An intergeneric hybrid between Er. orientale and Ae. squarrosa was reported. The spike shape of the F1 was intermediate between the parents but the spikelets showed the characters of Eremopyrum. In the majority of cells no chromosome pairing was observed. Average chromosome pairing was 0.1II+20.8I. This shows that the genomes of Er. orientale are quite different from the D-genome of Ae. squarrosa.
The effects of nitrosoguanidine on Bacillus subtilis were studied. Lethal damage produced by nitrosoguanidine was repairable in the sense that the repair was inhibited by acriflavine. Mutation was induced more efficiently at the initial period of the treatment when the killing effect was not high. The repairable damage seems to have little connection to the potent mutagenic action of nitrosoguanidine. It was also found that less amount of DNA could be isolated from nitrosoguanidine-treated cells, and the genetic linkage was lowered in the DNA isolated from treated cells, as compared with DNA isolated from untreated cells. It was postulated from these results that nitrosoguanidine would produce some unknown damage on DNA or on some other cellular components which would then act to induce mutation at very high efficiency.
The length at maturity of various organs and other agronomic characters were measured in 33 mutant lines radiation-induced from a rice variety, Norin 8, which were selected for high fertility and yield. Principal components were extracted from the genetic correlations of organ length. The first component showed an “isometric” phase of variation (general size), in which various organs varied proportionally in length. The second vector showed a variation in the relative length of organs (“allometry”). In this phase of variation, the organs in a stem sequentially increased or decreased in relative length from the top to the base, bringing about the contrast between “upper- elongation” and “lower-elongation” types. In the same manner as in our previous work on F3 lines, the α (“panicle-number” vs. “panicle-length” type, the former having more but smaller panicles and leaves than the latter) and the β (“internode-length” vs. “internode-number” type, the former having fewer but longer internodes and more erect leaves than the latter) variations in plant type were obtained from the mutant lines, when the data for panicle number and mean internode length were adjusted by the score for general size. The α and β plant-type scores were correlated with the scores showing general size and differential relative size of organs, respectively. Possibly, variations in agronomic characters of cereal crops may be largely conditioned by such an isometric and an allometric factor, the former involving the size-number relationship of stems, and the latter representing sequential change in the relative length of organs in a stem.
Between-line variations in the final size, the time at which half of the final size was attained (t1/2), and the growth rate at t1/2, were studied for the panicle and first to fourth (from the top) internodes. Materials used were 23 mutant lines radiation-induced from a rice variety, Norin 8, which were selected for high fertility and yield. For each of the above three values, principal components were extracted from correlations between the five organs, and the “genetic vectors” showing genetic contributions of the components to the respective organs were computed. In the final size, as reported in our previous paper, two latent phases of genetic variation were distinguished, one showing the general size (isometry), and the other showing an allometric pattern that brought about the variation between “upper-elongation” and “lower-elongation” types. Variations in the growth rate of organs similarly comprised an isometric and an allometric phase. Lines with a generally high growth rate had a large general size at maturity. In the allometric phase, lines whose panicle and third internode elongated relatively slowly had a relatively high growth rate for the first and second internodes. Such lines tended to be the “upper-elongation” types at maturity. As the panicle and third internode elongate some days before the elongation of first and second internodes that results in heading, the allometric pattern of growth rate suggests that the lines vary in the rhythm of development. This was proved by an observation of the change of relative growth rate in the period from panicle elongation to heading. It was suggested that genes modify the rhythm of development and bring about the size variations observed at maturity.
1. Four kinds of quadruple monosomics and one kind of quintuple monosomics were produced by a systematic procedure in a variety Chinese Spring of common wheat, Triticum aestivum ssp. vulgare. 2. Quadruple monosomics (17II+4I) were selected in the progeny of the cross between triple monosomics (18II+3I) and a nullisomic, which lacks the fourth pair of chromosomes. The quadruple monosomics were pollinated with pollen grains of a nullisomic, which lacks the fifth pair of chromosomes, and in their F1's quintuple monosomics (16II+5I) were selected. 3. Quadruple monosomics were more or less smaller in size, and reduced in vigor with somewhat later maturity, but they were fertile in both sexes. Quintuple monosomics were still inferior to the quadruple monosomics in their various characters, though they retained reproductive ability. 4. Crosses between quadruple monosomics (_??_) and normal plants (_??_) were made to maintain the quadruple monosomic strains; F1's obtained had 38 to 42 chromosomes. The 38-chromosome plants appeared at a frequency of 21.2 per cent, and showed the 17II+4I chromosome configuration at meiotic metaphase I, which indicated that they were quadruple monosomics. 5. The present results indicated that the female gametes with the least chromosome number in expectation participate at a high frequency in fertilization in every kind of hypoaneuploids, so far produced in hexaploid wheat.