Frequency and types of mutations induced in bread wheat by some physical and chemical mutagens

B. P. PAL, S. M. SIKKA, M. S. SWAMINATHAN and A. T. NATARAJAN

Indian Agricultural Research Institute, New Delhi, India

Seeds of C-591, a cultivated bread wheat variety, were irradiated in 1956 with X-rays, fast neutrons and beta particles from radioactive phosphorus (P³²) and sulphur (S³⁵) with a view to compare the frequency and types of mutations observed in the M₂ progenies derived from the different treatments. Following the observation made in our Laboratory that vegetable oils such as those derived from groundnut (Arachis hypogaea) caster (Ricinus communis) and mustard (Brassica campestris var. toria and B. juncea) are capable of inducing chromosome breakage in species of Triticum (Swaminathan and Natarajan, Curr. Sci. 25: 382-84; 1956), dry seeds of C-591 were soaked in these oils for 24 hours and then sown in the field. The M₂ brogenies (the term M₂ is being used to designate second generation progenies of all treated material irrespective of the mutagen involved) from these treatments were also screened for mutations. The variety C-591 is highly stable and homogeneous and is characterised by a fully bearded earhead, white and pubescent glumes, amber coloured grains and medium maturity. No spontaneous mutation has been observed in the large control material of this variety grown each year. The frequency and types of mutations observed in the different M₂ progenies are given in the following tables (Tabs. 1 , 2).

From the data it is seen that (1) a high frequency of viable mutations is induced in bread wheat by radio-isotope and groundnut oil treatments; (2) 16,000 r of X-rays yields a higher percentage of mutations than either 11,000 or 22,000 r; (3) besides albina mutation which was found only in Fast Neutron treatment and a fine and thin straw mutation which was found only in X-ray treatment, the same types of mutations occur in all the treatments and (4) a large proportion of the viable mutations in all treatments consists of speltoids. An interesting feature of the material from radioisotope treatments was the occurrence of several chimeras and haploid plants (2n=21). A common chimeral change was the appearance of brown glume colour and long tipped condition in some tillers of a plant in which other tillers have the normal white glumes and fully bearded earheads.

The albina mutation found by us in fast neutron irradiated material is the first record of its type in an induced mutation experiment in bread wheat. Another mutation of genetic interest is a completely beardless type obtained in material treated with groundnut oil; associated with this change there was a heavy reduction in tillering. Crosses have been made between the control and several of the mutants and the material is also being studied cytologically. It is particularly interesting that while chemical mutagens like nitrogen mustard have not been useful for inducing viable mutations in bread wheat, agents like groundnut oil are very effective (cf. MacKey, J. Acta Agric. Scand. 4: 419-29, 1954). The restricted group of morphological mutations observed by us lends support to MacKey's (Hereditas 40: 65-180, 1954) conclusion that the "diploid sector" of the germ plasm of bread wheat is limited and that polyploidy while imposing a restriction on the morphological frame permits a more varied and subtle differentiation within this frame.

(Received May 20, 1958)