Morphological and molecular characterization of the second backcross progenies of Ogu-CMS Chinese kale and rapeseed

Ogura cytoplasmic male sterility (Ogu-CMS) is widely used in the production of commercial hybrids of Brassica oleracea. However, the widespread application of the Ogu-CMS system in B. oleracea has hindered the germplasm innovation of Ogu-CMS resources due to the lack of a natural restorer line. Previously, the Ogu-CMS fertility-restored interspecific hybrids between rapeseed 15Y403 (2n = 38, AACC) and Chinese kale JL1 (2n = 18, CC) have been successfully produced. However, these progenies, which still contained a large proportion of rapeseed genomic components, showed poor fertility and a low seed setting rate under natural pollination. To improve fertility and seed setting, a successive backcross with JL1 was performed to produce BC₂ progenies. Screening with the Rfo-specific marker, five individuals harboring the Rfo gene were identified among 98 BC₂ progenies. These five individuals underwent background marker screening and an evaluation of agronomic traits and fertility. One individual (code: 15Q23) was identified with higher pollen viability, better seed setting under natural pollination, and a closer genetic background to the parent Chinese kale JL1. Many morphological traits showed no significant differences (P < 0.05) between 15Q23 and the backcross parent JL1. However, the average seed setting of 15Q23 under natural pollination was 0.72 seeds per pod, which was 50 times higher than that of BC₁ progenies, and the average pollen viability was 87.07%, which was significantly better than that of the F₁ and BC₁ plants (P < 0.01). The genetic background of 15Q23 was more closer to the parent JL1 than that of BC₁ plants and another BC₂ fertility-restored individual, with 82% of the polymorphic alleles being the same as those of the parent Chinese kale JL1. Thus, the individual 15Q23 could be used as a donor plant for further backcrosses. This study lays the foundation for the development of Ogu-CMS restorer material in B. oleracea.     

Broadening the genetic base of <Emphasis Type="Italic">Brassica napus</Emphasis> canola by interspecific crosses with different variants of <Emphasis Type="Italic">B. oleracea</Emphasis>

Broadening the genetic base of the C genome of Brassica napus canola by use of B. oleracea is important. In this study, the prospect of developing B. napus canola lines from B. napus?×?B. oleracea var. alboglabra, botrytis, italica and capitata crosses and the effect of backcrossing the F₁’s to B. napus were investigated. The efficiency of the production of the F₁’s varied depending on the B. oleracea variant used in the cross. Fertility of the F₁ plants was low—produced, on average, about 0.7 F₂ seeds per self-pollination and similar number of BC₁ seeds on backcrossing to B. napus. The F₃ population showed greater fertility than the BC₁F₂; however, this difference diminished with the advancement of generation. The advanced generation populations, whether derived from F₂ or BC₁, showed similar fertility and produced similar size silique with similar number of seeds per silique. Progeny of all F₁’s and BC₁’s stabilized into B. napus, although B. oleracea plant was expected, especially in the progeny of F₁ (ACC) owing to elimination of the A chromosomes during meiosis. Segregation distortion for erucic acid alleles occurred in both F₂ and BC₁ resulting significantly fewer zero-erucic plants than expected; however, plants with?≤?15% erucic acid frequently yielded zero-erucic progeny. No consistent correlation between parent and progeny generation was found for seed glucosinolate content; however, selection for this trait was effective and B. napus canola lines were obtained from all crosses. Silique length showed positive correlation with seed set; the advanced generation populations, whether derived from F₂ or BC₁, were similar for these traits. SSR marker analysis showed that genetically diverse canola lines can be developed by using different variants of B. oleracea in B. napus?×?B. oleracea interspecific crosses.     

Genetic relationships among resynthesized,semi-resynthesized and natural <Emphasis Type="Italic">Brassica napus</Emphasis> L. genotypes

The allopolyploidization event that created cultivated oilseed rape Brassica napus L, followed by intense breeding, reduced its genetic diversity. Resynthesized (RS) B. napus L. obtained by interspecific hybridization between genotypes of B. rapa L. and B. oleracea L. can be a valuable source for broadening genetic diversity in cultivated oilseed rape. In this study, we determined the extent of DNA polymorphism among natural accessions of oilseed rape, resynthesized B. napus, their parental species and double-low quality semi-RS lines carrying the Rfo gene. Using 10 selected primer combinations, 522 polymorphic AFLP markers were scored in the complete set of 100 Brassica sp. To detect relationships between these genotypes, a cluster analysis was performed using the Jaccard’s distance. Resynthesized allopolyploids clustered directly between their diploid parents. Cultivated accessions of oilseed rape created a compact group away from resynthesized allopolyploids as well as semi-RS lines. The natural oilseed rape group, which consists of 49 cultivars and breeding lines of oilseed rape, is characterized by lower genetic diversity than the group of 33 accessions of resynthesized oilseed rape, and the analysis showed that the double-low quality semi-RS lines represent a specific genetic variation of B. napus. The de novo resynthesized B. napus lines and the semi-RS lines of double-low quality generated from them, provide a significant opportunity for enrichment the gene pool of oilseed rape.     

EMS-induced mutation of an endoplasmic reticulum oleate desaturase gene (<Emphasis Type="Italic">FAD2</Emphasis>-<Emphasis Type="Italic">2</Emphasis>) results in elevated oleic acid content in rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

The development of rapeseed cultivars (Brassica napus L.) with high oleic acid and low linolenic acid is highly desirable for food and industrial applications. In this study, the Korean rapeseed cultivar Tamla was used for ethyl methanesulfonate (EMS)-induced mutagenesis and seed oils were screened up to generation M₇ for high oleate mutants. Two mutant populations (M₇) with an average of approximately 76% oleic acid content were isolated. Yield components between two mutant populations and untreated Tamla plants were not substantially different, although the mutants in the vegetative stage were slightly smaller in size than Tamla. Genomic analyses of six fatty acid desaturase (four FAD2 and two FAD6) genes revealed that the elevated oleic acid content in the mutants is the result of single gene mutations. Changes in DNA sequence were observed in two genes out of six fatty acid desaturase (four FAD2 and two FAD6). FAD2-2 exhibited a 2-bp deletion in the upstream region of the gene in the two mutants, resulting in a severely truncated polypeptide (57 aa instead of 469 aa), while six point mutations in the other gene did not result in changes in the amino acid sequence. Based on these results, FAD2-2, an endoplasmic reticulum (ER) oleic acid desaturase, is affected in the mutants, resulting in a ~ 7% increase in oleic acid content in comparison to untreated Tamla plants. The induced mutants could be utilized for the development of high oleic oil rapeseed varieties and for regulatory studies of lipid metabolism in seed oils.     

Resistance to the cabbage root fly, <Emphasis Type="Italic">Delia radicum</Emphasis> (Diptera,Anthomyiidae), of turnip varieties (<Emphasis Type="Italic">Brassica rapa</Emphasis> subsp. <Emphasis Type="Italic">rapa</Emphasis>)

The cabbage root fly Delia radicum L. (Diptera: Anthomyiidae) is one of the major pests of many Brassica crops in the temperate areas of Europe and North America. At present, turnip (B. rapa ssp. rapa L.) varieties resistant to the pest does not exist. With the aim to fill this gap, a no-choice tolerance test of 56 accessions among turnips, turnip tops and turnip greens was performed under controlled conditions by introducing D. radicum eggs. Plant survival, leaf and root conditions, pupae number and weight significantly varied among plant accessions. Ten putatively resistant and ten susceptible accessions (control group) were selected from this first screening, transplanted in the field and exposed to natural infestation to detect antibiosis and antixenosis mechanisms. Both in the laboratory and in the field, pupae number significantly varied within accessions and between resistant and susceptible group, although pupal weight did not, indicating the absence of antibiosis effect on this early stage. In the field, the number of galleries was significantly lower in the resistant group in comparison with the control. Resistant accessions had smaller size, and a smaller, white and mostly buried root. Within the resistant and susceptible accessions, larger plants harboured more pupae, however purple roots were those most preferred, and the hosted pupae weighed most. Three accessions from the resistant group (MBGBR0178, MBGBR0570 and MBGBR0371) stand out for resistance to D. radicum possibly through antixenosis mechanisms.     

Marker assisted backcrossing for introgression of Fusarium wilt resistance gene into melon

Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis is a common vascular wilt fungal disease in melon across the world. The resistance gene to race 1 of this causal agent, Fom-2, has been previously cloned and its sequence is available. The objective of this research was the introgression of Fom-2 from one resistant (Isabelle) genotype into two susceptible cultivars (Garmak and Tile-torogh) via marker assisted backcrossing. First, the leucine-rich repeats (LRR) domain of Fom-2 from resistant and susceptible genotypes was sequenced to develop functional markers. A length of 1274 bp of the 3′ end of this gene was isolated, cloned and sequenced. The difference between resistant and susceptible genotypes in this region was 28 nucleotide substitutions. Two allele specific primer pairs, Fom2-R409 and Fom2-S253, were designed based on nucleotide substitutions to amplify resistant and susceptible alleles, respectively. For introgression of the gene, donor (Isabelle) and recurrent (Garmak and Tile-torogh) parents were crossed. Resistant plants in BC₁F₁ and BC₂F₁ generations were first detected using artificial pathogen inoculation and later the plants were genotyped by functional markers to validate their resistance. The resistant plants were also selected phenotypically in each generation for background genome recovery, which conduced to high similarity of BC₃ generation with the recurrent parents. It was proved the developed markers are more precise and efficient than inoculation trial and could be used as confident tools for screening of resistant melon genotypes to Fusarium wilt.     

The sporophytic self-incompatibility mating system is conserved in <Emphasis Type="Italic">Olea europaea</Emphasis> subsp. <Emphasis Type="Italic">cuspidata and O. e. europaea</Emphasis>

Fruit setting after self-pollination, crosses and free-pollination appears to be erratic in the cultivated olive tree [Olea europaea subsp europaea L. (O. e. europaea L.)] because of a lack of a suitable model to enable prediction of rates. The same lack of prediction also applies to the wild taxon Olea europaea subsp cuspidata (O. e. cuspidata). Because of their close phylogenetic relationships, we hypothesize that O. e. cuspidata and cultivated olive share the same self-incompatibility system. We used data recently published in a wide study involving four O. e. cuspidata accessions and four olive cultivars. Because the olive varieties have been deciphered for their S-allele pair, that infer determinants present in the stigma and pistil, and that coat the pollen, we deciphered the S-alleles carried by three of the O. e. cuspidata accessions. Data are too scarce and the number of accessions too small to speculate on the O. e. cuspidata genetic population structure. The working hypothesis is confirmed. This study and data from the Italian team will enable us to embark on a large-scale hybridization program between the two subsp. to obtain a wide range of progenies for screening for responses to cold, diseases and pests.     

Genomic changes in generations of synthetic rapeseed-like allopolyploid grown under selection

Resynthesized Brassica napus L. is an important source for broadening genetic diversity and producing lines with desired characteristics. It is also a fine model to study the processes of genomic reorganizations in recently formed polyploids. We firstly performed molecular cytogenetic characterization of newly resynthesized rapeseed (B. rapa ssp. narinosa × B. oleracea ssp. capitata) and its parental species, and also examined genomic changes in hybrids of the succeeding generations grown under pressure of selection of yellow-seeded progeny. For karyotype studies, FISH/GISH with 45S, 5S rDNA, C genome specific BoB014O06 BAC clone and genomic DNA of parental B. rapa was performed. Synthetic S0–S2 hybrids had common rapeseed karyotypes (2n = 38) including 14 loci of 45S rDNA sites and 10 loci of 5S rDNA. Progeny selection led to gradual deletion of C genome chromosomes in hybrid karyotypes. So, in karyotypes of S6 and S7 hybrids, the chromosome number was reduced to 2n = 20–22, and only chromosomes of A genome bearing 10–13 loci of 45S rDNA and 8–10 loci of 5S rDNA, variations in chromosome number, chromosome rearrangements as well as examples of trisomy and monosomy were revealed. Our findings indicate an enhanced genome instability in resynthesized rapeseed lines developed under the pressure of selection which might lead to chromosome rearrangements or/and deletions and even elimination of the whole parental genome in hybrids in succeeding generations. The approach can be useful for the development of rapeseed lines with trisomy, chromosome addition/substitution lines important for genetics and plant breeding.     

Further QTL mapping for yield component traits using introgression lines in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under drought field environments

To better understand the underlying mechanisms of agronomic traits related to drought resistance and discover candidate genes or chromosome segments for drought-tolerant rice breeding, a fundamental introgression population, BC₃, derived from the backcross of local upland rice cv. Haogelao (donor parent) and super yield lowland rice cv. Shennong265 (recurrent parent) had been constructed before 2006. Previous quantitative trait locus (QTL) mapping results using 180 and 94 BC₃F_6,7 rice introgression lines (ILs) with 187 and 130 simple sequence repeat (SSR) markers for agronomy and physiology traits under drought in the field have been reported in 2009 and 2012, respectively. In this report, we conducted further QTL mapping for grain yield component traits under water-stressed (WS) and well-watered (WW) field conditions during 3 years (2012, 2013 and 2014). We used 62 SSR markers, 41 of which were newly screened, and 492 BC₄F_2,4 core lines derived from the fourth backcross between D123, an elite drought-tolerant IL (BC₃F₇), and Shennong265. Under WS conditions, a total of 19 QTLs were detected, all of which were associated with the new SSRs. Each QTL was only identified in 1 year and one site except for qPL-12-1 and qPL-5, which additively increased panicle length under drought stress. qPL-12-1 was detected in 2013 between new marker RM1337 and old marker RM3455 (34.39 cM) and was a major QTL with high reliability and 15.36% phenotypic variance. qPL-5 was a minor QTL detected in 2013 and 2014 between new marker RM5693 and old marker RM3476. Two QTLs for plant height (qPHL-3-1 and qPHP-12) were detected under both WS and WW conditions in 1 year and one site. qPHL-3-1, a major QTL from Shennong265 for decreasing plant height of leaf located on chromosome 3 between two new markers, explained 22.57% of phenotypic variation with high reliability under WS conditions. On the contrary, qPHP-12 was a minor QTL for increasing plant height of panicle from Haogelao on chromosome 12. Except for these two QTLs, all other 17 QTLs mapped under WS conditions were not mapped under WW conditions; thus, they were all related to drought tolerance. Thirteen QTLs mapped from Haogelao under WS conditions showed improved drought tolerance. However, a major QTL for delayed heading date from Shennong265, qDHD-12, enhanced drought tolerance, was located on chromosome 12 between new marker RM1337 and old marker RM3455 (11.11 cM), explained 21.84% of phenotypic variance and showed a negative additive effect (shortening delay days under WS compared with WW). Importantly, chromosome 12 was enriched with seven QTLs, five of which, including major qDHD-12, congregated near new marker RM1337. In addition, four of the seven QTLs improved drought resistance and were located between RM1337 and RM3455, including three minor QTLs from Haogelao for thousand kernel weight, tiller number and panicle length, respectively, and the major QTL qDHD-12 from Shennong265. These results strongly suggested that the newly screened RM1337 marker may be used for marker-assisted selection (MAS) in drought-tolerant rice breeding and that there is a pleiotropic gene or cluster of genes linked to drought tolerance. Another major QTL (qTKW-1-2) for increasing thousand kernel weight from Haogelao was also identified under WW conditions. These results are helpful for MAS in rice breeding and drought-resistant gene cloning.     

Identification of the <Emphasis Type="Italic">S</Emphasis> locus core sequences determining self-incompatibility and <Emphasis Type="Italic">S</Emphasis> multigene family from draft genome sequences of radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> L.)

The S core and its flanking sequences were identified from two independent draft genome sequences of radish (Raphanus sativus L.). After gap-filling with PCR, the S core regions and full-length S receptor kinase (SRK) genes from two radish genomes were obtained. Phylogenetic analysis of the SRK genes clearly showed that one S core region belonged to the class I S haplotypes, but the other was included in the class II S haplotypes. Three sequences showing homology with known transposable elements were identified in the core regions, and one intact copia-type long terminal repeat (LTR)-retrotransposon containing a 4125-bp open reading frame (ORF) was identified in the class I S haplotype. A total of 61 genes showing homology with the SRK genes were identified from two draft genome sequences. Among them, the RsKD1 showed the highest homology with the SRK genes. There was 90% nucleotide sequence identity between the RsKD1 and RsSRK1 genes in the kinase domains. The phylogenetic tree of SRK genes and 13 most closely related homologs showed that all homologs were more closely related to the class II SRK genes than to the class I SRKs. Physical mapping of radish SRK-homologous genes and their B. rapa orthologs showed that two radish homologs and their B. rapa orthologs were tightly linked to the SRK genes in radish and B. rapa genomes. Sequence information about multiple SRK-homologs identified in this study would be helpful for designing reliable primer pairs for faithful PCR amplification of the SRK alleles, leading to improvement of the S haplotyping system in radish breeding programs.     

Combination of resistance to Verticillium longisporum from zero erucic acid Brassica oleracea and oilseed Brassica rapa genotypes in resynthesized rapeseed (Brassica napus) lines

Resynthesized (RS) forms of rapeseed (Brassica napus L.; genome AACC, 2n = 38) generated from interspecific hybridization between suitable genotypes of its diploid progenitors Brassica rapa L. (syn. campestris; genome AA, 2n = 20) and Brassica oleracea L. (CC, 2n = 18) represent a potentially useful resource to introduce resistance against the fungal pathogen Verticillium longisporum into the gene pool of oilseed rape. Numerous cabbage (B. oleracea) accessions are known with resistance to V. longisporum; however, B. oleracea generally has high levels of erucic acid and glucosinolates in the seed, which reduces the suitability of resulting RS rapeseed lines for oilseed rape breeding. In this study resistance against V. longisporum was identified in the cabbage accession Kashirka 202 (B. oleracea convar. capitata), a zero erucic acid mutant, and RS rapeseed lines were generated by crossing the resistant genotype with two spring turnip rape accessions (B. rapa ssp. olerifera) with zero erucic acid. One of the resulting zero erucic acid RS rapeseed lines was found to have a high level of resistance to V. longisporum compared with both parental accessions and with B. napus controls. A number of other zero erucic acid RS lines showed resistance levels comparable to the parental accessions. In the most resistant RS lines the resistance and zero erucic acid traits were combined with variable seed glucosinolate contents. Erucic acid‐free RS rapeseed with moderate seed glucosinolate content represents an ideal basic material for introgression of quantitative V. longisporum resistance derived from B. oleracea and B. rapa into elite oilseed rape breeding lines.     

Identifying apomixis in matroclinal progeny from an interspecific crossing between <Emphasis Type="Italic">Iris domestica</Emphasis> and three different colors of <Emphasis Type="Italic">Iris dichotoma</Emphasis>

In a previous investigation on the reciprocal difference of interspecific hybridization between three different flower colors of Iris dichotoma and Iris domestica in the F₁ offspring from crosses where I. domestica was a maternal parent were similar in morphological and cytological characters to their maternal parent. This could be evidence of apomixis; however, matroclinal progeny with complete morphological similarity to the maternal parent could be attributed to the heterozygosity for these characters in the pollen parent. The F₁ plants were investigated in order to identify apomixis in I. domestica. Four matroclinal plants were randomly selected from each F₁ population produced from Iris domestica × Iris dichotoma that had three different colors of flowers and were allowed to self-pollinate to establish an F₂ population. All of the F₂ plants had no segregation to I. domestica in their morphological characters. In addition, 13 reciprocal F₁ plants were detected by 25,719 single nucleotide polymorphism (SNP) markers. When I. dichotoma plants with three different flower colors were used as maternal parents, all the progenies were genuine hybrids. When I. domestica were used as maternal parents, all the F₁ plants were apomictic progenies. Apomixis of I. domestica was successfully identified and SNP markers identified F₁ hybrids derived from six interspecific crosses between I. dichotoma and I. domestica, which provides a reference for authenticating offspring identity during Iris cross breeding in the future.     

Development of late-bolting F<Subscript>1</Subscript> hybrids of Chinese cabbage (<Emphasis Type="Italic">Brassica rapa</Emphasis> L.) allowing early spring cultivation without heating

We developed new F₁ hybrids of Chinese cabbage (Brassica rapa L. ssp. pekinensis) that allow cultivation earlier in spring without heating by introducing extremely late-bolting alleles at two homologs of the flowering repressor Flowering Locus C (BrFLC2 and BrFLC3) from non-heading ‘Leafy Green Parental Line No. 2’. These new F₁ hybrids were produced by the following four steps. First, the extremely late bolting selected lines were developed. These selected lines headed in spring after overwintering cultivation, whereas the conventional F₁ cultivars flowered. Secondly, an investigation of the three plantings showed that our F₁ hybrids formed heads when seeds were sown from mid-February to early March, whereas the conventional F₁ cultivar did not form heads because of premature bolting. Thirdly, we identified some F₁ hybrids with extremely late bolting during early spring cultivation in an investigation of many F₁ hybrids. Finally, based on an investigation across four cold regions for 2 years, we compared the commercialization rate, defined as the proportion of plants greater than 2000 g in weight and with a flowering stalk less than 10 cm long. Then we identified a F₁ of MS02 × 12-04 which had a high commercialization rate on average (92%), whereas the rates of three conventional F₁ cultivars were only 0–2%. In the near future, these F₁ hybrids will be valuable late-bolting cultivars despite climate change, permitting stable cultivation and harvest over wide regions.     

Linkage between genes for hairy first leaf and chlorophyll deficiency in Brassica oleracea

The fourth linkage group of B. oleracea L. has two genes: Hr-1, (hairy first leaf), a dominant seedling marker from “Dwarf Green” curly kale, and pg-2, (pale green seedling), a recessive chlorophyll mutant from green sprouting broccoli. Recombination between Hr-1 and pg-2 ranged from 7.4 to 20.1% in the six progenies studied, with a mean of 13.15±0.68%. Hr-1 segregated independently of the three other linkage groups (two genes of each were tested) and of two unlocated genes for male sterility.     

Effects of <Emphasis Type="Italic">Solanum demissum</Emphasis> chromosomes on crossability in the backcross progeny to <Emphasis Type="Italic">Solanum tuberosum</Emphasis>

A balance of maternal and paternal genetic factors, conceptually named the endosperm balance number (EBN), is required for normal endosperm development in interspecific crosses in potato. We previously found that Solanum demissum (D), a hexaploid wild species widely used in potato breeding, has a slightly lower EBN than S. tuberosum (T). To explore the genetic nature of the EBN, the berry-setting rate, seed number/berry, and seed weight were evaluated in BC₁ [(D?×?T)?×?T] plants, each possessing different portions of the S. demissum chromosomes, by reciprocal crosses with D and T, and a quantitative trait locus (QTL) analysis was performed. At least 99 S. demissum-derived QTLs were detected, of which 29 were associated with differential responses to D and T. Three QTLs were possibly co-localized on chromosomes 7A and 10D1, while the remaining 23 QTLs were independently located. The QTLs in the three S. demissum homoeologous chromosomes exhibited three types of interaction: (1) positive, (2) negative, and (3) one positive and one negative effect on the same trait. We found that several major genes, one of which was localized in the S. demissum chromosome 9A, and many minor genes controlled the crossability of BC₁ plants. The QTLs responsible for the differential responses to D and T were different between the BC₁ plants used as male and female parents, indicating that different genes control the male and female EBNs. Consequently, we conclude that the EBN is represented by the sum of various genetic effects controlled by a large number of genes.     

Karyotype analysis of eight wild <Emphasis Type="Italic">Tulipa</Emphasis> species native to China and the interspecific hybridization with tulip cultivars

The information of ploidy, karyotype and genetic relationship is useful for interspecific hybridization in ornamental plants. For Tulipa species native to China, very limited cytological information is available now. The objective of this study was to verify the chromosome number, karyotype and genetic relationship of the eight Tulipa species: T. edulis, T. schrenkii, T. iliensis, T. thianschanica, T. altaica, T. sinkiangensis, T. heterophylla and T. buhseana. And the interspecific crosses were made between T. altaica and ten tulip cultivars to obtain novel germplasm. The ovary-swelling, fruit-setting and bulblet formation rates were surveyed when different ploidy cultivars were used as female parents. This work confirmed that all eight species collected in China were diploid (2n?=?2x?=?24), among which chromosome numbers of T. thianschanica, T. sinkiangensis and T. heterophylla were firstly reported and the karyotypes of all any other species except for T. edulis were determined for the first time. The karyotypes of eight Tulipa species were classified as 3A, 4A or 3B. The results of interspecific hybridization showed significant difference when different ploidy cultivars were used as female parents. The highest fruit-setting rate was obtained when diploid cultivars were used as female parents crossed with diploid T. altaica, whereas the ovary swelling was observed in two out of four triploid cultivars as female parents, and no seeds were harvested when tetraploid cultivars were used as female parents. Our findings provided an effective means of cultivar improvement in tulip.