II. 48. Frequency of chlorophyll mutations in ontogenetically different tillers of barley (Hordeum vulgare).
J. Singh and R.M. Singh. Department of Genetics and Plant Breeding, Banaras Hindu University, Varanasi-221005, India.
The present study was undertaken to evaluate the mutagenic effect of gamma rays at different seed moisture levels in ontogenetically different tillers of barley based on the criteria of frequency of chlorophyll mutations in M2 generation. Seeds of barley variety 'Amber' (11.2 percent seed moisture) were adjusted to 7.5, 6.0, 5.5, 4.5, 3.5 and 3.0 percent seed moisture levels and irradiated with 15 kR dose of gamma rays. After treatment seeds were stored for 72 hrs to realize maximum storage effects. Seeds of all the treatments were sown in the field to raise M1 generation. Twenty plants from each treatment were selected randomly and the first five tillers of each plant were tagged in order of emergence. These five tillers of each plant were harvested separately at the time of maturity with remaining tillers of the same plant, to investigate the association between sequence of emergence of tillers and the chlorophyll mutation frequency in the progeny of these tillers in M2 generation. The perusal of data on frequency of chlorophyll mutations (Table 1) indicates that frequency of mutations was higher at low seed moistures and the majority of these originated from the progeny of first and second tillers and their frequency decreased in the progeny of third, fourth, fifth and bulk of remaining tillers in all the treatments. It is significant to note that the frequency of chlorophyll mutations at normal seed moisture (11.2 percent) in the progeny of fifth tiller was zero whereas at low seed moisture levels, it varied from O.O to 14.0. This observation suggests that at low seed moisture level the effect of radiation persists for longer duration as compared to normal seed moisture level. Our findings in barley support the findings of Gaul (1961) in barley and Osone (1963) in rice that frequency of mutations in M2 generation were less among the later formed tillers than among the older ones. These results can be easily explained that the main and primary tillers are derived from the shoot meristems which are relatively more highly developed than the meristems of the secondary tillers at the time of treatment. The observed differences in mutation frequencies of ontogenetically different tillers might be due to variation in the degree of differentiation of the various shoot meristems.
On the basis of the above findings, it would be desirable to increase the number of seeds for irradiation and restrict the selection of only the first and second tiller's spike from M1 plants. This will help in selecting a large number of M1 plants for raising M2 generation ultimately resulting in higher percentage of mutations.
References:
Gaul, H. 1961. Studies on diplontic selection after X-irradiation of barley seeds. Effects of Ionizing Radiation on Seeds, IAEA, Vienna, 117-138.
Osone, K. 1963. Studies on the development mechanism of mutated cells induced in irradiated rice seeds. Jap. J. Breeding, 13:1-12.
