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Genomic characterization of the germplasm in peppers (Capsicum - Solanaceae) by fluorescent in situ hybridization
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... Polyploid forms can also be induced as has been shown (Gyorffy 1939;Nishiyama 1939Nishiyama , 1940Pal and Ramanujam 1939;Pal et al. 1941;Aleksic 1960;Palfi et al. 1961;Ohta 1962c;Siskovic 1962;Raghuvanshi and Joshi 1964;Indira and Susan 1977;Panda et al. 1984;Rao 1987;Ishikawa et al. 1997;Ishikawa 2001;Kumar and Raja Rao 2003;Kumar et al. 2004;Takizawa et al. 2008;Kulkarni and Borse 2010). Pickersgill 1971 -24 10 m + 1 sm + 1 st 11 sm 1.80 (68.51) 3.41* Moscone et al. 1993, 1996aNMCA 10544, 10272 -24 10 m + 1 sm + 1 st 11 sm, 12 st 2.88 (70.40) 3.32* Moscone et al. 1993, 1996a et al. , 1996a , 1996a Moscone et al. 1993Moscone et al. , 1995Moscone et al. , 2003Moscone et al. *, 2007Scaldaferro et al. 2006Moscone 1990Moscone et al. 1993Moscone et al. , 1995Moscone et al. , 2003 Pickersgill 1977EAM 198, 202, 208, 256, 257 -24 11 m + 1 st 10 m, 12 st 18.95 (80.53) 4.47* Moscone et al. 1993, 1996a Cytogenetics provides a valuable and irreplaceable source of information for solving taxonomic, evolutionary and applied questions (Poggio 1996;Guerra 2012). To this end, a comprehensive cytogenetic characterisation has been carried out in a large number of species in the genus. ...
... To this end, a comprehensive cytogenetic characterisation has been carried out in a large number of species in the genus. Techniques have included classical staining to indicate chromosome number and karyotype formula, silver staining to expose chromosomes with active nucleolar organiser regions (NORs), fluorescent banding to show heterochromatin amount (Hc) and distribution, fluorescence in situ hybridisation (FISH) to denote number and distribution of rDNA sites and flow cytometry and Feulgen densitometry to estimate nuclear DNA content (Pickersgill 1971(Pickersgill , 1977(Pickersgill , 1991Moscone 1990Moscone , 1993Moscone , 1999Moscone et al. 1993Moscone et al. , 1995Moscone et al. , 1996aMoscone et al. , b, 1999Moscone et al. , 2003Moscone et al. , 2007Belletti et al. 1998;Park et al. 2000;Scaldaferro et al. 2006Scaldaferro et al. , 2013Scaldaferro et al. , 2016Barboza et al. 2011Barboza et al. , 2019Barboza et al. , 2020bJarret et al. 2019;Scaldaferro and Moscone 2019;Carrizo García et al. 2020). ...
... DNA content analysis and characterisation of the 5S and 18S-5.8S-26S (45S) rDNA by FISH has been completed for only a few species of Capsicum (Belletti et al. 1998;Park et al. 2000;Moscone et al. 2003;Scaldaferro et al. 2006Scaldaferro et al. , 2016Jarret et al. 2019;Scaldaferro and Moscone 2019). Although information is still lacking for many species/clades (e.g. the complete Atlantic Forest clade), genome sizes are highly variable between Capsicum species. ...
Capsicum L. (tribe Capsiceae, Solanaceae) is an American genus distributed ranging from the southern United States of America to central Argentina and Brazil. The genus includes chili peppers, bell peppers, ajíes, habaneros, jalapeños, ulupicas and pimientos, well known for their economic importance around the globe. Within the Solanaceae, the genus can be recognised by its shrubby habit, actinomorphic flowers, distinctive truncate calyx with or without appendages, anthers opening by longitudinal slits, nectaries at the base of the ovary and the variously coloured and usually pungent fruits. The highest diversity of this genus is located along the northern and central Andes. Although Capsicum has been extensively studied and great advances have been made in the understanding of its taxonomy and the relationships amongst species, there is no monographic treatment of the genus as a whole. Based on morphological and molecular evidence studied from field and herbarium specimens, we present here a comprehensive taxonomic treatment for the genus, including updated information about morphology, anatomy, karyology, phylogeny and distribution. We recognise 43 species and five varieties, including C. mirum Barboza, sp. nov. from São Paulo State, Brazil and a new combination C. muticum (Sendtn.) Barboza, comb. nov. ; five of these taxa are cultivated worldwide (C. annuum L. var. annuum, C. baccatum L. var. pendulum (Willd.) Eshbaugh, C. baccatum L. var. umbilicatum (Vell.) Hunz. & Barboza, C. chinense Jacq. and C. frutescens L.). Nomenclatural revision of the 265 names attributed to chili peppers resulted in 89 new lectotypifications and five new neotypifications. Identification keys and detailed descriptions, maps and illustrations for all taxa are provided.
... On the other hand, no variations in the 5S locus have been recorded throughout the genus so far (Park et al. 2000;Scaldaferro et al. 2006Scaldaferro et al. , 2016Kwon and Kim 2009;Romero-da Cruz et al. 2016). Previous cytogenetic studies showed the presence of the constitutive CMA + heterochromatic region coinciding with the location of the 5S locus (Moscone et al. 1996, 2007, Scaldaferro et al. 2013). ...
... Our results, together with general data from the genus Capsicum (Scaldaferro et al. 2006, Scaldaferro and Moscone 2019, demonstrate that at least the distribution of the 35S locus is variable among species, unlike the 5S locus, which is always constant in number, except for C. regale. To date, our findings in the genus partially agree with information from the Plant rDNA database, which indicates that about 51% of diploid karyotypes have a single 5S rDNA locus and circa 35% have a single 35S locus, the latter being more variable among plants (Garcia et al. 2017). ...
Fluorochrome chromosome banding and fluorescent in situ hybridization were used to cytogenetically characterize the striking tropical Andean clade species of Capsicum. An adapted dendrogram of the Capsicum phylogeny is presented, showing taxonomic relationships between karyotypes of the Andean clade species, C. baccatum var. pendulum, C. flexuosum, and the sister group Lycianthes. To date, the Andean clade includes nine species: C. dimorphum, C. geminifolium, C. hookerianum, C. lanceolatum, C. longifolium, C. lycianthoides, C. piuranum, C. regale and C. rhomboideum, all displaying 2n = 26. This group is characterized by conspicuous cytogenetic characters that are very useful in the identification of their species and allow them to be distinguished from the other group of species with x = 13 from the Atlantic forest, and definitely from the clades with x = 12. The species of the Andean clade possess relatively short genomes, with one NOR per haploid complement. The distribution of the heterochromatin is mainly subterminal. A single locus of the 35S and 5S rDNA was found per haploid complement. The discovery of three pairs of 5S rDNA sites in C. regale was surprising. The chromosomal features of these highland clade species could be considered adaptive characters to their geographical distribution.
... The observation of a single interstitial locus of 5S rDNA using a species specific probe is in agreement with previous findings in C. pubescens (Park et al. 1999;Scaldaferro et al. 2006) and other Capsicum taxa using genus specific (Aguilera et al. 2016) or heterologous probes . The difference in localization of the 5S locus -in this report at p3 instead of at pair 1 as was reported before (Park et al. 1999) -arose in the fact that the latter author used the tomato karyotype as a reference to order the chromosomes bearing rDNA loci in Capsicum, while here the order was established following exclusively the cytological parameters of C. pubescens. ...
... Thus, the mapping of probes comprising different 18S-25S rDNA structural portions in this work and Grabiele et al. (2018) significantly increased the power of discrimination of chromosomes in C. pubescens when compared with previous reports using the wheat pTa71 probe (Park et al. 1999) or the Arabidopsis R2 probe (Scaldaferro et al. 2006). ...
Capsicum pubescens is a cultivated hot chili pepper, consumed in Latin American cuisine as a distinctive ingredient, and popularly known as "locoto" or "rocoto". This taxon is also an outstanding source of resistance to biotic and abiotic stresses as well as other valuable fruit traits for breeding of the worldwidely cultivated C. annuum and related species. In this study, the chromosome complement of C. pubescens cv. "locoto" (2n = 24) was deeply characterized through a sequential combination of conventional and molecular cytogenetics approaches comprising: Ag-NOR staining, heterochromatic fluorescent C-DAPI, DAPI/AMD-CMA/DA bandings, fluorescence in situ hybridization (FISH) of Capsicum-derived probes of the 5S and 18S-25S rRNA genes and different regions of spacers of the ribosomal unit, as well as telomeric probe. The markers identified were systematically combined with morphological karyotype parameters-number, size, centromeres, satellites-to produce a physical map which allowed the identification of several landmarks in each individual chromosome. The reference chromosomal map of C. pubescens here presented is the most comprehensively developed in Capsicum so far. It is envisioned that this chromosomal map will serve as a reference framework for the upcoming sequencing projects and as starting point to assist future genetic mapping of important agronomic traits.
... The physical distribution of such families, and copy number may help in differentiation of various linkage groups of the chromosomes complement (Abbasi et al. 2010). In the genus Capsicum, FISH revealed the presence of one 5S intercalary locus per haploid genome in all cases (Park et al. 1999(Park et al. , 2000Scaldaferro et al. 2006;Kwon and Kim 2009;Scaldaferro et al. 2016), and one to several 45S loci (Scaldaferro et al. 2016). The latter loci mostly coincide with GC-rich heterochromatic regions and likely have given rise to satellite DNAs in some species (C. ...
... The latter loci mostly coincide with GC-rich heterochromatic regions and likely have given rise to satellite DNAs in some species (C. pubescens; Scaldaferro et al. 2006), affecting total genome size (Moscone et al. 2007;Scaldaferro et al. 2013). In this sense the length of the haploid karyotype increased with increasing Hc, probably reflecting the tandem repeated sequences constitution of the constitutive heterochromatin (Scaldaferro et al. 2013). ...
A hybrid individual between two taxa from "the Purple Corolla clade of the genus Capsicum", C. exi-mium  C. cardenasii (2n ¼ 24) was found during a cytogenetic study of a population belonging to C. cardenasii cytotype 1, from Bolivia. 5S and 45S rDNA probes were located on mitotic chromosomes by fluorescent in situ hybridization. The hybrid haploid karyotype length was an average value of the two taxa; the hybrid presented 24 45S loci in the diploid complement, 18 45S sites belonged to C. car-denasii cytotype 2, and six came from C. eximium cytotype 2, although this cytotype of C. eximium has been mentioned only for Argentina. Whereas hybrids were previously reported in the purple flower group, their existence has not been cytologically corroborated. This finding constitutes the first molecular cytogenetic evidence of hybridization between two taxa from this group. ARTICLE HISTORY
... The physical distribution of such families, and copy number may help in differentiation of various linkage groups of the chromosomes complement (Abbasi et al. 2010). In the genus Capsicum, FISH revealed the presence of one 5S intercalary locus per haploid genome in all cases (Park et al. 1999(Park et al. , 2000Scaldaferro et al. 2006;Kwon and Kim 2009;Scaldaferro et al. 2016), and one to several 45S loci (Scaldaferro et al. 2016). The latter loci mostly coincide with GC-rich heterochromatic regions and likely have given rise to satellite DNAs in some species (C. ...
... The latter loci mostly coincide with GC-rich heterochromatic regions and likely have given rise to satellite DNAs in some species (C. pubescens; Scaldaferro et al. 2006), affecting total genome size (Moscone et al. 2007;Scaldaferro et al. 2013). In this sense the length of the haploid karyotype increased with increasing Hc, probably reflecting the tandem repeated sequences constitution of the constitutive heterochromatin (Scaldaferro et al. 2013). ...
A hybrid individual between two taxa from ‘the Purple Corolla clade of the genus Capsicum’, C. eximium × C. cardenasii (2n = 24) was found during a cytogenetic study of a population belonging to C. cardenasii cytotype 1, from Bolivia. 5S and 45S rDNA probes were located on mitotic chromosomes by fluorescent in situ hybridization. The hybrid haploid karyotype length was an average value of the two taxa; the hybrid presented 24 45S loci in the diploid complement, 18 45S sites belonged to C. cardenasii cytotype 2, and six came from C. eximium cytotype 2, although this cytotype of C. eximium has been mentioned only for Argentina. Whereas hybrids were previously reported in the purple flower group, their existence has not been cytologically corroborated. This finding constitutes the first molecular cytogenetic evidence of hybridization between two taxa from this group.
... The genus is of great economic importance because it includes sweet and hot chilli peppers, which are cultivated and consumed around the world. Previous studies on Capsicum have focused on taxonomic, cytogenetic and phylogenetic issues (Hunziker, 2001;Pozzobon et al., 2006;Scaldaferro et al., 2006Scaldaferro et al., , 2013Scaldaferro et al., , 2016Barboza et al., 2022). However, few studies have analysed intraspecific genetic diversity across the total geographical distribution in order to reconstruct the natural evolutionary history of Capsicum species (but see Scaldaferro et al., 2018). ...
Phylogeographical studies combined with species distribution modelling can provide evidence for past climate refugia. During the Pleistocene, the Chaco phytogeographical province (ChPP) underwent changes in the distribution range, and the flora might have found refugia in different habitats according to their climatic requirements. This contribution aims to infer the effects of historical geoclimatic changes on the evolutionary history of Capsicum chacoense, the southernmost chilli pepper growing in the ChPP. We analysed 27 localities with plastid markers and 23 with nuclear markers, covering the geographical range of the species. We performed statistical phylogeography, in addition to current and past species distribution modelling. We found three haploclades, diverging 2.3–1 Mya, intermingled throughout the mountain ranges of the ChPP as a consequence of glacial cycles. According to the species distribution modelling, the expansion of the species distribution occurred during interglacial periods. We found two dispersal routes from south to north of the species distribution, concomitant with the migration routes of birds that disperse their fruits. The spatial distribution of genetic diversity showed the highest genetic diversity values at higher elevations. The main orographic systems of the study area were identified as areas of presumed population stability. Consequently, mountains are priority regions for conservation because they contain areas with high genetic diversity.
... The genus is of great economic importance because it includes sweet and hot chilli peppers, which are cultivated and consumed around the world. Previous studies on Capsicum have focused on taxonomic, cytogenetic and phylogenetic issues (Hunziker, 2001;Pozzobon et al., 2006;Scaldaferro et al., 2006Scaldaferro et al., , 2013Scaldaferro et al., , 2016Barboza et al., 2022). However, few studies have analysed intraspecific genetic diversity across the total geographical distribution in order to reconstruct the natural evolutionary history of Capsicum species (but see Scaldaferro et al., 2018). ...
... Makino, Aureliana (Hunziker, 2001). More recently, different classical and molecular cytogenetic analyses, crossing experiments, enzymatic studies, and chloroplast and nuclear DNA sequence studies (Scaldaferro et al., 2006), have allowed considerable progress in the characterization of infrageneric groups in Capsicum. ...
Species of Capsicum L. are closely related plants whose taxonomic status has remained controversial among different taxonomists. This study was designed to examine the taxonomic status of the species of Capsicum in Nigeria in order to establish the genetic variation between the species for the purpose of identification, as well as review the infrageneric classification (INC) of the members of the genus. Germplasm collection of the seeds of five cultivars of Capsicum were regenerated and nurtured to fruiting. Variations in their vegetative and reproductive morphology were macroscopically evaluated in replicates of 30 individuals per cultivar for each character, which equals 150 samples altogether. The cultivars of each species was hierarchically clustered as operational taxonomic units (OTUs) using Ward’s method with squared Euclidean distance. Artificial key was also constructed for the identification of the species in the genus. The twenty-three (23) morphological characters adopted gave useful insights into the INC of the species and were sufficiently diagnostic of the species as evidenced by the artificial key. Through this study, some light has been shed on the delimitation of species and varieties of the Nigerian Capsicum.
... Cytogenetics has thus become an integral part of genome analysis and no more a 'dead discipline' as was thought during the 1970s [42,43]. Chromosome analysis of Capsicum species has been given special importance for conservation of genetic diversity [30,33,[44][45][46][47][48][49][50][51][52][53], taxonomic works [12] and global compendium [3]. ...
Capsicum as a spice crop, has wild and cultivated forms admired globally, including Indian subcontinent with vast climatic ranges. Systematic representation of the Indian Capsicum is required to address species relationships and sustainable agriculture, in face of unpredictable climatic conditions. We have updated the catalogue of Indian ‘C. annuum complex’ with 28 landraces and populations from different agro-climatic regions. The agro-climatic influence on the origin of stable chili landraces in India is remarkable, especially in the North East. The floral and fruit morphotype standards and chromosomal attributes have been considered for four distinct ‘C. annuum complex’ members under three species. The highlights of study are: (1) comparative profiling of Indian Capsicum species revealing less infraspecific variation within C. frutescens and C. chinense than C. annuum, at par with cultivation status, (2) karyotype analysis of some unique diploid landraces of C. annuum, (3) karyotypic confirmation of the polyploid Dalle Khursani landraces exclusive to India. To obtain more information, we attempted to correlate diversity of fruit and floral morphotype with chromosomal diversity. Existence of elite and rare germplasm found in the regional pockets offer great scope for enriching the agricultural tradition. The present dataset may serve as a template to be continuously upgraded by taxonomists, genomicists and breeders.
... Makino, Aureliana (Hunziker, 2001). More recently, different classical and molecular cytogenetic analyses, crossing experiments, enzymatic studies, and chloroplast and nuclear DNA sequence studies (Scaldaferro et al., 2006), have allowed considerable progress in the characterization of infrageneric groups in Capsicum. ...
Species of Capsicum L. are closely related plants whose taxonomic status has remained controversial among different taxonomists. This study was designed to examine the taxonomic status of the species of Capsicum in Nigeria in order to establish the genetic variation between the species for the purpose of identification, as well as review the infrageneric classification (INC) of the members of the genus. Germplasm collection of the seeds of five cultivars of Capsicum were regenerated and nurtured to fruiting. Variations in their vegetative and reproductive morphology were macroscopically evaluated in replicates of 30 individuals per cultivar for each character, which equals 150 samples altogether. The cultivars of each species was hierarchically clustered as operational taxonomic units (OTUs) using Ward’s method with squared Euclidean distance. Artificial key was also constructed for the identification of the species in the genus. The twenty-three (23) morphological characters adopted gave useful insights into the INC of the species and were sufficiently diagnostic of the species as evidenced by the artificial key. Through this study, some light has been shed on the delimitation of species and varieties of the Nigerian Capsicum.
A digoxigenin-labelled 5S rDNA probe (pTa-794) and a rhodamine-labelled 18S-5.8S-25S rDNA probe (pTa71) were used for double-target in-situ hybridization to root-tip metaphase, prophase and interphase chromosomes of cultivated beet,Beta vulgaris L. After in-situ hybridization with the 18S-5.8S-25S rDNA probe, one major pair of sites was detected which corresponded to the secondary constriction at the end of the short arm of chromosome 1. The two rDNA chromosomes were often associated and the loci only contracted in late metaphase. In the majority of the metaphase plates analyzed, we found a single additional minor hybridization site with pTa71. One pair of 5S rRNA gene clusters was localized near the centromere on the short arm of one of the three largest chromosomes which does not carry the 18S-5.8S-25S genes. Because of the difficulties in distinguishing the very similarly-sizedB. vulgaris chromosomes in metaphase preparations, the 5S and the 18S-5.8S-25S rRNA genes can be used as markers for chromosome identification. TwoXbaI fragments (pXV1 and pXV2), comprising the 5S ribosomal RNA gene and the adjacent intergenic spacer, were isolated. The two 5S rDNA repeats were 349 bp and 351 bp long, showing considerable sequence variation in the intergenic spacer. The use of fluorescent in-situ hybridization, complemented by molecular data, for gene mapping and for integrating genetic and physical maps of beet species is discussed.
Since clear identification of individual chromosomes in Capsicum species was not possible due to the gradient in sizes and similar morphology, in situ hybridization using 5S rDNA and 18S-26S rDNA probes was utilized to karyotype the chromosomes of the five species, Capsicum annuum, C. chinense, C. frutescens, C. baccatum, and C. pubescens. The 5S rDNA located on only one pair of chromosomes in all five species. The 5S rDNA carrying chromosome was designated as chromosome I by the synteny relationship with tomato. In two species, C. baccatum and C. pubescens, the 5S rDNA was physically linked with a 18S-26S rDNA locus. The number and chromosomal location of 18S-26S rDNA loci were highly variable among the species. The number of loci was as few as two in C. annuum and as many as 14 in C. baccatum. The chromosomal positions of the 18S-26S loci were in the telomere regions in the corresponding chromosomes and some chromosomes showed hybridization signals in this region of both long and short arms. A pair of acrocentric chromosomes carrying the 18S-26S rDNA locus in the satellite region was found in all five species. The in situ and Southern hybridization patterns of the rDNAs were similar between C. annuum and C. chinense. C. frutescens was similar to C. chinense. C. baccatum and C. pubescens were speculated to be less related to the former three Capsicum species. The variable nature of the 18S-26S rDNA loci in the Capsicum species might provide a good model for rDNA evolution.
Flow cytometric measurements of nuclear DNA content were performed using ethidium bromide as the DNA stain (internal standard, Hordeum vulgare 'Ditta', 1C = 5.063 pg) in 25 samples belonging to nine diploid species and four varieties of Capsicum: C. chacoense, C. parvifolium, C. frutescens, C. chinense, C. annuum var. annuum, C. baccatum var. baccatum, C. baccatum var. pendulum, C. baccatum var. umbilicatum, C. eximium and C. pubescens, all with 2n = 24, and C. campylopodium with 2n = 26. In addition, one sample each of C. annuum var. annuum and C. pubescens were also analysed using Feulgen densitometry (standard, Allium cepa 'Stuttgarter Riesen', 1C = 16.75 pg). Both staining methods resulted in very similar relative values. Genome size displays significant variation between but not within species (except in C. campylopodium), and contributes to their taxonomic grouping. 1C-values range from 3.34-3.43 pg (3273-3361 Mbp) in C. chacoense and the C. annuum complex to 4.53-5.77 pg (4439-5655 Mbp) in C. campylopodium and C. parvifolium. The data obtained support conclusions on phylogenetic relationships in the genus derived from karyotype analyses using chromosome banding approaches. In Capsicum, constitutive heterochromatin amount is correlated with genome size, except in C. parvifolium, and is regarded as an additive genomic component.
An approximately 135-bp sequence called the A1/A2 repeat was isolated from the transcribed region of the 26-18S rDNA intergenic spacer (IGS) of Nicotiana tomentosiformis. Fluorescence in situ hybridization (FISH) and Southern blot analysis revealed its occurrence as an independent satellite (termed an A1/A2 satellite) outside of rDNA loci in species of Nicotiana section Tomentosae. The chromosomal location, patterns of genomic dispersion, and copy numbers of its tandemly arranged units varied between the species. In more distantly related Nicotiana species the A1/A2 repeats were found only at the nucleolar organizer regions (NOR). There was a trend toward the elimination of the A1/A2 satellite in N. tabacum (tobacco), an allotetraploid with parents closely related to the diploids N. sylvestris and N. tomentosiformis. This process may have already commenced in an S(3) generation of synthetic tobacco. Cytosine residues in the IGS were significantly hypomethylated compared with the A1/A2 satellite. There was no clear separation between the IGS and satellite fractions in sequence analysis of individual clones and we found no evidence for CG suppression. Taken together the data indicate a dynamic nature of the A1/A2 repeats in Nicotiana genomes, with evidence for recurrent integration, copy number expansions, and contractions.
Homologies of tomato and pepper genes have been compared, and genetic linkage maps have been constructed based on a common set of cDNA clones and selected single-copy genomic clones. We report here that the gene repertoire of these two species is highly conserved, yet the linear order of the genes on the chromosomes has been greatly modified. Although the two species share the same number of centromeres, the chromosomal regions around those centromeres have undergone extensive rearrangements. Accompanying the extensive chromosome rearrangement has been a change in locus number for approximately 12% of the loci detected by random cDNA clones. Duplicated loci within each genome are normally found on different chromosomes and are not confined to one species, thus ruling out gene duplication as an explanation for the 4-fold higher DNA content of pepper. At least one of the duplications occurred since the divergence of tomato and pepper from their last common ancestor.
The chromosomes of Brassica species are small and poorly differentiated, and their identification is extremely difficult using conventional cytogenetic methods. Progress in molecular analysis of Brassica species requires cytogenetic maps of their chromosomes. Chromosome-specific markers are needed to distinguish particular pairs of homologous chromosomes and for karyotyping. In this study, three morphological groups of chromosomes in B. campestris (genome A) and B. oleracea (genome C) and two in B. nigra (genome B) were distinguished by the morphometric features of the chromosomes, based upon arm ratio and absolute length. Using fluorescence in situ hybridization and differential stainings it was possible to establish further markers for five pairs of chromosomes in genome A, three in genome B and two in genome C, and to present idiograms of the chromosomes for three diploid Brassica species. However, for clear identification of all chromosome pairs more cytogenetic markers are needed.
An ∼135-bp sequence called the A1/A2 repeat was isolated from the transcribed region of the 26-18S rDNA intergenic spacer (IGS) of Nicotiana tomentosiformis. Fluorescence in situ hybridization (FISH) and Southern blot analysis revealed its occurrence as an independent satellite (termed an A1/A2 satellite) outside of rDNA loci in species of Nicotiana section Tomentosae. The chromosomal location, patterns of genomic dispersion, and copy numbers of its tandemly arranged units varied between the species. In more distantly related Nicotiana species the A1/A2 repeats were found only at the nucleolar organizer regions (NOR). There was a trend toward the elimination of the A1/A2 satellite in N. tabacum (tobacco), an allotetraploid with parents closely related to the diploids N. sylvestris and N. tomentosiformis. This process may have already commenced in an S3 generation of synthetic tobacco. Cytosine residues in the IGS were significantly hypomethylated compared with the A1/A2 satellite. There was no clear separation between the IGS and satellite fractions in sequence analysis of individual clones and we found no evidence for CG suppression. Taken together the data indicate a dynamic nature of the A1/A2 repeats in Nicotiana genomes, with evidence for recurrent integration, copy number expansions, and contractions.
A germplasm collection of 70 cultivars and wild species of Capsicum was evaluated for resistance to tomato spotted wilt virus (TSWV) under field (natural inoculum) conditions. Different levels of resistance to the disease caused by this virus were observed among the tested lines. High degree of field resistance was detected in two Capsicum baccatum var. pendulum, two C. chinense, and three C. annuum lines. Controlled greenhouse tests were also carried out to confirm the resistant reaction of these seven field selected lines. These lines were mechanically inoculated with two serologically distinct isolates of TSWV obtained from different geographic regions of Brazil. The two C. chinense lines (CNPH 275 and PI 159236) were virtually immune against one specific (TSWV-BsB) isolate but were susceptible to another isolate (TSWV-SP) used in this assay. Sources of resistance for both isolates were not found. Our experimental results strongly indicate there exists a number of genetic mechanisms (probably including action of vertical and horizontal genes) to TSWV resistance in Capsicum spp.
Fluorochrome chromosome banding is applied for the first time to 15 samples of five cultivatedCapsicum species, all with 2n = 24, and allows a detailed analysis of the karyotypes (Tables 2–3, Fig. 8). Banding patterns differ between cytotypes, species and groups, reflecting the dynamics of chromosomal differentiation and evolutionary divergence. Taxa have from 1 to 4 NOR-bearing satellited chromosome pairs and exhibit increasing numbers of terminal (rarely intercalary and indistinct centromeric) heterochromatic fluorescent bands. Amounts of heterochromatin (expressed in % of karyotype length) increase from the group withC. annuum (1.80–2.88),C. chinense (3.91–5.52), andC. frutescens (5.55) toC. baccatum (7.30–7.56), and finally toC. pubescens (18.95). In all taxa CMA+DAPI—(GC-rich) constitutive heterochromatin dominates, onlyC. pubescens has an additional CMAo DAPI+ (AT-rich) band. The fluorochrome bands generally (but not completely) correspond to the Giemsa C-bands. Structural heterozygosity can be demonstrated but is not prominent. The independent origin of at least three evolutionary lines leading to the cultivated taxa ofCapsicum is supported.