Genetic effects of the male sterile Triticum timopheevi cytoplasm on common wheat cultivars were investigated using the cytoplasm substitution lines of 18 Japanese and 11 American cultivars. The following six characters were investigated; heading date, plant height, number of ears, ffag leaf length, and selfed and open-pollinated seed fertilities. Data of the first five characters were subjected to statistical analysis. All the characters analyzed were infiuenced by the timopheevi cytoplasm, to which the Japanese and American cultivars responded diffeirently. Correlation and covariance analyses revealed that interrelationships between the first four characters were more or less affected by the timopheevi cytoplasm; in four cases, positive correlation observed in the normal lines disappeared in the cytoplasm substitution lines, and in one case, , significant correlation not found in the normal lines appealed in the cytoplasm substitution lines. Furthermore, developmental stability, that was measured by interplant variation within the lines, was reduced by the timopheevi cytoplasm in two of the four characters investigated.

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The dry seeds of three rice varieties with different grain shape were treated with 0.3 and 0.50% of ethylene imine (EI). The relationships of EI sensitivity to the frequency of chlorophyll mutations at M₂ and the direction of quantitative mutations of grain size were examined. There were distinct differences of EI sensitivity among varieties in survival, seed fertility and the frequency of chlorophyll mutations in M₂. Century Patna with slim grain size was the most resistant, followed by Arborio with big grain size, and Amonoquilli with small grain size was the most sensitive. The distribution patterns of grain size observed in M₂ of the tested plots of three varieties were comparatively in accord with those of corresponding theoretical distributions which were computed by using the estimated means and variances of the non-treated plots, but a few individuals deviated from the theoretical distribution range in grain length. The increasing of the variance and the shifting of the mean value either {n grain length or grain breadth may indicate the induction of micromutations by EI treatment and the posibility of independent genetic control on grain length and breadth. There were clear differences in the size and direction of micromutation among the varieties.

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The wheat varietie, s: C273. MexiPak 65 and Chenab 70 and their mutant lines: 3, 17, 216, 244, 399 and 432 derived after a treatment with different doses of gamma radiation from C0⁶^0 source, were grown in a randomized complete block design at Nuclear Institute fcr Agriculture and Biology, Lyallpur. Correlations between various morphological characters and yield component were worked out. Pleduction in plant height from optimum level showed an adverse effect on one thousand grain weight and yield per plant except semi-dwarf mutant line 216. Plant height was negatively correlated with spike length and number of spikelets per spike. Spike length showed a positive correlation with number of spikelets per spike and yield per plant. Correlation between number of spikelets per spike and one thousand grain weight was negative.

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Degree of heterosis and relative value of GCA and SCA were discussed in the crosses between male sterile plants and normal plants and between normal plants and normal plants. One hundred and eight hybrids produced by crossing 17 cytoplasmic male sterile plants with 19 normal plants, 158 hybrids produced by crossing 15 normal plants with 18 normal plants and 13 S₁ progenies were evaluated with the spaced-planting condition (O.5mXO.25m) for plant height, yielding ability and fall vigor in 1974 and 1975. Forage yields of S₁ progenies were quite low and the ratios of mean yield of S₁ progeny to mean yield of crossed progenies of their parental plants were 80.4%, 74.6% and 76.2% in total yield in 1974, 1975 and total yield of two years, respectively. MSXNor progenies of which maternal parents were male sterile showed higher yield than NorxNor progenies of which maternal parents were normal. Twenty three hybrids outyielded the check variety, Dupuits by 20% or more and 9 hybrids outyielded DuPuits by 30% or more. GCA in fall vigor was particularly important and it was also important in plant height and yield. SCA was considerably important in plant height and yield and among them, it was relatively more important in first harvest in 1974 and 1975. In pooled population of MS×Nor and Nor×Nor, variance components due to female parents, σ²F greater than those due to male parents, σ²hi. Variance components due to male parents, σ²N for fall vigor, second harvest in 1974 and third harvest in 1975 were greater than those due to female parent, σ²F in MSxNor population. Relative importance of GCA due to male parents in MSXNor population was great in these characteristics. Ratios of genotypic variance to phenotypic variance in fall vigor and second harvest in 1974 were relatively high and those magnitudes ranged from 61.8% to 69.7% SCA variances in these characteristics were especially low.

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Seedlings of photo-insensitive varieties of soybean, as well as 3 photo-sensitive varieties, were grafted onto 36 to 41 day-old soybean plants and served as either donors or lreceptors of the floral stimulus. Thus, the productivity of, and the sensitivity of growing points to the floral stimulus were compared between the photo-insensitive and sensitive varieties and within the photo-insensitive varieties. When the photo-insensitive varieties were used as donors, flowering times of the receptor stocks did not significantly difEer with the donor varieties. On the other hand, flowering times of the receptor scions differed significantly with the scion varieties; photo-insen-sitive varieties flowered earlier as receptor scions than the ph.oto-sensitive varieties, and the earliness of the receptor scions was almost in the order of the inherent earliness of the scion varieties. The varietal differences in flowering time of the receptor scions became more conspicuous on the later stock varieties. It was suggested that the photo-insensitive early varieties had acquired the higher sensitivity to the floral stimulus in their growing points than the photo-sensitive varieties, and that the response of growing points to the floral stimulus at the early growth stages could be a causal factor for determining the inherent earliness of the photo-insensitive early varieties.

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The effect of natural selection and of competition were studied by the use of five artificial mixtures of rice varieties. Each mixture was made by mixing equal amount of seeds of two contrasting varieties, the Japanese lowland and the Japanese upland ones. These five mixtures were grown under three conditions, Iowland, upland ordinary and upland nursery, for one to three years (Table 1). The proportion of upland variety increased substantially after only one year of cultivation in all mixtures under the two upland conditions. These increases were slightly higher undr the upland nursery than the upland ordinary condition (Fig. 1). The sirnilar increase of upland variety also occurred to a lesser extent in the three out of the five mixtures. under the lowland condition. A comparison of the five mixtures confirmed that the survival of upland variety was infiuenced not only by the growing condition but also by the lowland variety combined. The mixtures planted under the lowland condition were grown repeatedly under the same condition for three years. The increasing trend of upland variety varied in each mixture the increase was moderate but clear in some mixtures while it was not clear in the others (Fig.2).

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Studies on development in vitro of excised ovaries in the sibmate of diploid Brassica campertris L. ssp. chinensis (L.) Makino cv. Seppaku-taina and in the sibmate of autotetraploid Brassica calprpestris L. ssp. pekileensis (Lour.) Olsson cv, Nozaki-hakusai were carried out. Development in vitro of ovaries excised at fcur days after pollination was studied in various culture media, temprature and light intensities. Results obtained were as follows. (1) Seed set in the capsules and percentage of germnated seeds in diploid Seppaku-taina were higher in each mineral of Nitsch, White and Heller than that of Murashige and Skoog. But the reverse was observed in autotetraploid Nozaki-hakusaki. (2) Seed set in the capsules was observed in all the culture media without vitarnins. (3) Seed set in the capsules and percentage of germinated seeds were good from 17°C to 27°C in diploid Seppaku-taina and were best at 17°C in autotetraploid Nozaki-hakusai. (4) Seed set in the capsules and percentage of germinated seeds were good in comparatively wide range light intensity in both diploid Seppaku-taina and autotetraploid Nozaki-hakusai. (5) Seed set in the capsules and percentage of germinated seeds in excised ovaries were different between the sibmate of diploid Seppaku-taina and autotetraloid Nozaki-hakusai.

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In a host-pathogen system which includes fcur genotypes for true resistance, AB, A+, +B and ++, in a host population, and four genotypes (races) for avirulence, ab, a+, +b and ++, in an airborne pathogen population, we established equations for following the race frequency changes on a given host population. Here, A and B are resistance genes, and a and b are avirulence genes which specifically correspond to the respective resistance genes. [numerical formula]where p^(t) is the frequency of each race after the i-th generation, r is the multiplication rate of each race, and Q is the product of the percent of growing area (q) of a variety with a genotype for resistance and its field susceptibility (s). Subscripts 1, 2, 3 and 4, correspond to genotypes (races) fcr avirulence, ab, a+, +b and ++, in the pathogen, and to genotypes for resistance, AB. A+, +B and ++, in the host, respectively. p₁+p₂+p₃+p₄=1 and Q₁+Q₂+Q₃+Q₄=1. An equilibrium of race frequency is achieved under the following condition: [numerical formula]

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Using equations developed in a previous paper, the race frequency change of a race with the genotype Av-a Av-k⁺ (Av=a the avlrulence allele and Av-k⁺= the virulence allele) from 0 to 0.8 was traced. Shift in the frequency of occurrence of genotypes Av-a⁺ Av-k and Av-a⁺ Av-k⁺ from O.5 to O.1 were also traced. These shifts occurred over a several year period in Kanagawa Prefecture, Japan. These results indicate that an average multiplication rate more than 1.32 by the avirulence gene compared to the virulence gene is necessary to explain the change in race frequency. Under the same conditions, races Av-aAv-k⁺ and Av-a⁺ Av-k⁺ reduce when a variety with the Pi-k resistance gene is eliminated. Through these simulations, we thought that races Av-aAv-k⁺ and Av-a⁺ Av-k origin ated from race Av-a Av-k which decreased with release of a variety with Pi-k according to the rule that avirulent races decrease under the existence of resistant plants in a large proportion.

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The inheritance modes of the cytoplasmic male sterility induced by gamma irradiation were studied in F₂ populations of the crossings between complete sterile plants in M₂ generation of five γ-lines and the plants of three tester strains with N cytoplasm. It may be said that at least two major genes well responsible for pollen restoration in each type of cytoplasmic male sterility. The mode of segregation in F₂ populations of the crosses involving fcur kinds of γ-1ines differed from the 9 : 6 : 1 ratio which is seen in the presence of cytoplasmic factor S. Namely, in the F₂ populations of crosses between γ-20 or γ-60 and H-2002, the recessive allele in one locus was epistatic to the, dominant allele in the other locus, while in the case of γ-130 or γ-165, the dominant allele in one locus was epistatic to the recessive allele in the other locus, showing 9 : :3 : 4 and 12 : 3 : 1 ratios, respectively. In addition, it was demonstrated from the results of test crossings with the type-0 plants (N rf₁rf₁, rf₂rf₂) that a different nuclear gene or genes other than Rf₁ and Rf₂ fcr S cytoplasm is required for the pollen restoration in the sterile cytoplasms of γ-1ines which were induced by the gnmma irradiation. An independent relation between the genes for pollen restoration and monogerm character in the induced male sterile cyto-plasrns suggested that the gene of Rf₁ locus is not responsible for the pollen restoration in these cytoplasrns. On the basis of the results mentioned above, the new genetic interrelation between nuclear genes and genetic factors of the sterile cytoplasms may be indicated diagram-matically in Fig. I as a probable consequnce of the cytoplasmic mutation induced by gamma irradiation.

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