Tetraploid Material Research Articles

Biogeographic, climatic, morphological, cytological and molecular data reveal a new diploid species from China in the genus Xanthocyparis (Cupressaceae)

AbstractThe genus Xanthocyparis was described in 2002 for a new conifer species X. vietnamensis from northern Vietnam, which became well‐known for its rarity. Recently, natural diploid populations were found in a small area of northern Guangxi, China, whereas material from Vietnam plus newly discovered populations from southern Guangxi were determined to be tetraploids. We integrated evidence from multiple data sources to perform a taxonomic evaluation of the two ploidy levels present in Xanthocyparis. Morphometric analyses detected statistically significant differences in cone and leaf characters, whereas microsatellite and transcriptome analyses revealed clear genetic divergence between diploid and tetraploid material. Furthermore, analysis of bioclimatic variables confirmed divergence in ecological niches. Gene trees from homologous sequences indicate that tetraploid material might have arisen via allopolyploidy from the extant diploid material and a third, possibly extinct lineage. Therefore, we recognize and describe a new diploid species from northern Guangxi China: Xanthocyparis guangxiensis.

Potato soup: analysis of cultivated potato gene bank populations reveals high diversity and little structure.

Cultivated potatoes are incredibly diverse, ranging from diploid to pentaploid and encompass four different species. They are adapted to disparate environments and conditions and carry unique alleles for resistance to pests and pathogens. Describing how diversity is partitioned within and among these populations is essential to understanding the potato genome and effectively utilizing landraces in breeding. This task is complicated by the difficulty of making comparisons across cytotypes and extensive admixture within section petota. We genotyped 730 accessions from the US Potato genebank including wild diploids and cultivated diploids and tetraploids using Genotype-by-sequencing. This data set allowed us to interrogate population structure and diversity as well as generate core subsets which will support breeders in efficiently screening genebank material for biotic and abiotic stress resistance alleles. We found that even controlling for ploidy, tetraploid material exhibited higher observed and expected heterozygosity than diploid accessions. In particular group chilotanum material was the most heterozygous and the only taxa not to exhibit any inbreeding. This may in part be because group chilotanum has a history of introgression not just from wild species, but landraces as well. All group chilotanum, exhibits introgression from group andigenum except clones from Southern South America near its origin, where the two groups are not highly differentiated. Moving north, we do not observe evidence for the same level of admixture back into group andigenum. This suggests that extensive history of admixture is a particular characteristic of chilotanum.

Back to Linnaeus: Proper Botanical Naming of the Tetraploid Indian Acorus (Acoraceae), an Important Medicinal Plant

The basal monocot genus Acorus comprises essential oil-producing plants widely used in traditional medicine in various countries, including India. Acorus calamus sensu lato is a polyploid complex where the essential oil composition, to some extent, depends on the ploidy level. The literature recognizes diploids (in temperate Asia and North America), triploids (Asian in origin, naturalized elsewhere) and tetraploids (temperate to tropical Asia) at the rank of varieties of A. calamus. We show that the current use of the name A. calamus var. angustatus for the tetraploids is not properly justified. The earliest name based on the Asian material is A. calamus var. verus published in 1753 by Linnaeus. We justify the use of the Linnaean variety for tetraploids by selecting an epitype based on the material cultivated in Peninsular India, for which direct chromosome counts are provided. The name A. verus is available if the tetraploid cytotype is recognized at the species rank. We support earlier data on the importance of leaf anatomy for cytotype diagnostics in Acorus, but also show the limitations of the use of this approach. The growth pattern of the tropical Indian tetraploid material is discussed, and the evergreen nature of the accession studied here is documented. The exact chromosome number of the tetraploid Acorus requires further clarification. All metaphase plates examined here showed at least 44 chromosomes, but plates apparently showing more than 44 chromosomes were found as well. They may be explained by technical difficulties in counting chromosomes in Acorus. Alternatively, our data may indicate the occurrence of aneuploid mixoploidy.

Physiological and Metabolic Changes in ‘Xinyu Mandarin’ Following Natural Tetraploidization

The mandarin is an important fruit crop worldwide, and ‘Xinyu mandarin’—a local Citrus reticulata variety—is widely cultivated in Jiangxi Province, in China. Autopolyploidy has frequently been used for the improvement of crop varieties. In a previous study, we identified a tetraploid (4X) material of ‘Xinyu mandarin’ generated from its diploid (2X) mother seedling via a spontaneous mutation. However, the physiological and metabolic variations after polyploidy are not clear enough, which is not conducive to the early screening. In the present study, we analyzed the morphological, physiological, and metabolic differences between the tetraploid and diploid plants. The tetraploids had larger and thicker leaves, and the activities of key enzymes in photosynthesis, the total chlorophyll, phenolic, and proline contents, were all higher in tetraploids. In the non-targeted metabolomic profile, a total of 522 metabolites were identified, of which 61 were significantly different between diploids and tetraploids. The differential metabolites included similar proportions of primary and secondary metabolites, and most of these were up-regulated in tetraploids, especially stress-related metabolites such as phenolic acids, flavonoids, alkaloids, and so on, indicating that tetraploids may possess better stress tolerance ability and vigor. Therefore, the tetraploids of ‘Xinyu mandarin’ may serve as an excellent female parent for the improvement of citrus varieties.

Discovery and characterization of sweetpotato's closest tetraploid relative.

Summary The origin of sweetpotato, a hexaploid species, is poorly understood, partly because the identity of its tetraploid progenitor remains unknown. In this study, we identify, describe and characterize a new species of Ipomoea that is sweetpotato’s closest tetraploid relative known to date and probably a direct descendant of its tetraploid progenitor.We integrate morphological, phylogenetic, and genomic analyses of herbarium and germplasm accessions of the hexaploid sweetpotato, its closest known diploid relative Ipomoea trifida, and various tetraploid plants closely related to them from across the American continent.We identify wild autotetraploid plants from Ecuador that are morphologically distinct from Ipomoea batatas and I. trifida, but monophyletic and sister to I. batatas in phylogenetic analysis of nuclear data.We describe this new species as Ipomoea aequatoriensis T. Wells & P. Muñoz sp. nov., distinguish it from hybrid tetraploid material collected in Mexico; and show that it likely played a direct role in the origin of sweetpotato’s hexaploid genome. This discovery transforms our understanding of sweetpotato’s origin.

Polyploid breeding strategies for developing hop cultivars in New Zealand

The main objective of the New Zealand hop breeding programme is to develop triploid cultivars with unique brewing properties. Created from crosses between diploid and tetraploid parents, these genotypes have the advantage of being seedless as well as high yielding. Population improvement procedures are used independently for both diploid and tetraploid populations. Restricted maximum likelihood statistical procedures are used for the selection of both male and female genotypes for tetraploid and diploid parental material. In this regard, particular emphasis is placed on identifying sexually derived tetraploids to widen the gene pool. Crosses using tetraploids, as both female and male parents, hybridised with diploid genotypes, are described. Gender segregation ratios from recent triploid seedling populations vary considerably. The statistical analysis of triploid seedling female genotypes from these populations for several key traits is presented. A summary of main chemistry features of New Zealand bred polyploid cultivars is presented. Future breeding strategies for triploid hops are discussed.

An update to the Canadian range, abundance, and ploidy of Camelina spp. (Brassicaceae) east of the Rocky Mountains

The distribution and abundance of three Camelina species introduced to Canada is unknown, but critical for evaluating the risks associated with unconfined release of transgenic Camelina sativa (L.) Crantz (2n = 40). Furthermore, previous reports suggest Canadian populations of Camelina microcarpa Andrz. ex DC. vary for ploidy and ability to hybridize with C. sativa. We completed 8 weeks of field work in Alberta, Saskatchewan, Manitoba, southern Ontario, Quebec, and the Maritimes. We determined the ploidy composition of the populations found. We did not locate Camelina alyssum (Mill.) Thell., but located four sites with C. sativa and 34 with C. microcarpa. Eleven C. microcarpa populations were tetraploid (2n = 26, 1.00pg/2C) and 22 were hexaploid (2n = 40, 1.50pg/2C), while two populations were mixed. We examined material from botanical gardens and plant gene resource centres assessing total nuclear DNA content and completing chromosome counts for each species and cytotype identified, to determine whether tetraploid and hexaploid C. microcarpa were included in these collections. No tetraploid material was included in the C. microcarpa accessions received; however, a diploid (2n = 12, 0.54pg/2C) was found. Given the current geographic ranges, abundance, and chromosome counts of these species, the greatest risk of hybridization with transgenic C. sativa is from hexaploid C. microcarpa.

The Rpi‐blb2 gene from Solanum bulbocastanum is an Mi‐1 gene homolog conferring broad‐spectrum late blight resistance in potato

The necessity to develop potato and tomato crops that possess durable resistance against the oomycete pathogen Phytophthora infestans is increasing as more virulent, crop-specialized and pesticide resistant strains of the pathogen are rapidly emerging. Here, we describe the positional cloning of the Solanum bulbocastanum-derived Rpi-blb2 gene, which even when present in a potato background confers broad-spectrum late blight resistance. The Rpi-blb2 locus was initially mapped in several tetraploid backcross populations, derived from highly resistant complex interspecific hybrids designated ABPT (an acronym of the four Solanum species involved:S. acaule, S. bulbocastanum, S. phureja and S. tuberosum), to the same region on chromosome 6 as the Mi-1 gene from tomato, which confers resistance to nematodes, aphids and white flies. Due to suppression of recombination in the tetraploid material, fine mapping was carried out in a diploid intraspecific S. bulbocastanum F1 population. Bacterial artificial chromosome (BAC) libraries, generated from a diploid ABPT-derived clone and from the resistant S. bulbocastanum parent clone, were screened with markers linked to resistance in order to generate a physical map of the Rpi-blb2 locus. Molecular analyses of both ABPT- and S. bulbocastanum-derived BAC clones spanning the Rpi-blb2 locus showed it to harbor at least 15 Mi-1 gene homologs (MiGHs). Of these, five were genetically determined to be candidates for Rpi-blb2. Complementation analyses showed that one ABPT- and one S. bulbocastanum-derived MiGH were able to complement the susceptible phenotype in both S. tuberosum and tomato. Sequence analyses of both genes showed them to be identical. The Rpi-blb2 protein shares 82% sequence identity to the Mi-1 protein. Significant expansion of the Rpi-blb2 locus compared to the Mi-1 locus indicates that intrachromosomal recombination or unequal crossing over has played an important role in the evolution of the Rpi-blb2 locus. The contrasting evolutionary dynamics of the Rpi-blb2/Mi-1 loci in the two related genomes may reflect the opposite evolutionary potentials of the interacting pathogens.

In vitro chromosome-doubling in tulip (Tulipa gesneriana L.)

SummaryMost current tulip cultivars are diploid (2n = 24), some are triploid (Darwin Hybrids) and there are some rare tetraploid cultivars. Crosses between diploids are generally successful, but crosses between diploid cultivars and tetraploid selected species often fail, which constitutes a major obstacle to broadening of the genetic base. Our objective was thus to develop a method to obtain tetraploid material from diploid genotypes using a stem-disc regeneration process and the chromosome-doubling agent oryzalin, applied in different ways. Tetraploid clones were obtained from all treatments and from all cultivars tested. The final yield of tetraploids was low (0 – 3.75 tetraploids for one treated flower stem), but was sufficient to initiate crossing experiments between diploid and tetraploid progenitors to obtain triploid offspring.A genotypic effect was observed during the regeneration process.The cultivars ‘Lucky Strike’ and ‘Gander’ were more responsive in vitro than cvs. ‘Lustige Witwe’ and ‘Don Quichotte’. However, the percentage of tetraploid clones finally obtained was not influenced by genotype or by the way in which oryzalin was applied.

Inter-intraspecific variation of chloroplast DNA of European Plantago spp.

Inter- and intraspecific chloroplast DNA variation in four species of Plantago (P. lanceolata, P. major, P. media and P. coronopus) were analysed by comparing DNA fragment patterns produced by seven restriction endonucleases. Plant material was collected in seven European countries. Only 21.3 per cent of the 409 restriction sites were shared by all four species. Phylogenetic analysis, performed by constructing the most parsimonious trees, showed that genetic differentiation in cpDNA was very high among P. lanceolata, P. coronopus and the species pair P. media and P. major, which were more closely related. At the intraspecific level, four restricted site mutations were detected. Most of the variation was due to numerous small length mutations, one of which (70 bp) discriminated between the two subspecies of P. major (i.e. ssp. major and ssp. pleiosperma). This mutation was used successfully to show that, in Denmark, cpDNA introgression occurs from pleiosperma into major in the areas where the two subspecies grow together, whereas previous studies of the same subspecies in the Netherlands suggested introgression in the reverse direction. In P. lanceolata, five distinct types of cpDNA genome could be distinguished, one of these being widely distributed. Therefore, DNA variation was present both between and within populations. In P. media, three distinct cpDNA genomes were found, one being specific to diploid and tetraploid material from the Pyrenees, suggesting multiple origins of the autotetraploids in this species. Whereas cpDNA variation was observed in the two outcrossing species of Plantago (P. media and P. lanceolata) no variation was detected in the two autogamous subspecies of P. major. This suggests that chloroplast DNA variation may be related to nuclear genome diversity.

Genetic analysis of photosynthetic variation in hexaploid and tetraploid wheat and their interspecific hybrids

Intra- and inter-specific variation in CO2 assimilation rate (A) in Triticum spp. is well documented for reproductive growth stages. Research was conducted to characterize early vegetative photosynthetic variation in a diverse set of cultivated hexaploid wheat (T. aestivum L.) germplasm and in wild tetraploid (T. dicoccoides Korn) and hexaploid x tetraploid populations. Choice of hexaploid genotypes was based on maximum genetic distance between cultivars within the HRW and SRW wheat classes of the USA. The tetraploid material was produced by hybridizing two accessions of T. dicoccoides previously shown to differ widely in A and A/Chl but with similar leaf morphology. Genetic variability in the HRW and SRW gene pools was attributed to more recently developed descendent lines and unrelated lines rather than parental lines. Phenotypic distributions for A, stomatal conductance (gs), and internal CO2 concentration (Ci) in the F2 tetraploid population were continuous and showed transgressive segregation, reflecting quantitative inheritance with intermediate heritability. Variability in A was not associated with chlorophyll content or CO2 supply to the mesophyll measured as Ci. Genetic variability in A was also observed in the interspecific backcross population, 2*TAM W-101/PI 428109, thereby providing a germplasm pool to select for high A while restoring the D genome of hexaploid wheat. These results suggest that genetic improvement of vegetative assimilation rate is feasible in hexaploid wheat via homologous transfer from an alien source.

C-Glycosylxanthones in Diploid and Tissue Culture-Induced Autotetraploid Davallia fejeensis

Rhizome tips (about 2 cm long) of diploid Davallia fejeensis were collected in the Enid A. Haupt Conservatory of the New York Botanical Garden, cleaned, rinsed in tap water and further trimmed. Voucher specimens are at NY. Explants (6-8 mm long) were cultured on 1% agar-gelled sterile nutrient medium of Knudson as modified by Steeves et al. (1955) and supplemented with 2% sucrose in order to provide control diploid sporophytes growing in axenic culture. Roots, leaves, and rhizomes of the resulting plants were excised and induced to differentiate into aposporous diploid gametophytes. Stock cultures of diploid gametophytes were multiplied and further grown on liquid media supplemented with 0.6% agar to effect fertilization and raise tetraploid sporophytes. Tetraploid gametophytes were isolated from this tissue culture-induced tetraploid material by repeating the procedure followed at the diploid level. In this way, both diploid and tetraploid sporophytes and gametophytes were made available for this study. Phenolic compounds were isolated by two-dimensional paper chromatography of an 80% methanol extract of green material in t-BuOH-HOAc-H20, 3:1:1 (TBA) and 15% aqueous acetic acid (HOAc), followed by one-dimensional paper chromatography in water. C-glycosylxanthones appeared as orange compounds in ultraviolet light and turned yellow when fumed with ammonia. Both purified compounds were co-chromatographed with mangiferin and isomangiferin isolated from Asplenium montanum Willd. (Bozeman & Radford 11552, NY). Rf values in TBA, BAW, HOAc, and H20 were: mangiferin, 0.31, 0.43, 0.43, 0.12; isomangiferin, 0.19, 0.29, 0.23, 0.04; Asplenium mangiferin, 0.34, 0.42, 0.42, 0.11; Asplenium isomangiferin, 0.21, 0.32, 0.23, 0.03; and rutin standard, 0.43, 0.45, 0.56, 0.25. The BAW and HOAc values are very similar to those of Smith and Harborne (1971), but the TBA and HOAc values differ from those of Markham and Wallace (1980). Absorption spectra (MeOH, nm) were: mangiferin, 232, 260, 270sh, 310, 364; isomangiferin, 240, 258, 270sh, 312, 365. The compounds were unaffected by acid hydrolysis (1 hr, 2N HC1, 100?C).

Autotetraploidy in caraway (Carum carvi L.) for the increase of the aetheric oil content of the seed

An autotetraploid population of caraway (Carum carvi L.) was produced by treating the growing points of young plants with a 0.2% colchicine solution. Selection on morphology, pollen size and pollen shape, followed by a selection on seed size proved to be an effective way to identify the mixoploid C0 plants. Three percent of the treated plants produced a tetraploid progeny. Moderate selection in the C1 and the C2 population resulted in an improvement of the average seed-set to the amount of 50% of the diploid control, with a range of 21–78%. The 1000-kernel weight of the tetraploid material was 7 g, compared to 3 g in the diploid control. The oil content of the autotetraploid seed was increased with 35.6%; the increase in carvone amounted to 6.9%. The results of the experiment indicate that breeding work in autotetraploid caraway may result in a new cultivar.

Cytogenetical Studies on Ecological Races of <i>Mecardonia dianthera</i> (SW) Pennel

Mecardonia dianthera, a Scrophulariaceous weed of Tropical America comprises of two edaphic ecotypes viz. erect and repent. While the former is a facultative calcicole, the latter is an obligate calcifuge. The present paper gives an account of plant performance and cytological behaviour of colchicine induced tetraploids that were produced by treating the inbred lines of these plants with 0.3% colchicine for 12 hours. Majority of the surviving plants were tetraploids exhibiting a slower growth delayed phenological events, deep green thick green rough foliage, increased dry matter production, enlarged epidermal and mesophyll cells, chloroplast, stomatal apparatus and frequency, pollen grains and a reduced seed viability than that of the diploids. While repent ecotype tetraploids had increased flower number per plant than that of the diploids, reverse was observed in the erect ecotype tetraploids.At metaphase I, uni, bi, tri, tetra and hexa-valents in a varying frequency were observed in the colchiploids and the total number of multivalent associations and univalents per PMC on an average was equal in the tetraploids of each ecotype. This indicates a competition for pairing between homologous chromosomes which is supported by the fact that a significant positive correlation between chiasma frequency and multivalent formation was also observed. However, the colchiploids of the erect ecotype possessed greater number of multivalents and univalents than those of the repent ecotype colchiploids. Further stages of meiosis in the colchi-ploids were abnormal and resembled the typical autoploid meiois. Multiple spindles, complement fractionation and secondary association were also observed. The contribution of univalents and multivalents in inducing pollen sterility in the tetraploid material is significant. Attempts to cross these colchiploids with diploids produced non-viable abortive seeds. Artificial crossings amongst these colchiploids resulted in an early degeneration of the ovary and a failure of the seed formation. Natural self pollination yielded 5-9% of seeds that died after an extrusion of radicle when germinated.The study indicated that the two edaphic ecological races (ecotypes) exhibit a differential susceptibility to colchicine in relation to frequency of induced polyploids, morphological and reproductive features, number and frequrncy of chromosomal associations and univalents, pollen and seed fertility. However, a general agreement in having a morphological gigas, slowed growth rate, delayed phenological events and reduced reproductive capacity occurs in the tetraploids in comparison to the diploid progenitors, of both the ecotypes. A tendency to change the plant form (repent erect), which is governed by a single gene, was not observed, indicating thereby that the gene remains uneffected by the drug, in both the ecological races of M. dianthera.

Crosses between Beta intermedia bunge and B. vulgaris L.

A tetraploid annual male sterile form of Beta vulgaris L. (2n=4x=36) was crossed with the wild beet species Beta intermediaBunge (2n=36). The resulting F1-plants were male sterile annuals being two or three times back-crossed to diploid and tetraploid sugar and fodder beets in the next years. Apart from tetraploid material (36 chromosomes) hexaploid (54 chromosomes) and a number of aneuploid plants developed.

Fertilization with irradiated pollen in Tradescantia

Flowers of diploid and tetraploid material of Tradescantia paludosa were pollinated with irradiated pollen. X-ray exposures of 1, 5, 10, 50 and 150 kR as well as gamma ray exposures of 500 kR from Co 60 were used. The flowers were fixed in Carnoy 1–56 hr and 3–15 days after pollination. At all the exposures studied the pollen was capable of germinating on the stigmas and the tubes were able to grow down to and penetrate the embryo sacs. In the pollen tube mitoses the following abnormalities were seen: chromosome stickiness, bridges and fragments. After exposures of 1–5 kR two sperm nuclei of equal or unequal size were formed, and these were not accompanied by fragments or connected by bridges. After exposures of 10–50 kR the sperm chromatin was highly variable and the following types were seen: undivided generative nuclei, two sperm nuclei of equal or unequal size with or without extra nuclear fragments and free or connected by bridges. After exposures of 150–500 kR undivided generative nuclei with or without nuclear fragments were found. The same types of nuclei were found in pollen tubes that had entered the embryo sac and their fusion with the female nuclei could be observed. Largely as a consequence of the differences in type of the male chromatin, the following different types of fertilization were observed, ( a) Both the egg nucleus and the polar nuclei are fertilized by sperm chromatin from one or two pollen tubes, ( b) Fertilization of only the egg nucleus or only the polar nuclei occurs, the other of these two kinds of female nuclei remaining unfertilized. The following types were observed with respect to nuclear fusion, ( a) A normal fusion as in untreated material (1–500 kR). ( b) Nuclear fusion occurs but the normal changes in chromatin structure of the zygote nucleus do not occur (150–500 kR). Most of these nuclei do not divide, but a few do. ( c) Nuclear fusion does not occur but the male chromatin is appressed to the female nucleus, which may sometimes be stimulated to start DNA synthesis and division (150–500 kR).

DOSAGE EFFECTS OF THE LANCEOLATE GENE IN TOMATO

In contrast to the odd‐pinnately compound leaf of the normal (+/+) tomato plant (Lycopersicon esculentum), the single‐gene mutant lanceolate (La/+) generally has a simple leaf. Lanceolate plants, also, have small fruits and flowers, weak apical dominance, and exhibit variation in the position and fusion of cotyledons. Homozygous mutants (La/La) appear in 3 different phenotypes, 1 of which, narrow, has narrow simple leaves, sterile inflorescences, and extremely weak apical dominance. The other 2, modified, and reduced, lack an organized shoot. After selfing La/ + plants for 9 generations, autotetraploids were produced with the aid of colchicine. In addition, several triploid plants arose spontaneously. The study of diploid, triploid, and tetraploid material with various proportions of the La allele revealed in many characters a graded series as a function of the La dosage. With increasing La dose, there was a gradual reduction in: (1) total leaf length; (2) the number and size of primary and secondary lateral leaflets; (3) the number and size of marginal lobes of the terminal leaflet, associated with an increase in the proportional length of the terminal leaflet. Many leaves were found with the basal lobes of the terminal leaflet resembling incompletely separated lateral leaflets. The differences in leaf shape between different genotypes came about before the leaf primordium was 3 mm long. There was a progressive delay in the initiation of lateral primordia with increasing La dosage. It is proposed that the gradual changes from compound to simple leaves with increasing La dosage are produced by successively greater restrictions of meristematic activity after the terminal leaflet is formed. With increasing proportion of La alleles, the reproductive structures showed: (1) a decrease in the number of flowers per inflorescence; (2) a decrease in the length of the sepals; (3) an increase in the proportion of flowers with dialytic anthers. Dialytic anthers had narrow adaxial lobes and were frequently twisted along their main axes. The common denominator for most trends affected by the La allele seems to be a general reduction of growth, but more so in lateral than in longitudinal growth. Histological data suggest that the reduction in lateral growth is mainly brought about by a reduction of cell division in lateral meristems.

The creation of tetraploid beets

The purity of the tetraploid material may decrease through various causes. In the first place foreign monoploid pollen exerts a detrimental influence because it has a greater germination energy and a greater mobility than diploid pollen. A good impression of the purity can be obtained by cytologically investigating the C2 of a few beets from an isolated plot. For this purpose seed is sown out in the greenhouse in winter and at least 25 plants of the C2 of some beets per plot are investigated. By taking care that material of early flowering and late flowering beets is disposed of, a sufficiently reliable impression of the purity of the tetraploid progeny can be obtained. The result of the cytological checking which was carried out in the winter of 1952/53, was disappointing. That a single aberrant beet can exercise a detrimental influence was proved in the varietyAlpha when an aberrant plant was not rejected. The number of non-tetraploids of this beet was much greater, while in a neighbouring plant 30% triploids were present on investigation. It is important that cytological investigation of further generations of the tetraploid material be continued because otherwise the material will soon become very impure. Finally it should be mentioned that the influence of early bolters was insignificant because of a different flowering time and that the occurrence of “break down” could not be established.