Lm which belongs to the linkage group I is one of the primary loci controlling heading time of cultivated rice and is also associated with photoperiod sensitivity. The effects of alleles of the Lm locus on two phases of the vegetative growth duration, the basic vegetative phase and the photoperiod-sensitive phase, were analysed by growing two isogenic lines with Lm^e and Lm^u allelles under natural and controlled daylengths. Heterozygotes (Lm^e/Lm^u) were maintained during 15 generations Lrom F₁ through BC₄F₁₁ in the cross between the Malaysian cultivar Morak Sepilai and the Japanese cultivar Fujisaka 5, which was used as the recurrent parent for the successive four backcrosses. Fujisaka 5 and Morak Sepilai transmitted the early-maturing allele Lm^e and the late-maturing allele Lm^u to their hybrid progenies, respectively.

View full abstract

Relations between fioral characters and the degree of cold tolerance were studied in segregating generations of the hybrid between the varieties, Kinmaze and Somewake. A cold sensitive variety Kinmaze has short anthers and short stigmas. On the contrary, an extremely cold tolerant Japanese local variety Somewake has long anthers and long stigmas. The following two methods were adopted in this experiment ; ( 1 ) Anther and stigma lengths of F₂ plants were measured at the heading time. To estimate the degree of cold tolerance, Iow temperature treatment (17°C day, 12°C night) was conducted on the suc-ceeding F₃ Iines for five days at the meiotic stage using phytotron. ( 2 ) Genetically identical varieties were obtained by dividing F₂ seedlings into three plants with a razor at the early tillering stage. As shown in Fig. 1, one of them was grown under natural conditions as a control, another one was placed under low temperature L0r five days at the meiotic stage and the third one was fixed in F.A.A. for measurement of fioral characters at the heading. Prior to analysis, seed sterility percentages (degree of cold tolerance) were transformed to angles as follows : sterility index=arcsiri√(percent of sterility), Characters recorded in each method were statistically analyzed. In method ( 1 ) anther length in F₂ negatively correlated with sterility index (Fig. 2). In method (2) both lengths of anther and stigma negatively correlated with sterility index (Fig.5 and Fig.6). Moreover there were significant correlations between the product of anther and stigma lengths and sterility index in both methods (Fig.4 and Fig.7). The multiple regression analysis based on I84 observations in F₂ yielded the following equation :y = 122. 944- 17. 462 x₁ -45. 877 x₂ where x₁ : anther length, x₂ : stigma length, y : steruty index. By uslng the above multiple regression equation, contribution was calculated (R2=0. 3449). It was sugested from these results that the plants with long anthers and/or long stigmas were cold tolerant and these floral characters could be useful as the selection criteria in the process of rice breeding aimed for cold tolerant varieties.

View full abstract

Five alkylating agents, ethylenimine (EI), ethyl methanesuifonate (EMS), N-nitroso-N -ethyl urea (NEUA), N-nitroso-N-methyl urea (NMUA) and N-nitroso-N-methyl urethane (NMUT), were compared on the mutagenic effectiveness and efficiency in a few agronomic characters of rice. The modes of dose-response of seedling height, survival rate of seedlings and seed fertility in M₁ generation were remarkably different with the different agents used : Methylating agents brought about more toxic effects on M₁ plants than ethylating agents. The data obtained in M₂ indicated that ethylating agents induced the mutations in chlorophyll, heading date and culm length more easily than methylating agents : In comparison of the highest frequency of chlorophyll mutants and variants in the two agronomic characters, NEUA ranked first, followed by EMS, EI, NMUA and NMUT in turn. The orders of the effectiveness and efficiency of mutagens were NEUA>NMUA >EI>NMUT>EMS and NEUA>EI>EMS>NMUA>NMUT, respectively. These results suggest that NEUA is one of the best mutagens in practical plant breeding. The frequency of variants in each of two agronomic characters was quite exactly proportional to that of chlorophyll mutations throughout all the agents applied.

View full abstract

Cytological study was conducted in the intraspecific and interspecific crosses of Tulipa gesnerlana and T. fosterlana. The fertilization occurred in 5 days after pollination, that is, 5 to 7 days after anthesis when the emblryo sacs were developed to the 8 nuclei. This slow fertilization may be associated with the slow maturation of the embryo sacs or the long styles which may cause the retardation of the pollen tubes to reach the micropyles. The study of the chromosome numbers of the developing embryos and endosperms revealed that in the emblryo sacs the 4 nuclei at the micropylar end were haploid, while the 4 nuclei at the chalazal end were diploid. Triple nuclear fusions of a male gamete and two polar nuclei did not occur to form the endosperm. The endosperms were formed mostly from the development of a single polar nucleus or the double nuclear fusions of a male gamete and a polar nucleus. The difficulty of the interspecific crosses was due to poor development of the endosperms and incompatibility between the embryos and endosperms. In the interspecific crosses between T.gesneriana Niphetos (2X) and T, fosteriana Red Emperor (2X), two seeds were triploid and another one was diploid. It was suggested that some of the interspecific crosses between T.gesneriana and T.fosteriana may often produce triploid seeds because, the triploid Darwin Hybrids had been produced from the same interspecific crosses besides the result of this observation.

View full abstract

The sizses of F₂ and F₃ populations are investigated based on the two criteria, i. e., the probability that promising genotypes are selected in the F₂ and F₃ Selection, and the economic advantage which is expected to be gained by obtaining the promising genotypes. In formulating these criteria, a selection system is assumed where within and among cross selection is made in F₂ regarding qualitative and some highly heritable continuous charaters, selection for these and other less heritable characters being operated in F₃. The optimurn. sizes of the populations are differently estimated according to the quantity of breeding cost and the number of cross combinations available for the breeding programme at issue, but it may be safely adopted as a standard in a routine selection work that several hundred and a few to several thousand plants are grown for the F₂ and. F₃ selection respectively. The genetic potentiality of individual crosses may not be fully tested in this scale of selection, but the economic advantage in the long run will be enlarged. Only one out of hundreds of crosses can lead to a new variety in highly improved crops such as rice and wheat. With such a poor identification of desirable crosses, spending a large cost for a limited number of crosses may cause a serious waste of breeding cost unless the crosses are pre-confirmed to be more promising than others.

View full abstract

Magnitude of heterosis and estimates of additive (a), mean dominance (b₁), additional dominance (b₂) and residual dominance (b₃) effects for four sucker-producing characteristics of tobacco were studied by using a diallel set of crosses excluding reciprocals among eight tobacco cultivars differing widely in sucker productivity. Tobacco plants were grown in randomized complete block field with two replications at the Utsunomiya Tobacco Experiment Station in 1980. Significant differences in sucker productivity were observed among eight cultivars and their 28 F₁ hybrids. The heterotic response of the hybrids was toward lower sucker productivity. Diallel analysis of variance of the F₁ hybrid generation and estimation of genetic parameters indicated that a large amount of variance was due to additive genetic effects and that small amount of variance was due to dominant genetic effects. These estimates suggest a predominance of additive genetic variance in the population for sucker productivity. Heritabilities of four characteristics, that is, the number and dry weight of ground suckers and the number and dry weight of upstalk suckers, were O.689, O.323, 0.414 and O.512, respectively, Correlations among four sucker-producing characteristics were significant.

View full abstract

On the culture media differing in the concentration of mineral microelements (B, Mn, Zn, I, Mo, Cu and Co), japoleica varieties except for Somewake and Daikoku 1 generally exhibited high abilities of callus formation. Indica and large grain varieties (assumed to be javanica type), japonica-indica hybrids, however, showed relatively poor and varying abilities of callus formation, especially on the mediurm with reduced mineral microelements. These results suggest that there may be different requirerments for the concentration of mineral microelements in callus formation among ecospecies and hybrids. From a comparison between Murasaki-Daikoku and Daikoku 1 having the same d-1 gene, it was presumed that the d-1 gene would not directly affect the callus formation, and some background genes, i. e. the suppressors may relate with the depresssion of callus formation. Likewise, it appears that semidwarf genes in Dee-geo-woo-gen and Taichung native 1 would not also suppress the calus formation. Slight depressions in many japonica-indica hybrids and IR-8, therefore, were attributed to some background genes, i. e. the sup-pressors of callus formation other than the semi-dwarf genes. Such suppressors appeared to occur most frequently in inedica and large grain varieties. Variations on morphological appearance of callus in japoleica, indica, their hybrids and large grain varieties were observed. The calluses of japonica and large grain varieties tended to be friable, those of japonica-iledica hybrids compact and those of indica intermediate. Diversities from the expected callus formation, i. e normal plant growth, white hairs, root cluster, white region and root-like structures were liable to occur most frequently in the hybrids. Necrosis and/or brownish color of calius tissues were likely to occur in the varieties which showed the reduced ability of callus formation.

View full abstract

This paper deals with agronomic tiraits, chromosomal behavior, loss of incompatibility of stylar variants and inheritance of heterostyly in the progenies of colchicine-induced autotetraploid. Because of a small amount of aneuploids and low frequency of multivalent formation in M₁, autotetraploids resulted neither terrible reduction of pollen fertility nor decline of seed set. Grain yield, therefore, increased rather than the original diploid strain and some native varieties. Two types of homostyled variants, namely one reduced style length in pin (PH) and the other increased style length in thrum (TH), were found in the progenies. Of these types, PH plants lost self-incompatibility and, therefore, set selfed seeds. Genetic analysis of heterostyly and incompatibility was attempted in connection with cytological evidences of autotetraploid.

View full abstract

If a set of traits which can be easily selected are represented by A genes, and another set of traits which are desired, but not easily selected are by B genes, a combination of an intensive selecton for A genes and a recurrent backcross of a donor of B genes may be of plant breeders' interest. To study the feasibility of such a breeding scheme, two genotypes of parents are herewith designated as AAbb and aaBB. To obtain the aimed type AABB a combinatin of backcross and selection can be practiced in such a way as to backcross aaBB to AAbb for introducing B genes, while restoring initial number of A genes through repeated selection. In the present simulation model, eight pairs of chromosomes are assumed, where A₁ and b₁ (i=1-8) are located in i-th pair of chromosomes in one of the parents, and a₁ and B₁ in the corresponding chromosomes of the other. Genetic value is assumed as 2 for AA and BB, 1 for Aa and Bb, and 0 for aa and bb. Three intensities of linkage in repulsion phase are assumed uniformly over the independent eigrht pairs of loci. To obtain AABB each of the backcross of aaBB to AAbb was followed by the selection for A under a heritability of O.8. One, two and three backcrosses were tested. Initial population size was set at 400 for each scheme which was repeated ten times. In each test the progress toward AABB was measured in terms of the genetic value defined above. From the results, it seemed possible to transfer nearly 90 percent of the aimed B genes by three backcrosses under the recombination values of 0.3 or O.5. In case of two backcrosses, about 70 percent of the desired B genes were introduced even under the recombination value of O.3 over eight pairs of loci. The progress was attained with simultaneous selection for A genes. And the number of A genes ranged from 61 to 70 percent and 55 to 63 percent, for two and three backcrosses, respectively. Despite the repeated selection for A genes, the progress for restoring all A genes seemed difficult after a single backcross. Particularly, an increase in the frequency of B genes and that of A seemed exclusive for each other, when the recombination value between A and b is O.1. A combination of repeated selection for visible traits (A genes) and recurrent backcrosses of a donor of traits desired, but not easily selected (B genes) seemed effective to obtain interim lines. In such lines, desired traits from both of the parents are partially combined depending on the intensity of the linkages between the two groups of genes. Initially aimed type AABB can be bred out through the secondary step of crossing the interim lines. Since they may have a high frequency of B genes, selection for A genes should be the main objective in the second step.

View full abstract

The members of the wabisuke group are usualiy placed in Camellia japonica but are distinct from most strains of C.japonica in several morphological characters. Then, they have been sometimes excluded taxonomically out of C.japonica. In the present study, isozyme variations in the wabisuke group were compared in detaii with those of the related species, C.japonica, C.reticulata, C, saluenensis and C. x williamsii, in order to clarify the origin and taxonomic position. In esterase, zymograrn types of the wabisuke group excepting Tarokaja were commonly detected in C.japonica cultivars but not in the C.reticulata, C.saluenelesis and C, x williamsii cultivars. Tarokaja showed a band which was rarely observed in C.japonica, but frequently observed in C.reticulata and C. saluenensis. In acid phosphatase, all of the six bands detected in the wabisuke group were also observed in C.japonica, and three of them were observed only in the wabisuke group and C.japonica. Two cultivars including Tarokaja of the wabisuke group showed zymogram types not detected in the other species. Among seven wabisuke cultivars, four cultivars showed zymogram types observed in C.japonica but not in the other species. These results indicate that the isozyme variation of the wabisuke group excepting Tarokaja is more similar to that of C.japonica than those of the other species. Therefore. it is considered that most wabisuke cultivars have originated and are placed in C.japonica. However, only Tarokaja may have been derived from an interspecific cross between C.japonica and other species.

View full abstract