Ploidy races in Actinidia chinensis

Summary Ploidy levels were examined in 26 accessions of Actinidia chinensis: 20 accessions were diploid (2n=2x=58) and 6 accessions were tetraploid (2n=4x=116). There was no evidence of variation in ploidy level within an accession. Our results are consistent with tetraploid A. chinensis coming from a restricted part of China.Interploid crosses within A. chinensis produced only low numbers of seedlings which were mainly triploid. Crossing hexaploid A. deliciosa with pollen of tetraploid A. chinensis produced a large family of plants and those checked were pentaploid.Counts on 83 genotypes of different ploidy levels (2x, 3x, 4x, and 5x) confirmed that the basic chromosome number in Actinidia is 29.     

The transfer of triazine resistance from Brassica napus L. to B. oleracea L. III. First backcross to parental species

Summary Atrazine resistant Brassica napus × B. oleracea F₁ hybrids were backcrossed to both parental species. The backcrosses to B. napus produced seeds in both directions but results were much better when the F₁ hybrid was the pollen parent. Backcrosses to B. oleracea failed completely but BC₁s were rescued by embryo culture both from a tetraploid hybrid (2n = 4x = 37; A₁C₁CC) and sesquidiploid hybrids (2n = 3x = 8; A₁C₁C). Progeny of crosses between the tetraploid hybrid and B. oleracea had between 25 and 28 chromosomes. That of crosses between the sesquidiploid hybrid and B. oleracea had between 21 and 27. A few plants that had chromosome counts outside the expected range may have originated from either diploid parthenogenesis, unreduced gametes or spontaneous chromosome doubling during in vitro culture. Pollen stainability of the BC₁s ranged from 0% to 91.5%. All the BC₁s to B. oleracea were resistant to atrazine.     

Variation for crossability in a reciprocal,interspecific cross involvingHordeum vulgare andH. lechleri

Summary Several crossing series including the hexaploid (2n=6x=42), South American speciesHordeum lechleri and diploid (2n=2x=14) cultivated barley (H. vulgare) were performed. Barley functioned better as the paternal than as the maternal parent in all cases. Viable offspring were only obtained from one hybrid combination when barley was used as the maternal parent. There was an environmental influence on the success of crosses. A high seed set was counteracted by a lower germination frequency. The outcome is that different crossing series give similar results. As a result of chromosome elimination and in a few cases duplication of especially the barley chromosomes, the chromosome numbers of the offspring (239 plants) varied from 2n=21 (trihaploids ofH. lechleri) to 2n=30. Fifty-five % of the plants were euploid with the number expected for a hybrid (2n=28). The frequency of hyperploids, euploids, hypoploids (2n=22–27) and trihaploids varied by year, locality, type (winter/spring) of barley,H. lechleri population, and crossing direction.     

A new source of cytoplasmic male sterility in sunflower

Summary Interspecific substitutions of the nucleus of Helianthus annuus (2n=34) cv. Saturn into the cytoplasm of H. petiolaris (2n=34) by successive backcrossing, resulted in progenies with indehiscent anthers containing white, rather than normal yellow, pollen. Further backcrossing by cv. Saturn failed to restore pollen shed, suggesting that the male sterility was cytoplasmic. In vivo germination tests of pollen from 23 such plants from eight BC₅ lines, indicated complete pollen sterility for 14 plants, but normal seed set, suggesting that female fertility was not affected. Meiosis in all plants examined was normal.Crosses between seven sources of pollen-fertility restorer, one collection of wild H. annuus, and an existing source of cytoplasmic male sterility, resulted in a high frequency of plants with normal pollen shed in all F₁ progenies. However, no normal pollen shed was evident in F₁ progenies for similar crosses between BC₅ male-steriles and three of the seven restorer sources, nor for the single wild H. annuus evaluated. The foregoing suggests that the backcross substitution lines are a new source of cytoplasmic male sterility. The inheritance of restoration of pollen shed was complex and not fully elucidated. Some data suggested that two independent, complementary, dominant genes were required, but others indicated two to three independent, dominant genes.     

Breeding barriers between the cultivated strawberry, Fragaria × ananassa, and related wild germplasm

Five-hundred interspecific and intergeneric crosses were performed among accessions of the wild strawberries Fragaria vesca(2x), Duchesnea indica (8x), Potentilla tucumanensis (2x) and 9 genotypes of the cultivated strawberry, Fragaria×ananassa (8x), following an incomplete diallele mating design. Crosses between D. indica and F.×ananassa produced many putative hybrids when D. indica was used as female but a few achenes and plants when used as male; therefore, pollen-pistil compatibility relations were analyzed by fluorescence microscopy in this direction of the cross. Of the genotypic combinations, 78.6% were incompatible at the stigma level and 17.2% at the first third of the style. Only 3.6% were pollen-pistil compatible and produced fruits with achenes (seven did not germinate or originated short-lived plants and nine produced normal plants). F.vesca×F.×ananassa crosses produced 35 hybrid achenes but only 14% germinated, yielding short-lived plants; histological analyses revealed that inviable seeds had less developed (or collapsed) endosperms and smaller embryos than control plump F. vesca seeds. P.tucumanensis was only used as male, with negative results. These species and genera are partially isolated by a complex system of pre- and post-zygotic barriers. Knowledge of their nature would allow the breeder to devise strategies to put the genetic variability available in the group into a useful form. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Characterization of morphological variation and cold resistance in interspecific somatic hybrids between potato (Solanum tuberosum L.) and S. brevidens Phil.

Summary Somatic hybrids between Solanum tuberosum L. cv. Gracia (2n=4x=48) and Solanum brevidens Phil. (2n=2x=24) were produced via fusion of mesophyll protoplasts. Selection of the protoplast derived putative hybrid calli was based on their vigorous growth. Additive isozyme patterns and chromosome numbers as well as the expression of parental morphological characters have proved the hybrid origin of the selected regenerants. Extensive chromosome loss during the regeneration process resulted in aneuploid hybrids with high frequency. Genomic instability could not be detected in these plants during the period of vegetative propagation. Regenerants from hybrid tissues exhibited wide morphological variation especially in tuber formation. The detailed morphological analysis based on the use of multivariate method (principal component analysis, PCA) enabled to identify morphological groups among the hybrid clones. The positioning of hybrid clones in the PCA space could not be correlated with chromosome numbers. The genomic ratio represented by the tetraploid and diploid parents influenced the morphology of somatic hybrid population according to the applied analytical system. Two selected hybrid clones have exhibited an intermediate degree of frost tolerance compared to the parents, based on the recovery of plants from lower buds after freezing of potted plants.     

An evaluation of intergeneric hybridization of Fragaria spp. x Potentilla spp. as a means of haploid production

Summary Unidirectional intergeneric crosses using octoploid and hexaploid Fragaria species as a female parent and diploid and tetraploid Potentilla species as a male parent were performed, producing in toto 1345 fruits with an estimated 46089 seeds. The germinating seeds obtained by using P. anserina mostly perished at the cotyledon stage, a few developing into matroclinous octoploid seedlings. The seeds obtained by using P. fruiticosa produced two types of seedlings: matroclinous octoploids and genuine intergeneric hybrids. It is considered that the matroclinous octoploids resulted from contamination during the emasculation process. A great majority of the hybrid seedlings were slow in growth and development and perished before reaching the flowering stage. No haploids have been recovered. Possible reasons for absence of haploid genotypes in the progenies of these intergeneric crosses are considered. Among the seedlings of F. x ananassa cv. Tioga x P. fruiticosa, a seedling of an unusual phenotype was noticed, which upon chromosome determination, proved to be 2n=9x=63. This genotype displayed complete male and female sterility. The implication of the sterility of this seedling for bridging of the two genera is discussed.This research was performed as part of a cooperative project on genetic improvement of cultivated strawberry between the Fruit Laboratory, USDA, Beltsville and NJAES. Paper of the Journal Series, D-12102-16-83. New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08903.     

A self-fertile trigeneric hybrid in the Triticeae involving Triticum,Hordeum, and Secale

Summary A self-fertile trigeneric hybrid in the Triticeae involving species from the Hordeum, Triticum and Secale genera has been produced. The trigeneric hybrid was obtained by crossing octoploid triticale (x Triticosecale Wittmack) with octoploid tritordeum (H. chilense × T. aestivum amphiploid). The trigeneric hybrid presented a genome constitution AABBDDRH^ch and 2n=8X=56 chromosomes. The cytogenetical analyses showed no chromosome instability nor homeologous pairing between Hordeum and Secale chromosomes. In the F₂ generation the chromosome number ranged from 42 to 52. Within this range, the plants with smaller numbers of chromosomes were more frequent. A preferential transmission of rye chromosomes could be inferred.     

Interspecific hybrids of Cyclamen persicum Mill. and C. purpurascens Mill. produced by ovule culture

Summary Interspecific crosses were made to introduce the scent of flowers of C. purpurascens into C. persicum cultivars and ovule culture was used to rescue the abortive hybrid embryos. Cultivars of C. persicum diploid (CPD, 2n=2×=48) and C. persicum tetraploid (CPT, 2n=4×=96) were the pistillate parents and wild species of C. purpurascens (CP, 2n=34) were staminate parents. After pollination, crossed ovaries were collected periodically and examined using paraffin sections. Histological observations suggested that both hybrid ovules of CPD x CP and CPT x CP should be transferred to culture medium 35 days after pollination. Based up on this observation, crossed ovaries were collected 28 days after pollination and ovules with placenta were transferred to MS (1962) medium containing 3% sucrose. These ovules were cultured in the dark at 25° C. The hybrids (2n=41) derived from CPD x CP had the scent of C. purpurascens, whereas the hybrids (2n=65) derived from CPT x CP had the scent of C. persicum. Although both hybrids had complete genomes from the parents and produced a few viable pollen grains, they failed to yield viable seeds by self- and cross-pollination with fertile pollen grains of C. persicum cultivars.Abbreviations CPD C. persicum diploid - CPT C. persicum tetraploid - CP C. purpurascens     

Cytological mechanism of 2n pollen formation and unilateral sexual polyploidization in Lolium

Summary Plants of Lolium perenne, L. multiflorum and L. hybridum (331, 51 and 18, respectively) were screened for 2n pollen production. The screening was based on the size differences that are expected to be found between n and 2n pollen of a plant. It was found that 28 plants of perennial ryegrass-belonging to 13 cultivars-produced produced pollen grains of heterogenous size (big and small). The estimated frequency of big pollen grain production was higher than 10% in ten out of 28 plants and in three of them it reached a value of 100%. Eight plants obtained from two 4x × 2x crosses, in which the male parent had been previously identified as producing pollen grains of heterogenous size, was tetraploid. The cytological mechanism of big pollen grain formation observed in three plants consists in the lack of spindle formation and, consequently, of chromosome migration in anaphase II. From these breeding and cytological results, it was concluded that the big pollen grains observed were viable 2n pollen grains. The nuclei of the 2n pollen grains produced by this mechanism are genetically equivalent to those formed by the restitution of the second meiotic division. The value of these gametophytes in a breeding program of Lolium is discussed.     

Resynthesizing <Emphasis Type="Italic">Brassica napus</Emphasis> from interspecific hybridization between <Emphasis Type="Italic">Brassica rapa</Emphasis> and <Emphasis Type="Italic">B. oleracea</Emphasis> through ovary culture

Using three varieties of Brassica rapa, cv. Hauarad (accession 708), cv. Maoshan-3 (714) and cv. Youbai (715), as the maternal plants and one variety of B. oleracea cv. Jingfeng-1 (6012) as the paternal plant, crosses were made to produce interspecific hybrids through ovary culture techniques. A better response of seed formation was observed when ovaries were cultured in vitro at 9–12 days after pollination on the basal MS and B5 media supplemented with 6-benzylaminopurine (BA) and naphthylacetic acid (NAA). The best response was observed for cross 714×6012 with the rate of seeds per ovary reaching 43.0%. Seeds for cross 715×6012 showed the best germination response (66.7%) on the regeneration medium (MS+1.0 mg l^–1 BA+0.05 mg l^–1 NAA). In all three cross combinations, good response in terms of root number and length of plants was observed on the root induction medium (MS+1.0 mg l^–1 BA+0.1 mg l^–1 NAA). A better response was observed for the regenerated plants cultured for 14 days than for 7 days. The ovary-derived plants with well-developed root system were hardened for 8 days and their survival rate reached over 80%. Cytological studies showed that the chromosome number of all plants tested was 19 (the sum of both parents), indicating that these regenerated plants were all true hybrids of B. rapa (n = 10) × B. oleracea (n = 9). The regenerated plants were doubled with colchicine treatment, and the best response in the crosses 708×6012, 714×6012 and 715×6012 was observed when treated with 170 mg l^–1 colchicine for up to 30 h and their doubling frequency reached 52, 56 and 62%, respectively.     

Chromosome associations and crossability with Iris ensata Thunb. in induced amphidiploids of I. laevigata Fisch. × I. ensata

Summary The chromosome associations of amphidiploids of I. laevigata × I. ensata were analysed and compared with those of the parental species and F₁ hybrids of I. laevigata × I. ensata. The F₁ hybrids showed partial chromosome associations. Their mean chromosome association per cell was 20.73I+3.63II, although the mean chromosome association per cell in the parental species was 0.09I+15.96II for I. laevigata and 0.03I+11.98II for I. ensata, respecively. In contrast, the normal association (28II) was partially restored in the amphidiploids. Their mean chromosome association per cell was 1.93I+26.48II+0.28III+0.03IV+0.03V. In this study, moreover, the crossability between I. ensata (2X and 4X) and the amphidiploids and between I. laevigata and the amphiliploids was examined. No hybrid plants were obtained from both reciprocal crosses between I. ensata (2X) and the amphidiploids and between I. laevigata and the amphidiploids. Only the cross of I. ensata (4X) × the amphidiploids in the reciprocal crosses produced hybrid plants. The observation of their somatic chromosome numbers indicates that these are true hybrid plants between autotetraploid I. ensata and the amphidiploids, and such plants can be called autoallotetraploids between I. ensata and I. laevigata. The interspecific cross-breeding of I. ensata using the autoallotetraploids is discussed.     

Crossability and embryo rescue enhancement in wide crosses between wheat and three Agropyron species

Summary Soft winter wheat lines were crossed with Agropyron intermedium, A. elongatum and A. trichophorum using pollen from single plants of Agropyron spp. to pollinate wheat spikes. Not only species but also individual plants within varieties of Agropyron species differed in percent seed set with a wheat genotype. In two arrays of crosses between two phenotypically different plants of A. elongatum and nine wheat lines, one Agropyron plant gave higher seed set (overall=27.1%) than the other (overall=3.7%). The differences were significant in seven of the nine cross combinations. Results are consistent with the hypothesis that these two plants differ in their crossability as pollen parents with wheat, and suggest the possibility of occurrence of crossability genes in wheatgrasses. The success rate of hybrid embryo rescue was higher (87.5%) with cold treatment (4°C) than without cold treatment (75.0%) of excised embryos on culture media. Results underscore the significance of genotype of the alien species for crossing with low crossable wheats, and of the physical factors for improving embryo rescue in wide crosses.Contribution No. 11,825, Purdue Agric. Exp. Stn., West Lafayette, Indiana 47907, USA. The research was supported in part by Public Varieties of Indiana.     

The stabilization of chromosome numbers and the maintenance of euploidy in Brassicoraphanus

Summary To examine whether chromosome numbers of Brassicoraphanus (amphidiploids between Brassica japonica Sieb. and Raphanus sativus L.) are stable or not, the following four items were studied with some plants during the 2nd–11th generations: (1) chromosome numbers of open-pollinated progenies from eu-, hyper-, and hypoploids, (2) chromosome distribution at metaphase II in these plants, (3) frequency of euploids in relation to flower colour and generation, (4) seed fertility in eu-and aneuploids in relation to flower colour. In early generations, hyper-and hypoploids were frequently produced from euploids. In later generations, however, the chromosome number became less unstable. In euploids (2n=38), chromosome numbers at metaphase II showed some variation, and the mean frequency of the euploid chromosome number (n=19) was approximately 78%. This value was almost the same in white-and yellow-flowered plants through early and late generations. Nevertheless, yellow-flowered plants tended to produce euploids more frequently than did white-flowered ones. It is assumed that the difference in euploid productivity between yellow-and white-flowered plants is due to the difference in seed fertility between them. The progeny of each hypoploid showed higher chromosome numbers than their parents. The progeny of each hyperploid showed lower chromosome numbers than their parents: they were approaching to euploidy. This phenomenon, together with higher fertility of euploids and lower fertility of aneuploids, will favor the maintenance of euploidy of this strain.     

Effects of aminoethoxyvinylglycine (AVG), environment,and genotype in overcoming hybridization barriers between Cucumis species

Summary It was attempted to overcome crossing barriers between the cucumber (Cucumis sativus L.), the melon (C. melo L.) and two wild Cucumis spp. (C. metuliferus Naud. and C. zeyheri 2x Sond.) by application of aminoethoxyvinylglycine (AVG) and by limiting the amount of rooting substrate. The reciprocal crosses between both wild species were used as a model system.Crosses between C. metuliferus and C. zeyheri 2x succeeded well if the maternal plants were grown in containers of 10 or 25 1 instead of in open soil. This treatment also improved crossability in the cross C. metuliferus x C. melo. It strongly enhanced the number of female flowers per plant in C. metuliferus. Application of AVG to pollinated flowers initially seemed also to improve crossability in these cross combinations, but later on this effect was not found again.Significant genetic variation for crossability was found in C. zeyheri 2x. Rare plants yielded numerous fruits with embryos after crosses with C. metuliferus and also with C. sativus. Clones from these plants gave similar results.Excessive temperature and radiation decreased crossability especially in crosses with C. metuliferus and C. sativus as maternal parent.     

Intergeneric crosses with Fragaria and Potentilla. I. Crosses between Fragaria moschata and Potentilla fruticosa

Summary Crosses between Fragaria moschata (2n=42) and Potentilla fruticosa (2n=14) produced many seeds; about half of these germinated, but only nine plants were obtained from 554 seedlings. Five plants died without flowering, and four were vigorous but sterile. Four plants had the expected chromosome number (2n=28), one plant had 21 chromosomes, and four were aneuploid with 23, 24, 25 and 27 chromosomes respectively. Response to growth substances giving elongated stem internodes and swollen but not succulent receptacles provided evidence that two of the plant were hybrids. It is suggested that all nine plants originated from a normal fertilisation which was followed in some cases by chromosome elimination at an early stage of embryo development.     

A New Intergeneric Hybrid between Triticum aestivum L. and Agropyron fragile (Roth) Candargy: Variation in A. fragile for Suppression of the Wheat Ph-Locus Activity

New intergeneric hybrids were obtained between Triticum aestivum L. cv. Tukuho’ (2n = 6x = 42, AABBDD) and Agropyron fragile (Roth) Candargy PGR 8097 (2n = 4x = 28, PPPP) at a frequency of 1.06 %, through the use of direct embryo culture and in ovulo embryo culture. Such hybrids could be used to transfer barley yellow dwarf virus (BYDV) resistance and winterhardiness into bread wheat. The somatic chromosome number in all the hybrid plants was 2n = 5x = 35, as expected. Considerable variation in chromosome pairing was observed among the different hybrid plants. Average meiotic chromosome configuration at metaphase I was 17.29 Is + 6.57 rod Us + 1.97 ring Us + 0.18 III + 0.03 IV + 0.002 VI. The high level of chromosome pairing in some F₁ hybrids was attributed to Ph-suppressor gene(s) present in A. fragile. The hybrids could not be backcrossed to wheat, but amphiploid seeds have been obtained by colchicine treatment.     

Karyotype analysis and interspecific hybridisation in three perennial Sesbania species (Leguminosae)

Summary The somatic chromosome number in Sesbania sesban var. nubica, S. goetzei and S. keniensis (Leguminosae; Papilionoidae) was found to be 2n=12. These findings were in agreement with earlier reports on S. sesban and S. keniensis. The chromosome number 2n=12 is a new record for S. goetzei. Similarities in karyotypes were found in the three species. All species had one pair of long metacentric chromosomes; the second pair was submedian, followed by four smaller pairs of metacentric chromosomes. Nucleolar organiser regions in the form of satellites were found on the short arm of the fourth chromosome pair in S. sesban and S. keniensis. Interspecific crosses in all possible combinations were carried out, resulting in pod and viable seed formation for the crosses S. sesban x S. goetzei, S. sesban x S. keniensis, S. goetzei x S. sesban and S. goetzei x S. keniensis. The two crosses with S. keniensis as a female parent were unsuccessful. The hybrid plants established normally and produced viable seeds.     

Incompatibility in diploid and tetraploid crosses of Cucumis sativus and Cucumis metuliferus

The African horned cucumber (Cucumis metuliferus Naud.; 2x = 2n = 24) contains genes that can confer resistance to many important cucumber (C. sativus L.; 2x = 2n = 14) pests [e.g., root-knotnematode, Meloidogyne incognita (Kofoid & White) Chitwood]. Cucumber is highly susceptible to this root-knot nematode species, and a recent screening of C. sativus accessions in the U.S. National Plant Germplasm collection did not identify sources of resistance. Thus,autotetraploids of Cucumis sativus and C. metuliferus were created to recover fertile resistant interspecific progeny. Autotetraploids were obtained at the highest rate when seeds were immersed in 0.5% colchicine for a period of 6 to 8 hrs. Treatment durations less than 6 hrs produced few tetraploids, and durations of 10 hrs or more were lethal to seeds or developing seedlings. Crosses between C. sativus and C. metuliferus were made using diploid and tetraploid lines in all possible combinations, including reciprocals. Fruit development occurred in crosses when diploid and tetraploid C. sativus were used as the female parent. However, seeds developed only in fruit of C. sativus (4n) ×C. metuliferus (2n) crossings. Seeds from these crosses, however,were flat and not viable. No fruit development occurred in crosses whereC. metuliferus was used as the female parent. This revised version was published online in August 2006 with corrections to the Cover Date.