JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND 109 Maatalouslieleellinert Ai\akaurkirja Vol. 11.109-112, 1981 The response of the mutation frequency of barley in M 2 to the M, harvesting method E.l. KIVI Uankkjja Plant Breeding Institute, SF-04300 Hyrylä, Finland Abstract. This paper deals with the frequencies of albina and xantha seedlings in an M 2 generation of six- rowed Pokko barley treated with sodium azide, NaN ? . The dependency of these frequencies on the harvesting method of M, plants is considered. The results demonstrate that "one-grain-one-ear” harvesting in M, produced higher frequencies of both albinas and xanthas in M 2 compared with an M 2 originating from whole ear harvesting of M|. For albinas the difference is significant. In spite of the increased mutation rate, the laboriousness of the "one-grain-one-ear” harvesting method restricts its feasibility in practical mutation breeding. 1. Introduction The efficiency of a mutagen treatment can be measured in terms of the frequency of mutants in the generations subjected to selection. In addition to the quality and dosage of a mutagen, many other factors influence the mutation yield obtained. For instance, the mutation frequency is higher in the main ear of the barley plant treated at the seed stage than in the ears of the subsidiary tillers (GAUL 1961). Likewise, it has been surmised that the mutation frequency in the M 2 generation might be high in cases where the M 2 bulk originates from the maximal number of initial cells subjected to mutagen treatment. Such a situation could be attained, for instance, by taking only a single grain from each main ear of M, plants, which would ensure that every M 2 plant originates from a different initial cell. Idea outlined above was suggested to the author in 1977 by Dr. R.D. BROCK, then working at the Joint FAO/lAEA Division in Vienna. On the basis of this idea, a practical mutation breeding programme was initiated on a six-rowed spring barley. 2. Treatment and handling of the M, generation Using sodium azide, NaN 3 , as mutagen, a breeding programme was started in May 1978. The subject was a six-rowed barley line, Hja 70352, which was https://www.c-info.fi/en/info/?token=OOhlXGiPStOiycIm.V4ztlHDm5uypEcWScJotHg.dn1MN6IqeIn2tnq-DgxFTpBILXtGyZJqpITlT8shhWwXgRFBeebgwyf70cyqtTS7mM77Lhr8JOYnvngpkzSM3Ii9ECuTsv4TAVX3oQEO37s_Ciem1HdObkGQs0YIRMuuC-Mdg5xbgjEEfEtrRH4mDWa2DKTbNmc subsequently released under the name Hankkija’s Pokko (KIVI and REKUNEN 1980). Pokko barley carries large spikes. In the control material grown in 1979 in the same field with the M 2 bulk, the average number of grains per spike was 50.3. The chemical mutagen used, NaN 3 , has shown very high efficiency, producing a frequency of upto 7.7 % of morphological and physiological mutations in M 2 (KLEINHOFS et al. 1974). Its effectiveness can be increased by an B—l 6 h prewetting treatments. In particular, NaN 3 treatment increases the number of point mutations, though not that of chromosomal aberrations (NILAN et al. 1976). Following the method of NILAN and SANDER (1974), dry grains of Pokko barley were treated with phosphate buffered 0.3 M NaN 3 solution, pH 3. The lot comprised a 2 kg sample of screened barley, with 1000 gwt of 35 g and a germinability of 97 %. The treated seed was sown in a trial field with irrigation possibilities. An ordinary plot seeder and normal seeding rate were used. The M ( generation consisted of approximately 20.000 plants. The control material of similar extent was sown in the same field. M, plants were harvested by hand, taking the main ear of each plant. From each ear separately, one grain was taken at random. The harvesting of 20.000 plants in this way took 28 working days. 3. The M 2 generation In May 1979, an ordinary plot seeder was used to drill the M 2 in 8 m 2 plots. From both the control and the whole ear M, harvest samples were taken at random to compose two lots, each of equal weight to the ”one-ear-one-grain” M, lot. Thus, three lots of approximately the same size were grown in 1979 (Table I). The rest of the M, yield, corresponding to the total whole-ear lot, was sown in the same field. This excess totalled about 350.000 plants, and was subjected to single plant selection for practical breeding purposes. Table 1. The frequencies of albina and xantha seedlings in the M 2 bulks of treated Pokko barley originating from M,:s harvested in various ways. M, M 2 Harvesting No. of Albinas Xanthas method seedlings no. % no. % Whole ear (WE) 20500 82 040 22 Ojl One grain (OG) 20500 127 0.62 31 0,15 Control (CO) 19800 0