Variety HD 1982 which yielded the highest at 120 kg N/ha level exhibited nearly 7.5% decreased yield return at 160 kg N/ha level. Similarly the mutants HUW-Df8 and HUW- Df-Hp 3 exhibited nearly 3.5 and 6.4% decreased yield at this level as compared to 120 kg N/ha. Reduction was probablly due to deleterious effects of higher does of nitrogen leading to the lodging of crop. It is evident from the results that for the mutants HUW-Df8, HUW-SdfI and HUW-Df-Hp3 and the variety HD 1982, 120 kg N/ha seems to be the optimum economic fertilizer requirement. These findings are in agreement with those of SINGH et al. (1971) who have reported the optimum requirement for 'chotti lerma' as 120 kg N/ha.

Kalyan Sona yielded quite high at 160 kg N/ha level and exhibited nearly 9.4% increased yield as compared to 80 and 120 kg N/ha levels respectively. Similarly, variety K 852 exhibited 13.7% increased yield at 120 kg N/ha as compared to 80 kg N/ha and 16.7% at 160 kg N/ha as compared to 120 kg N/ha level. Yield behaviour of HD 2028 with increased level of nitrogen was also the same as that of K 852. Thus, the yield of Kalyan Sona, HD 2028 and K 852 might be increased by applying nitrogen levels upto 160 kg/ha and this level seems to be the optimum dose for these varieties. High tillering ability (though not presented here) of these varieties may be responsbile for this type of nitrogen response.

Study on polled data for all the mutants and varieties at different levels of nitrogen showed increased yield return with increasing nitrogen level. There was 11.4 and 4.7% increased yield return from 80 to 120 to 160 kgN/ha level respectively. Which indicated that 160 kg N/ha level gave the optimum but uneconomic yield return.

Statistical analysis (Table 2) of data indicates a significant effect of nitrogen on varieties and interaction between nitrogen levels and the varieties. Thus, it is concluded from the results (Table 2) that induced mutants, tested, were as good as the released varieties through conventional breeding procedures with regard to their yielding ability.

High yielding ability of the mutant(s) is attached to their improved plant type, i.e. short and stiff straw ; erect and synchronized growth habit and high fertility. Gamma-ray treatment has thus been quite effective in improving tall growing wheat var. K68 by induction of macromutants better in above yield components (for yield components of these mutants. KUMAR and SINGH 1974).

Literature Cited

BAKER, RI., V.M. BENDELOW and M.L. KAUFMAN 1968. Inheritance and inter-relationships among yield and several quality traits in common wheat. Crop Sci. 8: 725-728.

FUTSUHARA, Y., K. TORIYAMA and K. TSUNODA 1967. Breeding of a new rice variety 'Remei' by gamma-ray irradiation. Jap. J. Breed. 176-190.

KHAN, A.H. 1973. Improvement of quality and yield of wheat by mutation breeding. Wheat Inform. Serv. 36: 7-9.

KUMAR, D. and R.M. SINGH 1974. Role of low seed moisture in increasing the effectiveness of gamma-rays for plant type and grain quality mutations in wheat Triticum aestivum var. K 68. Proc. Symp. on "Use of Radiations and Radioisotopes in Studies of Plant Productivity". Pantnagar, April 12-14: 77-83.

MEHDI, V. 1970. Studies on the caryopsis of some of the recently evolved varieties of T aestivum with special reference to nutritional constituents. Ph. D. Thesis, Dept. of Botany. A.M.U., India.

SINGH, A., R.B.L. BHARDWAJ, R.G., GAUTAM and M. SINGH 1971. Optimum seed rate and nitrogen requirement of dwarf wheat varieties under different sowings. Ind. J. Agron. 16: 23-27.