The Indian rice variety HR-22 is highly resistant to most of the Japanese strains of the blast fungus. This high resistance was determined to be mainly controlled by the gene Pi-k^h allelic to the Pi-k.

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In rice, vegetative vigor as a varietal trait is characterized by rapid weight increase, big leaf area, and thin and long leaves at early stage of growth. There exists a negative association between varietal degree of vegetative vigor and the degree of yield response to nitrogen application. In the vast genetic diversity of tropical rice varieties, vegetative vigor and growth duration are two major genetic measures in ecological reactions. Varieties with high vegetative vigor and long growth duration have poorest nitrogen response in grain yield.

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Selections for cool tolerance were practised in F₃ under two different selection intensities, and their effects were evaluated in F₄ generation. It was found that through the selection for cool tolerance, the noticeable genetic shifts were produced not only for cool tolerance, but also for several characters such as culm length, ear length and number of ears to which selections were not applied. As for these characters, in general, there was observed close agreement between the expected and observed responses of the F₃ population to selection.

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Influences of low water content, post-irradiation storage, low temperature at germination, pre-irradiation heat-shock and nitrogen during irradiation on the varietal differences in radiosensitivity measured by reduction in root growth were studied. The effect of heat-shock was larger for more sensitive varieties. The change in the radiosensitivity by the other factors showed no correlation to the varietal radiosensitivity.

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Comparative studies were made on eight strains of Metctha aquatica L. collected from 6 districts among 5 different countries in Europe with regard to their morphological peculiarities, variation of fertility, number of chromosome, karyological characteristics and so on. The genome constitution was analysed in one strain which has 60 chrornosomes in the somatic cells.

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Several commercial varieties of Oxalis were used to exarnine the chromosome numbers and to clear up the heavy sterility. Oxalis bowieana, O. cernua var, flore-pleno, and O. variabilis were tetraploid (2n=28), and O. cernua was pentaploid (2n=35). Furthermore, O. versicolor was triploid (2n=27) and O. hirta was allohexaploid (2n=30). Each of these two species was composed with the different kind of genome from the former, respectively. Severe seed-sterility observed in all varieties was caused chiefly by the destructive gametogenesis due to polyploidy, in addition to the self-incompatibility connected with trimorphic stylism.

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Uunder the restriction of field size, the optimum replication was determined to maximize (1) genetic gain and (2) the lower α Percent point of genetic value at the point of truncation by phenotypic value, assurning that genotypic and environmental value of a given trait are random variates having normal density function independent of each other, and phenotypic value is given by the sum of these two variates.

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Minimum number of individuals required for combining ability tests in reccurent selection methods and the change rate of that number were estimated by numerical computations derived from theoretical formulae.

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