In order to investigate the genic imbalance caused by addition of an extra chromosome to normal diploid and haploid complements, an experiment was carried out on the production of trisomic (2n+1) and disomic haploid (n+1) plants in Nicotiana sylvestris (n=x=12). F₁ plants between triploid and diploid were backcrossed with the diploid plants. By the examination of chromosome number, 61 trisomic plants were selected from the B1 progenies. These trisomic plants were grouped into 12. types by the leaf shape and flower morphology. The anther culture was perfrmed using the 12 types of trisomic plants. The frequencies of androgenetic plantlet production varied greatly among the types of trisomic plants. This result indicates that the variety of the extra chromosome in the trisomic plants effects the frequency of plantlet production. In this anther culture, disomic haploids were obtained from 7 types of trisomic plants. No disomic haploid was obtained in the other 5 trisomic types. Besides the production of euhaploids and disomic haploids, several kinds of polyploids and mixoploids. were also obtained. The frequencies of androgenetic plants derived from the pollen grains with 12 chromosomes were apparently higher than those of plants derived from the pollen grains with 13 chromosomes, except for 2 trisomic types, B220 and Q480, in which the frequencies of plants with and without the extra chromosomes were almost the same. These 2 trisomic types tended to produce at a high frequency the androgenetic plants with no extra chromosome in early stages of buds, and those with the extra chromosomes in late stages of buds. This was assumed to be due to unsynchronized development of pollen grains with and without the extra chromosome. Among the disomic haploids obtained, 5 types of plants developed flower organ. The flower of disomic haploid derived from B 220 trisomic plant was conspicuously small and malformed, while the corresponding trisomic plant produced normal and remarkably larger flowers than the normal diploid. The mechanism of reversed effects caused by the addition of the same extra chromosome on diploid and haploid level, however, was not clarified in this study.

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In the previous reports, it was shown that the superiority of pollen grains from F₁ plants in selective fertilization of maize existed. Clarification, however, was needed for possible linkage of any gametophyte factor(s) to the marker gene and for the factor responsible for maintaining the superiority of F₁'s pollen grains. At first, the present study dealt with conducting two kinds of back-crossing, all possible selfing of four F₁s, and all possible crossing among F₁s. The existence of gametophyte factor(s) relating to the marker gene could not be found out in back-crossing used F₁s as pollen parents. In selfing in part, crossing, and another type of back-crossing, however, aberrant segregation ratios of the marker gene were found out in particular pollination combinations. Secondly, pronounced superiority of F₁'s pollen grains was well confirmed in the mixed-pollination experiments (YAMADA 1982). It was, moreover, shown that the superiority of pollen grains from Fl plants in selective fertilization is due to the grains per se which are produced by the sporophyte of F₁ in heterozygosity.

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In practical hybrid maize breeding, it is necessary to select combinations with a high degree of specific combining ability as well as to improve general combining ability. It is well-known that more genetically distant combinations induce higher specific combining ability and result in more yielding hybrids. Although SUTO et al. (1956) classified the flint types present in Asia into five types, namely, North American, Caribbean, European, Aegean, and Persian, there have been no reports on the specific combining ability between the six types which are composed of the above five flint types in addition to a dent type, American dent. The purpose of this study was to investigate the relationship between the modes of varietal combinations and specific combining ability effects estimated from the analysis of a diallel set of eleven open-pollinated varieties belonging to the six types, and to identify a general trend of specific combining ability between the six types. The results obtained here were as follows: l) Combinations between different types, especially between flint and dent types, were superior to those within same types in specific combining ability effect and F₁ yield. 2) High specific combining ability was observed in crosses between Caribbean and American dent, and between Persian and other types except for European and Aegean. 3) Specific combining ability effects were closely related to genetic divergence estimated from the previous classification results, in which the values of specific combining ability effects increased with increasing genetic divergence.

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The acetylene-reducing activity (ARA) of Oryza species including two cultivated species (156 strains) and ten wild species (76 strains) was investigated. Generally, the cultivated rice, O. sativa showed higher ARA compared with the other Oryza species. The ARA of the Japanese cultivars was lower than that of the tropical ones. Significant positive correlations were found between ARA/plant and root weight/plant and between ARA/plant and ARA/g dry root, indicating that both the amount of root and the efficiency of root play a role for nitrogen fixing activity of rice plants.

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A theory of selection index using estimates and/or guessed values of genetic parameters was presented. A computer program with Monte Carlo simulation for the index selection was developed for half-sib structured data. It provides the distributions of heritability, genetic correlation, coefficients of the index, response to selection, correlations among the true breeding value of sire, and scores of optimum and actual indices. The program can be used to evaluate the effects of the number of sires and dams, and the use of estimates and/or guessed values of parameters on goodness of the index. The flow of, and outputs from, the program were described for potential users.

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This study was undertaken to test the allelism of the genes for wrinkled endosperm in rice and to identify the chromosome on which these genes are located. From the results obtained in the F₁ and F₂, it was concluded that the four genes controlling the wrinkled endosperm character are located at three different loci. The authors propose to designate these four genes as su, shr-1s shr-1a and shr-2, respectively. Segregation ratio in the F₂ of the cross between EM-5 (su) and trisomic D was fitted to that of a trisomic segregation. The gene shr-1 was found to be linked to the rolled leaf gene (rl-2) with the recombination value of 23.6%These results suggest that su and shr-1 are located on Chromosome 12 and 3, respectively.

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In order to elucidate cytogenetical relationships among three Capsicum species, C. chinense, C, frutescens and C.baccatum, intra- and inter-specific hybrids were examined cytologically. In intraspecific hybrids of C.baccatum and C, frutescens, chromosome pairing at MI of PMCS was regular with 12 bivalents, and their pollen stainability was high. For the interspecific hybrids between C. chinense and C.frutescens, meiotic chromosome pairing was also very regular with 12 bivalents. The average was 0.06 univalents and 11.97 bivalents (9.81 rings and 2.16 rods). Their pollen stainability was relatively high. Therefore, it was suggested that C.chinense and C.frutescens are not two distinct specles but a single species involving two different varieties as seen in C.baccatum. For the interspecific hybrids of C.baccatum × C.frutescens, few univalents were observed at MI, and the average meiotic chromosome pairing was 0.87 univalents, 10.22 bivalents, 0.31 trivalents, 0.34 quadrivalents and 0.06 hexavalents. Considering the present results and the geographical distribution of wild progenitors, it can be concluded that C.baccatum and C.chinese/C.frutescens complex were originally derived from a common ancestral species monophyletically, and that their geographical distribution occurred subsequently, resulting in reproductive isolation among them.

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In some instances, in the Japanese rice cultivars (O.sativa L.) shift in heading may occur with the change in seeding time. However it had been hitherto difflcult to determine whether variations in the temperature or day length could account for this phenomenon. In this paper, the author reports on the influence of ambient temperature and day length on the shift in heading. Six cultivars were seeded in four cropping seasons under a constant phtoperiod of 14.5 hours, which corresponds to the natural day length of August 1 at 36°North latitude in adding 30 minutes for the morning and evening twilight. The influence of ambient temperature was evaluated by the difference of growth duration at different seeding times under a constant photoperiod of 14.5 hours. The influence of natural day length was also evaluated by the difference of growth duration under natural day length and a constant photoperiod of 14.5 hours, for the same seeding time. As compared with standard cultivation in which seeding took place on May 26, the growth duration in the early season culture (seeding on April 16) became longer due to the cool temperature prevailing in May and June rather than to the increase in day length before August 1. On the other hand, the growth duration of three photosensitive cultivars in the late season culture (seeding on June 15) became shorter due to the effect of the decrease In day length after August 1 which was more significant than the effect of the warm temperature in July and August.

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Seeds from three cultivars of the tobacco species, Nicotiana tabacum L. and Nicotiana rustica L., respectively, were tested in order to evaluate the effect of the sowing density on the seed germination percentage. Sowing density was expressed by the number of seeds per circle of 8.03cm2 on a filter paper. Seed germination percentage of either of the cultivars of the two species was negatively correlated with the sowing density. When five hundred seeds were sown in the circle, the germination percentage decreased remarkably due to seed-to-seed interaction. After mixing an equal number of seeds, namely 250 seeds for each of the two species, seeds were sown at the density of 500 seeds/circle with nine combinations. N.rustica L. could be differentiated from N.tabacum L. by the size of the seeds and seedlings. Total number of germinated seeds was significantly increased by interspecific interaction in the three combinations. Seed size had no influence on the interspecific interaction.

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In a study on inter-monogenomic hybridization in genus Brassica, the cross compatibility between B.nigra and other two species of B.campestris and B.oleracea were investigated. Twenty five cross combinations examined in B.campestris×B.nigra showed their pollen germination indices to range from 1.9 to 3.5 with mean value of 2.7 suggesting relatively sufficient pollen tube growth for pre-zygotic phase of fertllization. Postzygotic barrier was not so serious that alive hybrid seeds were obtained in some cross combinations. In B.nigra×B.campestris, on the other hand, post-zygotic barrier was severe upon the development of hybrid embryos although the pollen behavior was normal. In -24 cross combinations in B.oleracea×B.nigra, pollen germination indices were observed to be from O.4 to 3.5 with mean value of 2.2. In spite of the insufficient pollen tube growth, comparatively large hybrid embryos were obtained in some cross comblnations. The reciprocal cross, B.nigra×B.oleraced, exhibited both pre- and post-zygotic phases to be relatively normal and hybrid seeds were obtained.

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The response of barley cultivars to excess soil molsture was studied in 1979-1981. Number of cultivars used was 103 in 1978/l979, 19 in 1979/l980 and 76 in 1980/1981 growing season, respectively. Cultivars were grown under excess soil moisture condition (irrigated condition) at the internode elongation stage. Excess soil moisture reduced culm length and all of the yield components investigated in comparison with nonirrigated condition. The reduction was especially evident in the number of ears and seed fertility. Degree of toleran.ce to excess soil moisture was estimated from the mean value of excess soil moisture plots/that of control plots×1OO for six characters. There were significant varietal differences in the response to excess soil moisture. The reduction of seed fertility was considered to be a reliable index for tolerance of barley cultivars, since it showed larger varietal difference than any other characters. Further, it may be useful for rough screening of tolerant genotypes from a number of cultivars or from bulk populations, because the evaluation of tolerance based on seed fertility does not always need control plots. In case of lesser effect of excess soil moisture, like in 1978/1979 growing season, highly tolerant cultivars tailed to be discriminated from medium ones.

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In order to clarify the mechanism of the sex differentiation of plants using the monoecious Begonia flower (B.semperflorens LINK et OTTO), the inflorescence, peduncle and comparative anatomy of the unisexual flower were investigated. The results obtainecl were as follows

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A method of making three step cultures for rapid regeneration of adventitious shoots from tobacco protoplasts was established through determining the culture conditions and controlling the growth of callus. By using this method, many adventitious shoots could be obtained from very small calli in only a month.

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