Dry seeds of five barley varieties (Table 1) were irradiated with gamma rays, the dosages being 100, 200, 300 and 400 Gy. Treated seeds were sown in the field along with control. At maturity, main spikes of 200 M 1 plants from each variety in each treatment were harvested and threshed. M 2 seeds were bulked treatment-wise for each variety and were divided into four lots. They were sown in the field in a randomized block design with four replications. Chlorophyll deficient seedlings were scored in field condition.

Varieties differed significantly regarding mutation frequency. Dosage of gamma rays and the interaction effects (Variety X Dose) were also significant. The mutation frequency based on total M 2 seedlings of four replications is presented in Table 1. The highest mutation frequencies in the varieties DL 36, Mex 22, BR 31, P 167 and KN 27 were 1.896, 2.9O6, 2.240, 2.315 and 4.428 %, respectively. KN 27 showed higher mutation frequencies than other varieties at all the dosages of gamma irradiation. At 300 Gy gamma rays, KN 27 showed the highest mutation frequency which reduced at 400 Gy. A similar trend was observed for P 167 (Table 1). The variety DL 36 was found to be comparatively less mutable. Mutant spectrum in different varieties induced by 300 Gy gamma rays is presented in Table 2. A total of nine types of chlorophyll deficient mutants were observed. KN 27 showed all the 9 mutant types while the other varieties were lacking in one or more types. Frequencies of mutant types differed in different varieties. Albina was more frequent in Mex 22 (52.1%) and less frequent in DL 36 (18.4%) while viridis and xantha were more frequent in DL 36 and less frequent in Mex 22. Main types of mutant were albina, viridis and xantha with the overall frequencies of 33.9, 28.6 and 19.1 %, respectively, induced by 300 Gy gamma rays.

Mutagens induce various kinds of damage such as, growth reduction, chromosome breakage, DNA damage and gene mutation and all the organisms have developed repair mechanisms for such damages. The frequency and type of mutations produced depend on chromosome and DNA repair mechanisms. Certain chemicals are known to enhance radiation effects by inhibiting the energy rich enzymatic repair processes and protein synthesis and by retarding the DNA polymerase activity ( Jagannath and Bhatia, 1974; Kamra et al., 1975). Present results indicated that KN 27 was a highly mutable variety. This variety may be lacking in DNA repair mechanisms more than other varieties of this study. Such a highly mutable variety may be used for induction of desirable mutants with a high frequency.

References :

Gaul, H. 1965. The concept of macro- and micro-mutations and results on induced micro-mutations in barley. In: The use of induced mutations in plant breeding (Rep. FAO/IAEA Tech. Meet. Rome, 1964), Pergamon Press, pp. 408-426.

Jagannath, D.R. and Bhatia, C.R. 1974. Effect of sodium fluoride on radiation sensitivity of barley seeds. Mutation Res. 22: 51-56.

Kamra, O.P., Mikaelsen, K., Brunner, H. and Rajaraman, R. 1975. Potentiation of radiosensitivity of barley seeds by sodium fluoride in relation to the repair process. Barley Genetics III, pp. 155-160.

Lundqvist, U. and Lundqvist, A. 1987. Barley mutants diversity and genetics. Barley Genetics V, pp.251257.

Nilan, R.A. 1981. Recent advances in barley mutagenesis. Barley Genetics IV, pp. 823-831.

Veleminsky, J. and Gichner, T. 1975. Recovery from mutagen-induced injury and DNA repair in barley. Barley Genetics III, pp. 146-154.

Table 1. Mutation frequency (MF) induced by gamma rays barley varieties, based on M2 seedlings.

_______________________________________________________________
Variety                   Dosage of gamma rays (Gy)
        _______________________________________________________
             100          200          300           400
        _______________________________________________________

        Seed-   MF    Seed-    MF   Seed-    MF    Seed-    MF
        lings  (%)    lings   (%)   lings   (%)    lings   (%)
_______________________________________________________________


DL 36   7,741  .607   6,424   .996  5,787  1.503   4,746  1.896
               (47)           (64)          (87)           (90)

Mex 22  7,634  .969   6,457  1.363  7,105  1.703   4,886  2.906
               (74)           (88)         (121)          (142)

BR 31   7,559  .437   7,695   .936  7,414  1.646   5,313  2.240
               (33)           (72)         (122)          (119)

P 167   8,313  .577   6,976  1.949  8,640  2.315   4,706  1.381
               (48)          (136)         (20O)           (65)

KN 27   7,612 1.235   6,226  3.341  6,165  4.428   4,621  4.285
               (94)          (208)         (273)          (198)
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Table 2. Mutant spectrum in different barley varieties induced by gamma rays (300 Gy)

_______________________________________________________________
Variety         Mutant types* and frequencies (%)        Total
______________________________________________________   mutant
                                                         seed-
         A    V     X     T    S     M   VA    AV    XA  lings
_______________________________________________________________

DL 36  18.4  34.5  27.6   8.0   -   5.7  3.5   2.3    -      87

Mex 22 52.1  16.5   8.3  11.6  1.6  3.3  2.5    -    4.1    121

BR 31  39.3  29.5  10.7   9.8   -   8.2   -    2.5    -     122

P 167  39.5  27.5  19.0   2.0   -   4.5   -     -    7.5    200

KN 27  24.1  32.6  24.9   3.3  1.5  5.9  1.1   5.1   1.5    273
_______________________________________________________________

Total
mutant 272   230    153  46    6    44   9     19    24     803 
seedlings
  %   33.9  28.6   19.1 5.7  0.7   5.5  1.1   2.4   3.0   100.0
_______________________________________________________________