QTL mapping in diploid potato by using selfed progenies of the cross S. tuberosum × S. chacoense.

Usually, mapping studies in potato are performed with segregating populations from crosses between highly heterozygous diploid or tetraploid parents. These studies are hampered by a high level of genetic background noise due to the numerous segregating alleles, with a maximum of eight per locus. In the present study, we aimed to increase the mapping efficiency by using progenies from diploid inbred populations in which at most two alleles segregate. Selfed progenies were generated from a cross between S. tuberosum (D2; a highly heterozygous diploid) and S. chacoense (DS; a homozygous diploid clone) containing the self-incompatibility overcoming S locus inhibitor (Sli-gene). The Sli-gene enables self-pollination and the generation of selfed progenies. One F2 population was used to map several quality traits, such as tuber shape, flesh and skin color. Quantitative trait loci were identified for almost all traits under investigation. The identified loci partially coincided with known mapped loci and partially identified new loci. Nine F3 populations were used to validate the QTLs and monitor the overall increase in the homozygosity level.

The inheritance of chilling tolerance in tomato (Lycopersicon spp.).

During the past 25 years, chilling tolerance of the cultivated (chilling-sensitive) tomato Lycopersicon esculentum and its wild, chilling-tolerant relatives L. peruvianum and L. hirsutum (and, less intensively studied, L. chilense) has been the object of several investigations. The final aim of these studies can be seen in the increase in chilling tolerance of the cultivated genotypes. In this review, we will focus on low-temperature effects on photosynthesis and the inheritance of these traits to the offspring of various breeding attempts. While crossing L. peruvianum (male symbol) to L. esculentum (female symbol) so far has brought the most detailed insight with respect to physiological questions, for practical purposes, e.g., the readily cross ability, crossing programmes with L. hirsutum as pollen donor at present seem to be a promising way to achieve higher chilling-tolerant genotypes of the cultivated tomato. This perspective is due to the progress that has been made with respect to the genetic basis of chilling tolerance of Lycopersicon spp. over the past five years.

Parthenocarpic fruit development in tomato.

Parthenocarpic fruit development is a very attractive trait for growers and consumers. In tomato, three main sources of facultative parthenocarpy, pat, pat-2, pat-3/pat-4, are known to have potential applications in agriculture. The parthenocarpic fruit development in these lines is triggered by a deregulation of the hormonal balance in some specific tissues. Auxins and gibberellins are considered as the key elements in parthenocarpic fruit development of those lines. An increased level of these hormones in the ovary can substitute for pollination and trigger fruit development. This has opened up genetic engineering approaches for parthenocarpy that have given promising results, both in quality and quantity of seedless fruit production.

The integration of recombination and physical maps in a large-genome monocot using haploid genome analysis in a trihybrid allium population.

Integrated mapping in large-genome monocots has been carried out on a limited number of species. Furthermore, integrated maps are difficult to construct for these species due to, among other reasons, the specific plant populations needed. To fill these gaps, Alliums were chosen as target species and a new strategy for constructing suitable populations was developed. This strategy involves the use of trihybrid genotypes in which only one homeolog of a chromosome pair is recombinant due to interspecific recombination. We used genotypes from a trihybrid Allium cepa x (A. roylei x A. fistulosum) population. Recombinant chromosomes 5 and 8 from the interspecific parent were analyzed using genomic in situ hybridization visualization of recombination points and the physical positions of recombination were integrated into AFLP linkage maps of both chromosomes. The integrated maps showed that in Alliums recombination predominantly occurs in the proximal half of chromosome arms and that 57.9% of PstI/MseI markers are located in close proximity to the centromeric region, suggesting the presence of genes in this region. These findings are different from data obtained on cereals, where recombination rate and gene density tends to be higher in distal regions.

Biodiversity assessment based on cpDNA and crossability analysis in selected species of Allium subgenus Rhizirideum.

The chloroplast DNA diversity of 33 accessions belonging to 16 species of five sections in Allium subgenus Rhizirideum was studied by analysing the sequence of three fragments: the trnL-F intergenic spacer, the rps 16 intron and rbcL (rubisco large subunit). The three sections Cepa, Schoenoprasum and Rhizirideum, representing the majority of the included species, each possess a separate clade after phylogenetic analysis. Exceptions to this general rule are the placement of Allium pskemense (section Cepa) connected to Allium senescens (section Rhizirideum) and Alium roylei, taking an intermediate position between sections Cepa and Schoenoprasum. Both species were located in their own section after nuclear DNA analysis. A range of crossing experiments has been carried out. The different position of A. roylei when comparing cpDNA and nDNA diversity was not confirmed with the production of hybrid seeds after crossing A. roylei with species other than those of section Cepa. The different position of A. pskemense in the cpDNA and the nDNA tree can not be compared to its crossability, since only a few crossing experiments are reported for this species. The hypothesis that a shorter distance between two species in a cpDNA tree compared to their distance in a nDNA tree will indicate interfertility at a certain level, is neither confirmed nor rejected by the currently available results.

GATA- and GACA-repeats are not evenly distributed throughout the tomato genome.

This paper describes the distribution of highly polymorphic GATA- and GACA-containing DNA regions in tomato. To study the distribution of these polymorphic regions, a mapping experiment was done. The segregation of 32 GATA- and GACA-containing loci was analyzed in a F2 population from a cross between Lycopersicon esculentum and L. pennellii. From these loci, 28 could be mapped to 8 of the 12 tomato chromosomes. Both the GATA- and GACA-containing loci seem to cluster in the same chromosomal regions. To our knowledge, this is the first report on mapping of GATA- and GACA-containing loci in plants.