Double-bridge hybrids of Solanum bulbocastanum and cultivars of Solanum tuberosum

Summary Solanum bulbocastanum (2n=2x=24) has valuable characters for potato breeding, but cannot be hybridized directly with S. tuberosum cultivars. Both S. acaule (2n=4x) and S. phureja (2n=2x) were used as bridging species. Triploid S. acaule × S. bulbocastanum were doubled with colchicine and the resulting fertile hexaploid F₁'s crossed with S. phureja. The triple hybrids obtained were tetraploid or nearly so. The two genomes of S. acaule in these triple hybrids probably pair preferentially, which may provoke pairing and possibly crossing over between the chromosomes of S. bulbocastanum and S. phureja.More than 20000 pollinations of the triple hybrids with four potato cultivars had to be made to produce 40 quadruple hybrids. These highly vigorous hybrids varied greatly in many morphological characters, resistance to Phytophthora infestans, fertility and crossability. The chromosome numbers are 48 (24 hybrids), 49 and 46, but some higher ploidy levels (65, 66, 72 chromosomes) were found as well. Their origin is to be sought in the fusion of an unreduced egg cell from triple hybrids (either euploid or hypoploid) and a reduced male gamete from the cultivars. This view is corroborated by their extreme resistance to Phytophthora. Also some 48-chromosome hybrids are highly resistant, which may indicate introgression from S. bulbocastanum.Most quadruple hybrids are readily inter-crossable and crossable as females with cultivars; several also as males. Two could be hybridized with S. bulbocastanum, but the few seeds dit not germinate.Studies of pachytene stage of meiosis revealed the presence of a S. bulbocastanum chromosome in at least one tetraploid hybrid, which is highly resistant to Phytophthora. At metaphase I of meiosis chromosome associations higher than quadrivalents were not found. Except in one hybrid, the frequency of quadrivalents did not exceed one per cell and the average proportion of chromosomes associated as bivalents amounted to 90%.The quadruple hybrids (double-bridge hybrids) appear good starting material for breeding programmes aimed at introducing genes from S. bulbocastanum into S. tuberosum cultivars.     

Meiosis in different F1-hybrids of Solanum acaule Bitt. x S. bulbocastanum Dun. and its bearing on genome relationship,fertility and breeding behaviour

Summary Meiosis was studied in some triploid, tetraploid and hexaploid F₁-hybrids from Solanum acaule x S. bulbocastanum and in a triploid F₁-hybrid from S. acaule x S. tuberosum-haploid.The only anomaly found was stickiness at metaphase I, the degree of which appeared to be related to the proportion of the S. bulbocastanum chromosomes in the hybrids. No stickiness occurred at pre- and post-metaphase stages.A clear allosyndetic pairing between chromosomes of the two S. acaule genomes was observed in all triploid and tetraploid hybrids. These genomes apparently are closely related and little differentiated. The triploids S. acaule x S. bulbocastanum had 0–1 trivalent per cell, whereas 2–5 trivalents per cell were observed in the triploid S. acaule x S. tuberosum-haploid. Therefore S. acaule is more closely related to S. tuberosum L. than to S. bulbocastanum. A small amount of pairing between S. acaule and S. bulbocastanum is apparent from the occurrence of multivalents in all hybrids.Hexaploid F₁'s (2n=72) showed a nearly complete homologous pairing of chromosomes (35.2 bivalents per cell) and generally a normal separation of chromosomes at anaphase: 36-36. This offers an explanation for their high fertility. Triploid F₁'s from S. acaule x S. bulbocastanum have a high frequency of univalents leading to irregular separation of chromosomes at anaphase and consequently to unbalanced gametes and extreme sterility. In the tetraploid F₁'s (2n=48) nearly complete bivalent pairing was observed, 50% expectedly being homologous and 50% homoeologous pairing. Separation of chromosomes at anaphase was generally normal 24-24. In spite of this normal behaviour and allowing for tight stickiness at metaphase the tetraploids are very sterile. A satisfactory explanation cannot yet be given.Selfing and intercrossing hexaploid F₁'s gives normal berry set and many seeds per berry. However crosses with S. tuberosum and even those with the fertile hexaploid hybrid from 8x-S. acaule x 4x-S. tuberosum are little successful: berry set is far below normal and the berries are either parthenocarpic or contain only one or two seeds. These rather unexpected results warrant further investigation. Large-scale selfings and intercrosses of triploid and tetraploid hybrids have not been successful as yet. Among the female gametes of tetraploid hybrids a few appeared to be functional in crosses with hexaploid hybrids and in those with S. bulbocastanum.     

Somatic chromosome elimination and meiotic chromosome pairing in the triple hybrid 6x-(Solanum acaule × S. bulbocastanum) × 2×-S. phureja

Summary Two selected hexaploid F₁ clones from the cross Solanum acaule x S. bulbocastanum were intercrossed and the resulting hybrid plants pollinated with the diploid species S. phureja, in order to obtain tetraploid triple hybrids with the same ploidy level as S. tuberosum cultivars (2n=4x=48).Apart from three trihaploids a large population of triple hybrids was obtained, showing chromosome mosaicism in root tip cells (euploid + hypoploid chromosome numbers) and a uniform, mostly hypoploid chromosome number in the pollen mother cells. It is demonstrated that somatic chromosome elimination in the early stages of development is the most probable cause.From detailed pachytene observations as well as from the chromosome associations observed at metaphase I it is evident, that there is normal pairing between the four genomes in the triple hybrids. Although S. bulbocastanum is a quite distinct species with a rigid crossability barrier with S. phureja, the chromosomes of these two species appear to have a high degree of homology. Especially the formation of quadrivalents involving all twelve groups of four homeologous chromosomes, indicated that the four parental genomes (two from S. acaule, one from S. bulbocastanum and one from S. phureja) are not differentiated to the extent of affecting normal pairing and chiasma formation. These results support the view, that the transfer of valuable characters from S. bulbocastanum to S. tuberosum cultivars is feasible even when these characters are polygenically controlled.     

Crossability,fertility and cytogenetic studies in Solanum acaule × Solanum bulbocastanum

From 538 cross combinations made between 20 accessions of S. acaule and 28 clones of S. bulbocastanum 150 different F₁'s were obtained. Average berry set was 11%, average number of seeds per berry 0.7. The accessions of both parent species could be divided into distinct groups on the basis of the crossability. Of the 72 F₁-clones examined 59 were triploid and 13 were tetraploid. Evidence is presented that the 4x-F₁'s originated from unreduced gametes produced by two bulbocastanum accessions. Pollen stainability of the 6x-, 8x-, 4x- and 3x-F₁'s was 85, 29, 12 and <5% respectively. The genomic constitutions of the F₁'s adequately accounted for these fertility relations. Selfing of F₁'s was successful with 6x-F₁'s only. Crosses between the F₁'s and S. tuberosum, tuberosum-haploids and S. demissum did not succeed in spite of the large number of pollinations made. A breeding programme is recommended to be carried out within the hexaploid hybrid populations which aims at late blight resistance and crossability with S. tuberosum. The quadruple cross (acl × blb) × (acl × tbr) and the direct cross between S. tuberosum and S. bulbocastanum are discussed.     

Barriers to hybridization of Solanum bulbocastanum Dun. and S. Verrucosum Schlechtd. and structural hybridity in their F1 plants

Summary Results of reciprocal crosses between Solanum verrucosum (2n=2x=24) and S. bulbocastanum (2n=2x=24) are described in terms of pollen tube behaviour in styles, of berry and seed set, of fertility and of meiotic behaviour of the F₁ hybrids. Pollen tube growth of S. verrucosum is strongly inhibited in styles of S. bulbocastanum, whereas no inhibition is observed in the reciprocal cross. Therefore S. bulbocastanum x S. verrucosum fails to set berries or seeds, whereas the reciprocal cross produces both berries (54.4% berry set) and seeds (0.3 per berry). Only 14.6% of the seeds germinate. Both the diploid and corresponding tetraploid hybrid plants are vigorous, flower abundantly, have a rather regular meiosis (mainly rod bivalents), but show a high degree of cytoplasmic-genic male sterility. Crossability of the diploid hybrid plants is nil when used as pollen parents and near to zero when used as pistillate parents. The barriers to hybridization of the parent species (unilateral inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and structural differences of the parental chromosomes) are discussed and methods are suggested to overcome these barriers.     

Natural hybridization between Solanum acaule Bitt. and S. megistacrolobum Bitt. in the province of jujuy,Argentina

Summary Evidence is provided that hybridization of the tetraploid (2n=4x=48), self-fertile tuber-bearing species Solanum acaule Bitt. with the diploid (2n=2x=24), self-incompatible, tuber-bearing S. megistacrolobum Bitt. takes place in several localities of the province of Jujuy in the high, cold plateaux of the Argentine Puna. The triploid hybrids (2n=3x=36) closely resemble S. acaule in growth habit, leaf morphology and floral structures and for this reason they can be easily overlooked for that species in the field. Experimental data show that S. acaule can be crossed with S. megistacrolobum though the crossability is rather low and variable according to the particular cross considered. The artificial hybrid obtained compares well with the natural hybrid in morphology and chromosome number. The hybrids, though almost completely male sterile, are successful colonizers of disturbed areas around farmers' dwellings, cattle enclosures and other areas where the soil is rich in organic matter.There is some evidence that the Tilcara material of S. acaule subsp. aemulans and the hybrids of S. acaule x S. megistacrolobum have some characters in common, which can be interpreted as having a similar origin.It is postulated that S. acaule subsp. aemulans, in Jujuy at any rate, is not a primitive form of S. acaule as thought by Hawkes and Hjerting, but rather a fertile hybrid derivative of S. acaule x S. megistacrolobum through the functioning of 2n gametes.We also provide evidence that S. bruecheri Correll should not be considered a hybrid of S. acaulle x S. megistacrolobum but a synonym for S. gourlayi Hawkes. The new name, S. x indunii Okada et Clausen, is proposed to designate this hybrid.     

Induction of an alloplasmic male-sterile Brassica oleracea by substituting cytoplasm from ‘Early Scarlet Globe’ radish (Raphanus sativus)

Summary Alloplasmic male-sterile Brassica oleracea L. was synthesized in a backcrossing program through amphidiploid Raphanobrassica by using Early Scarlet Globe radish (Raphanus sativus L.) as the donor of cytoplasm and B. oleracea broccoli and cabbage as recurrent pollen parents. Persistence of radish chromosomes and high female sterility were encountered in the first four backcrosses. Following use of colchiploid 4x broccoli as pollen parent, a BC₅ plant was obtained that had 2n=3x+1=28 chromosomes, improved seed set, and no radish traits. The BC₆ with recurrent 2x broccoli contained male-sterile plants with 2n=18 or 19 chromosomes, increased seed set, and broccoli morphology. Subsequent generations segregated for male-sterile and restored male-fertile plants, some with variable development of stamens and pollen. Leaf color of the alloplasmic plants, especially seedlings, was lighter green than normal.     

Crosses between Beta vulgaris L. and Beta lomatogona F. et M.

Summary A population of 2x^ms sugar beets was crossed with 4x Beta lomatogona F. et M. The 3x F₁-plants were male sterile and were backcrossed with 2x and 4x sugar beets and multiplied without pollination as well. After the 1st backcross mainly 3x apomict types arose again and, among others, a small number of successful 4x backcrosses. After pollination by 4x sugar beets this 4x F₁ B₁ produced. besides predominatly apomictically multiplied 4x plants, also about 7% haploid 2x hybrids. The latter probably possess 1 genome from B. vulgaris and 1 genome from B. lomatogona. In the meiosis of the PMC's a certain amount of homeology between a number of chromosomes of both species could be established. The amphihaploid hybrids can be used as breeding parents for the creation of types in which introgession can occur. During hybridization in addition to 2x and 4x B. vulgaris types a number of 2x-, 3x-, 5x- and 6x-hybrids arose. This is presumably caused by the presence of gametes with the somatic number of chromosomes and the occurrence sometimes of haploid apomictic multiplication.The presence of large numbers of bolters in the F₁ and F₁ B₁ suggests that the bolting tendency of both species is based on different genes.     

The breeding of the cultivated potato species solanum x juzepczukii and S. x curtilobum II. The resynthesis of S. x juzepczukii and S. x curtilobum

Summary The possibility of combining anew the genomes of wild and cultivated progenitors of triploid S. x juzepczukii and pentaploid S. x curtilobum by following the known evolutionary pathway of these species was investigated.The resynthesis of S. x juzepczukii was easy, and a wide range of synthetic forms was bred. Among these were forms with higher frost resistance (-5°C) than has been found in natural S. x juzepczukii. The total tuber glycoalkaloid content of several synthetic hybrids was lower than or as low as that of natural clones. Most synthetic hybrids were more vigorous than natural S. x juzepczukii and produced about the same types of tubers as are found in the natural range of variation. The best diploid parents were found in the species S. goniocalyx.The attempt to resynthesize pentaploid S. x curtilobum has not been successful but tetraploid plants were obtained in the process. An explanation for the occurrence of tetraploids resulting from triploid x tetraploid and/or diploid crosses is offered.The newly bred tetraploids contain at least one genome from S. acaule (possibly two) and hybridize easily with ssp. andigena. They thus provide a means for the transfer of S. acaule germ plasm into the tetraploid cultivated gene pool which would profit from the frost resistance of S. acaule.     

Breaking the crossability barriers between disomic tetraploid Solanum acaule and tetrasomic tetraploid S. tuberosum

Summary A combination of compatible second pollinations and embryo rescue was applied for systematic production of true tetraploid hybrids from crosses between disomic tetraploid Solanum acaule and tetrasomic tetraploid potato, S. tuberosum. Several genotypes of tetraploid potatoes were pollinated with S. acaule, and the compatible second pollinations were made on the following day, with a genotype of S. phureja, IvP 35 to promote fruit development. Embryo rescue was carried out in 21 families, 14 to 27 days after the first pollination. A total of eight plants were obtained from the embryo rescue and their chromosome numbers were counted in the root tips. Three of the eight plants were identified as tetraploid, and five others as diploid. Morphology, isozyme banding patterns, and pollen stainability, as well as potato spindle tuber viroid (PSTVd) resistance, indicated the hybrid nature of the three plants. This is the first report of successful tetraploid hybrid production between disomic tetraploid S. acaule (4x) and tetrasomic tetraploid potatoes. Seed set from the crosses between one of hybrids and diploid potatoes indicated workable levels of both male and female fertility for introgression of valuable genes from S. acaule into the cultivated potato gene pool. The methodology used may be applied to other disomic tetraploid tuber-bearing Solanum species and with some modifications also to distantly related solanaceous species and genera.     

Transfer of resistance to race 2 of Plasmodiophora Brassicae from Brassica napus to cabbage (B. oleracea var. Capitata). I. Interspecific hybridization between B. napus and B. oleracea var. Capitata

Summary Interspecific hybridization between Brassica napus L. (2n=38, a₁a₁c₁c₁) and B. oleracea var. capitata L. (2x- and 4x-cabbage; 2n=2x=18, cc and 2n=4x=36, cccc) was carried out for the purpose of transferring clubroot disease resistance from the amphidiploid species to cabbage. Nineteen hybrids with three different chromosome levels (2n=28, a₁c₁c; 2n=37, a₁c₁cc and 2n=55, a₁c₁cccc) were obtained. The F₁ plants were mostly intermediate between the two parents but as the number of c genomes in the hybrids increased, the more closely the hybrids resembled the cabbage parent. All F₁ hybrids were resistant when tested against race 2 of Plasmodiophora brassicae wor. The complete dominance of resistance over susceptibility suggested that the gene(s) controlling resistance to this particular race of the clubroot pathogen is probably located on a chromosome of the a genome in Brassica.Contribution No. J654.     

Amphidiploids between Cyclamen persicum Mill. and C. purpurascens Mill. induced by treating ovules with colchicine in vitro and sesquidiploids between the amphidiploid and the parental species induced by conventional crosses

Summary We cultured colchicine-treated hybrid ovules in vitro to produce fertile amphidiploids of C. persicum (2n=2x=48. referred to as AA) × C. purpurascens (2n=2x=34, referred to as BB). Seedlings and mature plants were obtained from the ovules without colchicine and those exposed to 50 mg/l colchicine for 5, 10 and 15 days, whereas they were not obtained from the ovules exposed to 50 mg/l colchicine for 20 days and 500 mg/l for 5, 10, 15 and 20 days. Although 8 mature hybrids derived from the ovules without colchicine produced a few fertile pollen grains, they failed to produce viable seeds by self-fertilization. The hybrids had 41 somatic chromosomes. Four and 3 mature plants were derived from ovules exposed to 50 mg/l colchicine for 10 and 15 days, respectively. One each among 4 and 3 mature plants showed a high frequency of pollen grain fertility, produced several seeds by self-fertilization, and had 82 somatic chromosomes which is twice the number of hybrid chromosomes (2n=41, AB). These findings indicated that these plants are amphidiploids (2n=82, AABB) between C. persicum and C. purpurascens. Three and 2 viable seeds were derived by the conventional crosses of diploid C. persicum × the amphidiploid and the amphidiploid × C. purpurascens, respectively. Flowering plants that developed from the seeds of diploid C. persicum × the amphidiploid were barely fertile and had 65 somatic chromosomes (2n=65, AAB), whereas those that developed from the seeds of the amphidiploid × C. purpurascens were barely fertile and had 58 somatic chromosomes (2n=58, ABB). The somatic chromosomes indicated that these plants are probably sesquidiploids between the amphidiploid and either C. persicum or C. purpurascens. The interspecific cross-breeding of cyclamen using the amphidiploids and the sesquidiploids is discussed.     

Glandular hair densities in three perennial Medicago species

Summary Eight triazine resistant (Brassica napus x B. oleracea) x B. oleracea interspecific hybrids with chromosome numbers ranging from 25 to 27 were backcrossed a second time to B. oleracea but no seed was formed. However, in vitro embryo rescue on 77 developing ovules yielded nine BC₂ plants with chromosome numbers between 19 and 25 and in which the herbicide resistance was still strongly expressed. Three of these plants (NOH-8B2B1, 2n=20; NOH-8B2B3 and NOH-8B2B4, 2n=19) were backcrossed again to B. oleracea. Two of the three plants produced seed which germinated to produce triazine resistan BBC₃s with 18, 19 or 20 chromosomes. The triazine resistant B. campestris cytoplasm has now been stabilized in B. oleracea.     

Elymus canadensis×Secale cereale Amphiploids. II. Chromosome Constitutions and Pairing of Open-Pollinated Progeny

Eleven C₂ and two C₃ 0pen-pollinated plains from Elymus canadensis × Secale cereale amphiploid plants (2n = 6x = 42, SSHHRR) were examined for chromosome constitution and meiosis. Chromosome numbers of the progeny varied: 2n = 26, 27, 28, 36, 37, 39, 40, and 41. Elimination of portions of genome constituents were made at random and were irregular in all o the progeny. Monosomic (2n = 41) and nullisomic (2n = 40) plants lost one to two E. canadensis or S. cereale chromosomes and showed average of 17 to 18 bivalents and 4 to 5 univalents per cell at Ml. The C₂, aneuploid plants with 36 to 41 chromosomes seemed to result from selfing or intercrossing among; the C₁ amphiploid plants, while the plants of 2n = 26 to 2S (6–9 II + 10–141) might originate from outcrosses of the C_l amphiploid to S. cereale. Bivalent pairing might be preferentially intragenomic (S-S, H-H, or R-R). The occurrence of multivalents indicates a low potential of both intragenomic and intragenomic pairing; Pollen of the lour plants showed poor stainability (1 to 13 %) and no seed set in any of the progeny.     

Use of Vaccinium octoploids to facilitate 4x-6x gene transfers

The use of an 8x Vaccinium produced through doubling a tetraploid hybrid with colchicine was studied as a means of facilitating gene exchange between V. corymbosum L. and V. ashei Reade. Analysis included meiotic observations and crossability studies of the 8x plant, as well as attempting to develop 6x breeding lines. Meiotic analysis revealed the presence of micronuclei in Telphase II products and polyspory in sporads. In the crossability studies five 4x highbush plants were pollinated with 8x o2 4x pollen. Data gathered included: % fruit set, average weight/fruit, average number of seeds/fruit, average number of seedlings/pollination, and number of 6x seedlings. Octoploid pollinations were significantly lower than 4x pollinations in all parameters. One 6x plant was produced from the 4x-8x crosses but was found to be mitotically unstable, having somatic cells with chromosome numbers ranging from 48 to 168.     

Colchicine, trifluralin, and oryzalin promoted development of somatic embryos in Ilex paraguariensis (Aquifoliaceae)

A protocol for somatic embryogenesis and plant regeneration of Ilexparaguariensis St. Hil. from embryos cultures was developed. Heart stage zygotic embryos were removed from seeds of immature, light green fruit and treated with antimicrotubule agents (0.1; 0.2, and 0.5% colchicine for 24 and 48 h; 1; 10, and 20 M of either trifluralin, - trifluoro- 2,6-dinitro-N,N- dipropyl-p-toluidine, or oryzalin, 3,5-dinitro-N₄, N-dipropylsulphate during 48 h). The embryos were cultured aseptically on quarter-strength Murashige and Skoog medium containing 3% sucrose, 0.65% agar (1/4MS), and 0.46 M zeatin. Cultures were incubated in darkness at 27 ± 2 °C. All thetreatments provoked a diminution of the number of germinated embryos and in some of the treated embryos somatic embryogenesis was induced. Somatic embryo maturation and conversion into whole plants could be achieved by culturing the embryos on 1/4MS lacking hormones and incubated at 27 ± 2 °C, 14 h photoperiod (116 mol m^-2s^-1). Mostof the plants regenerated from somatic embryos appeared morphologically normaland grew under greenhouse conditions. Only 2 plants out of 152 studied contained the tetraploid number of the chromosomes (2n = 4x = 80), meanwhile the rest of the plants had the normal diploid number of chromosomes (2n =2x = 40). Somatic embryos with abnormal morphology were also observed.     

Identification of primary trisomics and other aneuploids in foxtail millet

A complete set of nine primary trisomics (2n+ 1) for cv.‘Yugu No. 1’of foxtail millet, Setaria italica (L.) Beauv. (2n= 2x= 18), was identified cytologically from progenies derived from crosses between autotriploids(2n= 2x= 27) and their diploid counterparts. Five autotriploid plants were identified from 2100 seedlings derived from 4x-2x crosses; the reciprocal crosses (2x-4x) failed to produce autotriploids. Autotriploids grew vigorously and were morphologically very similar to diploids. Theprimary trisomics (2n= 2x= 19) constituted ?32.5% of the total progeny from the 3x-2x crosses, whereas 59.8% of the descendants were aneuploids with chromosome numbers ranging from 20 (double trisomics and tetrasomics) to 37 (2n= 4x+ 1; or autotetraploid with one additional chromosome). The nine primary trisomics identified were self-fertile; seven had characteristic morphology, whereas trisomics VIII and IX resembled the disomics. The seed set for trisomic V was the lowest (20%), and trisomic VIII the highest (74%). Other aneuploids with 20 or more somatic chromosomes were either self-sterile or partially fertile with various, but low, levels of seed set. Each of the primary trisomics showed its unique transmission rate when self-pollinated; trisomic IX had the highest (45.8%), whereas trisomic V had the lowest (19.6%) transmission rate.     

Studies on the use of Solanum acaule as a bridge between Solanum tuberosum and species in the series Bulbocastana,Cardiophylla and Pinnatisecta

Preliminary results have indicated that Solanum acaule can serve as an intermediate for gene transfer from Solanum species in the Mexican series Bulbocastana, Cardiophylla and Pinnatisecta to Solanum tuberosum. Clones of S. acaule vary in their effectiveness as female parents in crosses with the Mexican species. The F1 hybrids obtained were sterile triploids. Fertile hexaploids were produced from the triploids by colchicine treatment. The hexaploid from the cross S. acaule x S. pinnatisectum was successfully crossed with diploid and tetraploid forms of series Tuberosa. Some of the resultant triple hybrids were self-fertile.     

Development of tetraploid plants from an interspecific hybrid between mungbean (Vigna radiata) and rice bean (Vigna umbellata)

Mungbean (Vigna radiata) and rice bean (V. umbellata) (both species 2n = 2x = 22) have desirable traits that complement each other. In this study, we rescued embryos from a cross between mungbean cv. “Kamphaeng Saen 2” and rice bean cv. “Miyazaki” and resolved the hybrid sterility problem by colchicine treatment. The interspecific hybrids were obtained when Kamphaeng Saen 2 was used as the female parent. Four out of 80 immature seeds at 12 days old were able to germinate on an MS medium supplemented with 1 mg L^?1 IAA, 0.2 mg L^?1 kinetin, and 500 mg L^?1 casein hydrolysate. Forty random amplified polymorphic DNA (RAPD) primers were screened for polymorphism among the parents, and two specific primers were finally chosen for testing of hybridity. Using the two primers, all putative F₁ hybrids were confirmed as the interspecific hybrids. To observe their fertility, some of the hybrid seedlings were transplanted. The hybrid produced flowers profusely but failed to set pods. To overcome the sterility, plants were induced to become tetraploid by colchicine treatment in vitro. The ploidy level of the regenerated seedlings was confirmed from leaf DNA using a flow cytometer. Three out of 20 hybrid seedlings (15%) were successfully induced from diploid to tetraploid by a colchicine concentration of 2 g L^?1. The tetraploid hybrids were able to produce flowers and set pods normally.     

Induction of haploids and aneuhaploids in colchicine-induced tetraploid Solanum chacoense Bitt.

Summary The species Solanum chacoense BITT. (2n=2x=24) is a tuber-bearing, self-incompatible species which is important both for breeding and for genetic research. It crosses readily with most other tuber-bearing Solanum species including the common potato S. tuberosum (2n=4x=48). Gametophytic incompatibility hampers research in and utilization of this species. Doubling the chromosome number by colchicine makes it a self-compatible autotetraploid. By crossing selfed progeny of 4x-S. chacoense with a number of haploid-inducing diploid Solanum species a high yield of different dihaploid S. chacoense individuals (2n=24) could be obtained from one originally diploid clone: S. chacoense CPC 1153. More than 160 haploids showing a large variability were identified. The average haploid frequency was 53.7 per 100 berries. Most hybrid plants (70–100%) from four 4x × 2x crosses studied were tetraploid. The frequency of triploid hybrids was low (0–10%). Haploid-inducing capacity of fifteen male parents used in this study varied from 0–141 haploids per 100 berries. Careful examination of 156 haploids revealed 15 viable aneuhaploids (2n=25, 26, and 27), i.e. 9.4%. The potential value of these aneuhaploids is discussed.About 50% of the haploids were sufficiently male fertile to use them in crossing. A few of them set berries after selfing. Five aneuhaploids including the one with 27 chromosomes were successfully crossed as females with a diploid hybrid clone.