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Wheat Information Service
December 79: 33-36 (1994)

Telosomic mapping of wheat genes for resistance to inappropriate formae speciales of Erysiphe graminis

Y.Tosa* and H.Tsujimoto**

* Faculty of Agriculture, Kochi University, Nankoku, Kochi 783, Japan
**Kihara Institute for Biological Research, Yokohama City University, Mutsukawa 3-122-20, Minami-ku, Yokohama 232, Japan


Summary

Pm11 and Pm15 are wheat genes for resistance to Erysiphe graminis f.sp. agropyri. Telosomic analyses suggested that genetically Pm11 on chromosome 6B short was closely linked to the centromere but that Pm15 on chromosome 7D short was very distant from the centromere.


Introduction

Erysiphe graminis is the causal agent of powdery mildews of gramineous plants, and widely distributed in the world. It comprises several formae speciales, e.g., f.sp. tritici parasitic on Triticum, f.sp. secalis parasitic on Secale, and f.sp. agropyri parasitic on Agropyron. In other words, Triticum spp., for example, are susceptible to only f.sp. tritici and resistant to f.sp. agropyri, f.sp. secalis, and so on. This type of host-parasite specificity has been called forma specialis - genus specificity (Tosa et al. 1987).

Tosa (1989) crossed f.sp. agropyri, Ak-1 with f.sp. tritici, Tk-1, and obtained 240 F1 cultures between them. Using these hybrids, Tosa and his coworkers (Tosa et al. 1987,1988; Tosa and Sakai 1990) identified several genes that controlled the resistance of wheat to f.sp. agropyri. The wheatgrass mildew fungus, Ak-1, was avirulent on both of common wheat cultivars, Norin 4 (N4) and Chinese Spring (CS), and the wheat mildew fungus, Tk-1, was highly virulent on both. However, Gw-180, an F1 culture between Ak-1 and Tk-1, was avirulent on CS but highly virulent on N4. This culture revealed a phenotypic difference between the two cultivars, and made genetic analyses possible. When F2 seedlings derived from the cross, CS x N4, were inoculated with Gw-180, resistant and susceptible seedlings segregated in a 3:1 ratio, indicating that the resistance of CS to Gw-180 was controlled by one major gene. This gene was designated as Pm11 (Tosa et al. 1988). Subsequently, we found an F1 culture, Gw-121, that was avirulent on both CS and N4, but highly virulent on another cultivar Red Egyptian (RE). When F2 seedlings from CS x RE and N4 x RE were inoculated with Gw-121, resistant and susceptible seedlings segregated in a 3:1 ratio. A cross between CS and N4 yielded no susceptible F2 seedlings. These results indicated that the resistance of CS and N4 to Gw-121 was controlled by the same major gene. This gene was designated as Pm15 (Tosa and Sakai 1990). Pm11 and Pm15 were considered to be involved in the resistance of wheat to f.sp. agropyri.

Pm11 and Pm15 are located on the short arms of chromosomes 6B and 7D, respectively (Tosa et al. 1988; Tosa and Sakai 1990). In this study we tried telosomic mapping of these genes.


Materials and methods

1. Fungal cultures: Fungal cultures used were Gw-180 and Gw-121, F1 hybrids derived from the cross between Erysiphe graminis DC. f.sp. agropyri Em. Marchal, Ak-1, and f.sp. tritici Em. Marchal, Tk-1. They were maintained at 3 plus or minus 1C on susceptible seedlings growing in 2 x 35cm glass test tubes with paper plugs.

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