Backcross Progeny Research Articles

Genetic analyses of Glu-1S sh in wheat/Aegilops sharonensis hybrid progenies and development of alien HMW-GSs gene-specific markers

Aegilops sharonensis is a diploid relative of wheat and has novel high molecular weight glutenin subunits (HMW-GSs) encoded by Glu-1Ssh. Hybrids of tetraploid wheat species and Ae. sharonensis have been successfully created by wild crosses. In our study, we conducted backcrosses and introduced the novel HMW-GSs of Ae. sharonensis into hexaploid wheat species. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and cytogenetics indicated that lines carrying the HMW-GSs encoded by Glu-1Ssh had varied chromosome numbers ranging from 35 to 50. Among these, three lines with 42 chromosomes (25-8, 33-1, and 42-2) were identified by visual examination. Except for possessing the alien HMW-GSs of Ae. sharonensis, the agricultural traits of the three lines were similar to those of common wheat, indicating their potential for wheat breeding. Additionally, we developed two molecular markers specific to the x- and y-type HMW-GSs genes of Ae. sharonensis. These two molecular markers were validated in backcross progenies and were proven to accurately trace and distinguish Ae. sharonensisGlu-1Ssh from Glu-1A, Glu-1B, and Glu-1D of wheat. Therefore, the Glu-1Ssh HMW-GSs lines with 42 chromosomes, together with gene-specific markers, will be valuable for molecular-assisted selection in alien genes utilization and wheat breeding.

A Major Locus Controls a Genital Shape Difference Involved in Reproductive Isolation Between Drosophila yakuba and Drosophila santomea.

Rapid evolution of genitalia shape, a widespread phenomenon in animals with internal fertilization, offers the opportunity to dissect the genetic architecture of morphological evolution linked to sexual selection and speciation. Most quantitative trait loci (QTL) mapping studies of genitalia divergence have focused on Drosophila melanogaster and its three most closely related species, D. simulans, D. mauritiana, and D. sechellia, and have suggested that the genetic basis of genitalia evolution involves many loci. We report the first genetic study of male genitalia evolution between D. yakuba and D. santomea, two species of the D. melanogaster species subgroup. We focus on male ventral branches, which harm females during interspecific copulation. Using landmark-based geometric morphometrics, we characterized shape variation in parental species, F1 hybrids, and backcross progeny and show that the main axis of shape variation within the backcross population matches the interspecific variation between parental species. For genotyping, we developed a new molecular method to perform multiplexed shotgun genotyping (MSG), which allowed us to prepare genomic DNA libraries from 365 backcross individuals in a few days using little DNA. We detected only three QTL, one of which spans 2.7 Mb and exhibits a highly significant effect on shape variation that can be linked to the harmfulness of the ventral branches. We conclude that the genetic architecture of genitalia morphology divergence may not always be as complex as suggested by previous studies.

Transfer of sclerotinia stem rot resistance from wild Brassica oleracea into B. rapa

Brassica crops suffer heavily from sclerotinia stem rot which is caused by the necrotrophic fungal pathogen Sclerotinia sclerotiorum. A wild B. oleracea accession, C01 (B. incana), was identified to have good resistance to S. sclerotiorum, while B. rapa was highly susceptible. In order to improve the resistance level of B. rapa, a haploid was generated from a hybridization between a B. rapa accession 6Y733 and C01, where the major resistance quantitative trait loci (QTL) have been identified from chromosome C09. Molecular-assisted selection and resistance evaluation were performed in the backcross progenies with 6Y733 as the recurrent parent. Among 17 BC1F1 plants, one individual with the highest resistance level (1.2- and 1.7-fold higher resistance than 6Y733 in leaf and stem, respectively) and carrying resistance QTL was selected to develop BC2F1. One resistant BC2F1 plant carrying 20 chromosomes and resistance loci, and having similar morphology and fertility to 6Y733, was selected from 254 BC2F1 genotypes and further self-pollinated, resulting in 145 BC2F2 individual genotypes. One individual carrying 20 chromosomes and with good fertility (98.6 %) exhibited a significant higher resistance level than the parental B. rapa line (1.4- and 1.7-fold for leaf and stem resistance, respectively). Our data suggest that it is an effective strategy to transfer sclerotinia resistance from B. oleracea into B. rapa by using a haploid strategy which could prompt the genetic exchange of the A and C genomes.

Marker-assisted selection of low erucic acid quantity in short duration Brassica rapa

Low erucic acid (LEA) rapeseed, which has accumulated mutant fatty acid elongase genes at the BnFAE1.1 and BnFAE1.2 loci of the A- and C-genome, respectively, is an important oilseed crop. Short growing turnip rape (B. rapa) is also important as a catch crop in the continuous cropping of rice in Asia but there is no LEA B. rapa cultivar for cultivation in South Asia. In order to develop LEA turnip rape cultivars, high erucic acid turnip rape cultivars were interspecifically crossed as recurrent parents to a canola quality rapeseed. In the meantime, we monitored incorporation of the mutant bnfae1.1 (e1) gene into A-genome of turnip rape, using a dCAPS primer pair, which can amplify PCR fragment only for the mutant e1 gene from A-genome. The early backcross progenies showed poor seed set, but which was improved in advanced progenies. Finally, homozygous e1e1 genotypes were established in the selfed progenies of BC2–BC3, and their LEA content was confirmed by gas-chromatography analysis. Our results and promising lines will contribute to LEA-trait selection in turnip rape and rapeseed breeding.

High-density interspecific genetic linkage mapping provides insights into genomic incompatibility between channel catfish and blue catfish.

Catfish is the leading aquaculture species in the United States. The interspecific hybrid catfish produced by mating female channel catfish with male blue catfish outperform both of their parent species in a number of traits. However, mass production of the hybrids has been difficult because of reproductive isolation. Investigations of genome structure and organization of the hybrids provide insights into the genetic basis for maintenance of species divergence in the face of gene flow, thereby helping develop strategies for introgression and efficient production of the hybrids for aquaculture. In this study, we constructed a high-density genetic linkage map using the hybrid catfish system with the catfish 250K SNP array. A total of 26,238 SNPs were mapped to 29 linkage groups, with 12,776 unique marker positions. The linkage map spans approximately 3240 cM with an average intermarker distance of 0.25 cM. A fraction of markers (986 of 12,776) exhibited significant deviation from the expected Mendelian ratio of segregation, and they were clustered in major genomic blocks across 15 LGs, most notably LG9 and LG15. The distorted markers exhibited significant bias for maternal alleles among the backcross progenies, suggesting strong selection against the blue catfish alleles. The clustering of distorted markers within genomic blocks should lend insights into speciation as marked by incompatibilities between the two species. Such findings should also have profound implications for understanding the genomic evolution of closely related species as well as the introgression of hybrid production programs in aquaculture.

Inheritance of Flowering Habit in Russian Dandelion

Russian dandelion [Taraxacum kok-saghyz (TKS)] is a latex-producing, temperate species that has the potential to be grown as a source of natural rubber in North America. Flowering habit varies within the species; winter-type plants require a cold period or vernalization to flower, whereas spring-type plants flower without this treatment. Because flowering habit is correlated with rubber yield, understanding the genetic factors governing the trait would be useful for breeding. The objective of this research was to determine the inheritance of vernalization requirement in TKS. Winter-type and spring-type plants were intercrossed to create the F1, F2, and backcross generations and progeny segregation ratios were analyzed. A genetic model with three major genes is proposed, where a dominant allele at locus A, in combination with homozygous recessive alleles at either or both of two loci, B and C, confers winter type, whereas spring type is conferred by homozygous recessive alleles at A, regardless of genotype at B or C, or dominant alleles at A, B, and C.

Inheritance of Resistance to Powdery Mildew Race 1W in Watermelon.

Powdery mildew caused by Podosphaera xanthii is a major disease of watermelon in Israel. In this study, 291 accessions of Citrullus spp. were evaluated for resistance against P. xanthii race 1W. Only eight accessions exhibited high level of resistance. Inheritance of resistance against P. xanthii race 1W was studied by crossing three resistant accession of Citrullus lanatus var. citroides BIU 119, PI 189225, or PI 482312 with the susceptible cultivar 'Malali' or 'Sugar Baby'. Parents, F1, F2, and back cross progenies were evaluated for resistance in growth chambers at the cotyledon stage and the 4-leaf stage and in the field, at the 15-leaf stage. Resistance at the cotyledon stage was controlled by a single, partially dominant gene, whereas at the 4-leaf stage or the 15-leaf stage resistance was controlled by three complimentary, partially dominant genes. Crosses made among these resistant accessions revealed that BIU 119 and PI 189225 carry the same genes for resistance, whereas PI 482312 shares two out of three genes with both BIU 119 and PI 189225. A breeding line with high resistance level and good fruit qualities was developed from BIU 119 × HA5500.

Molecular and Cytogenetic Characterization of Wild Musa Species.

The production of bananas is threatened by rapid spreading of various diseases and adverse environmental conditions. The preservation and characterization of banana diversity is essential for the purposes of crop improvement. The world's largest banana germplasm collection maintained at the Bioversity International Transit Centre (ITC) in Belgium is continuously expanded by new accessions of edible cultivars and wild species. Detailed morphological and molecular characterization of the accessions is necessary for efficient management of the collection and utilization of banana diversity. In this work, nuclear DNA content and genomic distribution of 45S and 5S rDNA were examined in 21 diploid accessions recently added to ITC collection, representing both sections of the genus Musa. 2C DNA content in the section Musa ranged from 1.217 to 1.315 pg. Species belonging to section Callimusa had 2C DNA contents ranging from 1.390 to 1.772 pg. While the number of 45S rDNA loci was conserved in the section Musa, it was highly variable in Callimusa species. 5S rRNA gene clusters were found on two to eight chromosomes per diploid cell. The accessions were genotyped using a set of 19 microsatellite markers to establish their relationships with the remaining accessions held at ITC. Genetic diversity done by SSR genotyping platform was extended by phylogenetic analysis of ITS region. ITS sequence data supported the clustering obtained by SSR analysis for most of the accessions. High level of nucleotide diversity and presence of more than two types of ITS sequences in eight wild diploids pointed to their origin by hybridization of different genotypes. This study significantly expands the number of wild Musa species where nuclear genome size and genomic distribution of rDNA loci is known. SSR genotyping identified Musa species that are closely related to the previously characterized accessions and provided data to aid in their classification. Sequence analysis of ITS region provided further information about evolutionary relationships between individual accessions and suggested that some of analyzed accessions were interspecific hybrids and/or backcross progeny.

Enhancement of tocopherols in sweet corn by marker-assisted backcrossing of ZmVTE4

Vitamin E is a group of lipid-soluble antioxidants, which is indispensable and unable to be biosynthesized by the human body. Sweet corn is one of the most popular vegetables and important vitamin E resource for human. In this study, one common corn line with favorable allele on the InDel7 (deletion) and InDel118 (deletion) sites in the locus of ZmVTE4 (SY999) was introduced as the donor parent line, 4 elite sweet corn lines were selected as the recipient lines. The ZmVTE4 gene was introgressed into 4 sweet corn lines by functional molecular marker assisted selection. Two flanking SSR markers were selected to reduce the linkage drag. Few agronomic traits were investigated in the BC1F1 and BC2F1 generations and some individuals differing from the recurrent parents had been abandoned. The investigation of few agricultural traits showed no difference between the converted lines and their recipient lines. Five selected BC3F2 families per backcross progenies and their recurrent parent lines were sown to measure the content of tocopherols. The quantification showed that the α-tocopherol content of three backcross progenies increased except for M14. The introduction of ZmVTE4 gene also improved the content of γ-tocopherol and total tocopherols content. The average content of γ-tocopherol and total tocopherols content were 29.11 and 36.63 μg/g in the four selected elite sweet corn lines and the average content in the four converted lines were 51.45 and 63.34 μg/g. This result indicated that ZmVTE4 had different expression in the sh 2 genetic background or the non-target genome introgression into the recipient parent lines affecting the content of tocopherols.

Artificial interspecific backcrosses between the hybrid of female Crassostrea hongkongensis × male C. gigas and the two parental species

To explore the possibility of performance improvement in the hybrids of Crassostrea hongkongensis ♀×Crassostrea gigas ♂, backcross progeny and F2 hybrids were produced and evaluated. Three sets of replicates were successfully generated; each consisted of single crosses (HH, GG and HG), two female backcrosses between female hybrids and two male pure species (Hg/H and Hg/G), two male backcrosses between male hybrids and two female parents (H/Hg and G/Hg) and F2 hybrids (Hg/Hg). Fertilization, survival, growth and gonad development of these experimental groups were evaluated. All backcross groups exhibited high fertilization levels; however, the female backcrosses (Hg/H and Hg/G) and F2 hybrids exhibited a low hatching rate. Survival and growth superiority of the backcross progeny was observed from the larval stage to the adult stage, although outbreeding depression of the F2 hybrids occurred. Interestingly, all backcross progeny and F2 hybrids were fertile with functional gametes and normal sex ratios when fully matured. The genetic recombination of the backcross progeny and Mendel's genetic segregation of the F2 hybrids were detected with the nuclear gene marker in the backcross. Our results revealed that artificial interspecific backcrosses are successful, and the backcross progeny are viable, fertile, and fast-growing, and therefore hold promise for potential utilization in aquaculture as a new oyster stock resource. Statement of relevanceAll authors agree that the author list is correct in its content and order, and we have no conflict of interest to declare.

Genome-Wide Responses to Selection and Genetic Networks Underlying Submergence Tolerance in Rice.

Submergence is an important factor limiting rice (Oryza sativa L.) yield in many rain-fed lowland areas of Asia. Here we explored the genetic basis of submergence tolerance (ST) in rice and facilitated simultaneous improvement of ST of rice. The genome-wide patterns of donor introgressions in 162 backcross (BC) progenies selected for ST from 12 populations of nine crosses between three recipients and three donors were characterized using simple sequence repeat (SSR) markers. The genome-wide responses of donor alleles to strong phenotypic selection for ST were reflected in three aspects: (i) significant over introgression of the donor alleles at 295 loci in 167 functional genetic units (FGUs) across the rice genome, (ii) greatly increased homozygosity or loss of heterozygosity genome-wide, and (iii) pronounced nonrandom associations between or among the detected ST loci, which led us to discovery of putative genetic networks (multilocus structures) underlying ST of rice. Our results suggest that ST of rice is controlled by large numbers of loci involved in multiple positively regulated signaling pathways. Restoration of one or more of these broken pathways in the BC progeny by genetic complementation from introgressed functional donor alleles at ST loci provide an appropriate explanation for transgressive segregation of ST and other complex traits in rice.

Marker-Assisted Backcrossing to Develop an Elite Cytoplasmic Male Sterility Line in Rice.

Cytoplasmic male sterility (CMS) is a cornerstone of hybrid production in many crops. In three-line hybrid systems, use of CMS, maintainer, and fertility restorer lines is necessary for production of hybrid seeds. Limited resources of CMS and low variation of CMS lines cause genetic vulnerability to pathogens. Therefore, diversifying the CMS sources is indispensible for a sustainable production system of hybrid seed. In this study, we attempted for the first time to transfer CMS into maintainer line Yosen B in restricted generations using the marker-assisted backcrossing (MABC) method. The resultant F1 hybrid of IR68897 A/Yosen B cross was backcrossed to Yosen B, and CMS plants in each backcross generation (from BC1 F1 to BC3 F1 ) were selected based on phenotyping test and MABC. Molecular assessment of backcross progenies was conducted using a mitochondrial CMS-specific marker and 34 polymorphic nuclear simple-sequence repeat (SSR) markers in early generations (from BC1 F1 to BC2 F1 ) and was continued using 9 additional SSRs and 82 inter-simple sequence repeat (ISSR) markers in BC3 F1 . A MABC strategy could successfully recover the recurrent parent genome (RPG) in BC3 F1 generation, and decreased heterozygosity of final CMS plants. Restorability test with known wild-abortive restorer lines (viz. IR36 and IR24) showed that combination of Yosen A × IR24 could produce highly fertile F1 hybrid. Evaluation of some important agronomic traits of the final CMS line (BC4 F1 ) at field condition showed that it was comparable to the original maintainer fertile counterpart. Phenotypic and marker-assisted selections could considerably decrease the time needed for full recovery of RPG so that final CMS line could show a high similarity to original fertile counterpart.

Perennial aneuploidy as a potential material for gene introgression between maize and Zea perennis

Hybridization, which allows for gene flow between crops, is difficult between maize and Zea perennis. In this study, we aim to initiate and study gene flow between maize and Z. perennis via a special aneuploid plant (MDT) derived from an interspecific hybrid of the two species. The chromosome constitution and morphological characters of MDT as well as certain backcross progenies were examined. Results from genomic in situ hybridization (GISH) indicate that aneuploid MDT consisted of nine maize chromosomes and 30 Z. perennis chromosomes. The backcross progenies of MDT×maize displayed significant diversity of vegetative and ear morphology; several unusual plants with specific chromosome constitution were founded in its progenies. Some special perennial progeny with several maize chromosomes were obtained by backcrossing MDT with Z. perennis, and the first whole chromosome introgression from maize to Z. perennis was detected in this study. With this novel material and method, a number of maize-tetraploid teosinte addition or substitution lines can be generated for further study, which has great significance to maize and Z. perennis genetic research, especially for promoting introgression and transferring desirable traits.

Genome-wide QTL mapping of saltwater tolerance in sibling species of Anopheles (malaria vector) mosquitoes

Although freshwater (FW) is the ancestral habitat for larval mosquitoes, multiple species independently evolved the ability to survive in saltwater (SW). Here, we use quantitative trait locus (QTL) mapping to investigate the genetic architecture of osmoregulation in Anopheles mosquitoes, vectors of human malaria. We analyzed 1134 backcross progeny from a cross between the obligate FW species An. coluzzii, and its closely related euryhaline sibling species An. merus. Tests of 2387 markers with Bayesian interval mapping and machine learning (random forests) yielded six genomic regions associated with SW tolerance. Overlap in QTL regions from both approaches enhances confidence in QTL identification. Evidence exists for synergistic as well as disruptive epistasis among loci. Intriguingly, one QTL region containing ion transporters spans the 2Rop chromosomal inversion that distinguishes these species. Rather than a simple trait controlled by one or a few loci, our data are most consistent with a complex, polygenic mode of inheritance.

A genome-wide association study in catfish reveals the presence of functional hubs of related genes within QTLs for columnaris disease resistance.

BackgroundColumnaris causes severe mortalities among many different wild and cultured freshwater fish species, but understanding of host resistance is lacking. Catfish, the primary aquaculture species in the United States, serves as a great model for the analysis of host resistance against columnaris disease. Channel catfish in general is highly resistant to the disease while blue catfish is highly susceptible. F2 generation of hybrids can be produced where phenotypes and genotypes are segregating, providing a useful system for QTL analysis. To identify genes associated with columnaris resistance, we performed a genome-wide association study (GWAS) using the catfish 250 K SNP array with 340 backcross progenies derived from crossing female channel catfish (Ictalurus punctatus) with male F1 hybrid catfish (female channel catfish I. punctatus × male blue catfish I. furcatus).ResultsA genomic region on linkage group 7 was found to be significantly associated with columnaris resistance. Within this region, five have known functions in immunity, including pik3r3b, cyld-like, adcyap1r1, adcyap1r1-like, and mast2. In addition, 3 additional suggestively associated QTL regions were identified on linkage groups 7, 12, and 14. The resistant genotypes on the QTLs of linkage groups 7 and 12 were found to be homozygous with both alleles being derived from channel catfish. The paralogs of the candidate genes in the suggestively associated QTL of linkage group 12 were found on the QTLs of linkage group 7. Many candidate genes on the four associated regions are involved in PI3K pathway that is known to be required by many bacteria for efficient entry into the host.ConclusionThe GWAS revealed four QTLs associated with columnaris resistance in catfish. Strikingly, the candidate genes may be arranged as functional hubs; the candidate genes within the associated QTLs on linkage groups 7 and 12 are not only co-localized, but also functionally related, with many of them being involved in the PI3K signal transduction pathway, suggesting its importance for columnaris resistance.

Marker-assisted introgression improves Striga resistance in an Eritrean Farmer-Preferred Sorghum Variety

The parasitic weed Striga hermonthica hampers the production of sorghum, the most important cereal crop in Eritrea. This weed has a complex mode of infestation that adapts to many hosts and environments, complicating conventional breeding for resistance, which is the only form of crop improvement available to Eritrean breeders, but has failed. This study aimed at improving resistance against this parasite by transferring 5 Striga resistant Quantitative Trait Loci (QTLs) from resistance donor N13 to Striga susceptible Farmer-Preferred Sorghum Variety (FPSV) Hugurtay from Eritrea. The method involved backcrossing using marker-assisted selection (MAS) and evaluation of the best introgressed lines for Striga resistance in artificially infested fields. Foreground selection was performed with up to 11 polymorphic simple sequence repeat (SSR) markers linked to Striga resistance QTLs, while background selection was conducted in the BC3F2 generation with 27 polymorphic unlinked SSR markers to identify the best recovery of the recurrent parent (RP) genetic background. Out of 84 BC3F3 lines, L2P3-B, L1P5-A and L2P5P35 performed best with respect to both grain yield and reduced Striga infestation. These lines were more resistant to Striga than Hugurtay, but less resistant than N13. The three lines yielded twice as much as N13, with Area Under Striga Number Progression Curve (AUSNPC) values on average 18% higher than that of N13 and 38% lower than that of Hugurtay. This suggests that the introgressed QTLs conferred significant Striga resistance and yield advantage to these BC3F3 backcross progenies under Striga pressure. These lines have good potential for future release and demonstrate that when MAS is available to conventional breeders, even in countries with no genotyping facilities, it is a useful tool for enhancement, expediency and precision in crop improvement.

Divergent host preferences of above- and below-ground Culex pipiens mosquitoes and their hybrid offspring.

Culex pipiens form pipiens and Cx. pipiens form molestus (Diptera: Culicidae) belong to a cosmopolitan taxonomic group known as the Pipiens Assemblage. Hybridization between these forms is thought to contribute to human transmission of West Nile virus (WNV) in North America. Complementary choice and no-choice landing assays were developed to examine host acceptance by North American Cx. pipiens in the laboratory. Populations collected from above- and below-ground sites in suburban Chicago were identified as forms pipiens and molestus using a polymerase chain reaction-based assay. Avian and human host acceptance was then quantified for the two populations, as well as for their hybrid and backcross offspring. No-choice tests were used to demonstrate that both the pipiens and molestus forms were capable of feeding on human and avian hosts. Choice tests were used to demonstrate that form pipiens females were strongly avian-seeking; an individual's probability of accepting the chick host was 85%. Form molestus females were more likely to accept the human host (87%). Rates of host acceptance by F1 and backcross progeny were intermediate to those of their parents. The results suggest that host preferences in Cx. pipiens are genetically determined, and that ongoing hybridization between above- and below-ground populations is an important contributor to epizootic transmission of WNV in North America.

Effect ofopaque-2allele on accumulation of tryptophan among backcross-derived introgressed progenies of maize

The tryptophan concentration of the 85 BC2F2: 3 progenies derived from a cross between normal maize inbred line, Pant 10k1375 and o2 donor line, CML 161 were determined. The genic marker phi057 positive progenies showed significant variation for tryptophan concentration in BC2F2: 3 progenies with tryptophan as low as 0.046 per cent in BC2F2: 3-80, whereas BC2F2: 3-78 possessed maximum tryptophan concentration of 0.082 per cent. Normal maize line Pant10k1375 possessed tryptophan concentration of 0.040 per cent whereas o2 donor line CML161 had tryptophan concentration of 0.089 per cent. All the BC2F2: 3 progenies had tryptophan concentration higher than the normal maize inbred, whereas none of the progenies had tryptophan concentration higher than the donor line CML161. Twelve lines of BC2F2: 3 populations had tryptophan concentration 0.075 per cent or more, the level used to determine quality protein maize. Variability in amino acid modifier genes in the background and/or the insertion of transposable element at the regulatory sites indicated by unusual segregation pattern of phi057 and umc1066 in backcross progenies could be the possible reasons for such high level of variation in tryptophan concentration. The progenies with tryptophan concentration > 0.075 per cent may serve as potential germplasm in development of quality protein maize hybrids.

Multivariate analysis of backcross progeny of Passiflora L. (Passifloraceae) for pre-breeding genotype selection.

The Ward-MLM procedure was used to evaluate genetic variation in four backcross progenies and in their parents, hybrid F1 HD13 and donor parent Passiflora sublanceolata. Sixteen quantitative descriptors and five qualitative characteristics of relevance to ornamental flower production were assessed. Using the pseudo-F and pseudo-T² criteria, we identified four groups among these plants in two evaluation periods. In both evaluations, the BC1 plants showed greater dissimilarity to their recurrent parent, but showed high genetic similarity with the P. sublanceolata parent. The first two canonical variables produced by the Ward-MLM procedure accounted for over 90% of the variation in both evaluation periods, enabling the representation of diversity through two-dimensional graphics. Groups II and IV were formed in the first assessment period. Groups I and IV formed in the second period and showed plants with selection potential. We found that it was essential to use both qualitative and quantitative variables for this analysis. Assessments of quantitative descriptors indicate that the selection of BC1 plants can be performed in any of the four progenies. Because of the similarities observed for some floral descriptors between BC1 and the P. sublanceolata parent, a second generation backcross was not recommended. However, the selection of BC1 plants for evaluation and direct use as an ornamental cultivar, or as a resource in other breeding programs, can be recommended.

Karyological study in backcross hybrids between the sterlet, Acipenser ruthenus, and kaluga, A. dauricus (Actinopterygii: Acipenseriformes: Acipenseridae): A. ruthenus × (A. ruthenus × A. dauricus) and A. dauricus × (A. ruthenus × A. dauricus)

Background. Acipenserid fishes may be divided into three groups in terms of their ploidy levels: 1) 120-chromosomes, 2) 250–270-chromosomes, and 3) about 370-chromosomes. The experimental crosses show that sturgeon species with the same ploidy often produce fertile hybrids, whereas the hybrids between species with different ploidy cannot reproduce because of female sterility or full sterility. To date, the only case of backcross hybrids obtained by hybridization of sturgeons with different ploidy is known: in these crosses, the sterlet, Acipenser ruthenus Linnaeus, 1758, with about 120 chromosomes and kaluga, Acipenser dauricus Georgi, 1775, with about 270 chromosomes were used as parental species; numerous progenies were obtained for females of both species and fertile hybrid males. The aims of this study were to determine the chromosome numbers in hybrid spermatozoa, involved in the production of viable backcross progenies, and to ascertain the chromosome numbers in backcrosses. Materials and methods. The experiments for obtaining backcrosses were conducted in the Luchegorsk experimental station of the TINRO Centre in 2010. 16 one-year-old backcross hybrids sterlet × (sterlet × kaluga) and 14 one-year-old backcrosses kaluga × (sterlet × kaluga) were karyologically studied by using previously described method. From one to 23 metaphase plates were analyzed from every studied fish. Results. Average chromosome numbers in 14 backcross hybrids sterlet × (sterlet × kaluga) varied from 139 to 157. It means that hybrid males (sterlet × kaluga), participated in their origin, produced spermatozoa with 79–87 chromosomes. Two other backcrosses sterlet × (sterlet × kaluga) had about 178 and 184 chromosomes. Thus, they got 118–124 chromosomes from their fathers. Among backcrosses kaluga × (sterlet × kaluga), 11 specimens had 201–214 chromosomes, and three specimens: 219–223. It means that hybrid males, participating in their origin, should produce spermatozoa with 66–84 and 84–93 chromosomes, respectively. Conclusion. This study suggests non-random generation of chromosome sets in spermatozoa of fertile sterlet × kaluga hybrids. However, the mechanisms of meiosis, providing a non-random production of spermatozoa with similar numbers of chromosomes, are still unknown.