GrainGenes

II. 25. Powdery mildew resistance gene Ml-a8 (Reglh8) in northwest European spring barley varieties.

J. Helms Jørgensen and H. P. Jensen, Agricultural Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark. "R"

Powdery mildew resistance gene Ml-a8 (Moseman and Jørgensen 1971) or Reglh8 (Moseman 1975) or JMl^h4_sn (Hiura 1960) is apparently present in a number of northwest European barley varieties including e.g. 'Binder', 'Chevalier', 'German Summer', 'Heils Hanna', 'Maja', 'Opal', 'Primus', and 'Svanhals', conditioning resistance to several powdery mildew races in Japan, including Races I and XI, but not Race IX (Hiura and Heta 1955). This gene has, however, never shown susceptibility to powdery mildew from Europe.

Progeny from a cross between Race I from Japan and the Ml-a8 virulent culture TY4 from Denmark showed that gene Ml-a8 is also present in the Danish spring barley variety 'Carlsberg II' that is susceptible to all European and North American cultures of powdery mildew applied (cf. Torp et al. 1978).

Race I and Race IX from Japan avirulent and virulent on barleys with gene Ml-a8, respectively, and two selected cultures from Denmark were used to trace the presence or absence of gene Ml-a8 and of other resistance genes in a collection of northwest European spring barley varieties from the first half of the century. These tests showed that the 63 varieties described below do not possess any of the resistance genes Ml-a, Ml-a6, Ml-a7, Ml-a9, Ml-al2, Ml-al3, Ml-g, Ml-k, and Ml-(La) introduced by breeding in European spring barley in the 1950s, 1960s, and 1970s (cf. Torp et al. 1978). Forty of these 63 varieties had infection types and spectra of resistance identical to those of 'Heils Hanna' and 'Carlsberg II' indicating the presence of gene Ml-a8, and 23 varieties did not have gene Ml-a8. Thus, about two-thirds of the varieties have gene Ml-a8. The frequency of gene Ml-a8 is probably lower among more recent varieties because it has been replaced by other resistance genes in the Ml-a region. The two groups of varieties are listed below in alphabetical order. The origin of the varieties and their pedigree is given by Frydenberg et al. (1969).

Varieties with gene Ml-a8
Alfa
Balder
Beorna
Binder
Bonus
Carlsberg
Carlsberg II
Dana
Denso
Domen
Donaria
Drost
Drost A
Drot
Elbo
Fero
Goldthorpe
Gull
Hanna*
Hannchen*
Heils Hanna
Herta
Ingrid
Kenia
Kneifel
Kron*
Lenta
Maja
Mari
Maythorpe
Opal
Opal B
Pallas
Pendo
Proctor
Rika
Seger*
Spratt
Vollkorn
Ymer

*Heterogeneous in mildew reaction

Varieties without gene Ml-a8
Abed Archer
Archer
Bavaria
Birgitta
Danubia
Earl
Foma
Freja
Hafnia
Irish Archer
Isaria
Maris Baldric
Maskin
Morgenrot
Plumage Archer
Prentice, Abed
Prentice, Tystofte
Prinsesse
Provost
Rigel
Spartan
Spratt Archer
Vega

The high frequency of Ml-a8 in European barleys suggests that it has exerted a considerable selection pressure on the pathogen population so that the frequency of the corresponding virulence gene has become (nearly?) 100%. This may explain why gene Ml-a8 has never been detected with European powdery mildew. These results show that a wild-type or "susceptibility" gene in European spring barley may be a well defined resistance gene to which the corresponding avirulence gene is absent.

References:

Frydenberg, O., G. Nielsen and J Sandfaer. 1969. The inheritance and distribution of alpha-amylase types and DDT responses in barley. Z. Pflanzenzuchtg. 61:201-215.

Hiura, U. 1960. Studies on the disease-resistance of barley. IV. Genetics of resistance to powdery mildew. Ber. d Ohara Inst. landwirtschaftl. Biologie 11:235-300.

Hiura, U. and H. Heta. 1955. Studies on the disease-resistance of barley. III. Further studies on the physiological races of Erysiphe graminis hordei in Japan. Ber. d. Ohara Inst. landwirtschaftl. Biologie 10:135-156.

Moseman, J. G. 1975. Designation of genes in barley for reaction to Erysiphe graminis (DC) Merat hordei Em. Marchal. BGN 5:87-88.

Moseman, J. G. and J. Helms Jørgensen. 1971. Identification of genes at the Ml-a locus in barley for resistance to Erysiphe graminis f. Sp. hordei. Crop Sci. 11:547-550.

Torp, J., H. P. Jensen, and J. Helms Jørgensen. 1978. Powdery mildew resistance genes in 106 northwest European spring barley varieties. Kgl. Vet.- og Landbøhijsk. Arsskr. 1978. pp. 75-102.

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