In this thesis molecular genetic studies on Brassica rapa are described based on a collection of 256 accessions and 6 segregating populations. In chapter 2 and 3 the genetic variation and population structure are characterized in a set of genotypes from different geographical origins representing the various cultivar types. The association of traits with AFLP markers is analyzed in chapter 3, and the development of various mapping populations, linkage map construction and QTL analysis of phytate and diverse morphological traits are described in chapter 4 and 5. Genetic diversity in the primary gene pool of B. rapa was assessed by AFLP fingerprinting (chapter 2). The relationship between accessions was revealed by the dendrogram, indicating that different cultivar groups are often region (East Asia vs. Europe ) specific, emerging independently in the different geographic regions. The UPGMA dendrogram (chapter 2) and population structure (chapter 3) showed that grouping based on markers coincided often with morphotypes (cultivar groups) within a geographic region. However this clustering was not supported by significant bootstrap values, suggesting that only a few genes are involved in causing the large differences in morphologies. A number of markers differed between subpopulations thereby providing an example of linkage disequilibrium ( LD) due to population structure. Diversity collections can be used to survey the allele frequencies and to explore associations with traits (chapter 3). The STRUCTURE program indicated an association between population structure and trait values even for traits such as phytate and phosphate levels. The population structure should therefore be considered in association mapping studies in B. rapa . Markers that show association after correction for substructure can reliably be interpreted as being linked. Using the Composite Interval association mapping procedure, 54 markers were found significantly associated with at least one of the 9 different traits that were analyzed, 16 of which had known map positions. The observation that some of the marker-trait associations were confirmed by QTL analysis indicated that association mapping allows the detection of linkage with moderately frequent alleles. A multiple population approach was applied in QTL analysis for phy tate and morphological traits, in which the populations were developed from wide crosses and alleles of multiple parental accessions can be evaluated, revealing a large number of genomic regions harboring allelic variation for traits of interest. For phytate and phosphate contents in seeds and leaves, and 20 morphological traits involved in flowering time, seed traits, plant height, leaf traits and turnip formation we identified a total of 54 QTL positions. Co-location of QTL for different traits was found in many cases, which might suggest pleiotropy or tight linkage. The analysis of co-location of QTL for phytate/phosphate and parental allelic effects suggested that these QTL control total phosphorus levels or are specific for the phytate pathway in B. rapa. Principal component analysis and co-localization of QTL for morphological traits indicated that some components of the genetic control of certain leaf and seed-related traits, flowering time and turnip formation might be based on the same genes, indicating a common genetic regulation of correlated traits underlying these QTL. The comparative analyses of QTL for certain traits, such as phytate and phosphate contents and flowering time, between the 6 populations and with Arabidopsis thaliana or other related Brassica species are discussed.
The Song Hong (Red River) Basin is a typical pull-apart basin in Southeast Asia, located in northern Vietnam, extending from onshore to the offshore Gulf of Tonkin. It was formed by the Red River Fault displacement and South China Sea opening, and can be divided into three main parts due to stratigraphic distribution: onshore, northern offshore area and southern offshore area. This basin is considered to have a high potential for hydrocarbons, but only some gas fields have been found to date. In this study, we reinterpreted two-dimensional seismic data from the north Song Hong Basin to build structural maps of the study area. Reconstruction of the tectonic evolution of some typical sections illustrates the structural configuration and especially development of the fault system in the area. The newest results of re-interpretation reveal many flower structures and evidence for the right lateral displacement on the Red River fault after 5.5 Ma, unreported in previous works. This can be used to explain the complex structure of Song Hong Basin and suggests the reason why exploration for hydrocarbon traps is very difficult.
As part of a strawberry (Fragaria sp.) genome mapping project, we studied the linkage relationship between runnering and phosphoglucoisomerase PGI-2 allozymes in diploid strawberry. The respective r and Pgi-2 loci were found linked with a recombination frequency of 18.1% ± 1.6%(a map distance of 18.9 ± 1.6 cM). This is the second reported linkage in strawberry. The linkage between runnering and phosphoglucoisomerase allozymes, if conserved at the octoploid level, might provide a means of marker-assisted selection for the nonrunnering and bushy branching growth habits in cultivated strawberry. Severe distortion of monogenic segregation ratios was observed for runnering and PGI- 2, and also for an unlinked locus for shikimate dehydrogenase allozymes. Alleles from the perpetual flowering (alpine F. vesca) parents were favored in this distortion. This phenomenon should be considered in future genetic studies using crosses between alpine and nonalpine strawberries. The strawberry (Fragaria sp.) is an excellent subject for genetic and evolutionary studies for many reasons. It is a popular fruit of significant economic importance. The genus has widespread dis- tribution and high genetic diversity in its natural habitats across Asia, Europe, and the Americas (Hancock and Luby, 1993; Luby et al., 1992). There are at least 20 different species and four ploidy levels (Staudt, 1962, 1989). It frequently and spontaneously hy- bridizes to produce natural hybrids, including interspecific hybrids across ploidy levels (Bringhurst, 1990). The hybrid forms are preserved by vegetative propagation. However, genetic research has been hampered by the genetic complexity stemming from polyploidy, particularly in octoploid cultivated strawberry (F. ×ananassa Duch., 2n = 8x = 56). Several authors (Arulsekar and Bringhurst, 1983; Brown and Wareing, 1965; Davis and Pollard, 1991; Williamson et al., 1995) point out that, since there is a similar spectrum of character variation (e.g., seasonal vs. perpetual flow- ering, runnering vs. nonrunnering) and intercrossability between polyploid and diploid species, the most common diploid species, F. vesca L. (2n = 2x = 14), can be used as a model system to study strawberry genes and their linkage relationships. Only a few morphological traits of Mendelian inheritance have been studied in strawberry (Galletta and Maas, 1990). Of these, two are perpetual flowering (overbearing) and nonrunnering hab- its associated with the so-called alpine varieties, a group of F. vesca of European origin. Brown and Wareing (1965) found that each of these two traits was controlled by a single recessive gene (s/s and r/r, respectively). Their results indicated no genetic linkage between flowering and runnering, although the wild type (seasonal flowering, runnering) ceased runner production when
Thornthwaite's classification method. The result indicated that the number of climatic types classified on the basis of thermal efficiency, humidity, and seasonal distribution of water surplus or deficiency amounted to 42 for the regions concerned, so that a delineation of climatic regions corresponding to each type was highly difficult. Only a small-scale map with many inclusions could be produced with respect to humidity climatic types, taking seasonal distribution of water surplus or deficiency somewhat into consideration. Besides the difficulty in mapping, problems inherent to the method were also discussed; use of a parameter, i. e., potential evapotranspiration, is the essential feature of Thornthwaite's method, but there is no guarantee for the validity of the parameter when calculated for the tropical climate, as Thornthwaite himself admitted. Recently we examined the applicability of a numerical taxonomic method to the climatic classification of ]apan,2) with an intention to establish climatic regions of the country as a basis of classification of alluvial soils. As noted in this study the numerical method gave readily mappable climatic regions with a fairly good internal coherence, while Thornthwaite's method adopted for the purpose of comparison presented the same difficulty as stated above. In the present paper applicability of the numerical taxonomic method to a classi fication of the climate of South and Southeast Asia is tested. Here our intention is again to set up climatic regions as a basis for considering classification of alluvial soils in the rice-growing South and Southeast Asia.