Higher Polyploids Research Articles

Potentials, Challenges, and Genetic and Genomic Resources for Sugarcane Biomass Improvement.

Lignocellulosic biomass has become an emerging feedstock for second-generation bioethanol production. Sugarcane (Saccharum spp. hybrids), a very efficient perennial C4 plant with a high polyploid level and complex genome, is considered a top-notch candidate for biomass production due to its salient features viz. fast growth rate and abilities for high tillering, ratooning, and photosynthesis. Energy cane, an ideal type of sugarcane, has been bred specifically as a biomass crop. In this review, we described (1) biomass potentials of sugarcane and its underlying genetics, (2) challenges associated with biomass improvement such as large and complex genome, narrow gene pool in existing commercial cultivars, long breeding cycle, and non-synchronous flowering, (3) available genetic resources such as germplasm resources, and genomic and cell wall-related databases that facilitate biomass improvement, and (4) mining candidate genes controlling biomass in genomic databases. We extensively reviewed databases for biomass-related genes and their usefulness in biofuel generation. This review provides valuable resources for sugarcane breeders, geneticists, and broad scientific communities involved in bioenergy production.

Efficiency of Embryo Rescue Technology in St. Augustinegrass Breeding

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is a popular warm‐season turfgrass in Gulf Coast regions of the United States. Diploid St. Augustinegrass produces fertile seed, but triploids and higher polyploids are mostly sterile. Polyploid St. Augustinegrass cultivars have been selected for their resistance to southern chinch bugs, St. Augustine Decline, and drought tolerance but lack the cold hardiness and shade tolerance of diploids. However, because of sterility barriers, the polyploid germplasm had not been fully used as breeding material until 2009 when we reported the development of interploid hybrids using embryo rescue technology. The objective of the present study was to backcross these first‐generation interploid hybrids with diploid males to produce second‐generation hybrids. Sterility barriers were found to be much greater with second‐generation crosses yielding only 0.00 to 2.69% progeny per interploid hybrid. Using this technique, the embryos are generally rescued 3 wk postpollination, thereby causing a heavy demand on one's time to process spikelets before embryos abort. Our preliminary findings show the use of cold storage at 7°C to potentially extend the processing period up to 2 mo with a slight drop off in efficiency (4.37–6.03% crossability). Our results also show the potential of first‐generation hybrids to exhibit superior performance under drought when compared with diploid cultivars Palmetto and Raleigh. Tested second‐generation interploids did not exhibit superior performance in drought. Nonetheless, our results emphasize the utility of embryo rescue technology in facilitating gene exchange between ploidy levels to generate hybrids with superior performance.

A high-throughput flow cytometry system for early screening of in vitro made polyploids in Dendrobium hybrids

Orchids of the genus Dendrobium hold a high economical value in the international markets both as pot plants or cut flowers, and for the production of some metabolites with antioxidant and anti-tumoral activities. Manipulating ploidy levels of Dendrobium species is one of the possible methods to develop new varieties with increased ornamental value and a higher production of secondary metabolites. In this work, we present a new and fast flow cytometry approach to obtain and select Dendrobium phalaenopsis × Dendrobium loddigesii polyploids, through an early in vitro screening on protocorm like bodies (PLBs) after antimitotic treatment. Our approach allows the identification of the best time of treatment on control PLBs and the assessment of best conditions for polyploid recovery just one month after treatments, by using Cycle Value. We were able to discard about the two-third of the unchanged material by drastically reducing the explants to work with and the corresponding costs. Different conditions, regarding concentrations and exposition time, were tested using colchicine or amiprophos-methyl (APM). A high polyploids recovery, up to 80%, were obtained with both antimitotic agents, and those materials were further characterized by liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS), to identify independent polyploids explants with increased levels in high-value molecules as shihunidine and hircinol, together with stochastic events and genotype-specific metabolite fluctuations.

Mining sequence variations in representative polyploid sugarcane germplasm accessions

BackgroundSugarcane (Saccharum spp.) is one of the most important economic crops because of its high sugar production and biofuel potential. Due to the high polyploid level and complex genome of sugarcane, it has been a huge challenge to investigate genomic sequence variations, which are critical for identifying alleles contributing to important agronomic traits. In order to mine the genetic variations in sugarcane, genotyping by sequencing (GBS), was used to genotype 14 representative Saccharum complex accessions. GBS is a method to generate a large number of markers, enabled by next generation sequencing (NGS) and the genome complexity reduction using restriction enzymes.ResultsTo use GBS for high throughput genotyping highly polyploid sugarcane, the GBS analysis pipelines in 14 Saccharum complex accessions were established by evaluating different alignment methods, sequence variants callers, and sequence depth for single nucleotide polymorphism (SNP) filtering. By using the established pipeline, a total of 76,251 non-redundant SNPs, 5642 InDels, 6380 presence/absence variants (PAVs), and 826 copy number variations (CNVs) were detected among the 14 accessions. In addition, non-reference based universal network enabled analysis kit and Stacks de novo called 34,353 and 109,043 SNPs, respectively. In the 14 accessions, the percentages of single dose SNPs ranged from 38.3% to 62.3% with an average of 49.6%, much more than the portions of multiple dosage SNPs. Concordantly called SNPs were used to evaluate the phylogenetic relationship among the 14 accessions. The results showed that the divergence time between the Erianthus genus and the Saccharum genus was more than 10 million years ago (MYA). The Saccharum species separated from their common ancestors ranging from 0.19 to 1.65 MYA.ConclusionsThe GBS pipelines including the reference sequences, alignment methods, sequence variant callers, and sequence depth were recommended and discussed for the Saccharum complex and other related species. A large number of sequence variations were discovered in the Saccharum complex, including SNPs, InDels, PAVs, and CNVs. Genome-wide SNPs were further used to illustrate sequence features of polyploid species and demonstrated the divergence of different species in the Saccharum complex. The results of this study showed that GBS was an effective NGS-based method to discover genomic sequence variations in highly polyploid and heterozygous species.

Natural Allelic Variations in Highly Polyploidy Saccharum Complex.

Sugarcane (Saccharum spp.) is an important sugar and biofuel crop with high polyploid and complex genomes. The Saccharum complex, comprised of Saccharum genus and a few related genera, are important genetic resources for sugarcane breeding. A large amount of natural variation exists within the Saccharum complex. Though understanding their allelic variation has been challenging, it is critical to dissect allelic structure and to identify the alleles controlling important traits in sugarcane. To characterize natural variations in Saccharum complex, a target enrichment sequencing approach was used to assay 12 representative germplasm accessions. In total, 55,946 highly efficient probes were designed based on the sorghum genome and sugarcane unigene set targeting a total of 6 Mb of the sugarcane genome. A pipeline specifically tailored for polyploid sequence variants and genotype calling was established. BWA-mem and sorghum genome approved to be an acceptable aligner and reference for sugarcane target enrichment sequence analysis, respectively. Genetic variations including 1,166,066 non-redundant SNPs, 150,421 InDels, 919 gene copy number variations, and 1,257 gene presence/absence variations were detected. SNPs from three different callers (Samtools, Freebayes, and GATK) were compared and the validation rates were nearly 90%. Based on the SNP loci of each accession and their ploidy levels, 999,258 single dosage SNPs were identified and most loci were estimated as largely homozygotes. An average of 34,397 haplotype blocks for each accession was inferred. The highest divergence time among the Saccharum spp. was estimated as 1.2 million years ago (MYA). Saccharum spp. diverged from Erianthus and Sorghum approximately 5 and 6 MYA, respectively. The target enrichment sequencing approach provided an effective way to discover and catalog natural allelic variation in highly polyploid or heterozygous genomes.

INDUCTION OF TETRAPLOIDS IN ESCALLONIA SPP.

Escallonia is a genus of flowering shrubs, native to South-America. As for most woody ornamentals, current breeding efforts in Escallonia are low. In an attempt to enlarge the assortment and to introgress winter hardiness and a more compact growth habit, we performed in vitro polyploidization on Escallonia species. We collected 25 species and characterized their genome size, chromosome number, and leaf and flower parameters. Measured genome sizes of the collection varied between 1.01 and 1.31 pg/2C. In vitro polyploidization on E. rubra and E. rosea was more efficient when using oryzalin and trifluralin compared to colchicine. We obtained up to 56.7% E. rubra tetraploids using trifluralin (1 μM for 6 weeks) and 33.3% E. rosea tetraploids using oryzalin (150 μM for 3 days), compared to colchicine which only yielded 16.7% E. rubra (1000 μM for 3 days) and 3.3% E. rosea (2000 μM for 3 days) tetraploids. Short (2, 3 and 4 days) and chronic (6, 8 and 10 weeks) treatments on E. rubra displayed a higher polyploidization efficiency for trifluralin (28%) compared to oryzalin (18%). Ploidy doubled plantlets and diploid controls were acclimatized in the greenhouse for further morphological evaluation. The most efficient treatment was chosen to polyploidize other Escallonia species.

Patterns of flower microstructural variation within the genus Bromus

Twenty five species from four sections of the genus <em>Bromus</em> were evaluated by means of numerical analyses of characters of flower microstructures (lodicule, lemma, palea). Special development of lodicules (lobe and hairiness) and both glumellae (lemma and palea) similar in grasses evolutionarily close (<em>Bromeae</em>, <em>Brachypodieae</em>, <em>Triticeae</em>) was discovered. For most of the characters the original interspecific and intersectional relations were observed in a space of minimum spanning tree (MST). The evolutionary old section Pnigma occupies the largest space. Species of Pnigma having small chromosomes can be distinguished from those having large ones. The section <em>Ceratochloa</em> is scattered through the smallest space. The above points to the endemic evolution of high polyploids of the section. The sections <em>Bromus</em> and <em>Genea</em> are evolutionarily close and they distinctly overlap each other in the MST space. <em>Bromus sterilis</em>, <em>B. catharticus</em> and <em>B. riparius</em> are extremes in their own sections.

Deep cytogenetics analysis reveals meiotic recombination depletion in species of Senecio (Asteraceae).

BackgroundSenecio is the largest genus in the Asteraceae family growing in all environments around the world. It displays taxonomic and systematical difficulties. Cytogenetic knowledge of this genus is ancient, scarce and mainly restricted to chromosome number records.ResultsIn this study we analyzed chromosome number, meiotic configuration, bivalent morphology, meiotic behavior and pollen grain stainability on 100 accessions of 27 different polyploid Senecio L. sect Senecio entities. Median, standard deviation and mode were calculated for number and position of chiasmata and meiotic recombination was statistically evaluated. Although high frequency of multivalents and associated meiotic irregularities are expected in high polyploids, bivalents predominance and, consequently, regular meiosis were observed, with normal sporogenesis and high pollen grain stainability.ConclusionDepletion in the total chiasmata was significant only in some species but the terminal position was preferential in all the entities analyzed, indicating significant reduction in recombination. The regular meiosis observed suggest that intra and intergenomic reorganization process occur quickly and efficiently in this genus. Mechanisms of diploidization, common to all polyploids, are reinforced by the strong reduction in crossing-over rushing polyploids stabilization.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-20) contains supplementary material, which is available to authorized users.

Polyploidy, alien species and invasiveness in Polish angiosperms

Chromosome numbers, mainly for Polish flora, were examined in order to investigate whether such features as chromosome numbers and polyploid frequencies are correlated with a plant’s origin (native vs. alien) and invasiveness. Polyploid frequencies were estimated using three methods: the 11 and 14 thresholds and the 3.5 x value. Comparisons of the 2n values were done on different levels: in all angiosperms and in dicots and monocots separately. Invasive and non-invasive plants were compared in the entire dataset and in alien species only. Significant differences in both chromosome numbers and polyploid frequencies between alien and native species were observed. In most cases, native plants had more chromosomes and were more abundant in polyploids than in alien species. Also, monocots had higher polyploid frequencies than dicots. Comparisons of invasive and non-invasive plants done for all of the data and only for alien species showed that invasive species generally had more chromosomes and polyploids were more frequent in them than in the latter group; however, these differences were not always statistically significant. Possible explanations for these observations are discussed.

Haplotype structure around Bru1 reveals a narrow genetic basis for brown rust resistance in modern sugarcane cultivars

Modern sugarcane cultivars (Saccharum spp., 2n = 100-130) are high polyploid, aneuploid and of interspecific origin. A major gene (Bru1) conferring resistance to brown rust, caused by the fungus Puccinia melanocephala, has been identified in cultivar R570. We analyzed 380 modern cultivars and breeding materials covering the worldwide diversity with 22 molecular markers genetically linked to Bru1 in R570 within a 8.2 cM segment. Our results revealed a strong LD in the Bru1 region and strong associations between most of the markers and rust resistance. Two PCR markers, that flank the Bru1-bearing segment, were found completely associated with one another and only in resistant clones representing efficient molecular diagnostic for Bru1. On this basis, Bru1 was inferred in 86 % of the 194 resistant sugarcane accessions, revealing that it constitutes the main source of brown rust resistance in modern cultivars. Bru1 PCR diagnostic markers should be particularly useful to identify cultivars with potentially alternative sources of resistance to diversify the basis of brown rust resistance in breeding programs.

Inferring Species Networks from Gene Trees in High-Polyploid North American and Hawaiian Violets (Viola, Violaceae)

The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9–14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.

Characterization of Microsatellite Loci and Reliable Genotyping in a Polyploid Plant, Mercurialis perennis (Euphorbiaceae)

For many applications in population genetics, codominant simple sequence repeats (SSRs) may have substantial advantages over dominant anonymous markers such as amplified fragment length polymorphisms (AFLPs). In high polyploids, however, allele dosage of SSRs cannot easily be determined and alleles are not easily attributable to potentially diploidized loci. Here, we argue that SSRs may nonetheless be better than AFLPs for polyploid taxa if they are analyzed as effectively dominant markers because they are more reliable and more precise. We describe the transfer of SSRs developed for diploid Mercurialis huetii to the clonal dioecious M. perennis. Primers were tested on a set of 54 male and female plants from natural decaploid populations. Eight of 65 tested loci produced polymorphic fragments. Binary profiles from 4 different scoring routines were used to define multilocus lineages (MLLs). Allowing for fragment differences within 1 MLL, all analyses revealed the same 14 MLLs without conflicting with merigenet, sex, or plot assignment. For semiautomatic scoring, a combination of as few as 2 of the 4 most polymorphic loci resulted in unambiguous discrimination of clones. Our study demonstrates that microsatellite fingerprinting of polyploid plants is a cost efficient and reliable alternative to AFLPs, not least because fewer loci are required than for diploids.

Evolution of the south-western Pacific genus Melicytus (Violaceae): evidence from DNA sequence data, cytology and sex expression

Phylogenetic analyses of nuclear DNA external transcribed spacer (ETS) and chloroplast DNA trnL–trnF markers were undertaken to reconstruct the evolutionary history of the South Pacific genus Melicytus. Bayesian analyses of the ETS sequence data produced a phylogenetic tree with several well supported groups, including clades comprising: (1) species from Australia, Tasmania and Lord Howe Island; (2) the Norfolk Island M. latifolius and New Zealand off-shore island M. novae-zelandiae subsp. novae-zelandiae; (3) the large-leaved M. ramiflorus complex; (4) M. fasciger and M. micranthus; and (5) M. obovatus and allies from the Cook Strait region. Phylogenetic analysis of trnL–trnF sequence data also retrieved some of these groups although, in general, was not as well resolved. The relationships of M. lanceolatus are equivocal, as in the ETS phylogeny it is sister to a clade comprising the large-leaved tree species M. fasciger and M. ramiflorus complex and the small-leaved M. micranthus, whereas in the trnL–trnF phylogeny it is sister to a clade of small-leaved shrub species such as M. alpinus and M. crassifolius. Several biogeographic patterns are evident, with dispersal to the west from New Zealand, to Australia, involving small-leaved shrub species. Dispersal to the north from New Zealand, to Norfolk Island and Fiji, involves large-leaved tree species. The sex expression is documented for all named species and undescribed entities, with these being either hermaphroditic or dioecious. When sex expression is mapped onto the phylogeny, the hermaphroditic system is inferred to have evolved from the dioecious system. New chromosome counts are presented for M. angustifolius (2n = 64) and M. dentatus (2n = 32), and earlier counts of 2n = 64 are confirmed for M. crassifolius and M. alpinus. An additional 17 counts are provided for two natural hybrids and several undescribed entities from Australia and New Zealand. The polyploid chromosome number of 2n = 64 occurs most frequently in small-leaved divariate plants with hermaphroditic flowers. When chromosome numbers are plotted onto the phylogeny it is inferred that high polyploids (e.g. 2n = 64) and small-leaved shrubs have evolved from large-leaved trees with functional diploid (e.g. 2n = 32) chromosome numbers.

Polymorphism of Potentilla tabernaemontani and related taxa on Gotland

Potentilla tabernaemontani and P. cinerea are widely distributed in Europe and are linked together by hybrids. Sexual tetraploids occur, especially of P. cinerea in SE Europe. Biotypes from N Europe are high polyploids (2n=42 or more) and apomictic. On Gotland, a Swedish island in the Baltic sea, P. tabernaemontani shows a high degree of morphological variation, and hybrids with P. cinerea are not uncommon (Johansson 1905, Ark. Bot. 4: 1–18). Known chromosome numbers are 2n=42 (38 collections), 49 (11), 56 (6) and ±63 (3). Morphological variation and heteroploidy seem to be concentrated in NW Gotland. In other areas, hexaploids (2n=42) prevail, even where morphological variation is great (Faro). The polymorphism on Gotland exceeds that of most other parts of N Europe. Certain taxa seem in reappear in mountainous regions of Central and South Europe. More collections from Gotland and the Swedish mainland, as well as studies of material from other parts of Europe, are still needed for a taxonomic revision of this group.

Dated historical biogeography of the temperate Loliinae (Poaceae, Pooideae) grasses in the northern and southern hemispheres

Divergence times and biogeographical analyses have been conducted within the Loliinae, one of the largest subtribes of temperate grasses. New sequence data from representatives of the almost unexplored New World, New Zealand, and Eastern Asian centres were added to those of the panMediterranean region and used to reconstruct the phylogeny of the group and to calculate the times of lineage-splitting using Bayesian approaches. The traditional separation between broad-leaved and fine-leaved Festuca species was still maintained, though several new broad-leaved lineages fell within the fine-leaved clade or were placed in an unsupported intermediate position. A strong biogeographical signal was detected for several Asian–American, American, Neozeylandic, and Macaronesian clades with different affinities to both the broad and the fine-leaved Festuca. Bayesian estimates of divergence and dispersal–vicariance analyses indicate that the broad-leaved and fine-leaved Loliinae likely originated in the Miocene (13 My) in the panMediterranean–SW Asian region and then expanded towards C and E Asia from where they colonized the New World. Further expansions in America (10–3.8 My) showed a predominant migratory route from North to South (N America ↔ the Andes ↔ Patagonia). This late Tertiary scenario of successive colonizations and secondary polyploid radiations in the southern hemisphere from the northern hemisphere was accompanied by occasional transcontinental long-distance dispersal events between South America and New Zealand. Multiple Pliocene dispersal events (3.6–2.5 My) from the near SW European and NW African continents gave rise to the Macaronesian Loliinae flora, while a more recent Pleistocene origin (2–1 My) is hypothesized for the high polyploid lineages that successfully colonized newly deglaciated areas in both hemispheres.

Congruence, Conflict, and Polyploidization Shown by Nuclear and Chloroplast Markers in the Monophyletic ''Bristle Clade'' (Paniceae, Panicoideae, Poaceae)

Molecular phylogenetic analyses using the chloroplast marker ndhF and a single copy nuclear marker, knotted1, show that the panicoid grasses bearing sterile branches (bristles) in their inflorescences form a monophyletic group. The genus Cenchrus is monophyletic, and monophyly of Pennisetum cannot be ruled out. Setaria is not monophyletic, either as a whole, excluding the palm-leaved species from section Ptychophyllum ,o r excluding various uncertainly placed species such as S. grisebachii. There is also no evidence that Setaria and Paspalidium form a monophyletic group. The Australian genera Zygochloa, Spinifex, and Pseudoraphis are placed in the 'bristle clade', confirming that inflorescences of these grasses are homologous with the inflorescences composed of spikelets and sterile branchlets (bristles). Comparison of the nuclear and chloroplast gene trees identifies several taxa as tetra- or higher polyploids; these are confirmed by southern hybridization. In particular, the Australian species of Paspalidium are allopolyploid, a novel and unexpected result. Zuloagaea bulbosa, a species that lacks the synapomorphic bristles in its inflorescence, is confirmed as a morphologically anomalous member of the clade, and is clearly allopolyploid. This study demonstrates the utility of knotted1 as a phylogenetic marker; we show that it is single copy in diploid taxa and that it exhibits adequate variation to distinguish closely related species. Interestingly, inflorescence morphology correlates only partially with relationships suggested by either nuclear or chloroplast trees, suggesting that inflorescence form is easily changed over evolutionary time.

Untangling Complex Histories of Genome Mergings in High Polyploids

Polyploidy, the duplication of entire genomes, plays a major role in plant evolution. In allopolyploids, genome duplication is associated with hybridization between two or more divergent genomes. Successive hybridization and polyploidization events can build up species complexes of allopolyploids with complicated network-like histories, and the evolutionary history of many plant groups cannot be adequately represented by phylogenetic trees because of such reticulate events. The history of complex genome mergings within a high-polyploid species complex in the genus Cerastium (Caryophyllaceae) is here untangled by the use of a network algorithm and noncoding sequences of a low-copy number gene. The resulting network illustrates how hybridization and polyploidization have acted as key evolutionary processes in creating a plant group where high-level allopolyploids clearly outnumber extant parental genomes.

A High Polyploid Chromosome Complement of Ophioglossum nudicaule L. f.

The diploid (2n=720) and haploid (2n=360) chromosome numbers were determined in Ophioglossum nudicaule. The somatic chromosome count was made on the plant for the first time. O. nudicaule is a very high polyploid plant, either exhibiting 48-ploidy, if the basic chromosome number is x2=15 or a 24-ploid, originating from the basic chromosome number of x3=30.

Genetic mapping in sugarcane, a high polyploid, using bi-parental progeny: identification of a gene controlling stalk colour and a new rust resistance gene

Modern sugarcane cultivars (Saccharum spp) are highly polyploïd and aneuploid interspecific hybrids (2n = 100-130). Two genetic maps were constructed using a population of 198 progeny from a cross between R570, a modern cultivar, and MQ76-53, an old Australian clone derived from a cross between Trojan (a modern cultivar) and SES528 (a wild Saccharum spontaneum clone). A total of 1,666 polymorphic markers were produced using 37 AFLP primer combinations, 46 SSRs and 9 RFLP probes. Linkage analysis led to the construction of 86 cosegregation groups for R570 and 105 cosegregation groups for MQ76-53 encompassing 424 and 536 single dose markers, respectively. The cumulative length of the R570 map was 3,144 cM, while that of the MQ76-53 map was 4,329 cM. Here, we integrated mapping information obtained on R570 in this study with that derived from a previous map based on a selfed R570 population. Two new genes controlling Mendelian traits were localized on the MQ76-53 map: a gene controlling the red stalk colour was linked at 6.5 cM to an AFLP marker and a new brown rust resistance gene was linked at 23 cM to an AFLP marker. Besides another previously identified brown rust resistance gene (Bru1), these two genes are the only other major genes to be identified in sugarcane so far.

Chromosome numbers in plant taxa endemic to the Balearic Islands

Mitotic chromosome numbers are reported from 20 vascular plant taxa that are endemic to the Balearic Islands and poorly known cytogenetically. The chromosome numbers of Arenaria grandiflora L. ssp. glabrescens (Willk.) G. Lopez & Nieto Feliner (2n = 44), Dianthus rupicola Viv. ssp. bocchoriana L. Llorens & Gradaille (2n = 30), Solenopsis minuta (L.) C. Presl. ssp. balearica (E. Wimm.) Meikle (2n = 28), Romulea asumptionis Font Quer & Garcias Font (2n = 56), Scutellaria balearica Barcelo (2n = 22) and Galium balearicum Briq. (2n = 22) have been determined for the first time. A new chromosome number was found in two populations of Helictotrichon crassifolium (Font Quer) Holub (2n = c. 98) suggesting that this species is a high polyploid (14x), in contrast to an earlier report of a lower chromosome count (2n = 12x = 84). Cytogenetic observations suggest that Naufraga balearica Constance & Cannon has a diploid chromosome complement of 2n = 20, with 0–2 accessory chromosomes. The banded karyotype (chromomycin A3) of Crepis triasii (Cambess.) Fries was determined for individuals belonging to eight populations from three islands. Two chromomycin A3-positive regions were recorded in the diploid complement. These are present on the telomeric regions of the shortest subtelocentric chromosomes. This species is karyologically stable in chromosome number, karyotype and fluorochrome-banding pattern among populations from separate islands. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 148, 219–228.