The ability to initiate stem elongation at the early growth stages of a plant is the major survival mechanism of floating rice in the presence of flooding. We previously identified two quantitative trait loci (QTLs) for this “early elongation ability” on chromosomes 3 and 12 using a Patnai23 (a non-floating cultivar) × Goai (a floating cultivar) F₂ population. The objectives of the present study were: (1) to identify QTLs for early elongation ability in the cross Habiganj Aman VIII (a floating cultivar) × Patnai23, and (2) to confirm the results obtained in our previous diallel analysis indicating that Habiganj Aman VIII might harbour additional gene(s) for early elongation ability compared with Goai. The genotype of a total of 192 F₂ plants was investigated using 85 (9 RFLP and 76 SSR) markers and the plants were assessed for early elongation ability. We scaled early elongation ability based on the position of the lowermost internode that exhibited elongation (“lowest elongated internode”, LEI), since the LEI position parallels the time of the onset of stem elongation. As a result, a large QTL detected on chromosome 12 seemed to be common to the two crosses. A small QTL detected on chromosome 1 was unique to the Habiganj Aman VIII × Patnai23 cross, which was consistent with the results obtained in our previous diallel analysis. No QTLs were found on chromosome 3 in this cross. These results suggested that (1) the QTL on chromosome 12 might be the most important one for the expression of early elongation ability in terms of the to percentage of phenotypic variation and consistency in different backgrounds, and (2) diallel analysis might be an effective method for examining differences in genetic control among diverse parents.

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The genetic diversity and genetic relationships of three cultivated varieties (benitade, aotade and ayutade) and a wild race of water pepper, Persicaria hydropiper, were analyzed using RAPD markers. The proportion of polymorphic bands and Shannon’s index of phenotypic diversity within accession in five benitade and two aotade accessions were distinctly lower than those in six wild water pepper accessions, suggesting the presence of a decline in genetic diversity within accession in the cultivated varieties under cultivation. A neighbor-joining (NJ) tree for nine cultivated and 38 wild accessions indicated the incidence of the independent domestication of the three cultivated varieties, benitade, aotade and ayutade, from wild water pepper. The NJ tree of the individual plants for five benitade accessions revealed the presence of close relationships among the accessions, but also showed a slight divergence in the accessions from different locations.

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A spontaneous semi-sterile mutant, found from a japonica rice variety Nipponbare, shows pollen and spikelet semi-sterilities. On the basis of genetic analysis with reciprocal F₁ hybrids between the mutant line W207-2 and a wide-compatibility rice variety CPSLO17, the semi-sterility was found to be controlled by a recessive nuclear gene ss-1(t). A linkage map was constructed to determine the locus for the semi-sterility gene, using an F₂ population of W207-2/CPSLO17. Through linkage analysis it was found that the gene was located between SSR markers RM152 and RM6863 on chromosome 8, with map distances of 6.3 cM and 8.8 cM, respectively. The finding of the new sterility gene will be useful for handling semi-sterility mutants in seed production and for understanding the genetic mechanisms of spikelet fertility in rice.

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Wild soybean (Glycine soja) is a useful genetic resource for broadening the genetic background of cultivated soybean. We selected a wild type soybean line showing a unique character consisting of a green seed-coat color at Yeongchun in Korea 1996 and designated it as KLG10084. The objectives of the present study were as follows; (1) to evaluate the agronomic characters of KLG10084 by comparing them to those of other wild-type accessions and cultivars, and (2) to evaluate the possibility of improving the seed-coat color in an interspecific cross of G. max ×G. soja. The major agronomic traits of KLG10084 were investigated and a genetic relationship was analyzed by comparing it to wild soybean (G. soja) and soybean cultivars (G. max) using the RAPD technique. KLG10084 was similar to IT184256, one of the G. soja accessions tested, that was known as a wild soybean exhibiting typical wild-type characters in stem diameter, pod size at maturity, seed size, hard seed and viny growth habit. A cluster analysis using UPGMA suggested that KLG10084 belonged to the group of wild soybean. It strongly indicated that the KLG10084 line corresponded to an accession of G. soja showing a green seed-coat color, based on morphological and RAPD analysis. The populations were generated by crossing KLG10084 with two different G. max cultivars, ‘Sobaegnamulkong’ and ‘Eunhakong’, and backcrossing it to the G. max parent to obtain BC₀ to BC₃ populations. The seed-coat color was evaluated on the populations representing each generation. The percentage of acceptable seed-coat color was 74% in the BC₀F₂, 90% in the BC₁F₂ and 97% in the BC₂F₂ generations, and approximately 100% in the BC₃F₂ generation in the population of Eunhakong × KLG10084. These results indicated that a single backcross is required to recover a commercially desirable seed-coat color in a population derived from an interspecific cross of G. max × G. soja when KLG10084 is used as a G. soja parent. Therefore, KLG10084 was considered to be a valuable gene source in overcoming the seed-coat color in interspecific crosses and was particularly useful for shortening soybean breeding programs by reducing the number of backcrosses that are required.

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Transgenic Nitcotiana benthamiana expressing the sense NSs gene sequence from Tomato spotted wilt virus (TSWV) was further transformed with the sense or antisense NSs gene sequence. Three sense and 10 antisense lines with two transformations (hereafter referred to as “double-transformed lines”) that were expected to contain only the sense and both sense and antisense NSs gene sequences, respectively, were examined for homology-dependent virus resistance using the unrelated virus, Potato virus X containing the NSs gene sequence. As a result, it was shown that two antisense double-transformed lines contained plants that were symptom-free. Furthermore, both lines accumulated a small-interfering RNA. These results suggest that RNA silencing was operating in both lines. However, the lines exhibited little or no resistance to TSWV.

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The lateness gene ef2(t), formerly designated as lf-1, was induced by X-ray irradiation applied to a rice variety Taichung 65. The present study was performed to investigate the allelic relationship between ef2(t) and two earliness genes, Efx and Ef1, and the chromosomal location through trisomic analysis. Rice line T65-ef2(t) carrying gene ef2(t) was crossed with two tester lines, T65-ER-21 and T65-ER-1 harboring the earliness genes, Efx and Ef1, respectively and heading time in the F₂ plants was examined. F₂ plants of the cross T65-ef2(t)/T65-ER-21 showed a trimodal distribution: T65-ER-21 and T65 type, new type and T65-ef2(t) type. The F₂ segregation fitted to a 12: 3: 1 expected ratio. On the other hand, the F₂ plants of the cross T65-ef2(t)/T65-ER-1 exhibited a tetramodal distribution: T65-ER-1 type, T65 type, new type and T65-ef2(t) type, the segregation fitting to a 9: 3: 3: 1 expected ratio. These results suggested that ef2(t) was non-allelic to both Efx and Ef1. Trisomic analysis was performed using seven Triplo lines carrying extra chromosomes 2, 4, 5, 7, 9, 10 and 12, respectively. The trisomics were used as maternal parent for crossing with T65-ef2(t). Heading time in the F₂ plants obtained from self-pollination of F₁ plants (trisomics) was examined. F₂ population derived from a cross between T65-ef2(t) and Triplo 9 showed a typical trisomic segregation pattern, suggesting that ef2(t) was located on chromosome 9.

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A set of BC₁F₁, i.e., indica/japonica//japonica and indica/japonica//indica, were produced to specifically compare the effect of heterozygotes and homozygotes at each QTL locus in an indica-japonica hybrid in rice. Grain shape traits and seedling characteristics were measured, in BC₁F₁ and BC₁F₂, respectively. Five QTLs were detected for grain width on chromosome 1, 2, 5 and 7. Two QTLs were detected for the 1000-grain weight on chromosomes 4 and 5. Three QTLs were detected for the grain thickness on chromosomes 2 and 5. Four QTLs were detected for the seedling weight on chromosomes 5, 6 and 12, in addition to three QTLs for other seedling traits, length of first leaf, seedling height and chlorophyll content, on chromosomes 1, 3 and 6, respectively. In the comparison of marker genotypes of AA, Aa and aa, QTLs were detected either between AA and Aa or between Aa and aa, and there was no case in which Aa was superior to AA and aa. In both analyses, each positive effect was contributed from either one of the parents. So far as the present data concern, it was able to conclude that the high level of heterosis in the current indica-japonica hybrids was manifested by a cumulative partial dominant effect of the heterozygotes at many loci and not by overdominance. Then, the set of QTL data for positive effects are considered to be systematically utilized in breeding of parental lines by using molecular markers.

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We produced transgenic chrysanthemum (Dendranthema grandiflora) plants expressing double-stranded RNA-specific ribonuclease gene (pac1) derived from Schizosaccharomyces pombe using an Agrobacterium-mediated transformation method. Three transgenic lines stably expressing Pac1 protein were selected. After inoculation with chrysanthemum stunt viroid (CSVd), these lines showed a decreased frequency of infection, less accumulation of viroid, and attenuation of growth retardance compared with control plants. They also showed a significantly lower infection frequency against tomato spotted wilt virus (TSWV) than in control plants. Hybrid plants between one transgenic line and a wild chrysanthemum species, D. pacificum, were produced to test their susceptibility against TSWV infection. TSWV infected all the plants of the wild species resulting in a high mortality, whereas the hybrid plants expressing Pac1 protein showed either complete resistance or high susceptibility. These results suggest the presence of an endogenous tolerance gene against TSWV in the cultivar used for transformation. The virus infection was suppressed in transgenic plants, indicating that the commercial use of this transgene would limit the spread of viruses to wild populations of Dendranthema. This is the first study to demonstrate that a single tolerance gene in transgenic plants can attenuate both viroid and virus diseases.

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In plants, phenotypic variations have generally been found to be caused by genetic changes. However, it has recently been shown that phenotypic variations can also be potentially caused by epigenetic changes due to aberrant methylation states. To survey polymorphisms in methylation states in the genomic segments from nine strains of Oryza sativa and O. rufipogon, we employed the methylation-sensitive amplified polymorphism (MSAP) method based on AFLP analysis using isoschizomers differing in their methylation sensitivity, HpaII and MspI. In addition to MSAP analysis, we applied the MITE-transposon-display method to detect methylation-sensitive MITE-flanking polymorphisms (MSMPs) for surveying the methylation state of the genomes. The frequency of occurrence of the methylated fragments detected by these analyses varied depending on the three primers targeting two different MITE sequences for MSMP and EcoRI sites for MSAP. This suggests that MITEs are associated with the methylation state in their proximal regions. Comparison of the fragment patterns between any two of the nine strains revealed polymorphisms of the methylation state referred to as epigenetic markers (epi-markers). A phylogenetic tree based on epi-markers within non-polymorphic fragments was analogous to that based on genetic markers. On the other hand, the proportion of epi-markers in the total number of fragments was constant at 2–3% in all the combinations of two strains. Our results enabled us to predict that the epi-markers are potentially linked to phenotypic variations, and that this possibility is more likely to occur between closely related strains.

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To facilitate the genetic analysis of quantitative traits and the use of marker-assisted breeding in rice, we developed a novel mapping population consisting of 39 chromosome segment substitution lines (CSSLs). In each line, a different chromosomal segment of the indica cultivar ‘Kasalath’ was substituted in the genetic background of the japonica cultivar ‘Koshihikari’ (Japanese elite cultivar). The substituted chromosome segments in the 39 CSSLs covered most of the genome, except for small regions at the distal end of the short arm of chromosome 8 and at the distal end of the long arm of chromosome 12. To verify the potential advantages of quantitative trait locus (QTL) detection in these CSSLs, we used the CSSLs to locate QTLs for heading date under three different environmental conditions: a natural summer field in Tsukuba, Japan, long-day conditions (14.5-h light), and short-day conditions (10-h light). The results clearly demonstrated that the use of CSSLs enabled to identify a larger number of QTLs than did a BC₁F₃ population derived from the same cross combination. We examined several advantages of the use of CSSLs in terms of genetic analysis, molecular cloning of QTLs, and marker-assisted selection in rice breeding.

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Morphological changes in shoot apices of kenaf treated with benzyl adenine (BA) were compared with those of untreated control plants using light and scanning electron microscopy (SEM). Seven days after the start of BA treatment (day 7), meristematic regions appeared adjacent to the axillary buds, and on the abaxial surface of the primary leaf primordia. Some of these meristematic regions were later developed into shoots. Further, the cells in the primary shoot apical meristem were reprogrammed to induce several meristematic loci. At day 28 in culture, supernumerary vegetative shoot buds were observed in and near the axillary buds. In the control plants neither axillary nor adventitious buds developed. These results suggest that the treatment with BA reprogrammed the developmental fate of a large number of cells in the shoot apex of kenaf. Further, it reconfirmed the ability of BA to overcome the apical dominance of shoots.

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Duration from sowing to flowering is of critical importance for crop adaptation. Breeding for the optimal flowering time is one of the major factors, which confer maximal yields in a given environment. The timing of flowering is modulated primarily by responsiveness to photoperiod and temperature, and there are large differences in sensitivity among genotypes. In most spring wheat cultivars the duration of the vegetative period is strongly influenced by genes controlling photoperiod response. In this paper we report the photoperiod responses of a set of ‘Chinese Spring’ substitution and partial deletion lines of homoeologous group 2 chromosomes studied under natural short days. We confirmed the presence of dominant genes Ppd1 and Ppd2 on chromosomes 2D and 2B, respectively, and compared the effects of Ppd1 and Ppd2 for daylength response. The photoperiodic responses of partial chromosome deletion lines of ‘Chinese Spring’ allowed us to map Ppd2 physically between breakpoints 0.27 and 0.53 of the short arm of chromosome 2B. This result is consistent with the finding of a possible location of Ppd2 based on molecular marker studies. A dosage effect of the dominant gene Ppd2 was shown.

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