B. P. Pal, M. S. SWAMINATHAN and A. T. NATARAJAN
Indian Agricultural Research Institute, New Delhi, India
Several rust-resistant varieties of bread wheat evolved at this Institute, like N.P. 797, 798, 799 and 809, do not possess awns. N.P. 809 has resistance to many strains of black, brown and yellow rusts and has been found to perform well in the entire north-western hilly tract of India. It is somewhat late under the growing conditions in the plains. In order to try to get some early flowering mutants in this variety, N.P. 809 plants grown in pots were treated with radioactive, phosphorus in 1955. The treatments were carried out when the plants had reached the flag leaf stage and the dosages used were 12.5, 25.0 and 50.0 microncuries of P32 (given in the form of H3PO4) per 8 1bs of soil. Seeds from the treated plants were collected and were sown in the field during October, 1956. When the plants commenced flowering in February, 1967, it was found that several of them had fully bearded ear heads. In such plants all the tillers had bearded ear heads. A few plants were half-bearded. The data are given below :-
The awned plants resembled the normal plants in all the other characters and also came to flower at the same time as the rest. Since normal N.P. 809 plants are slightly tipped, it is presumed that the dominant awn inhibitors B1 or B2 present in them have been deleted or altered in the fully-bearded mutants. Reciprocal crosses between the awned mutants and the normal plants have been made and the study of the progenies of these crosses will help to understand the nature of the genetic changes involved. Another point of interest is the lower frequency of awned mutation obtained in the 50microc treatment. This is probably due to more drastic cytological changes caused by the high dosage and the consequent abortion of many of the aberrant gametes. In the year of treatment, pollen sterility in the 50microc treated plants was on an average 54% and these plants also showed reduced seed setting in comparison with the plants treated with the lower doses.
From the practical point of view, the awned mutants are of great value since awned varieties are preferred by the Indian farmers on the belief that the presence of awns reduces or prevents damage to grains by birds. Hence, a breeding programme employing conventional methods is also in progress at this Institute to introduce the character of awning into the otherwise desirable varieties. Also, such mutations, especially those in which only the loci relating to awn development are affected, would help to evaluate critically the contribution of awns to yield in wheat.
(Received May 1, 1957)