Tetraploid Seedlings Research Articles

Phylogenomics identifies parents of naturally occurring tetraploid bananas

BackgroundTriploid bananas are almost sterile. However, we succeeded in harvesting seeds from two edible triploid banana individuals (Genotype: ABB) in our conservation repository where various wild diploid bananas were also grown. The resulting rare offspring survived to seedling stages. DNA content analyses reveal that they are tetraploid. Since bananas contain maternally inherited plastids and paternally inherited mitochondria, we sequenced and assembled plastomes and mitogenomes of these seedlings to trace their hybridization history.ResultsThe coding sequences of both organellar genomic scaffolds were extracted, aligned, and concatenated for constructing phylogenetic trees. Our results suggest that these tetraploid seedlings be derived from hybridization between edible triploid bananas and wild diploid Musa balbisiana (BB) individuals. We propose that generating female triploid gametes via apomeiosis may allow the triploid maternal bananas to produce viable seeds.ConclusionsOur study suggests a practical avenue towards expanding genetic recombination and increasing genetic diversity of banana breeding programs. Further cellular studies are needed to understand the fusion and developmental processes that lead to formation of hybrid embryos in banana reproduction, polyploidization, and evolution.

Autotetraploid Induction of Three A-Genome Wild Peanut Species, Arachis cardenasii, A. correntina, and A. diogoi.

A-genome Arachis species (AA; 2n = 2x = 20) are commonly used as secondary germplasm sources in cultivated peanut breeding, Arachis hypogaea L. (AABB; 2n = 4x = 40), for the introgression of various biotic and abiotic stress resistance genes. Genome doubling is critical to overcoming the hybridization barrier of infertility that arises from ploidy-level differences between wild germplasm and cultivated peanuts. To develop improved genome doubling methods, four trials of various concentrations of the mitotic inhibitor treatments colchicine, oryzalin, and trifluralin were tested on the seedlings and seeds of three A-genome species, A. cardenasii, A. correntina, and A. diogoi. A total of 494 seeds/seedlings were treated in the present four trials, with trials 1 to 3 including different concentrations of the three chemical treatments on seedlings, and trial 4 focusing on the treatment period of 5 mM colchicine solution treatment of seeds. A small number of tetraploids were produced from the colchicine and oryzalin gel treatments of seedlings, but all these tetraploid seedlings reverted to diploid or mixoploid states within six months of treatment. In contrast, the 6-h colchicine solution treatment of seeds showed the highest tetraploid conversion rate (6-13% of total treated seeds or 25-40% of surviving seedlings), and the tetraploid plants were repeatedly tested as stable tetraploids. In addition, visibly and statistically larger leaves and flowers were produced by the tetraploid versions of these three species compared to their diploid versions. As a result, stable tetraploid plants of each A-genome species were produced, and a 5 mM colchicine seed treatment is recommended for A-genome and related wild Arachis species genome doubling.

Manipulation of ploidy for blueberry breeding: in vitro chromosome doubling of diploid Vaccinium duclouxii (Lévl.) Hand.-Mazz by trifluralin

The diversification, evolution, domestication, and breeding of many plant species have all been greatly aided by polyploidization. In this study, we reported a successful induction of autotetraploids of Vaccinium duclouxii (Lévl.) Hand.-Mazz, which was an important germplasm for developing highbush blueberry cultivars. The isolated stems of V. duclouxii were soaked in different concentrations of trifluralin solution, and then the ploidy of the seedlings sprouted from stems were identified by flow cytometry and chromosome counting analyses. The optimal condition for inducing tetraploid of V. duclouxii leaf bud was 0.002 % trifluralin for 48 h, which the induction rate reached 8.33 %. The morphological and anatomical characteristics of induced tetraploid seedlings were significantly different from those of the original diploid plants. The average stem diameter, leaf length, leaf width, and leaf thickness of the tetraploid plants showed significantly larger and thicker compared with the diploid progenitor plants. The stomata number of lower epidermis on the tetraploid seedling leaves only was 64.20 % of the diploid progenitors’, while the average stomatal area was increased by 166.67 %. In addition, the length and width of guard cells were 128.57 % and 141.18 % of its diploid progenitor, separatively, and the chloroplast numbers were in guard cells increased by 157.36 %. The main leaf vein diameter, the upper epidermal thickness, palisade tissue and sponge tissue of induced tetraploid leaves were all significantly increased in comparison to its diploid progenitor, indicating that these indexes can be used for screening tetraploid seedlings during breeding program.

Mutagenic effects of nitrogen protoxide and oryzalin on "41 B" and "Fercal" grapevine rootstocks seedlings.

In this study, the mutagenic effects of different doses and exposure times of oryzalin and Nitrogen Protoxide (N2O) were tested for stimulating polyploid on 41 B and Fercal grapevine rootstocks seedlings. Ploidy changes were examined by morphological, cytological, macroscopic, and microscopic methods. Leaf thickness, chlorophyll contents, stomatal sizes, and chloroplast numbers of polyploid seedlings stimulated with mutagens increased but their stomatal densities decreased. Flow cytometry (FC) analyses were performed on 50 samples selected by morphological and microscopic preliminary determinations. In FC analyses, 1 tetraploid seedling and 4 mixoploid seedlings from Fercal offspring and 1 mixoploid seedling from 41 B offspring were verified. The nuclear DNA content of tetraploid and mixoploid seedlings were increased by 2.00 and 1.34-fold, respectively, when compared to their diploid parents. Chromosome counts in root tip samples propagated in vitro from the tetraploid Fercal offspring confirmed a 2-fold increase compared to the diploid parent. In polyploidy induction studies, it was deemed appropriate to use FC analysis and chromosome count together to confirm the ploidy levels of mutants. Oryzalin and N2O applications at different doses and exposure times were found to be effective for inducing polyploidy in 41 B and Fercal grapevine rootstocks.

Induction and identification of tetraploids of pear plants (Pyrus bretschneideri and Pyrus betulaefolia)

Polyploid plants usually exhibit broader leaves, thicker stems, bigger flowers and fruits, dwarfing stature, as well as improved biotic and abiotic resistance. Therefore, increasing the polyploidy is one of the most important strategies used in plant breeding. Here, we reported the successful induction of tetraploids of two pear varieties, ‘duli’ pear (Pyrus betulaefolia), a wildtype pear used for rootstocks in grafting, and ‘Xinli No.7′ pear (Pyrus bretschneideri), a popular cultivated pear variety in China. This was achieved by treating their seeds, shoot tips of tissue cultured or field grown seedlings with colchicine and pendimethalin using three different methods: impregnation, mixed culture and smearing. The best tetraploids induction condition for ‘duli’ pear seeds was impregnating them with 0.4% colchicine for 24 h where the mutation rate of 2.0% was achieved with no chimera found. For shoot tips of tissue cultured seedlings the best condition was impregnating them with 0.2% colchicine where 6.67% of ‘duli’ (48 h) and 13.0% of ‘Xinli No.7′ (24 h) were mutated. In addition, we found that in the mixed culture method the best induction condition for ‘duli’ was mixing with 1.0% colchicine while for ‘Xinli No.7′ it was 0.5% colchicine. In the smear method, for the shoot tips of field grown seedlings of ‘duli’, the best induction condition was treating them with 0.4% colchicine for 24 h. Subsequently, the DNA content of these putative polyploid seedlings was estimated by the flow cytometry, confirming their ploidy nature. Also, we compared the morphological differences between the tetraploid seedlings and the diploid seedlings. Obviously, the tetraploid seedlings appeared to be dwarfed with shorter internode length and reduced internode number of their stems.

Tetraploidy in Citrus wilsonii Enhances Drought Tolerance via Synergistic Regulation of Photosynthesis, Phosphorylation, and Hormonal Changes.

Polyploidy varieties have been reported to exhibit higher stress tolerance relative to their diploid relatives, however, the underlying molecular and physiological mechanisms remain poorly understood. In this study, a batch of autotetraploid Citrus wilsonii were identified from a natural seedling population, and these tetraploid seedlings exhibited greater tolerance to drought stress than their diploids siblings. A global transcriptome analysis revealed that a large number of genes involved in photosynthesis response were enriched in tetraploids under drought stress, which was consistent with the changes in photosynthetic indices including Pn, gs, Tr, Ci, and chlorophyll contents. Compared with diploids, phosphorylation was also modified in the tetraploids after drought stress, as detected through tandem mass tag (TMT)-labeled proteomics. Additionally, tetraploids prioritized the regulation of plant hormone signal transduction at the transcriptional level after drought stress, which was also demonstrated by increased levels of IAA, ABA, and SA and reduced levels of GA3 and JA. Collectively, our results confirmed that the synergistic regulation of photosynthesis response, phosphorylation modification and plant hormone signaling resulted in drought tolerance of autotetraploid C. wilsonii germplasm.

Effect of medium composition, genotype and age of explant on the regeneration of hexaploid plants from endosperm culture of tetraploid kiwiberry (Actinidia arguta)

Endosperm, an ephemeral and storage tissue, serves as a source of nutrition and protection during embryo development and germination. It can be used for the cultivation of polyploid plants in vitro. Here, results of plant regeneration and acclimatization from the endosperm-derived calli of four cultivars of Actinidia arguta has been presented. Seeds excised from fresh fruit and dry seeds stored for one year served as the sources of endosperm explants of selected tetraploid cultivars of A. arguta. Callus Induction Medium (CIM; containing 0.25, 0.5, or 1 mg/l of TDZ) and Actinidia Endosperm Medium (AEM; containing 2 mg/l of 2,4-D and 5 mg/l of kinetin) were used to study the organogenic responses of the calli. On AEM, the source of explant did not significantly affect the rate of callus induction for any of the tested cultivars; no organogenic events were observed. In contrast, on CIM both the source of explants and the cultivar origin caused significant differences in callus formation and subsequent organogenic events. Histological and ultrastructural analyses revealed the adventitious nature of shoot bud formation on these media. The most efficient elongation of shoot buds was achieved after transferring organogenic calli with adventitious shoot buds to a medium supplemented with zeatin or meta-topolin. Robust root induction with minimal basal callus formation occurred on the medium with indole-3-acetic acid. Flow cytometric analysis revealed that the nuclear DNA content in the leaves of some regenerants was approximately 50 % higher (4.5 pg/2C) than that in leaves from the tetraploid seedlings (3.1 pg/2C),which confirmed that those regenerants originated from the endosperm. The regeneration of such hexaploid plants was more efficient when endosperm from fresh seeds served as an explant; therefore, fresh rather than dry seeds are recommended for endosperm-derived plant production. The hexaploid plants of A. arguta can serve as an important source of breeding material.

Physiological and molecular responses of the root system of indica–japonica intersubspecific tetraploid rice seedlings to ion beam stress

Low-energy ion beam bombardment can induce various biological effects on plants, including stimulation, damage, and mutation. However, the physiological and molecular mechanisms of the stress effects of indica–japonica intersubspecific tetraploid rice seedlings roots in response to ion implantation are not fully understood. In this work, indica–japonica intersubspecific tetraploid rice seeds were implanted with different doses of ion beam to explore the responses of their seedling roots. The investigation found that that high-dose ion implantation significantly reduced the total root length, root surface area, total root volume and root tips number, significantly increased MDA content in roots, and interfered with the expression level of IAA biosynthesis and transport related genes. Under low-dose radiation, the antioxidant enzyme activity in the roots of intersubspecific tetraploid rice increased significantly compared with the control, and remained at a high level during 5–15 days of culture, without significant change. Meanwhile, the expression of IAA biosynthesis and transportation related genes were up-regulated, and the IAA content was significantly increased, which was 20.12% higher than that of the control, which finally made the root activity significantly higher than that of the parents. The aforementioned results will be useful for further research on the physiological and molecular mechanisms of indica–japonica intersubspecific tetraploid rice seedlings roots to ion beam stress.

Production of doubled-haploid(DH) selfed-progenies in ‘Banpeiyu’ pummelo [Citrus maxima (Burm.) Merr.] and its genetic analysis with simple sequence repeat markers

The genetic analysis of five haploid plants (BX1-BX5) of ‘Banpeiyu’ pummelo (BP), [Citrus maxima (Burm.) Merr.] using 32 simple sequence repeat (SSR) markers carried out for the purpose of confirming their gynogenetic origin and genetic differences. As the results, all the haploid plants possessed only either one of the BP alleles, confirming that they are gynogenetic origin. We also confirmed that BX1 and its doubled haploid (BX1-DH) have exactly the same SSR alleles. Interestingly, all the five haploids had common alleles on the linkage group (LG) 6 in the case of three markers. Then, we performed self-pollination of DH plants and reciprocal crosses between DH and BP, which has strong self-incompatibility. The seeds obtained by these crosses germinated in vitro or ex vitro normally and developed into diploid seedlings, except for one tetraploid seedling. Genetic analysis of these seedlings with 32 SSR markers revealed that segregation ratios of the 32 loci in the 30 BP inbred, 30 BP x DH and 30 DH x BP progenies mostly fitted to the expected ratios. However, significantly distorted segregation ratios were found in one, five and three SSR markers for BP inbred, BP x DH and DH x BP progenies, respectively. All of the 30 DH inbred progenies showed exactly the same SSR alleles as the original DH. This is the first example in which self and back cross progenies of DH in fruit crops were genetically analyzed using SSR markers.

Polyploidy induction in Physalis alkekengi

Physalis alkekengi is an ornamental plant that can also be used as a medicinal plant due to its anti-inflammatory, bactericidal, antitumor and fungicidal properties. Polyploidization can be an important tool in the genetic improvement of this species. The objective this work was to obtain tetraploids in vitro and to evaluate the phytotechnical traits of P. alkekengi. For this, nodal segments of P. alkekengi var. Franchettii were inoculated into petri dishes containing 100 ml of MS medium supplemented with colchicine at concentrations 0; 0.04; 0.08; 0.12; and 0.16% and kept in the dark for 24 and 48h. After the respective treatment periods with colchicine the segments were inoculated into test tubes. The tetraploids were identified by flow cytometry and classical cytogenetics. In vitro seedlings were measured: root length, nodal segment length, leaflet number and total leaf area. In the acclimatization phase, the area of ​​the second leaf and total leaf, petiole radius, stem length, fruit weight with calyx, without calyx, fruit diameter, number of seeds and brix of the pulp were evaluated. Chlorophyll a, chlorophyll b, total chlorophyll, total carotenoid, total chlorophyll / total carotenoid ratio and chlorophyll a / b ratio were also estimated. The treatment that most produced tetraploid seedlings was with 0.08% colchicine per 24h. No significant difference was observed in 7 (seven) variables, these being all variables of photopigments, stem diameter (steam) and brix. In general, diploid (2x) plants were better in 9 (nine) while tetraploid seedlings were better in 6 (six) of the phytotechnical variables. It was concluded that the MS medium supplemented with 0.08% colchicine for 24 h allowed P. alkekengi tetraploides to be obtained with better phytotechnical qualities.

Polyploidy affects the seed, dormancy and seedling characteristics of a perennial grass, conferring an advantage in stressful climates.

Polyploidy (the state of having more than two genome copies) is widely distributed in flowering plants and can vary within species, with polyploid races often associated with broad ecological tolerances. Polyploidy may influence within-species variation in seed development, germination and establishment. We hypothesized that interactions between polyploidy and the seed developmental environment would affect subsequent dormancy, germination and early growth traits, particularly in stressful environments. Using seeds developed in a common garden under ambient and warmed conditions, we conducted germination trials under drought and temperature stress, and monitored the subsequent growth of seedlings. The study species, Themeda triandra, is a widespread, keystone, Australian native grass and a known polyploid complex. Tetraploid plants produced heavier, more viable seeds than diploids. Tetraploids were significantly more dormant than diploids, regardless of seed developmental environment. Non-dormant tetraploids were more sensitive to germination stress compared to non-dormant diploids. Finally, tetraploid seedlings were larger and grew faster than diploids, usually when maternal plants were exposed to developmental temperatures atypical to the source environment. Seed and seedling traits suggest tetraploids are generally better adapted to stressful environments than diploids. Because tetraploid seeds of T.triandra are more dormant they are less likely to germinate under stress, and when they do germinate, seedling growth is rapid and independent of seed developmental environment. These novel results demonstrate that polyploidy, sometimes in interaction with developmental environment and possibly also asexuality, can have within-species variation in seed and seedling traits that increase fitness in stressful environments.

Polyploidization enhances photoprotection in the first stages of Mangifera indica

The only documented tetraploid mango to date opens new options for a mango breeding programme. Gas exchange parameters, chlorophyll fluorescence, composition of photosynthetic pigments and tocopherol contents were analysed in mango with two ploidy levels (diploid and tetraploid). Additionally, putative changes with age in photosynthetic performance were monitored in two-year old seedlings and in thirteen-year old adult trees. Daily course measurements exhibited significant age-related differences with higher photosynthetic rates (Pn) in adult individuals (maximum mean value of 7.5 ± 0.25 μmol m−2 s−1). Tetraploid seedlings presented higher Pn values (5.9 ± 0.24 μmol m−2 s−1) than diploids (5 ± 0.21 μmol m−2 s−1) but these initial differences disappeared with age. These individuals maintained a higher maximum photochemical efficiency, reducing the chlorophyll content and increasing violaxanthin, as well as α- and δ-tocopherol at midday. This advantage could confer an improvement in the establishment of plants in their first stages, which is not required in adult trees.Polyploidization thus improves the response to high light intensity in the first stages of mango by optimizing photoprotection mechanisms. These results may contribute to enhance the establishment of the crop setting a baseline for future mango breeding programmes.

Genetic diversity and karyotype of Pitcairnia azouryi: an endangered species of Bromeliaceae endemic to Atlantic Forest inselbergs.

Plant species of various families, such as those of Bromeliaceae, occur on inselbergs where they are subject to geographic isolation and environmental conditions that can lead to genetic erosion. This, in turn, can result in the loss of natural populations due to homozygosis, or changes in ploidy that may lead to reproductive isolation. The genetic diversity of five natural populations of Pitcairnia azouryi was measured using nine microsatellite markers transferred from P. albiflos and P. geyskesii. Chromosome numbers and nuclear DNA content were also evaluated. The results indicated moderate genetic differentiation among populations (FST = 0.188), and significant gene flow (Nm = 1.073) in four of the five populations. P. azouryi has, predominantly, 2n = 50 chromosomes and DNA content of 2C = 1.16pg, but the tetraploid condition was found (2n = 100 and 2C = 2.32pg) in seedlings of an individual of the most geographically isolated population. The moderate level of genetic structuring observed for P. azouryi seems to be related to its disjoint geographical distribution and the locally aggregated spatial structure of the populations, which are isolated from each other, hindering the inter and intrapopulational gene flow. This interpretation was also evidenced by the mantel test (r = 0.777, P < 0.05). The occurrence of diploid individuals with tetraploid seedlings is indicative of events of eupolyploidization, possibly due to the environmental conditions of this geographically isolated population.

Developing polyploid genotypes of Leptospermum scoparium

ABSTRACTLeptospermum scoparium (‘Mānuka’) is native to New Zealand and South Eastern Australia. Throughout this range the species typically exists as a diploid. Only a single tetraploid accession has ever been reported and all the polyploid cultivars currently available are derivatives of that plant. Polyploidy in other species is known to influence vegetative and floral form, phenology and fertility. Floral diameter was therefore measured for the tetraploid L. scoparium ‘Keatleyi’, the triploid L. scoparium ‘Martinii’ and three diploid seedlings. The floral diameters of the tetraploid and triploid were significantly greater than those from diploid plants. However, the diploid flowers were also significantly different from each other, indicating that factors other than polyploidy influence this trait. Additionally, given the very limited number of polyploid clones available, methods were tested to generate more tetraploid plants for future study. Colchicine was effective at producing tetraploid seedlings with 6 mg/ml, the highest concentration tested, yielding the largest number of tetraploids. This method is now being used to generate tetraploids from a range of L. scoparium material.

Variation in ploidy level and morphological traits in the progeny of the triploid apple variety Jonagold

Variation with respect to both ploidy level and morphology was characterized for a set of 690 seedlings of the triploid apple variety Jonagold, of which 481 were obtained via in vitro culture of mature embryos, and 209 via conventional germination. Their ploidy level was determined by a combination of flow cytometry and root tip chromosome counting. The assessed morphological traits were leaf length, width and shape, stomatal density, guard cell length and chloroplast width and number. A total of 452 seedlings were aneuploid, 225 diploid, nine triploid and four tetraploid. All four tetraploid seedlings were derived by in vitro culture. When the triploid seedlings were genotyped at the S-locus and at selected microsatellite loci, we found that the Jonagold stigma was compatible with pollen which shared some of the maternal parent S-locus alleles.

Tetraploid teak seedling was more tolerant to drought stress than its diploid seedling

The demand of teak (Tectona grandis L.f.) wood for the national industry can only be fulfilled about 0.75 million m3/year from 2.5 million m3/year which is caused by the long of harvesting time and the derivation of suitable land for teak due to climate change. Indonesia has a wide area of dry land to develop teak plant, so that, fast growing and drought resistant teak seedling is needed. The aim of this research was to compare the resistance of tetraploid and diploid teak clone to drought stress. The research was conducted in the greenhouse using Randomized Block Design with two factors and 9 replications. The first factor was clone i.e. diploid (2x) and tetraploid (4x). The second factor was drought stress levels consisted of 5 watering intervals i.e. 3 days, 7 days, 14 days, 21 days, and watering only at the treatment began. Plant height, stem diameter, number of leaves, leaf area, leaf thickness, leaf water potential, stomata, root system, and plant dry weight were observed to evaluate the plant growth. The result showed that the growth of both tetraploid and its diploid seedling clones were declined under drought stress. However, the growth of tetraploid seedling is better than its diploid seedling.

Colchicine-induced polyploidy has the potential to improve rubber yield in Taraxacum kok-saghyz

Taraxacum kok-saghyz (TK), also known as rubber dandelion, is under development as a source of natural rubber but has not been fully domesticated. Rubber yield is highly variable and biomass is low compared with most crops. Therefore, it is imperative to apply breeding methods to improve rubber yield and accelerate the domestication process. One strategy to accelerate breeding is polyploid induction, which could improve rubber concentration and plant size. A gradient of colchicine concentrations ranging from 0% to 0.5% was used to treat approximately 5000 seeds for different periods of time (12h to 96h), followed by use of flow cytometry to confirm induced tetraploids. The optimal treatment of 0.1% colchicine for 48h resulted in an induction efficiency of 56.6%. An early-screening strategy successfully identified 2-month old tetraploid seedlings based on atypical leaf morphology. Comparisons of leaf, stomata, root morphological traits as well as biochemical traits including rubber, resin and inulin/sugars concentration were made between tetraploids and diploids. A 47.7% increase in rubber concentration but a decrease in inulin/sugars concentration was observed in tetraploid plants. However, there was no significant difference in the amount of rubber per root system among the greenhouse-grown plants in this research, likely due to root stunting observed in tetraploids and treated diploids. Evaluation of progeny is needed to circumvent the confounding physiological impact of colchicine treatment. However, the increase of rubber concentration observed in tetraploids suggests that polyploid breeding has the potential to improve rubber yield in TK.

Tetraploidy enhances the ability to exclude chloride from leaves in carrizo citrange seedlings

Tetraploid citrus seedlings are more tolerant to salt stress than diploid genotypes. To provide insight into the causes of differences in salt tolerance due to ploidy and thus to better understand Cl− exclusion mechanisms in citrus, diploid and tetraploid seedlings of Carrizo citrange (CC) were grown at 0 (control) and 40mM NaCl (salt-treated) medium for 20 days. Chloride uptake and root-to-shoot translocation rates were on average 1.4-fold higher in diploid than in tetraploid salt-treated plants, which resulted in a greater (1.6-fold) Cl− build up in the leaves of the former. Root hydraulic conductance and leaf transpiration rate were 58% and 17% lower, respectively, in tetraploid than in diploid control plants. Differences remained after salt treatment which reduced these parameters by 30–40% in both genotypes. Morphology of the root system was significantly influenced by ploidy. Tetraploid roots were less branched and with lower number of root tips than those of diploid plants. The cross-section diameter and area were lower in the diploid, and consequently specific root length was higher (1.7-fold) than in tetraploid plants. The exodermis in sections close to the root apex was broader and with higher deposition of suberin in cell walls in the tetraploid than in the diploid genotype. Net CO2 assimilation rate in tetraploid salt-treated seedlings was 1.5-fold higher than in diploid salt-treated plants, likely due to the loss of photosynthetic capacity of diploid plants induced by Cl− toxicity. Leaf damage was much higher, in terms of burnt area and defoliation, in diploid than in tetraploid salt-treated plants (8- and 6-fold, respectively). Salt treatment significantly reduced (37%) the dry weight of the diploid plants, but did not affect the tetraploids. In conclusion, tetraploid CC plants appear more tolerant to salinization and this effect seems mainly due to differences in morphological and histological traits of roots affecting hydraulic conductance and transpiration rate. These results may suggest that tetraploid CC used as rootstock could improve salt tolerance in citrus trees.

Progeny test of tetraploid Betula platyphylla and preliminary selection of hybrid parents

Estimating genetic parameters of parental lines through progeny testing and choosing good hybrid parents are important for genetically improving seed orchard trees. In this study, 24 tetraploid progeny seedlings were used as experimental materials, which came from test cross design: six tetraploid Betula platyphylla lines (Q33, Q13, Q103, Q19, Q83 and Q14) as female parents and four individual B. platyphylla diploid lines (F3, F4, F9 and F11) as male parents were crossed. Variance analysis of height, diameter, height-to-diameter ratio, and internodal distance showed that the differences between hybrid combinations reached highly significant levels. Using multi-objective decisionmaking, we performed a comprehensive assessment of the various hybrid combinations. Using a selection rate of 20 % of the standard, five hybrids were selected; their genetic gains in average height, diameter, height-to-diameter ratio, and internodal distance were 20.95, 6.07, 13.07 and 8.96 %, respectively. We also analyzed the combining ability and genetic parameter effect values of parents and hybrid combinations. The combined analysis revealed that Q13, Q103, Q33 and Q83 were superior females; F3, F4, and F9 were superior males; and F3 × Q13, F4 × Q83 and F9 × Q33 were superior hybrid combinations. The heights and diameters of these progenies were 22.49 and 11.48 % greater than average, respectively.

Stimulation of Cell Elongation by Tetraploidy in Hypocotyls of Dark-Grown Arabidopsis Seedlings.

Plant size is largely determined by the size of individual cells. A number of studies showed a link between ploidy and cell size in land plants, but this link remains controversial. In this study, post-germination growth, which occurs entirely by cell elongation, was examined in diploid and autotetraploid hypocotyls of Arabidopsis thaliana (L.) Heynh. Final hypocotyl length was longer in tetraploid plants than in diploid plants, particularly when seedlings were grown in the dark. The longer hypocotyl in the tetraploid seedlings developed as a result of enhanced cell elongation rather than by an increase in cell number. DNA microarray analysis showed that genes involved in the transport of cuticle precursors were downregulated in a defined region of the tetraploid hypocotyl when compared to the diploid hypocotyl. Cuticle permeability, as assessed by toluidine-blue staining, and cuticular structure, as visualized by electron microscopy, were altered in tetraploid plants. Taken together, these data indicate that promotion of cell elongation is responsible for ploidy-dependent size determination in the Arabidopsis hypocotyl, and that this process is directly or indirectly related to cuticular function.