The Japanese Journal of Genetics

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Seeds of 18 strains of 12 different species of Avena were irradiated with gamma-rays to evaluate the relationship between radiosensitivity and ploidy level. Germination, seedling growth and root growth were used as indices of radiosensitivity. Chromosome aberrations at anaphase of the first root-tip mitosis were also analyzed. There were little or no differences in radiosensitivity between diploids and tetraploids, while hexaploids exhibited higher resistance particularly in terms of germination and seedling growth. Within each ploidy group, marked variations in sensitivity were revealed between strains. Interphase chromosome volume (ICV) covered a rather narrow range among the strains used, and could not account for the within-ploidy variations or the high resistance of hexaploids. Judging from chromosome sensitivity expressed by the frequency of fragments per cell per genome, it seems that the within-ploidy variations are due to genetic differences modifying radiosensitivity and that there are no prominent differences on average in genetically determined sensitivity between different ploidy level. The main part of the observed high resistance of hexaploids can be best explained by genetic redundancy rather than by ICV and genetic differences.

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Anthers of Triticum aestivum L, cv. Chinese Spring and of some Japanese and Chinese wheat cultivars were cultured on the N6 basal medium supplemented with inositol, glutamine, serine and 2, 4-D after the treatment with low temperature (5°C) for 7 days. Haploid calluses were obtained from the pollen of Chinese Spring, Orofen, Dansheng 15 and (Orofen×Hsiaoyen)F1, and were maintained by continuous subcultures, in which calluses were transferred once for every 30 to 40 days on the PM-64 basal medium supplemented with 2mg/l of 2, 4-D. Many regenerated plantlets were obtained on the RM-64 basal medium supplemented with 1mg/l of IAA and kinetin. The regenerated plants were mostly haploid and green. A few plants from Orofen and Dansheng 15 were diploid. The haploid calluses remained capability of differentiation to plantlets for about a year, and normal plants were restored from them. These haploid calluses from wheat pollen may be useful in mutant selection studies.

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