II. 24. Mutants of barley with resistance to Erysiphe graminis D.C. f.sp. hordei March.
G. Kavacs, Latvian Academy of Sciences, Institute of Biology, 22902I Salaspils, USSR. "R"
We have obtained mutant lines resistant to Erysiphe graminis hordei from the most widely distributed variety of barley "Maja" in the Latvian SSR, the seeds of which were treated with N-nitrosomethylurea (0.01% solution in 12 hrs) or with the fast neutrons (1000 rad.). M2 plants were grown in families, but the genetic material of resistant forms were selected in families M3 (progenies of a separate plant M2) after infection of plants with races C5 or D7 in the greenhouse. Progenies of 1282 families M2 were tested. The selected forms were tested once more in families M4. Each plant was checked for resistance to 2-5 races of mildew, infecting pleces of leaves kept in 0.004% solution of benzimidazole.
Twelve families M2 were selected with mutations of resistance. Mutant plants had resistance at least to one of the used race E. graminis hordei. In the progeny of families M2 -- 477, 792, 1007 -- a number of families of the following generations were found resistant to all races of mildew used in the tests.
In the families M2 477 and 792 more than 60 families M4 were tested to the resistance of the local population of mildew (Table 1).
Table 1. Resistance of mutant lines of barley to the local population of powdery mildew.
The obtained facts show that in many of those resistant families M4 no further segregation takes place. These families can be considered as resistant lines. Such lines have been selected in the following M3 families -- 477-5, 477-6, 792-2, 792-4, 792-5, 792-9, 1007-2 and some others.
On the whole, mutations with resistance to mildew were induced in 10 M2 families from 1052 after treatment with NMU and in 2 M2 families from 230 after irradiating with fast neutrons. It forms 0.95 and 0.87% mutant families M2, respectively. At the same time the number of families with chlorophylI mutations makes 11.5% if being induced by NMU and 6.5% if induced by fast neutrons. Thus the frequency of mutations of resistance is about ten times lower than that of chlorophyll mutations.
The character of segregation into mutant families shows that the induced resistance in families 477, 792 and 1007 is determined by recessive mutations. This is confirmed by tests to resistance in F1 and F2 generations obtained from crossings between some mutant lines and the initial variety "Maja" (Table 2). Among tested hybrids F1, no resistant plant has been observed. Segregation in a ratio of 3 susceptible to l resistant plant indicates a monogene character of the induced resistance.
The resistance of F1 hybrids when crossing mutant lines from families 477, 792 and 1007 among them as well as the carriers of resistance gene ml-o -- Ab-6 and M.C.20 (Table 3), shows the noncomplementation of mutant genes of induced resistance either reciprocally or with gene ml-o. Consequently, the genes of induced resistance are allelic (or closely linked) with genes in locus ml-o.
