Rice breeders in Japan are increasingly attaching more importance to the so-called field resistance than to the true resistance in improving blast resistance of paddy rice. The former resistance is quantitative and controlled by several multiple genes or polygenes, while the latter is qualitative and affected by a single gene with major effect. Field resistance seems to be stable to changes in pathogenicity of blast fungus, but true resistance reacts specifically to different fungus strains. In the present study, two experiments were carried out to investigate the inheritance of field resistance to leaf blast in rice plants. The first experiment cosists of the analysis of genetic variations among progeny lines derived from tlvo different crosses which include Imochi 314 (a derivative line of an upland variety) and IR 279 (selected at IRRI) as donors of field resistance. The second experiment is an analysis of F₁ and F₂ diallel tables from a half diallel cross of seven cultivars or lines, i.e. Imochi 314, IR 279, an upland rice variety and four lowland cultivars differing in field resistance.

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The identification of genes fcr blast resistance was carried out in M.M. 10, 65A 15 Fuji 120, BR No. I and Tsuyuake. The results indicated that M.M. 10 and 65A-15 had the genes Pi-z and Pi-b, respectively. Fuji 120 had an allele on the locus Pi-k. The gene Pi-m which had been found in Minehikari and was linked with Pi-k was not separated from the gene Pi-k in hybrid progenies of BR No. I and Tsuyuake with Shin 2-type varieties. This indicates the possibility that Pi-m was also located on the locus Pi-k. Therefore Pi-m and Pi-k were named Pi-k^m as an allele. The reaction of Fuji 120, Tsuyuake. Kusabue, K2 and K3 to many isolates collected during the past four years were compared. The results showed that reactions of Fuji 120 were very similar to those of K3. Therefore, the gene in Fuji 120 was considered to be Pi-k^h which was found in K3. A cornparison among reactions of K3, Mutsunishiki. Chugoku 31 and Dawn to the seven fungus strains suggested that Mutsunishiki which originated from a sister line of Fuji 120 and whose resistance gene was derived from a Vietna-mese variety. ChugokLt 31 whose resistance gene was introduced from an Indian variety and Dawn, a U.S. variety, have Pi-k^h

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An amphidiploid cultivar of Camellia, 'Fragrant Plnk Imoroved syntheslzed by colchicine treatment from a di.ploid intersectional hybrid between a diploid clone of C.japoleica subsp. rustical (Honda) Kitamura and of C. Iu.tchuelesis T. Ito named 'Fragrant Pink' was studied to clarify genomic affilnity between species of Caleeellia. The majority of the pollen mother cells of 'Frag'rant Pink Improved' studied showed the predominant fcrmation of bivalents and high chiasma frequency except for a few univalents and multivalents at metaphase I in meiosis and rather high pollen viability with a mean of 77 percent. The diploid parental clones of the F₁ hybrid 'Fragrnta Pink' showed complete and normal 15 bivalent chromosomes at metaphase I in meiosis of pollen mother cells and high pollen viability, while 'Fragrant Pink' showed a single chromosome configulatlon of 15 bivalents and the chrasma frequency deviated only slightly from those of the parents, but very low pollen viability with a mean of four percent. Thus, each pair of partially homologous chromosomes from Calaeelliajaponica subsp. rusticana and that from C. Iutchuensis include different degree of homologous segrnents. Either cryptic structural differences or differences of the gene constitution without any chromosollrlal structural differences would be expected between the chro-mosomes of C.japoleica subsp. rusticana and of C. Iutchuensis. During the course of investigaton, two percent of the pollen mother cells of amph, idiploid 'Fragrant Pink Improved' showed complete and normal 15 bivalent chromosomes at metaphase I in meiosis. The presence of partial pollen sterility shown in the amphidiploid clone of 'Fragrant Pink Improved' might be due to both unstable meiotic chrornosome configurations at metaphase I and unusual nuclear divisions in meiosis in pollen mother cells, especially cytomixis.

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Effect of four types of media containing or not containing growth regulator on the chromosome numbers was studied by using haploid calluses induced by means of anther culture of Nicotialea tabacum (cv. Wisconsin 38). The occurrence of polyploid cells in the callus tissues was promoted by the media containing IAA alone or IAA and kinetin in combination. In addition, various kinds of aneuploid cells were observed, especially in the callus tissues cultured on the medium containing both IAA and kinetin. On the media containing' no growth regulator or kinetin alone, however, the haploidy of the callus tissues were m.aintained with the exception of a few aneuploid cells. Therefore, it was concluded that the chromosomal stability or instability in the callus tissues is greatly affected by the constituents of growth regulators in the medium. N.tabacule4. N.sylvestris and F₁ of their reciprocal crosses were compared with the attention on chromosomal stability of callus tissues. The callus tissues of N.tabacum showed a considerable stabilization of the original chromosome number, while a high frequency of the multiplicatian of chromosome numbers was fcund in the calluses of N.sylvestris. Furthermore, the calluses of N.tabacumXN.sylvestris showed considerable chromosomal stability, while a high frequency of chromosome multiplication was observed in the calluses of N.sylvestrisXN.tabacum. Therefore, it was suggested that the callus culture which is cytogenetically stable state depends upon the plant species and that the chromosomal stability or instability in the callus tissues may bp controlled by a factor or factors in the cytoplasm of the callus cells.

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Previously the authors (MURAKAMI et al. 1972) reported the predominance of pollen grains from F₁ plant in selective fertilization as compared wlth pollen grains from inbred lines. The selective fertilization of pollen graln.s from inbred lines and F₁s observed in that experiment was, however, tested by using one particular inbred line as a female parent to be pollinated and as a pollen source to be mixed with pollen grains from other lines. The present study was planned to confirm whether the predominance of pollen grains from F₁ plant in selective fertilization reported in th_e previous paper generally occurs in the pollination of all combinations of pollen and female parents including F₁. In thls experiment (Table 1), two sets of inbred lines and their F₁s were used as female parents, i.e. A34 (W₁)', CI 64 (W₂), and A34XCI 64 (WF₁) in Set I, and Koshu-564 (O₁)' Outomorokoshi-143 (0₂), and Koshu-564XOutomorokoshi-143 (O_F1) in Set II As regards endosperm character, the materials for female parents in Set I were white dent, and on the other hand those of in Set II were orange flint, respectively. Due to xenia, the kernels fertilized by pollen grains from the alternative endosperm characters in pollen-mixture always produced yellow kernel in the both sets. The pollination by pollenmixture consisting of equal volumes of pollen grains from an inbred line or F₁ plant of two different endosperm characters was performed (Table 2).

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Effects of seed storage and exposure of pre-soaked seeds to dry treasment (50°C) on chromosome aberrations were examined. Stored seeds of Allium fistulosum L. cv. Kujohosonegi and Ishikura-ippon-futonegi which was obtained from Mikado Seed Co., Ltd. were used in the present investigation. Chromosome aberrations at mitotic meta- and anaphase were examined in the primary root tips of germinated seeds. High frequency of spontaneous chromosome aberrations (mean 51%) was observed in the stored seeds, whose cytological characteristics were remarkable fragmentations of the chromosome-type. From this result, the most aberrations were thought to be induced before DNA synthesis stage. The present study showed a positive correlation between the frequency of spontaneous chromosome aberrations and the number of days to germination, and a negative correlation between the former and the length of the primary seedling root.

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A genetic variation was found in liver esterase isozyme of the Japanese quail. The six phenotypes such as AA, BB, CC, AB, AC and BC were observed. It was clarified that these phenotypes were under control of three co-dominant alleles, Es-2^A, Es-2^B and Es-2^c at the same locus located on the autosome. The gene frequency in Es-2 esterase isozyme of random-bred populations were estimated as very high for Es-2^B (0.77-0.88) Iow for Es-2^A (0.10-0.21) and the lowest for Es-2^c (0.01-0.02). Es-2 esterase isozyme showed organ specificity and was found only in liver. Es-2 esterase isozyme first appeared on the day of hatching but its activity was very weak. The activity was clearly observed in all individuals at about five days of age, thereafter the activity increased gradually with age. At 15 days of age, the activity was approximately the same as that of the matured quail at about 40 days of age. It was also revealed that the liver esterase is an aliesterase in characteristics.

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Five long-culm mutants (LM-1∼-5) induced from a rice cultivar Norin 8 by radia-tions and mutagenic chemicals, were genetically analyzed. The F₁ plants of LM-1x Norin 8 showed similar culm length to the original cultivar. The F₂ plants showed bimodal segregation for culm length and days to heading, respectively, and were grouped into two types in the combination of the above two characters. One type which was the majority corresponded with the Norin 8 type, short culm and early maturity, and the other type corresponded with the LM-1 type, Iong culm and late maturity. The segregation ratio of these two types showed a good fit to the 3 : 1 ratio. Hence, it was concluded that LM-1 was governed by a single recessive induced mutant gene. The F₁ plants of LM-3XNorin 8 had similar culm length to the mutant and their F₂ plants showed a bimodal segregation in the combination of culm length with panicle length; Iong culm and panicle type (LM-3 type) being the majority and Norin 8 type being the minority. It was concluded that LM-3 was governed by a single dominant induced mutant gene. The simultaneous changes in the above characters and probably in the other agronomic characters in these long-culm mutants were considered to be due to the pleiotropic effect of a single mutant gene or the simultaneously induced mutant genes at closely linked loci.

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The paper describes a method for analyzing the action and interaction of several major genes controlling a quantitative trait by means of diallel crosses, using a genetic model based on the factorial model in the design of experiments. A situation where lines having one of the major genes concerned and the line with no major genes are chosen as parents in diallel crosses was considered. The situation is specific, but seems to be one of the simplest and most realistic ones in major gene system. First, the utility of Hayman's diallel analysis based chiefly on (V_r, W_r) graph was investigated. It was found that (1) (W_r, V_r) is not constant and varies with dominance effect of individual major gene. Hence, test for epistasis from scatter of points (V_r, W_r) around the line of regression of W_r on V_r or from departure of the slope of regression from 1 becomes invalid. (2) Average degree of dominance estimated from the W. intersection of the regression line is subject to a marked over- or underestimation, depending on the average sign of dominance effect. (3) Position of the parental points on the regression line is influenced by the possible difference in dominance effect of major genes to a greater extent than in a polygenic case, although it still reflects the number of dominant genes the parent possesses. Thus, the (V_r, W_r) graph seems to give little information in the analysis of major gene effects.

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