II.22 Inheritance studies with a mildew resistant barley mutant.
Illse Nover and E. Schwarzbach. Institute fur Pflanzenbau und Pflanzenzuchtung, 8050 Freising-Weihenstephan, West Germany.
After EMS treatment of seeds of the Czechoslowak spring barley variety 'Diamant' a yellow green mildew resistant plant was found among about 20 000 M2-plants (each plant from a different M1-spike). A backcross experiment revealed that mildew resistance and yellowish leaves were inherited independently; both characters were recessive. The normal green mildew resistant segregate was given the stock number SZ 5139 b (Schwarzbach 1967). It was tested with the mildew races A11, B6, C2, C3, C4, C5, C7, C13, C14, C16, C17, C18, C20, D3, D11 and with the new races C2(Amsel) and C2(Emir). With all races the resistant reaction was similar: only a few pustules of infection type 4 occurred on the primary leaves. Older plants, however, reacted with small chlorotic, later necrotic spots. Isolates from the sporadic pustules gave the same resistant reaction as the original mildew races.
A cross of 'SZ 5139 b' with the spring barley 'MS 5455' (seed of which was provided by courtesy of Prof. W. Hoffman, Berlin-Dahlem) was made to test linkage with the mildew resistance locus Mla on chromosome 5. The gene of 'MS 5455' which provides resistance to all European mildew races known is a dominant allel of locus Mla (Lau 1962). In a simultaneous testcross of 'MS 5455' with a variety susceptible to all known European mildew races the presence of other than Mla -resistance factors was tested. After successive infection of the F2 population with the mildew races A13 and C7 it resulted a clear segregation for a single incompletely dominant mildew resistance gene.
The F2-population of the cross 'MS 5455' x 'SZ 5139 b' was successively infected with the mildew races A11, B6, and C2(Amsel). The segregation indicated the presence of two independent or almost independent factors for mildew resistance, one dominant and one recessive.
To test linkage between the mutant gene and the Mlg gene on chromosome 4 we crossed 'SZ 5139 b' with 'Weihenstephaner Mehltauresistente CP', the gene Mlg of which causes resistance to all mildew races of the groups A and D. Segregation in F2, after successive infection with the races A13 and C7, clearly indicated that there is no linkage between these two genes.
The barleys 'M 66' an x-ray mutant from 'Haisa' (Freisleben & Lein 1942), and 'Unbegrannte Nackte', probably of Ethiopian origin, are known to have also recessively inherited resistance to all known European mildew races, controlled by a single gene independent from Mla (Lau 1962). Seed of 'M 66' and 'Unbegrannte Nackte' was provided by courtesy of Dr. D. Lau (Hadmersleben). To test the possible identity of their resistant genes with that of 'SZ 5139', the two varieties were crossed with 'SZ 5139'. In both cases the F1 generations were resistant and no segregation for mildew resistance occurred in F2, whereas segregation in morphological characters was present. Thus it may be concluded, that the mildew resistance genes of 'SZ 5139 b', 'M 66' and 'Ungrannte Nackte' are identical or very closely linked.
In addition Jørgensen (1969) was able to show, that the gene for mildew resistance of 'M 66' is identical or very closely linked with those of 'MC 20', 'Refoma' and several other independently induced mutations. Our results indicate that in 'SZ 5139 b' the same gene must have mutated.
In further experiments Weihenstephan 'SZ 5139 b' has now been crossed with a set of translocation lines, received from Dr. A. Hagberg, Svalof, to detect linkage of the mildew resistance gene with breakpoints of known location.
Literature cited:
Freisleben, R., Lein, A. 1942 Naturwiss. 30:608.
Jørgensen, H. J. 1969 2nd Int. Barley Genet. Symp. Pullman, Wash., U.S.A.
Lau, D. 1962 Z. Pflanzenzuchtung 48:80-90.
Schwarzbach, E. 1967 Genetika a slechteni 3:159-161. (Czech. with Engl. sum.)