II.8 Inheritance of resistance to powdery mildew, derived from Nigrate (C.I.2444).
G. Fischbeck and E. Schwarzbach. Institute of Agronomy and Plant Breeding, Weihenstephan West Germany.
An unusual type of resistance to powdery mildew was recently found in the variety Nigrate (C.I.2444) and in the line N 404, derived from the cross C.I.2444 x Union. After inoculation with any pure mildew race, pustules of infection type 4 will occur on the primary leaves, but the number of pustules is very much reduced in comparison with susceptible varieties (Plate & Fischbeck 1969, Schulze & Fischbeck 1969).
Hiura (1960) describes 2 factors for mildew resistance present in C.I.2444, one of them being located in the Mla locus. Karimi (1965), however, found in crosses of C.I.2444 with barleys carrying resistance alleles of the Mla locus resistant, susceptible and several intermediate types in the F2 generation. He concluded, that if a gene for resistance in the Mla locus is present in C.I.2444, the mildew reaction depends on interactions with another gene, not linked with Mla. Whereas in crosses of C.1.2444 with susceptible barleys resistant types prevailed in F2, in crosses of N 404 with susceptible varieties intermediate and susceptible types prevailed in F2. Although Karimi accepted the two gene hypothesis for C.I.2444 and N 404, the inheritance of mildew resistance in these barleys is not very clear.
Several barley strains, carrying independently induced mildew resistance mutations (Favret 1965, Schwarzbach 1967, Jørgensen 1969) show a similar type of mildew reaction as C.I.2444 and N 404. It seems possible therefore, that a naturally occurring gene for mildew resistance, present in these barleys, may be identical with the mutated genes. To test this assumption, N 404 was crossed with the mutant SZ5139 b, which carries a single gene resistance to mildew, inherited recessively and independent from Mla (see Nover, Schwarzbach, this issue). Simultaneously we crossed N 404 with MK 1, a line susceptible to all known European mildew races, and with MS 5455, which carries a single dominant gene for mildew resistance, situated in or closely linked with the Mla locus. The F1 plants were grown and spontaneously infected with powdery mildew in the greenhouse. F1-plants from N 404 x MK 1 showed heavy infection, indicating a recessive mildew resistance in N 404. On F1-plants from N 404 x SZ 5139 b a small number of pustules, infection type 4, developed. This mildew reaction, similar to N 404, indicates a complementation or identity of two recessive factors. Plants from the cross N 404 x MS 5455 showed a hypersensitive necrotic mildew reaction similar to the dominant male parent.
The segregation of the F2 generations is at present under investigation. There are indications that the restricted number of pustules on plants showing a Nigrate-type of mildew reaction varies with temperature conditions. The F2 populations therefore are tested for mildew reaction in growth chambers with controlled temperature.
Literature cited:
Favret, E. 1965 Rad. Botany 5, Suppl. "The use of induced mutations in plant breeding"
Hiura, U. 1965 Ber. Ohara Inst. Landw. Biol. 11:235-300.
Jørgensen, J. H. 1971 2nd Int. Barley Genet. Symp., Pullman, Washington, U.S.A. (In press).
Karimi, H. 1965 Z. Pflanzenzuchtung 53:205-225.
Plate, D., Fischbeck, G. 1969 Z Pflanzenzuchtung 61:225-231.
Schulze, F. W., Fischbeck, G. 1969 Z. Pflanzenzuchtung 62:343-356.
Schwarzbach, E. 1967 Genetika a slechteni 3:159-161. (Czech. with Engl. summ.)