ABSTRACT
The physical localization and organization of a Procumbentes-specific repetitive DNA sequence, PB6-4, on the chromosomes of Beta procumbens (2n = 18) were studied, using FISH (fluorescence in situ hybridization) to mitotic chromosomes and extended DNA fibres. The chromosomes of B. procumbens were studied in metaphase complements of the species itself, as well as in preparations of a series of eight different B. procumbens-derived monosomic additions to B. vulgaris (2n = 18). FISH to chromosome spreads of B. procumbens revealed that PB6-4 hybridizes to all chromosomes, predominantly in the pericentromeric regions, but with differences in size and brightness of the signals. Hybridization of PB6-4 to metaphase complements of B. vulgaris revealed no signals, indicating that cross-hybridization with the genome of this species was negligible. Consequently, hybridization of PB6-4 to metaphase complements of the monosomic additions yielded fluorescent signals on the alien chromosomes only. The previously observed differences in size and brightness of the fluorescent spots were confirmed using the single alien chromosomes. FISH of PB6-4 to extended DNA fibres of the monosomic additions indicated differences in the fluorescent track lengths between the alien chromosomes. Measurements of the fluorescent tracts allowed classification into discrete groups, varying from one to three groups per B. procumbens chromosome. The data revealed that the brightness or size of the signal at mitotic metaphase and the length of the fluorescent tracks on the DNA fibres were correlated.
Subject(s)
Chenopodiaceae/genetics , Chromosomes/ultrastructure , DNA/ultrastructure , Mitosis , In Situ Hybridization, Fluorescence , Nucleic Acid Hybridization , Physical Chromosome Mapping , Repetitive Sequences, Nucleic Acid , Species SpecificityABSTRACT
Rhizomania is a serious disease of sugar beet, caused by beet necrotic yellow vein virus (BNYVV). The disease can only be controlled by the use of resistant cultivars. The accession Holly contains a single dominant gene for resistance, called Rz. The identification of a locus for resistance that differs from Rz would provide possibilities to produce cultivars with multiple resistance to BNYVV. Inheritance of resistance to BNYVV was studied by screening progenies of crosses between resistant plants of the accessions Beta vulgaris subsp. maritima WB42 and B. vulgaris subsp. vulgaris Holly-1-4 or R104. Observed and expected segregation ratios were compared to elucidate whether the resistance genes in the three accessions are alleles or situated on different loci. STS markers, linked to the genes for resistance, were used to study the segregation in more detail. The results demonstrated that the genes for resistance to BNYVV inHolly-1-4 and WB42 are closely linked. The gene for resistance in R104 is at the same locus as in Holly-1-4, and also closely linked to the gene in WB42. As the Holly resistance gene has been named Rz, the name Rz2 is proposed to refer to the resistance gene in WB42. Consequently, the gene Rz should be referred to as Rz1.
ABSTRACT
Molecular markers linked to resistance genes are useful to facilitate the introgression of one or more of these genes in breeding materials. Following the approach of bulked segregant analysis, RAPD markers linked to resistance genes against beet necrotic yellow vein virus were identified in the four Beta accessions Holly-1-4, R104, R128 and WB42. Two primers were found which generate RAPD markers tightly linked to resistance in segregating families of Holly-1-4, R104 and R128, indicating that the resistance genes in these accessions might be situated at the same locus. Other, specific, primers were identified which generate RAPD markers linked to resistance in each of these accessions. Short-range maps were established around the resistance locus in these accessions. For WB42, RAPD markers were only identified at a relatively large distance from the resistance gene. Conversion of three RAPD primers of Holly-1-4, R104 and R128 into STS primers resulted in STS markers which can be readily used for marker-assisted selection in breeding programmes.
ABSTRACT
The distribution of two repetitive DNA probes Sat-121 and PB6-4, specific for the section Procumbentes of the genus Beta, was tested in 16 B. patellaris monosomic addition families using a dot-blot hybridization procedure. All monosomic additions were accurately distinguished from diploid sib plants with both DNA probes. The probe PB6-4, with the strongest signal after hybridization, was selected for rapid screening of an extensive number of putative monosomic additions in B. patellaris or B. procumbens addition families using a squash-blot hybridization procedure. The probe PB6-4 detected 118 monosomic additions in 640 plants (18.4%) in eight different B. procumbens addition families. The addition family with chromosome 4 of B. procumbens was semi-lethal and could not be tested. The distribution of PB6-4 in B. patellaris addition families was confirmed in 63 addition families using the squash-blot procedure. In 4580 plants of these addition families, 628 individual monosomic additions (13.7%) were found. The relationship of the morphological characteristics of monosomic addition plants to the results of the squash-blot hybridization (plants with signal) using probe PB6-4 is quite rigorous but not complete. The correlation between plants with a signal and chromosome number (2n=19) is complete. These results indicate that sequences present on PB6-4 are probably present on all chromosomes of B. patellaris and B. procumbens. The possibility of utilizing the sequence information of Sat-121 for a PCR-based assay to screen for putative monosomic addition plants was also investigated as an alternative to chromosome counting. The DNA-amplification profiles using the primers REP and REP.INV clearly distinguished monosomic addition plants from their diploid sibs.
ABSTRACT
A beet cyst nematode (BCN)-resistant telosomic addition of B. patellaris chromosome 1 in B. vulgaris was used to isolate 6 RAPD markers linked to the BCN resistance locus Hs1 (pat-1). Southern analysis showed that the analyzed RAPD products contain either low-, middle or high-repetitive DNA. The relative positions of the random amplified polymorphic DNA (RAPD) markers and of the restriction fragment length polymorphism (RFLP) loci corresponding to the low-repetitive RAPD products were determined by deletion mapping using a panel of seven nematode-resistant B. patellaris chromosome-1 fragment additions. One RAPD marker, OPB11800, was found to be present in two copies on the long arm telosome of B. patellaris chromosome 1. These copies are closely linked to the BCN resistance gene and flank the gene on both sides. On the basis of the nucleotide sequence of OPB11800, sequence-tagged site (STS) primers were developed that amplify specific fragments derived from the two OPB11800 loci. These STS markers can be used in the map-based cloning of the BCN gene, as they define start and finishing points of a chromosomal walk towards the Hs1 (pat-1) locus. Two copies of the middle-repetitive OPX21100 marker were mapped in the same interval of the deletion mapping panel as the resistance gene locus and thereby belong to the nearest markers as yet found for the BCN gene in B. patellaris.
ABSTRACT
New members of a satellite DNA family (Sat 121), specific for wild beets of the section Procumbentes of the genus Beta, were isolated. Sequence analysis showed that the members of Sat-121 fall into two distinct classes. The organization of Sat-121 in the vicinity of a beet cyst nematode (Heterodera schachtii Schm.) resistance locus (Hs1) in B. patellaris and B. procumbens was investigated by pulsed-field gel electrophoresis (PFGE) using DNA from a series of resistant monosomic fragment additions, each containing an extra chromosome fragment of B. patellaris chromosome-1 (pat-1) in B. vulgaris. In this way several clusters of Sat-121 flanking the Hs1 (pat-1) locus were identified. In nematode resistant diploid introgressions (2n=18), which contain small segments of B. procumbens chromosome-1 (pro-1) in B. vulgaris, only two major Sat-121 clusters were detected near the Hs1 (pro-1) locus.
ABSTRACT
Alien chromosome transmission through the female germ line as well as meiosis in pollen mother cells were studied in disomic and ditelosomic alien chromosome additions of beet. Beta vulgaris, carrying an extra pair of chromosomes or telosomes of B. procumbens or B. patellaris, respectively. The alien chromosomes carried genes for resistance to the beet cyst nematode, Heterodera schachtii, and screening for this resistance was used to select plants with or without the alien chromosomes. A great variation for alien chromosome transmission was recorded and plants carrying two extra alien chromosomes were recovered in the backcross progenies of the disomic or ditelosomic additions. However, in these progenies the average frequencies of plants without alien chromosomes (86%) did not clearly differ from that in similar progenies of the original monosomic or monotelosomic chromosome additions, indicating that doubling the number of the alien chromosome did not enlarge their transmission to the next generation. The alien chromosomes fully paired at pachytene and desynapsed again before diakinesis, indicating decreased chiasma formation. At second metaphase nearly 60% of the cells had one extra chromosome, and the remaining cells carried two or no extra chromosomes in about equal proportions. The tetrads looked fully normal. The expected relation between the average number of alien chromosomes in the germ cells and in the plants of the progenies did not show up, indicating a strong selection favouring the female gametes without alien chromosomes.
ABSTRACT
Segregating families of beet (Beta vulgaris) were used to verify the monofactorial inheritance of two enzyme-coding loci, leucine aminopeptidase (Lap1) and glutamate oxaloacetate transaminase (Got3). With a series of primary trisomies and using three methods to discriminate between the critical trisomic (the locus is situated on the triplicated chromosome) and the non-critical ones, it was possible to allocate the two loci to beet chromosomes I and II, respectively. For the locus Lap1 distorted segregation ratios were estimated, and the incorporation of three alleles into one plant was attempted. In the case of Got3 the measurement of the allele dosage effect after electrophoresis was chosen as the major strategy. The output of laser densitometric scans were subjected to the non-parametrical Wilcoxon-Mann-Whitney test.
ABSTRACT
In cultivated beet no useful level of resistance of the beet cyst nematode (BCN) Heterodera schachtii Schm. has been found, unlike the situation in wild species of the section Procumbentes. Stable introgression of resistance genes from the wild species into Beta vulgaris has not been achieved, but resistant monosomic additions (2n = 18 + 1), diploids of B. vulgaris with an extra alien chromosome carrying the resistance locus, have been obtained. Here we describe a new series of resistant monosomic fragment addition material of B. patellaris chromosome 1 (pat-1). We further describe the cloning of a single-copy DNA marker that specifically hybridizes with a monosomic addition fragment of approximately 8 Mb (AN5-90) carrying the BCN resistance locus. This marker and another fragment-specific, single-copy DNA marker probably flank the BCN locus on the addition fragment present in the AN5-203 material, which is approximately 19 Mb in size. Furthermore, several specific repetitive DNA markers have been isolated, one of which hybridizes to AN5-90 and also to DNA from a smaller DNA segment of Beta procumbens, present in line B883, carrying a BCN resistance locus introgressed into the B. vulgaris genome. This suggests that the specific repetitive marker is closely linked to the BCN locus.
Subject(s)
DNA/genetics , Nematoda/pathogenicity , Plants/genetics , Animals , Base Sequence , Blotting, Southern , Chromosomes , Cloning, Molecular , DNA/isolation & purification , DNA Probes , Gene Library , Genetic Linkage , Genetic Markers , Molecular Sequence Data , Plants/parasitology , Sequence Homology, Nucleic AcidABSTRACT
Eleven isozyme systems were used to identify the extra chromosomes, originating from Beta procumbens, in progenies of 33 monosomic additions in beet (B. vulgaris). Nine groups of monosomic additions could be distinguished, representing the nine different chromosome types of B. procumbens.
ABSTRACT
Alien monosomic additions in beet (Beta vulgaris), each carrying one of the nine chromosomes of B. procumbens, were grown in vivo and in vitro to study the effect of the alien chromosomes on plant development. All additional chromosomes caused a reduction of the growth rate in vivo, which, in one case was so strong that some of the plants died as seedlings. In general, the morphological plant characteristics were not very useful to distinguish the addition types; this could have been the results of the wide variation in the recipient parent. However, some developmental characteristics proved to be highly chromosome-specific; for plants in vivo this was annuality, in combination with early or late flowering. If grown in vitro, chromosome specificity was observed for growth type (rosette or elongated stem), occurrence and rate of vitrification, occurrence and morphology of wound callus, formation of additional meristems on the midribs of leaves, formation of roots and a specific reaction to benzylaminopurine (BAP) the medium. Two chromosome types of B. procumbens caused resistance to the beet cyst nematode.
ABSTRACT
A tetraploid (2n=36) interspecific hybrid was obtained involving three species belonging to three different sections of Beta. The hybrid was highly sterile and did not show apomixis. At meiosis, up to nine bivalents were observed, most probably resulting from autosyndesis of the chromosomes of Beta lomatogona. For nine isozyme systems, individual enzyme expression was investigated in the parental species and in the hybrids. No silencing of genes or genomes was observed. In the case of some polymeric enzymes interspecific heteropolymers could be detected.
