SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS: III. AGROPYRON REPENS × TETRAPLOID AGROPYRON SPICATUM

Three hybrids of A. repens, 2n = 42, × A. spicatum, 2n = 28, and two reciprocal hybrids were obtained from emasculated and unemasculated crosses, respectively. The 35-chromosome hybrids tended to be morphologically intermediate between the parent species but resembled A. repens more closely than A. spicatum. A. repens behaved cytologically as a segmental autoallohexaploid, and A. spicatum acted cytologically as an autotetraploid. Mean chromosome associations of 8.04 I, 12.72 II, 0.41 III, 0.06 IV, and 0.009 V were observed in 116 hybrid cells at metaphase I. Most chromosome pairing in the hybrids was attributed to autosyndesis. A. spicatum, A. repens, and their hybrids were represented by genome formulas of SSSS, R₁R₁X₁X₁X₂X₂, and SSR₁X₁X₂, respectively. Hybrid fertility ranged from 0.02 to 0.69 seeds per spikelet.     

MORPHOLOGY,FERTILITY, AND CYTOLOGY OF AGROPYRON REPENS × AGROPYRON DESERTORUM F2'S

Dewey , Douglas R. (Crops Res. Lab., Agric. Expt. Sta., Logan, Utah.) Morphology, fertility, and cytology of Agropyron repens × Agropyron desertorum F₂'s . Amer. Jour. Bot. 49(1): 78–86. Illus. 1962.—An 82-plant population derived from F₁ hybrids of A. repens × A. desertorum included morphological types indistinguishable from the parent species as well as many intermediate forms. Most, if not all, of the F₂ population were products of backcrossing of F₁ hybrids to one of the parent species. Backcrossing of F₁ hybrids to A. repens and A. desertorum occurred with equal frequency. Fifty-four percent of the F₂ plants were completely sterile. Fertility in the F₂ population was related to the nature of the F₁ backcross. F₂ plants obtained from backcrossing to A. desertorum were more fertile than equivalent backcrosses to A. repens. Fertility in the F₂'s was concentrated in a few plants. Nine F₂'s accounted for 85% of the seed produced in the 82-plant population. The most fertile plant produced 441 viable seeds. Meiotic chromosome counts of 66 F₂'s ranged from 30 to 49 and averaged 36. Chromosome number was related to the direction of the backcross. Chromosome associations in all F₂ plants at metaphase I included many different combinations of univalents, bivalents and trivalents. Occasional pairing of A. repens and A. desertorum chromosomes were noted in some F₂'s. On the basis of morphology, fertility and chromosome pairing, genome formulae were assigned to the parent species. The genome formula of A. repens was given as BBBBCC and A. desertorum was designated as AAAA.     

GENOME RELATIONS OF AGROPYRON SERICEUM,HORDEUM JUBATUM AND THEIR HYBRIDS

Cytogenetic investigation of microsporogenesis in Agropyron sericeum, Hordeum jubatum, their spontaneous hybrid, Agrohordeum pilosilemma, its amphiploid, and the backcross of the amphiploid to A. sericeum, B₁, elucidated the genome relationships of A. sericeum and H. jubatum. The tetraploid parental species share a partially homologous genome which affects the pairing relationships evidenced in their hybrids. The genome formulae assigned to these plants are: A. sericeum, A“A”BB; H. jubatum, AAA'A‘; Agrohordeum pilosilemma, AA'A“B; the amphiploid, AAA'A‘A”A“BB; and B₁, AA'A”A“BB. Observed pairing configurations were compatible with the expected maximum pairing configurations predicted under the assumption of genetic control of pairing with dosage effects. This is interpreted as further support for the hypothesis that pairing in the hybrids of H. jubatum is controlled by the A genome, one dose of A allowing homeologous pairing and two doses of A promoting homeologous association.     

SYNTHETIC AGROPYRON-ELYMUS HYBRIDS: III. ELYMUS CANADENSIS X AGROPYRON CANINUM,A. TRACHYCAULUM,AND A. STRIATUM

Hybrids were produced with relative ease from controlled crosses of Elymus canadensis L. with European Agropyron caninum (L.) Beauv., North American A. trachycaulum (Link) Malte ex H. F. Lewis, and Asian A. striatum Nees ex Steud. All hybrids appeared to be completely sterile and were, for the most part, morphologically intermediate between their parents. The E. canadensis × A. caninum hybrids were exceptionally vigorous and leafy and may have some potential as forage grasses if fertility can be achieved. All parent plants were tetraploid, 2n = 28, and they behaved cytologically as alloploids. Chromosome pairing in the hybrids indicated that both E. canadensis genomes were closely homologous with those of A. trachycaulum and somewhat less homologous with those of A. caninum. Interchanged and inverted chromosome segments apparently constitute the major differences between E. canadensis, A. trachycaulum, and A. caninum genomes; however, cryptic structural differences must also exist. Partial homologies were detected between one A. striatum and E. canadensis genome, but their other genomes were distinctly different. The genome relations between the parent species were expressed in terms of the following genome formulas: E. canadensis, S₁S₁X₁X₁; A. trachycaulum, S₂S₂X₂X₂; A. caninum, S₃S₃X₃X₃ : and A. striatum S₄S₄YY or X₄X₄YY, where “S” refers to a genome derived from A. spicatum and “X” and “Y” are genomes of unknown origin.     

SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS. IV. TETRAPLOID AGROPYRON SPICATUM F. INERME X TETRAPLOID AGROPYRON DESERTORUM

Emasculated and unemasculated crosses of tetraploid A. spicatum f. inerme X A. desertorum yielded four hybrids. The hybrids were morphologically intermediate between the parent species but resembled A. desertorum more closely than A. spicatum. Both parents behaved cytologically as autoploids. Mean chromosome associations of 0.04 I, 8.60 II, 0.01 III, and 2.67 IV were observed at diakinesis in the 28-chromosome A. spicatum. The A. desertorum parent contained 30 chromosomes, 2 of which were likely supernumeraries, and averaged 0.03 I, 9.85 II, and 2.57 IV at diakinesis. Three hybrids contained 30 chromosomes, and one had 29. The most common chromosome association in the 30-chromosome hybrids was 2 I and 14 II; and the average was 3.00 I, 13.40 II, 0.06 III, and 0.01 IV. A. spicatum and A. desertorum chromosomes were usually distinguishable from each other in the hybrid cell on the basis of size. All pairing in the hybrids was attributed to autosyndesis within parental genomes. A. spicatum, A. desertorum, and their hybrids were represented by genome formulas of SSSS, CCCC, and SSCC, respectively. The hybrids produced 5 to 439 seeds under open pollination. Three controlled crosses between the hybrids yielded 2, 5, and 23 seeds, respectively, on 10 maternal spikes in each cross. The prospects of developing a fertile, cytologically stable allotetraploid species from the hybrids appear favorable.     

GENOME ANALYSIS OF AGROPYRON REPENS × AGROPYRON CRISTATUM SYNTHETIC HYBRIDS

Hexaploid A. repens, 2n = 42, and diploid A. cristatum, 2n = 14, were hybridized and gave rise to two 28-chromosome reciprocal hybrids. Approximately 1% of hand-emasculated florets of both parent species produced viable hybrid seed following controlled pollination. Early embryo abortion prevented greater hybrid seed set on A. repens, whereas failure of fertilization appeared to be the major cause of poor hybrid seed set on A. cristatum. Reciprocal differences in hybrid vegetative and spike morphology were striking. The A. repens × A. cristatum hybrid was vigorous, highly rhizomatous, and bore abundant spikes whose morphology was intermediate between that of the parent species. A. cristatum × A. repens hybrids were weak, non-rhizomatous with frequently-malformed spikes. Mean chromosome associations of 0.10 I, 20.10 II, and 0.43 IV were observed in 134 metaphase-I cells of A. repens. Subsequent meiotic stages were regular except for occasional laggards and bridges at anaphase I and II. Metaphase-I chromosome associations averaged 0.07 I and 6.97 II in 124 A. cristatum cells. Chromosome pairing in the hybrids was highly variable and averaged 11.45 I, 7.58 II, 0.44 III, and 0.02 IV per cell in 187 cells interpreted. From 5 to 14 laggards appeared in every hybrid cell at anaphase I. Bridges were observed in approximately 25% of the anaphase-I cells. Similar irregularities were observed at anaphase II. Pollen viability was estimated as 3%, and the hybrids failed to set viable seed. On the basis of chromosome pairing in the species itself and in the hybrids, A. repens was designated as a segmental autoallohexaploid with a genome formula of the type A₁A₁A₂A₂BB. Although A. repens and A. cristatum chromosomes paired occasionally, the genomes of the 2 species were essentially non-homologous. Some of the interpretational difficulties of genome analysis were discussed.     

MORPHOLOGY AND CYTOLOGY OF SYNTHETIC HYBRIDS OF AGROPYRON TRICHOPHORUM X AGROPYRON CRISTATUM

Dewey, Douglas R. (Utah State U., Logan.) Morphology and (cytology of synthetic hybrids of Agropyron trichophorum X Agropyron cristatum. Amer. Jour. Bot. 50(10): 1028–1034. Illus 1963.—Three hybrids were obtained from controlled crosses of pubescent wheatgrass, A. trichophorum (2n = 42), and hexaploid crested wheatgrass, A. cristatum (211 = 42). The hybrids were intermediate between the parent plants for all vegetative and spike characteristics observed. Under open pollination, 2 of the hybrids set 2 seeds each, and the other hybrid produced 60 seeds. Meiosis in the parent plants was basically regular. Average motaphase-I chromosome associations were 0.09 I, 20.56 II, 0.05 III, and 0.16 IV per cell in the A. trichophorum parent, which was described as a segmental autoallohexaploid. The hexaploid A. cristatum parent averaged 0.18 I, 7.44 II, 0.81 III, 2.86 IV, 0.08 V, and 2.11 VI per cell at diakinesis and was described as an autohexaploid. Chromosome pairing in the hexaploid hybrid averaged 5.08 I, 8.94 II, 4.33 III, 1.11 IV, 0.27 V, and 0.05 VI per cell. On the basis of chromosome pairing in the parent species and their hybrids, it was concluded that 1 of the A. trichophorum genomes was partially homologous with the 3 genomes of hexaploid A. cristatum. Genome formulae for hexaploid A. cristatum, A. trichophorum, and their hybrids were represented as AAAAAA, A₁A₁B₁B₁B₂B₂, and AAAA₁B₁B₂ respectively.     

CYTOGENETICS OF AGROPYRON FERGANENSE AND ITS HYBRIDS WITH SIX SPECIES OF AGROPYRON,ELYMUS, AND SITANION

Meiosis and mode of reproduction are described in Agropyron ferganense Drob., a perennial forage grass from Central Asia. This species is diploid (2n = 14); it exhibits normal meiosis and reproduces by cross-pollination. Hybrids were produced between A. ferganense and six species with known genome formulas: 1) North American A. spicatum (Pursh) Scribn. & Smith, an SS diploid (2n = 14), 2) Middle Eastern A. libanoticum Hack., an SS diploid (2n = 14), 3) North American A. dasystachyum (Hook.) Scribn., an SSHH tetraploid (2n = 28), 4) Eurasian A. caninum (L.) Beauv., an SSHH tetraploid (2n = 28), 5) North American Sitation hystrix (Nutt.) J. G. Smith, an SSHH tetraploid (2n = 28), and 6) South American Elymus patagonicus Speg., an SSHHHH hexaploid (2n = 42). Almost complete chromosome pairing in the A. ferganense x A. spicatum and A. libanoticum hybrids demonstrated that A. fergenanse is an SS diploid, but it is genetically isolated from the other SS diploids because of high sterility in the F₁ hybrids. S-genome diploids form a network of species that extend from the Middle East through Central Asia to western North America. Frequent occurrence of seven univalents and seven bivalents at metaphase I in the triploid hybrids of A. ferganense x A. dasystachyum, A. caninum and S. hystrix was consistent with the proposed genome formulas of SS for A. ferganense, SSHH for the three tetraploid species, and SSH for the hybrids. Chromosome pairing was highly variable in the A. ferganense x E. patagonicus hybrids; however, some cells had almost complete bivalent pairing, an expected observation in an SSHH hybrid from a cross between an SS diploid (A. ferganense) and an SSHHHH hexaploid (E. patagonicus). Various options were considered concerning the appropriate generic classification of the S-genome diploids, which are now commonly placed in Agropyron. The inclusion of these species in the genus Eiytrigia, as advocated by some Soviet taxonomists, appears to be a reasonable decision.     

THE ORIGIN OF AGROPYRON SMITHII

The hypothesis that North American octoploid Agropyron smithii Rydb., 2n = 56, originated by hybridization between tetraploid Agropyron and Elymus species, followed by chromosome doubling, was tested by observing chromosome pairing in hybrids of A. smithii with an induced amphiploid, 2n = 56, derived from E. canadensis L., 2n = 28, X E. dasystachys Trin., 2n = 28, F₁'s. Chromosome pairing in A. smithii averaged 0.52^I, 27.70^II, 0.01^III, and 0.01^IV in 184 metaphase-I cells; and the amphiploid averaged 1.13^I and 27.44^II in 195 cells. Chromosome pairing in A. smithii X amphiploid hybrids averaged 8.20^I, 23.38^II, 0.34^III, and 0.05^IV in 101 metaphase-I cells. It was concluded that A. smithii was genomically similar to the E. canadensis-E. dasystachys amphiploid. The basic genome formula of the amphiploid is SSHHJJXX, with the SSHH genomes coming from E. canadensis and the JJXX genomes coming from E. dasystachys. Consideration of the morphological, ecological, and reproductive characteristics of all North American species that contain the basic SSHH and JJXX genomes led to the conclusion that A. dasystachyum (Hook.) Scribn., SSHH, and E. triticoides Buckl., JJXX, are the probable progenitors of A. smithii.     

HYBRIDS AND INDUCED AMPHIPLOIDS OF ELYMUS CANADENSIS X AGROPYRON LIBANOTICUM

North American Elymus canadensis L., 2n = 28, and Asian Agropyron libanoticum Hack., 2n = 14, crossed with ease and yielded vigorous but sterile F₁ hybrids, 2n = 21. Chromosome pairing in the hybrids averaged 9.47^I, 5.38^II, and 0.26^III in 150 metaphase-I cells. One genome of E. canadensis is more or less homologous with the A. libanoticum genome. Treatment of the F₁ hybrids with colchicine produced 42-chromosome amphiploids, C₀, which were advanced through two seed generations, C₁ and C₂. More than half of the metaphase-I cells in the C₀ amphiploids contained 21^II; and average associations were 1.09^I, 20.16^II, 0.07^III, and 0.09^IV in 116 cells. Meiosis became increasingly irregular beyond metaphase-I; nevertheless, the C₀ amphiploids produced 68% stainable pollen and averaged 0.75 seed per spikelet. Multivalent frequencies increased in advanced generations, and the C₂ amphiploids averaged 1.11^I, 19.00^II, 0.23^III, and 0.55^IV in 100 metaphase-I cells. Meiosis was essentially regular in the C₁ and C₂ amphiploids beyond metaphase I, and the C₂ amphiploids averaged 73% stainable pollen and 2.28 seeds per spikelet. The amphiploids have an excellent chance of developing into a meiotically stable, fertile, new species. Forage characteristics of the amphiploids indicate that they have considerable economic potential as a forage grass.     

THE ORIGIN OF AGROPYRON LEPTOURUM

Colchicine-induced amphiploids, 2n = 42, of diploid Agropyron libanoticum Hack., 2n = 14, X tetraploid A. caninum (L.) Beauv., 2n = 28, were morphologically and cytologically similar to A. leptourum (Nevski) Grossh., 2n = 42. Both A. leptourum and the induced amphiploids were self-fertilizing. The induced amphiploids crossed readily with A. leptourum and gave rise to partially fertile hexaploid hybrids. Chromosome pairing in the hybrids averaged 0.60^I, 18.29^II, 0.36^III, 0.58^,v, 0.02^v, and 0.22^VI in 90 diakinesis or metaphase-I cells. The genomes of the induced amphiploids are essentially homologous with those of A. leptourum except for two or more reciprocal translocations. The morphological, cytological, fertility, and crossing data provide conclusive evidence that A. libanoticum and A. caninum, or their close relatives, are the parents of A. leptourum. The genome formulas of A. libanoticum, A. caninum, and A. leptourum may be written as SS, S_xS_xH_xH_x, and SSS_xS_xH_xH_x, respectively, where S is the basic A. libanoticum genome and H is a genome derived from Hordeum.     

THE ORIGIN OF AGROPYRON ALBICANS

Previous suggestions of introgression between Agropyron spicatum (Pursh) Scribn. & Smith, 2n = 14 & 28, and Agropyron dasystachyum (Hook.) Scribn., 2n = 28, were confirmed. Fertile, meiotically regular, 28-chromosome plants morphologically identical to Agropyron albicans Scribn. & Smith, 2n = 28, occurred in first- and second-generation open-pollination progenies of diploid A. spicatum × A. dasystachyum hybrids, presumably by backcrossing to A. dasystachyum. These A. albicans-like derivatives were fully cross-compatible with naturally occurring A. albicans. First and second generation open-pollination progeny of tetraploid A. spicatum × A. dasystachyum F₁'s contained approximately 5% A. albicans-like plants; but none was tetraploid, cytologically stable, and fertile. Although introgression occurs freely between tetraploid A. spicatum and A. dasystachyum, derivation of fertile true-breeding A. albicans from their early-generation progeny seems unlikely. Agropyron griffithsii Scribn. & Smith ex. Piper, the glabrous counterpart of A. albicans, probably originated from hybrids between diploid A. spicatum and Agropyron riparium Scribn. & Smith, the glabrous form of A. dasystachyum. Genome formulas of diploid A. spicatum, A. dasystachyum (riparium), and A. albicans (griffithsii) may be written as S₁S₁, S₂S₂XX, and S_1-2 S_1-2XX, respectively. The relationship between A. albicans and A. dasystachyum is so close that A. albicans should be regarded as no more than a subspecies of A. dasystachyum.     

SYNTHETIC HYBRIDS OF AGROPYRON ALBICANS X A. DASYSTACHYUM,SITANION HYSTRIX,AND ELYMUS CANADENSIS

Emasculated crosses of Agropyron albicans Scribn. & Smith with A. dasystachyum (Hook.) Scribn., Sitanion hystrix (Nutt.) J. G. Smith, and Elymus canadensis L. yielded 34, 5, and 9 viable hybrid seeds from 66, 45, and 52 florets, respectively. The hybrids were for the most part morphologically intermediate between their respective parents. The parents behaved cytologically as allotetraploids, 2n = 28; but meiosis in A. albicans was somewhat more irregular than in the other three species. Chromosome pairing was good in all hybrids and indicated that the genomes of the parent species were closely homologous, but only the A. albicans × A. dasystachyum hybrids set seed. Although closely related, A. albicans and A. dasystachyum are not fully conspecific. Agropyron albicans was considered to be a subspecies of A. dasystachyum, as were A. riparium Scribn. & Smith and A. griffithsii Scribn. & Smith ex Piper.     

Homoeologous relationships of Aegilops speltoides chromosomes to bread wheat

 Homoeologous pairing at metaphase I was analysed in the standard-type, ph2b and ph1b hybrids of Triticum aestivum (AABBDD) and Aegilops speltoides (SS). Data from relative pairing affinities were used to predict homoeologous relationships of Ae. speltoides chromosomes to wheat. Chromosomes of both species, and their arms, were identified by C-banding. The Ae. speltoides genotype carried genes that induced a high level of homoeologous pairing in the three types of hybrids analyzed. All arms of the seven chromosomes of the S genome showed normal homoeologous pairing, which implies that no apparent chromosome rearrangements occurred in the evolution of Ae. speltoides relative to wheat. A pattern of preferential pairing of two types, A-D and B-S, confirmed that the S genome is very closely related to the B genome of wheat. Although this pairing pattern was also reported in hybrids of wheat with Ae. longissima and Ae. sharonensis, a different behaviour was found in group 5 chromosomes. In the hybrids of Ae. speltoides, chromosome 5B-5S pairing was much more frequent than 5D-5S, while these chromosome associations reached similar frequencies in the hybrids of Ae. longissima and Ae. sharonensis. These results are in agreement with the hypothesis that the B genome of wheat is derived from Ae. speltoides. Received: 8 January 1998 / Accepted: 4 February 1998     

Metaphase I bound arms frequency and genome analysis in wheat-Aegilops hybrids

Summary Meiotic associations of different wheat-Aegilops variabilis and wheat-Ae. kotschyi hybrid combinations with low and high homoeologous pairing were analyzed at metaphase I. Five types of pairing involving wheat and Aegilops genomes were identified by using C-banding. A genotype that seems to promote homoeologous pairing has been found in Ae. variabilis var. cylindrostachys. Its effect is detectable in the low pairing hybrids but not in the high ones. Pairing affinity has been analyzed on the basis of metaphase I associations in the low and high homoeologous pairing hybrids, and in bivalents and multivalents in the high pairing hybrids. The results indicate that the amount of bound arms of each type of identifiable association relative to the total associations formed (relative contribution) was not maintained, either between the different levels of pairing (low and high) or between different meiotic configurations (bivalents and multivalents). These findings seem to indicate that quantifications of genomic relationships based on the amount of chromosome pairing at metaphase I must be carefully done in this type of hybrid combinations.     

Genome relationships between Hordeum procerum (6x) and H. lechleri (6x)

Investigations on the meiotic behaviour of chromosomes in interspecific hybrids (2n=6x=42) between Hordeum lechleri (6x) and H. procerum (6x) and in their component haploids have been utilized to assess the nature of pairing and the extent of genome homology between the two species. In the F₁ hybrids an average of 25 (60%) chromosomes associated at metaphase I, mostly as bivalents. A majority (60%) of the pollen mother cells (PMCs) in H. procerum haploids (2n=3x=21) displayed 21 univalents and even in the remainder, a maximum of two rod bivalents were formed resulting in an average of 0.52 bivalents per cell. In haploids of H. lechleri (2n=3x=21) however, 30% of chromosomes pair. The sum of the chromosomal associations in the component haploids represents only 17% of the complement, far below the observed frequency (60%) in the hybrids. Thus, the pairing displayed in hybrids between H. lechleri and H. procerum was mostly allosyndetic and suggestive of two genomes being common in these species.In haploid H. procerum 1/3 of the PMCs displayed a tripolar organisation of chromosomes leading to triad and hexad formation after divisions I and II respectively. The significance of hexad formation in the trihaploid H. procerum and a possible suppression of homoeologous pairing in H. procerum haploids are discussed.     

NEW INTERGENOMIC HYBRIDS AMONG SOME AFRICAN DIPLOID SPECIES OF HIBISCUS SECT. FURCARIA

Chromosome pairing was examined at Metaphase 1 in F₁ hybrids between Hibiscus surattensis L. (B genome) and three other diploid species, H. hiernianus Exell, H. mastersianus Hiern, and H. mechowii Garcke. The low level of chromosome association in all three types of hybrids indicated that the pollen parent of each hybrid contributed a genome that was meiotically nonhomologous with B. Earlier studies had shown that H. mastersianus and H. hiernianus have similar genomes that are nonhomologous with the genome of H. mechowii. Thus, these four African diploids with overlapping ranges encompass three different genome groups. Provisional genome designations were assigned as follows: H. hiernianus, X_hie; H. mastersianus, X_mas; H. mechowii, Y_mec.     

Homoeologous relationships of Triticum sharonense chromosomes to T. aestivum

 Homoeologous pairing at metaphase I was analyzed in standard-type, ph2b, and ph1b hybrids of Triticum aestivum (common, bread or hexaploid wheat) and T. sharonense in order to establish the homoeologus relationships of T. sharonense chromosomes to hexaploid wheat. Chromosomes of both species, and their arms, were identified by C-banding. Normal homoeologous relationships for the seven chromosomes of the S^sh genome, and their arms, were revealed, which implies that no apparent chromosome rearrangement occurred in the evolution of T. sharonense relative to wheat. All three types of hybrids with low-, intermediate-, and high-pairing level showed preferential pairing between A-D and B-S^sh. A close relationship of the S^sh genome to the B genome of bread wheat was confirmed, but the results provide no evidence that the B genome was derived from T. sharonense. Data on the pairing between individual chromosomes of T. aestivum and T. sharonense provide an estimate of interspecific homoeologous recombination. Received: 14 October 1996 / Accepted: 25 October 1996     

大鹅观草与蛇河披碱草属间杂种的细胞遗传学研究

为探讨大鹅观草(Roegneria grandis,2n=4x=28)的染色体组组成,为其正确的分类处理提供细胞学依据。该研究通过人工远缘杂交,成功获得3株大鹅观草与蛇河披碱草(Elymus wawawaiensis,2n=4x=28)属间杂种F1植株。杂种植株形态介于两亲本之间,不育。亲本及杂种经I2-IK溶液染色后进行花粉育性检测,结果显示Roegneria grandis和Elymus wawawaiensis的花粉可育,育性高达94.6%和90.5%;杂种F1不育。花粉母细胞减数分裂中期I染色体配对结果显示,亲本花粉母细胞配对正常,均形成14个二价体,以环状二价体为主,Roegneria grandis有频率很低(0.04/细胞)的单价体出现;杂种F1平均每个花粉母细胞形成6.46个二价体,变化范围为5~8;在观察的83个花粉母细胞中,有35.2%的花粉母细胞形成了7个二价体,形成6个二价体的细胞占42.59%,较少细胞形成8个二价体;平均每个细胞形成14.66个单价体,变化范围为10~18;平均每细胞观察到0.14个三价体;杂种花粉母细胞染色体构型为14.66 I+6.46 II+0.14 III;平均每细胞交叉数为9.83,C值为0.35。结果表明:(1)R.grandis与Elymus wawawaiensis有一组染色体组同源的St染色体组,另外一组染色体组不是St或者H染色体组,Roegneria grandis的染色体组组成不是St Stg;(2)较低频率的三价体(平均0.14个/细胞),可能是由于R.grandis的St和Y染色体组间具有一定的同源性,也可能是染色体易位等原因导致,对于Y染色体组的起源还需深入地研究;(3)在不同地理来源的披碱草属和鹅观草属物种中St染色体组同源性不同,R.grandis与来自于北美的Elymus lanceolatus与E.wawawaiensis的St染色体组较与分布于亚洲的E.sibiricus和E.caninus的St染色体组同源性反而更高,其原因还需要进一步地研究。     

CHROMOSOME HOMOLOGY IN SOME INTERCONTINENTAL HYBRIDS IN HIBISCUS SECT. FURCARIA

Ten kinds of interspecific hybrids were obtained involving the following species: H. surattensis L. (2x, genome constitution BB), H. sudanensis Hochr. (2x, GG), and H. rostellatus Guill. and Perr. (4x, GGHH) from Africa; H. furcatus Roxb. non Willd. (8x) from India and Ceylon; H. furcellatus Lam. and H. bifurcatus Cav. (both 4x, PPQQ) from South America; and H. heterophyllus Vent. (6x) from Australia. Chromosome pairing in pollen mother cells (PMC's) at metaphase I in the 4x hybrids H. bifurcatus-rostellatus and H. furcellatus-rostellatus indicated that the parents have one genome in common (Q = G or H). Hibiscus furcatus was shown earlier to have a B genome; hybrids of H. surattensis-sudanensis F₁ X furcatus were hexaploid, having received an unreduced gamete from their hybrid parent, and had approximately 36 II, 36 I in PMC's. The genome formula of H. furcatus may therefore be designated BBGGWWZZ. The hybrid H. rostellatus-furcatus (BGGHWZ) confirmed that H. furcatus has a G genome in common with H. rostellatus; pairing of the other three genomes was inconsistent, as was that in H. rostellatus-heterophyllus. Some samples of the latter approached 36 II, 36 I, expected if H. heterophyllus were GGHHJJ; other samples had less pairing. Hibiscus furcatus-heterophyllus hybrids apparently arose from unreduced gametes of H. heterophyllus and originated as decaploids rather than heptaploids; chromosome number was unstable in PMC's. Nevertheless, multivalents, especially trivalents, were frequent enough to suggest that H. furcatus and H. heterophyllus share G genomes. On the other hand, an 8x H. bifurcatus-furcatus hybrid, which apparently arose from an unreduced gamete of H. bifurcatus, had a low multivalent frequency. Hybrids were obtained of H. heterophyllus X sudanensis and H. surattensis-sudanensis X heterophyllus, but the plants were weak and were not analyzed cytologically. We suggest that the New World, African, Indian, and Australian genomes which retain a considerable degree of homology (G or H or both) were distributed by land prior to separation of the southern continents by continental drift.