Hexaploid Somatic Hybrids Research Articles

Nuclear and cytoplasmic genome composition of Solanum bulbocastanum (+) S. tuberosum somatic hybrids

Somatic hybrids between the wild incongruent species Solanum bulbocastanum (2n = 2x = 24) and S. tuberosum haploids (2n = 2x = 24) have been characterized for their nuclear and cytoplasmic genome composition. Cytologic observations revealed the recovery of 8 (near-)tetraploid and 3 hexaploid somatic hybrids. Multicolor genomic in situ hybridization (GISH) analysis was carried out to study the genomic dosage of the parental species in 5 somatic hybrids with different ploidy. The GISH procedure used was effective in discriminating parental genomes in the hybrids; most chromosomes were unambiguously colored. Two (near-)tetraploid somatic hybrids showed the expected 2:2 cultivated-to-wild genomic dosage; 2 hexaploids revealed a 4:2 cultivated-to-wild genomic dosage, and 1 hexaploid had a 2:4 cultivated-to-wild genomic dosage. Characterization of hybrid cytoplasmic genomes was performed using gene-specific primers that detected polymorphisms between the fusion parents in the intergenic regions. The analysis showed that most of the somatic hybrids inherited the plastidial and mitochondrial DNA of the cultivated parent. A few hybrids, with a rearranged mitochondrial genome (showing fragments derived from both parents), were also identified. These results confirmed the potential of somatic hybridization in producing new variability for genetic studies and breeding.

Development and characterization of potato-Solanum brevidens chromosomal addition/substitution lines

Solanum brevidens is a wild diploid potato species possessing high levels of resistances to several major potato diseases. We previously developed fertile somatic hybrids between S. brevidens and the cultivated potato (Solanum tuberosum) in order to introgress disease resistances from this wild species into potato. A series of backcross progenies was developed from a hexaploid somatic hybrid A206. Using a combination of S. brevidens-specific randomly amplified polymorphic DNA (RAPD) markers and a sequential genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) technique, we identified all 12 S. brevidens chromosomes in the backcross progenies. Seven potato-S. brevidens monosomic chromosome addition lines (chromosomes 1, 3, 4, 5, 8, 9 and 10) and one monosomic substitution line (chromosome 6) were identified, and the remaining four S. brevidens chromosomes (2, 7, 11, and 12) were included in two other lines. These chromosomal addition/substitution stocks provide valuable tools for potato cytogenetic research, and can be used to introgress disease resistances from S. brevidens into potato.

New Intergeneric Somatic Hybrids Combining Amblycarpa Mandarin with Six Trifoliate/Trifoliate Hybrid Selections for Lime Rootstock Improvement

No presently available rootstock combines all the available rootstock attributes necessary for efficient long-term citriculture (production and harvesting) of Mexican limes and other commercially important scions. In the present study, somatic hybridization techniques were used to combine the widely adapted Amblycarpa mandarin (also known as Nasnaran mandarin) with six different trifoliate/trifoliate hybrid selections: Benton, Carrizo, and C-35 citranges; Flying Dragon and Rubidoux trifoliate oranges; and a somatic hybrid of sour orange + Flying Dragon. The ultimate goal of this research is to generate polyploid somatic hybrids that express the complementary horticultural and disease resistance attributes of the corresponding parents, and have direct potential as improved tree-size controlling rootstocks. Somatic hybrids from all six parental combinations were confirmed by a combination of leaf morphology, flow cytometry, and randomly amplified polymorphic DNA (RAPD) (for nuclear hybridity) and cleaved amplified polymorphic sequence (CAPS) analyses (for mtDNA and cpDNA). This is the first report of citrus somatic hybridization using Amblycarpa mandarin. Unexpected hexaploid somatic hybrid plants were recovered from the fusion of Amblycarpa mandarin + C-35 citrange. Hexaploid hybrids should be very dwarfing and may have potential for producing potted ornamental citrus. Resulting somatic hybrid plants from all six combinations have been propagated by tissue culture and/or rooted cuttings and are being prepared for commercial field evaluation for their potential as improved rootstocks for Mexican lime and other important scions.

Barriers for Introgression of Solanum ochranthum into Tomato via Somatic Hybrids

Solanum ochranthum Dunal is a nontuber bearing wild relative of the cultivated tomato (Lycopersicon esculentum Mill.), and a potential source of new genes for disease and pest resistance. Because S. ochranthum is sexually isolated from tomato, somatic hybrids between tomato (PI 367942; L. esculentum Mill. var. cerasiforme (Dunal) A. Gray VFNT cherry × L. peruvianum (L.) Mill. backcrossed to VFNT cherry) and S. ochranthum (LA2117) were developed previously to overcome these crossing barriers. Attempts to backcross these hybrids to tomato have been unsuccessful. Pollen fertility and mitotic and meiotic studies in tomato + S. ochranthum somatic hybrids determined the cause of the sterility of the somatic hybrids and identified hybrids with moderate fertility. Chromosome counts of dividing root tip cells delineated tetraploid (2n = 4x = 48) and hexaploid (2n = 6x = 72) genotypes and aneuploidy in these hybrids. Meiotic analysis of developing microspores confirmed the presence of precocious division and laggard chromosomes at anaphase in both hexaploid and tetraploid hybrids. Bridges were observed in hexaploids at anaphase I and II and multivalent configurations were observed at diakinesis. Multivalents and univalents were evident in nearly all cells examined, proving that the two genomes are homoeologous. Aberrant microsporocytes with five to six developing microspores were noted in hexaploid hybrids. The occurrence of homoeologous pairing between chromosomes of both fusion parents is advantageous to effect recombination between these isolated species. However, the negative effects of multivalent formation and univalents likely contributed to observed sterility in these first generation fusion hybrids. Low to moderate levels of pollen fertility (0% to 52%) were found in tetraploid hybrids, while little or no viable pollen (0% to 4%) was observed in hexaploid somatic hybrids.

Production and characterization of “second generation” somatic hybrids derived from protoplast fusion between interspecific somatohaploid and dihaploidSolanum tuberosum L.

Protoplasts were fused to produce somatic hybrids between a triploid (2n=3x=32-34) interspecific somatohaploid betweenSolanum brevidens Phil. andS. tuberosum L., and a dihaploid (2n=2x=24) anther-derived line ofS. tuberosum cv. Van Gogh. A total of 265 plants were regenerated from protoplast fusion derived calli and their hybridity was verified using fusion partner specific RAPD markers. These “second generation” somatic hybrids were aneuploid pentaploids (2n=5x=51-65) with a 2C DNA content ranging from 3.36 to 4.43 pg, which corresponded to the sum of the 2C values of each of the fusion partners (somatohaploid: 2.22 pg; and the dihaploid line of cv. Van Gogh: 1.87 pg). Most of the “second generation” somatic hybrids were vigorous, but variable in morphology. They were extremely resistant to PLRV and they had tolerance to PVY infection derived from the somatohaploid fusion partner. Even though most of the “second generation” hybrids tuberized, the tuber morphology was variable and most were poorly shaped. InErwinia soft rot resistance tests, the tubers showed higher level of resistance than the tetraploidS. tuberosum cultivars, the dihaploidS. tuberosum fusion partners and the hexaploid somatic hybrids betweenS. brevidens andS. tuberosum. The “second generation” somatic hybrids were all male sterile and failed to produce berries or seeds.

Intertribal hexaploid somatic hybrid plants regeneration from electrofusion between diploids of Citrus sinensis and its sexually incompatible relative, Clausena lansium

Chinese wampee [Clausena lansium (Lour.) Skeels], a sexually incompatible relative of citrus, is commercially cultivated in South China. In this study, embryogenic protoplasts of ‘Bonanza’ navel orange [Citrus sinensis (L.) Osbeck] were electrically fused with leaf protoplasts isolated from ‘Chicken Heart’ Chinese wampee. After 8 months of culture, fusion products regenerated into shoots. More than 70% of the shoots unexpectedly rooted well. Chromosome counting of several shoot- and root-tips revealed that their chromosome numbers were not 2n=4x=36 as expected, but 2n=6x=54, suggesting that chromosome doubling occurred rather than chromosome elimination in this intertribal fusion combination. RAPD analysis of embryoids and the leaves of unrooted and rooted shoots verified their hybridity. This is the first report of hexaploid somatic hybrid plant regeneration from fusion between diploids in Aurantioideae.

Cytological and molecular characterization of BC1 progeny from two somatic hybrids between dihaploid Solanum acaule and tetraploid S. tuberosum

Two hexaploid somatic hybrids, DA12-3 (2n = 68) and DA28 (2n = 74), derived from cell fusion between dihaploid Solanum acaule and tetraploid Solanum tuberosum, were crossed with S. tuberosum. Two BC1 families, DA12T and DA28T, were generated, each containing 25 plants. Although the average of somatic chromosome numbers fitted hypothetical numbers assuming equal separation, considerable variation was found: 2n = 54-62 in DA12T and 2n = 58-65 in DA28T. Fifty-two of 80 RFLP single-copy probes generated 108 marker bands specific for S. acaule, by which BC1 progeny were analyzed. The segregation of marker bands from at least 44 probes was explained by two alleles per locus, which had to be heterozygous in dihaploid S. acaule and maintained in homozygous condition in homoeologous chromosomes of tetraploid S. acaule. On average, 73.7% of the chromosomes derived from S. acaule were detected as recombinants, suggesting that frequent homoeologous recombination occurred between S. acaule and S. tuberosum chromosomes. Therefore, S. acaule germplasm can be effectively transferred to the cultivated potato gene pool through backcrossing hexaploid somatic hybrids with S. tuberosum. In both BC1 families, S. acaule chromosomes 3, 4, 6, and 11 were detected as recombinants with higher frequencies (84-98%) than those of chromosomes 9 and 10 (60 and 58%, respectively), suggesting that chromosomal differentiation exists between S. acaule genomes.Key words: hexaploid somatic hybrids, Solanum acaule, homoeologous recombination, RFLP markers.

Interspecific somatic hybrids between wild potato Solanum acaule Bitt. and anther-derived dihaploid potato (Solanum tuberosum L.)

Solanum acaule Bitt. is a disomic tetraploid (4x) wild potato species which is resistant to several potato diseases. Introgression of disease resistance and abiotic stress tolerance to the tetrasomic tetraploid (4x) cultivated potato (S. tuberosum L.) gene pool via crossing has been limited due to the difference in the endosperm balance number. In the present study, protoplast fusion was applied to produce hexaploid (6x) somatic hybrids between the parental lines, tetraploid (4x) S. acaule and two anther-derived dihaploid (2x) lines of S. tuberosum cv. White Lady. One callus (0.4%) of a total of 229 calli obtained regenerated into shoots in the fusion combination S. acaule (+) White Lady 15.dh.8.2.2. All the regenerated shoots were confirmed to be interspecific somatic hybrids using species-specific RAPD markers. In another fusion combination, S. acaule (+) White Lady 7.dh.23.1.1, fifteen calli (5%) regenerated into a total of sixteen shoots from 289 calli. All the analysed somatic hybrids between S. acaule and S. tuberosum were hexaploid. The mean DNA content (2C value) of the combination S. acaule (+) White Lady 15.dh.8.2.2 somatic hybrids (4.55 pg), was approximately the sum (4.69 pg) of the DNA contents of the parental lines, S. acaule (2.95 pg) and S. tuberosum (1.74 pg). In the greenhouse, the two somatic hybrids analysed were normal in their morphological characteristics and more vigorous than their parental lines. Most of the morphological characteristics were closer to the tetraploid S. acaule than to the dihaploid S. tuberosum. The interspecific somatic hybrids are currently being tested for frost tolerance and glycoalkaloid composition.

Somatic hybrids between Solanum bulbocastanum and potato: a new source of resistance to late blight

Solanum bulbocastanum, a wild, diploid (2n=2x=24) Mexican species, is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato. However this 1 EBN species is virtually impossible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum PI 245310 and the tetraploid potato line S. tuberosum PI 203900 (2n=4x=48) yielded hexaploid (2n= 6x=72) somatic hybrids that retained the high resistance of the S. bulbocastanum parent. RFLP and RAPD analyses confirmed the hybridity of the materials. Four of the somatic hybrids were crossed with potato cultivars Katahdin or Atlantic. The BC1 progeny segregated for resistance to the US8 genotype (A-2 mating type) of P. Infestans. Resistant BC1 lines crossed with susceptible cultivars again yielded populations that segregated for resistance to the fungus. In a 1996 field-plot in Wisconsin, to which no fungicide was applied, two of the BC1 lines, from two different somatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late-blight epidemic. In contrast, under these same conditions the cultivar Russet Burbank yielded only 0.86 kg/plant. These results indicate that effective resistance to the late-blight fungus in a sexually incompatible Solanum species can be transferred into potato breeding lines by somatic hybridization and that this resistance can then be further transmitted into potato breeding lines by sexual crossing.

Fluorescence in situ hybridization of potato somatohaploids and their somatic hybrid donors using two Solanum brevidens specific sequences

Two Solanum brevidens specific repetitive DNA clones (pSB1 and pSB7) were used simultaneously as probes in fluorescence in situ hybridization (FISH) for cytological studies of somatohaploids and their somatic hybrid donors. pSB1 was labelled with digoxigenin-11-dUTP and pSB7 was labelled with biotin-14-dATP and they were detected with reporter molecules conjugated to fluorescent dyes using digital imaging. The tandemly repeated sequences hybridized mostly near the telomeres of the chromosomes of S. brevidens. Using these two probes, it was possible to identify chromosomes containing repetitive DNA of S. brevidens both in the somatic hybrids between S. brevidens and S. tuberosum, and somatohaploids derived from the somatic hybrids. These cytological analyses showed that for the largest part genomes of the hexaploid somatic hybrids and their anther-derived triploid somatohaploids were composed of the genome of S. brevidens.

Resistance to blackleg and tuber soft rot in sexual and somatic interspecific hybrids with different genetic background

Diploid interspecific hybrids from crosses between Solanum tuberosum haploids and S. canasense, S. multidissectum, and S. taTijense, along with tetraploid and hexaploid somatic hybrids S. tuberosum (+) S. commersonii, were screened for resistance to blackleg and tuber soft rot by Erwinia carotovora subsp, atroseptica and E. carotovora subsp, carotovora. Among the diploid hybrids, those involving clone mlt la of S. multidissectum and tar 2b of S. tarijense yielded the highest number of genotypes resistant to both blackleg and tuber soft rot. By contrast, all the hybrids involving clone tar 1 lb of S. tarijense were susceptible to both bacterial diseases. As far as resistance of somatic hybrids is concerned, the most interesting genotype was the tetraploid one which showed resistance to both blackleg and tuber soft rot. Significant correlations were found between E. carot0vora subsp, atroseptica and E. carotovora subsp, carotovora both in resistance to blackleg and in resistance to tuber soft rot, suggesting that resistance to the two subspecies is controlled by the same gene/s or that the relevant genes are linked. On the other hand, correlations between blackleg and tuber soft rot were never significant, indicating that different mechanisms may control resistance in tuber and stems. Alternatively, the resistance could be controlled by the same gene/s under a different spatial/temporal expression pattern. Twelve diploid sexual hybrids and one tetraploid somatic hybrid were selected for resistance to blackleg and/or tuber soft rot and for tuber characteristics.

Electrofusion of protoplasts of anther-derived dihaploid lines of commercial potato cultivars

Somatic hybrids of anther-derived dihaploid (2x) potato (Solanum tuberosum L.) lines were produced by electrofusion of protoplasts. Using RAPD (randomly amplified polymorphic DNA) markers, six new combinations of dihaploid parental lines from cultivars Matilda, Nicola, Pito, Stina, Van Gogh and White Lady were identified. RAPD marker identification of the putative hybrids was mostly done using two distinct parental line specific primers. 43% of the 76 regenerated calli from the six combinations produced hybrid shoots. Most of the somatic hybrids were tetraploid (4x), but in four fusion combinations plants of hexaploid (6x), octoploid (8x) or mixoploid level were also identified by chromosome counts or flow cytometric nuclear DNA analysis. The mean nuclear DNA content (2C value) of the tetraploid and hexaploid somatic hybrids was lower than the expected DNA content (i.e. the 2C values of the original tetraploid cultivars or the sum of the 2C values of the dihaploid fusion parents). Some somatic hybrids having the expected nuclear DNA content were also found.

Synthesis of hexaploid (AABBCC) somatic hybrids: a bridging material for transfer of ‘tour’ cytoplasmic male sterility to different Brassica species

Most of the alloplasmic cytoplasmic male sterility (CMS) systems are known to be associated with a number of floral abnormalities that result from nuclear-cytoplasmic incompatibilities. One such system, 'tour', which is derived from Brassica tournefortii, induces additional floral abnormalities and causes chlorosis in Brassica spp. While the restorer for this CMS has been reported to be present in B. napus, in B. juncea, where the abnormalities are more pronounced, no restorer has yet been identified. Rectification of these floral abnormalities through mitochondrial recombinations and chloroplast replacement might result in the improvement of this CMS system. As organelle recombinations can possibly be achieved only by somatic cell hybridization, fusion experiments were carried out between hygromycin-resistant B. juncea AABB carrying 'tour' cytoplasm and phosphinotricin-resistant, normal B. oleracea CC to generate AABBCC hexaploid somatic hybrids. The presence of selectable marker genes facilitated the selection of hybrids in large numbers. The resulting hybrids showed wide variation in floral morphology and organelle composition. Regenerants with normal, male-sterile flowers having recombinant 'tour'-or 'oleracea'-type mitochondria and 'oleracea'-type chloroplasts were obtained. Hybrids with male-fertile flowers were also obtained that had recombined 'tour' mitochondria. The AABBCC hexaploid hybrids synthesized in the present study were successfully utilized as a bridging material for transferring variability in the organelle genome simultaneously to all the digenomic Brassica species, and all of these hybrids are now being stabilized through repeated backcrosses to the allopolyploid crop brassicas.

Synthesis of hexaploid (AABBCC) somatic hybrids: a bridging material for transfer of ?tour? cytoplasmic male sterility to different Brassica species

Synthesis of hexaploid (AABBCC) somatic hybrids: a bridging material for transfer of ?tour? cytoplasmic male sterility to different Brassica species

Production and characterization of haploids derived from somatic hybrids between Solanum brevidens and S. tuberosum through anther culture

Somatic hybrids between dihaploid (2 n=2 x=24) cultivated potato Solanum tuberosum L.) and diploid (2 n=2 x=24), virus resistant wild potato species S. brevidens Phil., were tested for their feasibility for anther culture. A total of 17 shoots regenerated by embryogenesis from anthers of the hybrids. Five regenerants survived and were grown in vitro and in the greenhouse. The haploids were morphologically intermediate between S. brevidens and S. tuberosum. They were analysed for S. brevidens specific and S. tuberosum specific RAPD markers using four primers, and were found to contain the S. brevidens specific DNA markers and most of the S. tuberosum specific markers. The chromosome numbers of the haploids ranged from 34 to 36. According to flow cytometric analysis, the nuclear DNA contents of the haploids (2 C=2.15–2.30pg) were approximately half of the hexaploid somatic hybrids (2 C=4.47–4.53pg). The somatic hybrids were identified as chimeric (hypohexaploids), whereas the haploids derived from them using anther culture were all triploids according to flow cytometry. The haploids were extremely resistant to potato leaf roll virus.

Molecular, cytological and morpho-agronomical characterization of hexaploid somatic hybrids in Medicago

Somatic hybrid plants produced by protoplast fusion between tetraploid Medicago sativa (2n= 4x=32) and the diploid species Medicago coerulea (2n= 2x=16) have been RFLP fingerprinted to establish their nuclear composition. Although all of the chromosomes were present, molecular analysis revealed an incomplete incorporation of the alleles of the diploid parent in the fusion products. In the polycross progeny the alleles of both parents segregated in a Mendelian mode. Cytological observations indicated that in the somatic hybrid population minor abnormalities are present; these are restricted mainly to the formation of univalents and lagging chromosomes. Meiosis appeared to be more stable than has been previously reported in the hexaploids of alfalfa. The somatic hybrids grown in the field had a rather vigorous aspect, particularly with respect to the vegetative organs. Forage yield was comparable to that of thmore productive parent. The results are discussed with a view to utilizing the somatic hybrids as starting material for breeding alfalfa at the hexaploid level.

Resistance to potato virus Y in somatic hybrids between Solanum etuberosum and S. tuberosum x S. berthaultii hybrid

Somatic hybrids between a potato virus Y (PVY) resistant Solanum etuberosum clone and a susceptible diploid potato clone derived from a cross between S. tuberosum Gp. Tuberosum haploid US-W 730 and S. berthaultii were evaluated for resistance to PVY. All but one of the tested somatic hybrids were significantly more resistant than cultivars 'Atlantic' and 'Katahdin'. However, none was as resistant as the S. etuberosum parent. One hexaploid somatic hybrid, possibly the product of a triple-cell fusion involving one S. etuberosum protoplast and two haploid x S. berthaultii protoplasts, was as susceptible to PVY infection as the cultivars. Tetraploid progeny of the somatic hybrids, obtained from crosses with Gp. Tuberosum cultivars, were neither as resistant as the maternal somatic hybrid parent, nor as susceptible as the paternal cultivar parent. It appears that the introgression of PVY resistance from (1EBN) S. etuberosum into (4EBN) S. tuberosum (EBN-endosperm balance number) will be successful through the use of somatic hybridization and subsequent crosses of the somatic hybrids back to S. tuberosum.

Morphology, fertility and cross-compatibility of somatic hybrids between Brassica oleracea L. and B. campestris L.

Thirty-one somatic hybrids between a heat tolerant cabbage cultivar ‘Yoshin’ ( Brassica oleracea var. capitata L.) and a Chinese cabbage cultivar ‘Kenshin’ ( Brassica campestris var. pekinensis L.) were obtained with the aim of breeding new Brassica vegetables adapted to tropical areas. After excluding two hexaploid somatic hybrids, 29 individuals were investigated for pollen fertility and seed set after self-pollination and back-crossing with the parental species. All 29 amphidiploid somatic hybrids showed pollen fertility higher than 70%, and 28 set seeds by self-pollination (2.2 seeds per silique). The hybrids were cross-compatible with Chinese cabbage (1.5 seeds per silique), while practically incompatible with cabbage. Progeny lines obtained by self-pollination had larger leaves than, and intermediate leaf shape of, the parental species. The lines obtained by back-crossing with Chinese cabbage showed larger leaves than the parents and similar leaf shape to Chinese cabbage. These progeny lines, on the whole, exhibited an appreciably wide variation in both leaf size and shape. Variation was found also within the lines for leaf shape. The somatic hybrid method, therefore, could provide new genetic variations to be used to develop new vegetable cultivars.

RFLP analysis of chromosomal segregation in progeny from an interspecific hexaploid somatic hybrid between Solanum brevidens and Solanum tuberosum.

Segregation of restriction fragment length polymorphism (RFLP) loci was monitored to determine the degree of homeologous pairing and recombination in a hexaploid somatic hybrid, A206, the result of protoplast fusion between Solanum tuberosum (PI 203900, a tetraploid cultivated potato) and Solanum brevidens (PI 218228), a diploid, sexually incompatible, distant relative harboring several traits for disease resistance. Somatic hybrid A206 was crossed to Katahdin, a tetraploid potato cultivar, to generate a segregating population of pentaploid progeny. Although the clones of the tetraploid S. tuberosum lines PI 203900 and Katahdin were highly polymorphic, the diploid S. brevidens clone was homozygous at all but two of the tested RFLP loci. Thus, homeologous recombination could be detected only when S. tuberosum and S. brevidens chromosomes paired and the S. brevidens homologs then segregated into separate gametes. A bias toward homologous pairing was observed for all 12 chromosomes. At least four and perhaps six chromosomes participated in homologous pairing only; each of 24 progeny contained all S. brevidens-derived RFLP markers for chromosomes 4, 8, 9 and 10. The remaining six chromosomes paired with their homolog(s) about twice as often as expected if hexaploid pairings were completely random. Where detectable with RFLPs, homeologous recombination (both single and double) occurred at a frequency of 1.31 per chromosome. Cytological observations of meiosis I in the somatic hybrid indicated that homeologous pairing had occurred. Enhanced recombinational activity was observed for chromosome 2. A specific small deletion from chromosome 4 was detected in A206 and 11 other somatic hybrids out of 14 screened.(ABSTRACT TRUNCATED AT 250 WORDS)

Hybridization, Through Culture of Embryos and Immature Seeds, of a Range of Tomato Cultivars with a Tomato Somatic Hybrid [Lycopersicon esculentum (+) L. peruvianum]: Emergence of a Possible New Marker Gene for Tomato Breeding

AbstractTwo hexaploid somatic hybrids [Sh; L. esculentum (+) L. Peruvianum] accessions 6 and 18 were back‐crossed with two diploid L. Esculentum cultivars ‘Moneymaker’ (mm) and ‘pusa Ruby’ (pr). Twenty‐two plants of the bc2 generation were produced by backcrossing 7 bcl plants (mm x sh, 6, 18) with five tomato cultivars. Fourteen of the bc2 plants were self‐fertile, five produced anther cones with anthocyanin pigmentation not present in the parents. A bc3 generation was developed by crossing the four cultivars as female parent with three bc2 generation plants. The bc3 progeny derived from one pollen parent plant were produced without the need to culture immature seeds. They segregated with respect to pigmented anther cones and were self‐fertile. The anther cone pigmentation of the pollen parent plant was associated with increased seed set, greater fruit size and an orange‐red fruit colour. These features were transmitted to the fertile bc3 generation. Conversely, bc3 offspring involving the other two parent plants were only recovered by culture of immature seeds. The recovery of diploid plants in BCl and self‐fertility in BC2 resulted in almost total recovery of the tomato cultivar characteristics (fruit size, colour and number of seeds) by BC3.