9b were generally high.

Reference Stocks

i: Kenya 117A/6*Marquis, W2402 (Green et al., 1960; Watson and Luig, 1963); Kenya 117A/10*Marquis (Knott, 1965): Sr9b/10*LMPG (Knott, 1990).

s: Chinese Spring*7/Kenya Farmer 2B (McIntosh and Luig, 1973a).

v: Gamenya (Luig, 1983).

Source Stocks

Sr9b occurs in many wheats, especially those of Kenyan origin (see Luig, 1983; McIntosh, 1988a).

Africa: Romany Sr5 Sr6 Sr7a Sr30. Bonza 63 Sr6 Sr8a. Kenya 117A Sr7a Sr10. Kenya Farmer Sr7a Sr10 Sr11. Kenya W744 Sr15.

Australia: Gamenya. Aroona Sr5 Sr8a Sr15; Warigal Sr5 Sr8a Sr15. Egret Sr8a Sr12.

CIMMYT: Penjamo 62 Sr5 Sr6 Sr8a. Pitic 62 Sr8a. Nainari 60 Sr11.

South America: Frontana Sr8a; Rio Negro Sr8a.

USA: Atlas 66 Sr10. Lancota Sr10 Sr17.

 

Seedling leaves of (L to R): Kenya 117A, Camenya, Kenya 117A/6*Marquis, CS*7/Kenya Farmer 28 and Chinese Spring; infected with A. pt. 126-5, 6, 7, 11 [P9b], B. pt. 11 6-4, 5 [P9b] and C. pt. 116-2, 3, 7 [p9b]. The low infection type with pt. 126-5, 6, 7, 11 is usually characterised by smaller pustules and necrosis compared with that produced with pt. 116-4, 5. The chlorotic response of Kenya 117A with pt. 116-2, 3, 7 can be attributed to Sr7a. It is difficult to attribute the lower response of Kenya 117A with pt. 126-5, 6, 7, 11 to interaction between Sr9b and Sr7a, because this pathotype is considered virulent on seedlings with Sr7a alone.

 

Use in Agriculture

Sr9b is relatively common in spring wheats because the gene has been effective in many countries. In Frontana and many of its relatives, Sr9b is linked with Lr13. The presence of Sr9b in some wheats probably resulted from selection for leaf rust resistance.