Microsatellite markers, also known as simple sequence repeat (SSR) markers have been useful for the detection of genetic diversity. Twenty-four rice cultivars carrying good quality traits were evaluated for genetic diversity using 164 SSR markers. A total of 890 alleles were detected by 151 polymorphic markers with an average of 5.89 per locus. Out of these markers, 89 generated a total of 147 rare alleles. Based on Shannon’s diversity index, an overall genetic diversity of 0.71 was revealed indicating a high level of genetic variation among these cultivars. Polymorphism information content (PIC) values of the markers ranged from 0.18 (RM420) to 0.91 (RM473B) with an average of 0.68 per marker. Cluster analysis of these cultivars enabled to identify 3 groups at 40% level of similarity with additional sub-clusters within each group. Group 1 corresponded to the 8 japonica subspecies, whereas Groups 2 and 3 comprised the indica. Cultivars under groups 1 and 2 are known for their aroma and good cooking and eating quality traits. Between the 2 rice subspecies, indica gave more alleles than japonica and likewise displayed a higher genetic diversity. Genetic diversity of indica was high on chromosome 11, while that for japonica was high on chromosome 2. The study revealed that SSR markers facilitated the classification of these cultivars according to their subspecies. The results also indicated that these quality rice cultivars exhibited a higher genetic diversity and therefore very useful for rice breeding programs, especially for genetic mapping studies and eventually for application of marker-assisted selection (MAS) in the programs.
For clarifying the phylogenetic diversity of fifteen species of the subgenus Ceratotropis, including seven wild and three cultivated Vigna species collected from Myanmar, sequence variations in three trnT-F non-coding regions of the chloroplast genome were analyzed. The Myanmar materials were clustered into two well differentiated groups, the azuki bean group and the mung bean group. Six Myanmar species were clustered into the azuki bean group, and four species into the mung bean group. The azuki bean group consisted of three subclades: angularis-nepalensis subclade, minima subclade and riukiuensis-nakashimae-umbellata-hirtella-exilis subclade. No clear lineage differentiation was found among the three races of V. angularis and V. nepalensis. An accession from Myanmar, which showed similar morphological features to those of wild azuki bean, shared a 51-bp deletion with V. angularis and V. nepalensis. Three V. minima accessions showed a distinct clade. V. riukiuensis showed a nested relationship with V. nakashimae sistered to V. hirtella, V. umbellata and V. exilis. The mung bean group consisted of five radiated subclades. In the mung bean group, V. trinervia from Myanmar was clustered with V. reflexo-pilosa, and wild mung bean accessions with their cultivated accessions. A high level of substitution, indel and microsatellite variations in the trnT-F sequences indicated that mung bean (V. radiata) and black gram (V. mungo) are phylogenetically well differentiated in the mung bean group. Myanmar is considered to be an area overlapping two major groups of the subgenus Ceratotropis.
The weak growth occurring in hybrids derived from crosses between two normal strains is referred to as hybrid weakness. F1 hybrid weakness (F1HW) in a cross between a Peruvian rice cultivar ‘Jamaica’ and Japanese rice cultivars has been reported and was considered to be controlled by a set of complementary genes, Hwc1 and Hwc2. We observed the development of F1 plants between Nipponbare and Jamaica (NJF1s). NJF1s were characterized by short roots, rolled leaves and a short stature. Although the NJF1 embryos were normal, the growth of the primary roots was arrested and in most cases, they could not emerge from seeds of the hybrids. Histological observation of the root apical meristem (RAM) at 10 days after sowing revealed that the zone of cell division in the NJF1 plants was lost, and that the cells were not short enough to explain the reduced root length of the NJF1 plants. Thus, it was suggested that the shorter roots the NJF1 plants might be due to reduced cell division. Although no distinct morphological abnormalities in the shoot apical meristem were observed, leaf primordium production was delayed in the NJF1 plants. Inhibition of root elongation in this type of hybrid weakness was alleviated under high temperature (34°C) conditions in diverse genetic backgrounds. The threshold temperature required for the recovery of root growth from hybrid weakness seemed to range from 29 to 30°C. Among 85 NJF1 plants that germinated and grew at 34°C for 10 days, and then outdoors, 18 plants eventually flowered. These plants were dwarf and their flowering time was delayed compared with that of their parents. In spite of their abnormal development, they were fertile. Thus, it is suggested that high temperature treatment was also effective to overcome hybrid weakness and to obtain next generation in this cross combination.
Sixty-two novel microsatellites with tri- or hexa nucleotide motifs were developed in peach from enriched genomic libraries. Among them, 49, 6 and 7 microsatellites consisted of repeat motifs of trinucleotides, hexanucleotides, and a complex of tri-/hexanucleotides, respectively. The degree of polymorphism of these microsatellites was lower than that of dinucleotide microsatellites. Chromosomal regions of the Prunus genome were identified for 15 microsatellites using a bin mapping strategy with a Prunus reference map. Two of them could be positioned into a new bin. Cross-species amplification was tested for trinucleotide (hexanucleotide) microsatellites within Prunus and more than 90% of them were applicable to the tested species. Amplification across genera was also tested for Malus, Pyrus, Fragaria and Rosa in the family Rosaceae. A total of 40 to 51% of the tested microsatellites were amplified in the other genera examined. Therefore, newly developed microsatellites could be utilized for synteny analysis and construction of genetic linkage maps in Prunus. Conditions for constructing genomic libraries enriched for trinucleotide motifs were also examined.
Soybean is rich in various functional components such as isoflavones, saponins, tocopherols and sterols that are beneficial to human health. However, the contents of some of these components such as α-tocopherol (α-Toc) and lutein are relatively low in the seeds. Therefore, genetic manipulation to enhance the α-Toc and lutein contents is an important breeding objective in soybean. Recently, we have successfully identified soybean varieties and wild strains with high α-Toc and lutein contents, respectively. In the present investigation, we made a cross between a soybean variety with a high α-Toc content thereafter referred to as a high α-Toc soybean variety, Keszthelyi A.S. (female parent), and a wild soybean strain with a high lutein content thereafter referred to as a high lutein wild soybean strain, B09092 (pollen parent). We analyzed the α-Toc and lutein contents of the F2 seed and F2-plant (F3 seeds) populations by a single-pass method for extraction and quantification, using high performance liquid chromatography (HPLC). The α-Toc content of the F2 seeds ranged from 1.0 to 6.0 mg/100 g meal, whereas that of the high α-Toc parent, var. Keszthelyi A.S. varied from 4.27 to 6.43 mg/100 g meal, and that of the wild soybean parent, B09092 ranged from 1.74 to 2.30 mg/100 g meal. The lutein content of the F2 seeds ranged from 0.1 to 4.0 mg/100 g meal, while that of the var. Keszthelyi A.S. from 0.19 to 0.42 mg/100 g meal, and that of the high lutein parent, B09092 from 2.48 to 3.50 mg/100 g meal. Broad-sense heritability for the α-Toc and lutein contents in the F2 seeds was estimated to be 0.598 and 0.656, respectively. In the F2-plants (F3 seeds), the broad-sense heritabilities were 0.693 for the α-Toc content and 0.824 for the lutein content, respectively. The heritabilities in a narrow sense for the α-Toc and lutein contents in the F2 seeds were 0.598 and 0.413, respectively. In the F2-plants (F3 seeds), the estimates were 0.693 and 0.718, respectively. The results suggested that both high α-Toc and lutein contents are highly heritable. A significant positive correlation was observed between the α-Toc and lutein contents both in the F2 seeds (r = 0.420, P < 0.01) and in the F2-plants (F3 seeds) (r = 0.228, P < 0.01). In addition, a significant positive genetic correlation was observed between the α-Toc and lutein traits in the F2-plants (F3 seeds) (rG = 0.311, P < 0.01). No correlation was observed between the 100-kernel weight and lutein content in the F2-plants (F3 seeds). Likewise no correlation was obtained between the 100-kernel weight and α-Toc content. These results indicate that it is possible to simultaneously select individuals among the progenies with high contents of lutein and α-Toc without decreasing the kernel weight of the seeds.
To avoid drowning under flooded conditions, deepwater rice responds to rising water level by rapid internode elongation. Quantitative trait locus (QTL) analysis, using a deepwater rice cultivar (Oryza sativa) and a wild rice species (O. rufipogon) with deepwater characteristics, revealed the presence of major QTLs (qTIL12, qNEI12 and qLEI12) in a common chromosomal region that regulates internode elongation. Genetic analysis revealed that a QTL inherited in a dominant manner, was located on the long arm of chromosome 12. A nearly isogenic line (NIL), produced by backcross introduction of a chromosome fragment carrying this major QTL into non-deepwater rice, exhibited a dramatic internode elongation in response to water rise. This indicates that the difference between deepwater rice and non-deepwater rice is associated with the presence of the QTL, and that this sequence is sufficient to confer deepwater characteristics. Although deepwater rice and non-deepwater rice share a common machinery for internode elongation; non-deepwater rice cannot activate the machinery in response to flooding, unlike deepwater rice which harbors this major QTL.
Winter oilseed rape (Brassica napus L.) is the most important oil crop in Europe. Due to a continually increasing demand for rapeseed oil for food and non-food uses, the production of hybrid cultivars with higher seed and oil yields has become increasingly important in recent years. However, the systematic use of heterosis for hybrid breeding in oilseed rape is limited by the relatively narrow genetic basis of adapted germplasm, which can impede the generation of distinct heterotic pools. In the present study experimental hybrids were developed from a population of 190 DH lines derived from a cross between an elite, double-low seed quality (zero erucic acid, low glucosinolate content) winter oilseed rape variety and a semi-synthetic line derived from a genetically diverse resynthesised rapeseed line with high erucic acid and glucosinolate contents. The DH lines were crossed with a male sterile tester and the resulting test hybrids were examined for yield performance at two locations in Hesse, Germany, that exhibit extreme differences in climatic conditions and soil characteristics. Mid-parent heterosis for seed yield was determined at both the agronomically optimal location Rauischholzhausen and the marginal site Niederhörlen. A value of up to 43% mid-parent heterosis for seed yield could be observed among selected test hybrids compared to that of their parental DH lines. The heterosis level for yield was particularly high at the nutrient-poor site, where the best test hybrids showed significantly higher yields than elite open-pollinating and hybrid varieties. This demonstrates the suitability and adaptability of highly heterotic rapeseed hybrids on marginal locations and suggests the existence of a strong heterotic effect on nutrient uptake efficiency.
Integrated genetic linkage maps of the European pear (Pyrus communis L.) cultivars ‘Bartlett’ and ‘La France’ were constructed based on SSR markers developed from pear and apple, AFLP and other markers. The map of ‘Bartlett’, which was constructed using an F1 population derived from a cross between ‘Bartlett’ and ‘Housui’, consisted of 447 loci, including 58 loci revealed by pear SSR markers (hereafter referred to as “pear SSR loci”), 60 by apple SSR markers (hereafter referred to as “apple SSR loci”) and 322 by AFLP markers (hereafter referred to as “AFLP loci”). This map covered 17 linkage groups over a total length of 1,000 cM with an average distance of 2.3 cM between markers. Another genetic linkage map of ‘La France’ was constructed using F1 individuals obtained from a cross between ‘Shinsei’ and ‘282-12’ (‘Housui’ × ‘La France’). The map of ‘La France’ contained 414 loci, including 66 pear SSR loci, 68 apple SSR loci and 279 AFLP loci on 17 linkage groups encompassing a genetic distance of 1,156 cM. Using 97 common SSR markers, these two maps were well aligned together for all the 17 linkage groups, which corresponded to the basic chromosome number (n = 17). The positions of 66 SSR markers originating from apple were successfully determined in pear maps and showed a co-linearity with the saturated reference map of apple. Since the high-density genetic linkage maps of pear constructed in the present study covered almost the entire genome, they should be considered as pear reference maps. These pear reference maps may enable to identify the location of genes of interest and QTLs (quantitative trait loci), and to analyze the syntenic genome structure with other Maloideae species.
To gain a comprehensive understanding of the genetic regulation of male gametogenesis, we screened and identified mutants for abnormal pollen development in rice (Oryza sativa L.). We gamma-irradiated spikelets of a japonica rice cultivar, Taichung 65, just before and after anthesis. Among 1,000 M2 lines, 24 lines were identified as mutants for pollen sterility. Progeny tests in M3 demonstrated that pollen sterility in 12 lines was controlled by single recessive genes, designated sps1–sps12 (sporophytic pollen sterility). In the remaining 12 lines, pollen semi-sterility was under the control of gametophytic genes, designated gps1–gps12 (gametophytic pollen sterility). Linkage analysis revealed that sps6, sps9, and sps12 were mapped on chromosomes 3, 9, and 7, respectively.