Breeders seldom have enough time and labour to estimate the amount and nature of the genetic variation of segregating populations. Cross combinations therefore are assessed by the presence and absence of the promising phenotypes which appear to meet the breeding objective concerned. The application of this type of cross selection in F₂ is investigated to the conclusion that the breeding efficiency for a given breeding cost is increased by this selection ; F₂ populations should be entirely discarded if no promising" phenotype is found regarding qualitative characters and some continuous characters which are easily assessed and as heritable as regularly show significant correlations between F₂ plants and F₃ progenies. This holds even with a relatively small population size as 500-1, OOO and in the presence of a negative but not very close genetic association between these characters and the ones which also are concerned with the breeding objective but not assessed in F₂' With a large F₂ population, the selection among and within crosses is useful even when the characters are negatively and closely associated. The direct measurement of yield in F₂ as still proposed by some workers is not expected to be rewarding.

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The anthocyanin color of the apiculus, in the Japonica rice varieties, are caused by the existence of three genes, C (chromogen for anthocyanin), A (anthocyanin activator) and P (completely colored apiculus). In the Indica rice varieties, no definite information with respect to the applicability of this genic scheme has been existent. However, it is said that, as far as anthocyanin color of apiculus is concerned, the Indica and the Japonica rice varieties have at least the basic gene system in common.

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Thermo-sensitivity(X₁), photo-sensitivity(X₂) and basic vegetative growth(X₃) of 70 rice varieties in Japan were obtained by growing plants in growth cabinets under possible 4 combinations of different daylength and temperature : short(SD:10h) or long(LD:14h) daylength and low(LT:20'C) or high(HT:30'C) tempcrature. The X₁, X₂ and X₃ are expressed by n_SDLT-n_SDHT, n_LDLT-n_SDLT and n_SDHT, respectively, where n_SDLT Stands for the number of days from sowing to headlng under 10h and 20 C and so on. Duration (Y) from sowing to heading of the same varieties was examined in a paddy field with three different sowing dates. Multiple correlations between duration(Y) and a set of X₁, X₂ and X₃ of early, medium and late maturing varieties in all sowing dates were highly significant, showing thatvarietal differences in duration(Y) could be largely explained by the combination of the three factors.

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Anther ontogeny in an exotic cytoplasmic male-sterile (CMS) Iine 'Nadadores' and that in six indigenous CMS Iines obtained through crosses with the former have been compared. In the exotic CMS Iine, pollen abortion was associated with nondegenerating and persistant tapetum. Similar abnormalities were recorded in the indigenous CMS Iines also. Besides a few other tapetal abnormalities like degeneration of tapetum in premeiotic stages, tapetal hypertrophy in both pre and post-meiotic stages and pseudo-periplasmodium formation were also recorded. It is concluded on the basis of these observations that malfunctioning tapeta of various types are caused by inhibition of vascular tissue of the anther connective.

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n order to improve the efficiency of the asexual reproduction of pineapple plant (Ananas coleaosus MERR.), morphactins, known as plant regulator-like chemicals, were applied to the flower bud. Prior to the morphactin application, the apices of plant materials were pre-treated with ethrel to enforce the synchronous induction of compound flower buds. The flower buds thus induced were subsequently treated with various concentrations of morphactin solution, at different developmental stages, and different replications of treatment. Following the morphactin treatments, a number of foliar buds was developed from the fruitlets of a syncarp. This foliar bud development is not observed in natural pineapple plant and also had not been reported in the other plants treatecl with morphactin. These foliar buds were tentatively called "buds-from-fruit" in the present paper. When morphactin at concentrations of 80 and 100ppm was applied to the mater.ials in 6 to 12 days after ethrel pre-treatment, more than 80% of the plants produced "buds-from-fruit", and the average number of "buds-from-fruit" of single plant, i. e. single syncarp, obtained langed between 8.8 to 15.7 The maximum number of "buds from-fruit" obtained on a syncarp was 32. There was a certain stage in the development of the flower bud which was found to be critical as regards the effect of morphactin activity. This stage preceded the differentiation of the syncarp into flower primordium. In addition, morphactin treatrnent also gave rise to an increase in the number of natural foliar buds such as slips and suckers, a retardation in the emergence of the compound flower bud, and a tendency for the apical leaves of the treated plant to roll up which is a typical function of morphactin activity.

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30 cultivars of paddy were growh in a randomized block design with 4 replications. The rice plants were cut at 5cm above the ground at 4 different growth stages, i, e. 10, 20, 30 and 40 days after headingf. Ratoon weight, ratoon height and percentage of ratoon tillers to that of mother plant, were recorded 40 days after cutting. With respect to the 3 ratoon characteristics a significant decrease was observed to occur when the cutting time was delayed from 10 to 20 days after heading. The increase in the subsequent cutting was less marked. Analysis of variance suggests that ratoon weight, ratoon height and percentage of ratton tillers are heritable. In cuttings made 10 and 20 days after heading, there was a positive and highly significant phenotypic correlation between percentage of ripened grains of mother plant and these ratoon traits. Heritabilities in the broad sense for the ratoon traits became higher in the order, ratoon weight, ratoon height, percen-tage of ratoon tillers. Moreover, the heritability of percentage of ratoon tillers was nearly equal to that of culm length and panicle length. These facts show that ripening ability of rice plant may be tested by observing the ratoon, especially percentage of ratoon tillers.

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In order to determine whether it is possible to combine two or more resistance genes to the brown planthopper (BPH), allelic relationships among four resistance genes, Bph 1, bph2. Bph3 and bph4, were studied. Results indicate that bph 2, as well as Bph 1, segregates independently of both Bph 3 and bph 4, while Bph3 and bph4 as well as Bph 1 and bph2 were found to be closely linked. Therefore the combination of Bph I with Bph3, Bph I with bph4, bph 2 with Bph3 or bph 2 with bph4, respectively, in a cultivar could be achieved without any difflculty. Then, in order to search for new resistace genes, unclassified resistant cultivars were analyzed. The resistance of the cultivars, 'Andaragahawewa' and 'PTB 34' was found to be monogenically controlled by Bph I and bph2, respectively while the resistance in 'PTB 21' appeared to be controlled by the gene pair bph 2 and Bph3. Thirdly, according to the results of trisomic analysis, it was assumed that Bph3 and bph4 are located on chromosome 7.

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The present study was undertaken to investigate the changes in carbohydrate content in su1, bt1, su1bt1 and normal kernels during the grain filling period. The F₂ kernels of single-cross hybrids among near-isogenic lines with the identical genenetic background of the sweet corn inbreds, WI5125 and WI453, were harvested every three days from 16 days after pollination to maturity. These kernels were studied for the determination of fresh weight, dry weight and the amount of reducing sugars, sucrose, water soluble polysaccharides (WSP) and starch. The fresh weight of bt₁ and su₁bt₁ kernels sharply decreased at early stages of development, resulting in a collapsed endosperm appearance characteristic of bt₁ and su₁bt₁ kernels. The su₁ kernels showed a wrinkled endosperm appearance at maturity. In bt₁ and su₁bt₁ kernels the accumulation of dry matter did not increase from the early stages and levelled off soon. The amount of reducing sugars and sucrose of bt₁ and su1bt1 kernels was much higher than that of su₁ and nomal kernels at earlier stages. The sucrose content of bt₁ and su₁bt₁ kernels showed about a five-fold increase compared with that of su₁ kernels. The su₁bt₁ kernels contained about 16% of the WSP content in su₁ kernels during the eating period, about three weeks after pollination. The WSP content of su₁bt₁ ketnels was twice as high as that of bt₁ kernels. The starch accumulation in all the mutant kernels was less efficient than in the normal counterpart. One of the important problems in a sweet corn breeding program is to increase a substantial quantity of WSP associated with textural quality along with increasing the sweetness. The results suggest that the su₁bt₁ makes it possible to improve the eating quality of sweet corn.

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Twenty four Japanese varieties with known level of field resistance in Japan were tested with three Philippine fungus strains and two Japanese ones in a greenhouse experiThe three Philippine strains were chosen for their virulence to the tested ment. varieties out of 80 isolates. The three strains were confirmed to have differential virulence to some selected resistance types in the Philippines. Against two Japanese strains, the resistance manifested by four upland varieties was very high in accordance with previously reported data. Although the infection was too severe to differentiate clearly the level of field resistance among ordinary lowland varieties, several varieties including Yamabiko and Kogane Nishiki were less severely infected than Norin 29 and Koshihikari in accordance with a general tendency in Japan. Against the Philippine strains, the level of the infection was, as a whole, lower than those caused by Japanese ones. However, the highly susceptible reaction of Norin 6 and Aichi Asahi indicated that the infection was severe enough to differentiate the fleld resistance among the entry

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The present stucly was attempted to investigate how some dwarf genes act on cell division and cell elongation in internodes of rice plants. Materials used were five dwarf rice varieties differing one another in internode distribution patterns in culm, namely, M₃42, Tanginbozu, Sankei 10, Kotake-tamanishiki and Shoryu-shinriki, and four normal rice varieties having close genetic relations to each of the dwarf rice varieties mentioned above, namely, Norin 8, Ayanishiki, Tamanishiki and Shinriki 11. Two parenchyma cell files, file A, being in a row just inside the vascular bundle, and file B, the third cell file counted from the file A to the central lacuna of internode, were observed for measurement of cell numbers per file and cell length in each of upper five internodes.

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Various kinds of mutations for endosperm or embryo character were induced in rice by treatment with three kinds of chemical mutagens, ethyl methanesulfonate (EMS), ethylene imine (EI) and N-methyl-N-nitrosourea (MNU). MNU induced few mutations in the treatment of dry seeds, but considerably more through the treatment of fertilized egg cells. The frequency of endosperm mutations was lower than that of chlorophyll mutations. The white core mutation was induced most frequently among mutations for endosperm or embryo character. Each of the mutants, except for floury mutant CM 2055, was controlled by a single recessive gene. Dull mutants were intermediate between waxy and non-waxy rice in the degrees of translucence and of staining by I-KI solution. The degrees of them were different among lines, although they were almost the same within a line. The phenotypic manifestations of white core and floury mutants were caused by the loose packing of round compound starch granules in their endosperm cells. From the analogy of grain features of rice with maize, the glassy and the floury types of wrinkled mutation were named as 'sugary' and 'shrunken', respectively. In addition to various endosperm mutations, a mutation for embryo character, 'giant embryo', was induced.

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