SOMATIC INSTABILITY IN DERIVATIVES FROM AGROELYMUS TURNERI RESEMBLING AGROPYRON REPENS

Nielsen , E. L., and J. Nath . (U. Wisconsin, Madison.) Somatic instability in derivatives from Agroelymus turneri resembling Agropyron repens. Amer. Jour. Bot. 48(4): 345–349. Illus. 1961.—Variations in somatic chromosome numbers of 4 to over 80 were observed in root tip cells of Agropyron repens-like plants derived from Agroelymus turneri. The latter presumably had out-crossed to Agropyron repens. Split spindles in dividing nuclei and multinucleate cells were observed in the root tip meristem. The nuclear and mitotic behaviors observed can perhaps be attributed to an unbalanced ribonucleoprotein system resulting from the combination of distantly related genomes in the formation of the hybrid.     

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.     

Emergence of the Introduced Grass Agropyron cristatum and the Native Grass Bouteloua gracilis in a Mixed-grass Prairie Restoration

Abstract Prairie restoration at the northern edge of the Great Plains can be frustrated by previously established non‐native perennial grasses. We compared the emergence of a widely introduced grass, Agropyron cristatum, and a common native grass, Bouteloua gracilis, in a 4‐year‐old field experiment in which the Agropyron‐dominated vegetation had either been left intact or treated annually with herbicide. This was done at two levels of water supply, reflecting conditions expected in wet and dry years, to examine the effects of among‐year variability in precipitation. Water addition significantly increased the emergence of both surface‐sown and buried (1 cm deep) seeds. Herbicide treatment of neighbors did not increase the emergence of experimentally added seeds. Emergence was much greater for buried (80%) than surface‐sown seeds (20%). Significantly more Bouteloua than Agropyron germinated from experimentally buried seeds. Whereas only a single seedling of Bouteloua emerged from the existing seed bank, the mean density of Agropyron seedlings emerging from the seed bank was 930/m² (range, 0 to 6,455/m²). Surprisingly, the emergence of Agropyron from the seed bank was not decreased by 4 years of herbicide treatment, possibly because herbicide may release Agropyron from intraspecific competition and allow increased seed production to compensate for decreased plant abundance. In summary, we found few differences between Agropyron and Bouteloua in spring and summer emergence at high or low water availability. The persistence of Agropyron stands despite repeated herbicide application may be partly due to increased seed production.     

High Levels of Resistance in Agropyron Species to Barley Yellow Dwarf and Wheat Streak Mosaic Viruses

Several Agropyron species were tested for new sources of resistance to barley yellow dwarf virus (Bydv ) and wheat streak mosaic virus (WSMV). With BYDV strain PAV, 11 of the 17 Agropyron species showed no virus transmission when plants were given access feed by viruliferous Rhopalosiphum padi. Similar trials with BYDV strain RMV (vectored by R. maidis) indicated that all plants, except susceptible control plants, remained virus free. Virus status was confirmed by enzyme-linked immunosorbent assays. When plants were mechanically inoculated with WSMV, 11 Agropyron species failed to express symptoms, while five other species showed a segregating response or had some accessions segregating and some resistant. Test results suggest that resistance to BYDV and WSMV in Agropyron species does not appear to be correlated with any specific genome of Agropyron species although most of the Agropyron species containing S genome were resistant to BYDV and WSMV.     

GENOME RELATIONS AMONG ELYMUS CANADENSIS,ELYMUS TRITICOIDES,ELYMUS DASYSTACHYS,AND AGROPYRON SMITHII

Hand-emasculated Elymus canadensis pollinated by E. triticoides, E. dasystachys, and Agropyron smithii yielded 15, 21, and 1 viable hybrid seeds from 56, 52, and 52 florets, respectively. The 28-chromosome species—E. canadensis, E. triticoides, and E. dasystachys—behaved meiotically as allotetraploids and consistently formed 14 bivalents at metaphase I. Octoploid A. smithii, 2n = 56, averaged 0.41^I, 27.72^II, and 0.03^IV in 87 metaphase-I cells. Agropyron smithii is apparently an allooctoploid or a segmental autoallooctoploid. Meiosis was similar in the E. canadensis X E. triticoides and E. dasystachys hybrids. Chromosome pairing was very low in both hybrids, about two loosely connected open-ended bivalents per cell, and may not represent genuine homologies. The genomes of E. canadensis are distinctly different from those of E. triticoides and E. dasystachys. The E. canadensis X A. smithii hybrid averaged 13.37^I and 14.31^II in 76 metaphase-I cells. More than half of the bivalents were closed at both ends. Inability to distinguish between auto- and allosyndesis resulted in two interpretations of genome relations. Either A. smithii is an alloploid with two of its four genomes similar to those of E. canadensis, or it is a segmental autoalloploid genomically unrelated to E. canadensis. The first interpretation is favored. Agropyron dasystachyum, or one of its close relatives, and E. triticoides are suggested as possible parents of A. smithii.     

Studies of the functional activity of mitochondria and cell ultrastructure of the coleoptile in wheat,Agropyron and their hybrids (incomplete amphidiploids) during decreasing temperature

Summary The structure of the mitochondria and endoplasmic reticulum in the coleoptile of plants (Triticum aestivum var. Lutescens 329, Agropyron glaucum, Triticum × Agropyron 56-chromosome hybrids, incomplete amphidiploids, TAH, containing 42 wheat chromosomes and 14 chromosomes of genomes D or X of Agropyron), which differ in winterhardiness, was studied after exposure to 0 ° and -4 °C for periods varying from 10 min to 4 days. The functional activity of mitochondria isolated from 3 day old seedlings was also investigated in these cereals. The cells of Triticum and Agropyron seedlings grown at 23 °C were shown to differ in mitochondrial structure. In the cells of TAH both kinds of mitochondria were found.On day 4 of exposure to -4 °C, the mitochondria of Agropyron cells were not changed; the endoplasmic reticulum formed complex closed cavities. Under similar conditions most wheat mitochondria were destroyed and in the rest no cristae were observed.Morphometric analysis indicated that the volume of such mitochondria increases by two times, while the surface area of the internal membranes and cristae decreases by 1.54 times. In such cells, the endoplasmic reticulum is represented only by membranes of the smooth type. The structure of the mitochondria and endoplasmic reticulum in the seedling cells of TAH 829, which is more like Agropyron in winterhardiness, is similar to that of Agropyron cells; in hybrid 822 (more like wheat containing the D genome), changes arise resembling those observed in wheat. The existence of different types of mitochondria in seedling cells of TAH is especially distinct at low temperatures.The mitochondria of the cereals studied differ in biochemical activity after low temperature treatment (0 ° and — 4 °C). Phosphorylative and oxidative activity of mitochondria of the winterhardy forms (Agropyron glaucum, TAH 829) decreases just after the beginning of low temperature treatment. At the same time, the morphology of the mitochondria undergoes reversible changes. The mitochondria of cold-susceptible forms of wintering plants (Triticum aestivum, TAH 822) do not conform to this pattern. Under long-term low temperature treatment they display irreversibly damaged mitochondria. It is suggested that the winterhardy forms have high adaptability connected with a rapid protective response of the cell mitochondria and endoplasmic reticulum. This adaptability is regulated by nuclear genes: TAH have different mitochondria in the coleoptile cells; if genome X of Agropyron is present, which TAH derives from the male parent, the related mitochondria become more resistant to low temperature treatment.     

Cytogenetic studies on an intergeneric hybrid betweenAgropyron tsukushiense andElymus mollis

Elymus mollis is distributed widely from Korea to Japan, Kamchatka and Alaska, the northern part of U.S.S.R., and Northern and Eastern Canada, Greenland and Iceland. This species is tetraploid (2n=28). A strain of this species collected in Hokkaido was crossed withAgropyron tsukushiense var.transiens collected in Mishima. From this cross, 22 F₁ plants were produced. Crossability calculated from the number of hybrid plants produced and the number of floret pollinated was 30.6%. The shape of the F₁ spikes was of theAgropyron type but the glumes were hairy as were those of theElymus parent. One of the characteristics distinguishingElymus fromAgropyron is the production of two spikelets at almost all nodes of the rachis. This character was not expressed in the F₁ plants. All pollen grains of the F₁ plants were completely abortive. The average chromosome pairing at the MI of the PMCs of the F₁ amounted to 2.03 bivalents and 30.95 univalents. Almost all bivalents ranging from one to seven were rod-shaped connected with interstitial or terminal chiasma. These results indicate a lack of genomic homology between the three genomes ofA. tsukushiense and the two genomes ofE. mollis. Contribution No. 37 from the Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Kyoto, Japan.     

Overexpression of AeNHX1, a root-specific vacuolar Na+/H+ antiporter from Agropyron elongatum, confers salt tolerance to Arabidopsis and Festuca plants

Agropyron elongatum, a species in grass family, has a strong tolerance to salt stress. To study the molecular mechanism of Agropyron elongatum in salt tolerance, we isolated a homolog of Na⁺/H⁺ antiporters from the root tissues of Agropyron plants. Sequence analysis revealed that this gene encodes a putative vacuolar Na⁺/H⁺ antiporter and was designated as AeNHX1. The AeNHX1–GFP fusion protein was clearly targeted to the vacuolar membrane in a transient transfection assay. Northern analysis indicated that AeNHX1 was expressed in a root-specific manner. Expression of AeNHX1 in yeast Na⁺/H⁺ antiporter mutants showed function complementation. Further, overexpression of AeNHX1 promoted salt tolerance of Arabidopsis plants, and improved osmotic adjustment and photosynthesis which might be responsible for normal development of transgenic plants under salt stress. Similarly, AeNHX1 also functioned in transgenic Festuca plants. The results suggest that this gene might function in the roots of Agropyron plants, and its expression is involved in the improvement of salt tolerance.     

Hybridisation,genomic constitution and generic delimitation inElymus s. l. (Poaceae: Triticeae)

Intergeneric crosses were made between representatives of the genomically-defined generaElymus, Agropyron, Elytrigia, Pseudoroegneria, andThinopyrum. The genomic constitution ofElytrigia repens, the type species ofElytrigia, is shown to be SSH, a genomic combination otherwise found only inElymus. The S genome ofPseudoroegneria has almost always a dominant influence on the morphology of the taxa of which it is a component.Wang (1989) showed that the J genome inThinopyrum and the S genome have considerable homoeology, with a mean c-value of 0.35 in diploid SJ hybrids. A genetic coherence from S to SJ^e, J^e, J^eJ^b, and J^b can be expected, agreeing with the continuous morphologic variation pattern observed. Because of the absence of morphological discontinuities between the taxa,Pseudoroegneria (S),Elymus (SH, SY, sometimes with additional genomes),Elytrigia (SSH, SSHX), andThinopyrum (SJ, SJJ, J) are best treated as a single genus,Elymus, following the generic concept ofMelderis in Flora Europaea and Flora of Turkey. The basic genomic constituents ofElymus will then be the S and/or J genomes.Agropyron, with diploids, tetraploids, and hexaploids based on the P genome is morphologically distinct from other genera inTriticeae. In a few species ofElymus andPseudoroegneria, a P genome is an additional constituent. In these cases the P genome has a negligible morphological influence. Therefore, it seems reasonable to maintainAgropyron as a separate genus.     

Morphological plasticity following species-specific recognition and competition in two perennial grasses

Morphological characteristics and biomass allocation of two perennial grasses, Pseudoroegneria spicata (Pursh) A. Löve ssp. spicata (bluebunch wheatgrass) and Agropyron desertorum (Fisch. ex Link) Schult. (crested wheatgrass), were compared under different competition and nutrient treatments. The competitive responses of two plants grown in containers under field conditions were assessed in monocultures and mixtures in two experiments using different scales of nutrient application. In the Small-Scale Experiment, a localized fertilization was applied in the rooting zone between two plants; in the Large-Scale Experiment the entire container was supplied with nutrients. Agropyron responded more vigorously to fertilization than did Pseudoroegneria, but based on the relative performance of Agropyron in monoculture and mixture, it was not superior to Pseudoroegneria in resource competition. Pseudoroegneria was apparently able to recognize neighboring plants as either conspecifics or individuals of the other species. The responses included changes in shoot architecture, root morphology, and allocation between roots and shoots. Agropyron generally did not exhibit such morphological flexibility. In field plot plantings of 4-yr-old tussocks similar shoot differences were seen in Pseudoroegneria. There was, however, no indication of superior resource competition for Agropyron. Thus, any early advantage of Agropyron in vigorous growth of young plants in response to nutrients was apparently lost by the time the plants had reached this stage of development. Morphological and allocation flexibility of Pseudoroegneria may have compensated for slower, less vigorous growth. If species-specific recognition and morphological plasticity are common in nature, this complicates our attempts to understand mechanisms of competition.     

SYNTHETIC HYBRIDS OF HORDEUM BOGDANII WITH ELYMUS CANADENSIS AND SITANION HYSTRIX

Seven viable hybrid seeds were obtained from 48 hand-emasculated Elymus canadensis L., 2n = 28, florets pollinated by Hordeum bogdanii Wilensky, 2n = 14. The hybrids were large, vigorous, and completely sterile plants that bore a closer morphological resemblance to E. canadensis than to H. bogdanii. Chromosome associations in the 21-chromosome hybrids averaged 9.98^I, 5.40^II, and 0.08^III in 264 metaphase-I cells. Chromosome pairing was attributed to allosyndetic pairing between E. canadensis and H. bogdanii chromosomes. The H. bogdanii genome appears to be partially homologous with one of the two E. canadensis genomes. One Sitanion hystrix (Nutt.) J. G. Smith X H. bogdanii hybrid was obtained from a cross involving 37 emasculated S. hystrix florets. This triploid, 2n = 21, hybrid was morphologically intermediate between the parents and totally sterile. Averages of 9.09^I, 5.72^II, and 0.16^III were observed in 106 cells at metaphase I. A modified form of the H. bogdanii genome appears to occur in S. hystrix as well as in E. canadensis. Many allotetraploid Agropyron, Elymus, and Sitanion species apparently contain a genome derived from Hordeum.     

Cytogenetical studies on artificial hybrids amongElymus sibiricus,E. dahuricus andAgropyron tsukushiense in the tribe Triticeae,Gramineae

To explore the cytogenetical relationships ofElymus andAgropyron of the tribe Triticeae, Gramineae, two species of AsiaticElymus, E. sibiricus (2n=28) andE. dahuricus (2n=42), and a JapaneseAgropyron, A. tsukushiense (2n=42) were crossed. Pentaploid and hexaploid F₁ hybrids were vigorous. All pollen grains were aborted and none of the hybrids produced seed. For the crossE. sibiricus × A. tsukushiense, the average chromosome pairing per cell at the MI of the PMCs in the F₁ was 16.38 univalents, 8.93 bivalents, 0.25 trivalents and 0.01 quadrivalents; for the crossE. dahuricus × A. tsukushiense, it was 4.41 univalents, 17.67 bivalents, 0.32 trivalents, 0.28 quadrivalents and 0.04 quinquevalents; and for the crossE. dahuricus × E. sibiricus, it was 17.11 univalents, 8.74 bivalents, 0.04 trivalents and 0.07 quadrivalents. From the present results, it is concluded thatE. sibiricus contains one genome andE. dahuricus contains two genomes, which are homologous to those ofA. tsukushiense, and that the third genome ofE. dahuricus might be partially homologous to the remaining genome ofA. tsukushiense. This conclusion is also supported by the cytogenetical analysis ofE. dahuricus × E. sibiricus. Contribution No. 27 from the Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Kyoto, Japan.     

Competitive abilities of introduced and native grasses

Differencesin competitive ability may explain the maintenance of existing plantpopulationsand the invasion of new areas by plant species. We used field experiments toexamine the competitive responses of Agropyron cristatum(L.) Gaertn., an introduced C₃ grass, and Boutelouagracilis (HBK.) Lag., a native C₄ grass, and thecompetitive effects of Agropyron-dominated vegetation andsuccessional prairie. We also tested whether the outcome of competitiveinteractions varied with water availability. In each vegetation type,transplants of each species were grown under two levels of competition(presenceor absence of neighboring vegetation) and three levels of water availability(high, medium, or low). Transplant survival, growth, and biomass allocationpatterns were measured. Water availability had no effect on the measuredvariables, suggesting that both species were limited by another resource.Growthrates were affected more by competition, while survival and root: shoot ratiowere affected more by transplant species identity. In the successional prairie,neighboring vegetation suppressed the growth of Agropyrontransplants less than that of Bouteloua transplants,suggesting that Agropyron has a stronger ability to resistcompetitive suppression in that vegetation type. The spread ofAgropyron into surrounding vegetation may relate to itsability to resist competitive suppression. In theAgropyron-dominated vegetation, neighboring vegetationsuppressed the growth of both species by the same extent. However, competitionaccounted for more variation in transplant growth inAgropyron-dominated vegetation than in successionalprairie, suggesting that Agropyron has strong competitiveeffects which hinder plant growth and prevent other species from establishinginAgropyron fields.     

Impact of early root competition on fitness components of four semiarid species

Summary Plant demographic and root exclusion approaches were used to examine the influence of roots of adult Artemisia tridentata, Agropyron desertorum, and Agropyron spicatum individuals on seedling survival of four C₃ semiarid species, three perennials, Ar. tridentata, Ag. desertorum, Ag. spicatum, and an annual, Bromus tectorum. Furthermore, height of Ar. tridentata seedlings and seed production of B. tectorum were assessed. The probability of a seedling being alive significantly depended on the seedling species, the neighboring adult species, and on the depth to which root competition was excluded. As seedlings, survival of Agropyron species did not differ, whereas survival of Ar. tridentata seedlings was higher than Ag. desertorum and was similar to Ag. spicatum. Bromus tectorum maintained significantly higher survival rates than perennial seedlings. Established individuals of Ar. tridentata reduced seedling survival more than established individuals of either Agropyron species. Seedling survival significantly increased with greater depth of root exclusion for the perennials but did not significantly affect seedling survival of B. tectorum. Height of Ar. tridentata seedlings and seed production of B. tectorum significantly increased with depth of root exclusion. Seed production of B. tectorum was highest when competing with Ag. desertorum and was lowest with Ar. tridentata. Root competition decreased the seed population of B. tectorum in the next generation even though it had no impact on survival. Competition in the upper soil horizon occurs between seedlings and established adults early in the growing season and potentially restricts root growth of seedlings. In arid and semiarid ecosystems, soil moisture is depleted from the upper horizons first, resulting in the death of seedlings that do not have access to moisture.     

Inflorescence culture of wheat-Agropyron hybrids: Callus induction,plant regeneration,and potential in overcoming sterility barriers

Segments of young inflorescences of Triticum aestivum cv. Chinese Spring (CS), its F₁ hybrids with Agropyron trachycaulum and A. scirpeum and backcross derivatives with A. yezoense, A. intermedium and A. junceum, and of a A. yezoense x T. aestivum cv. Wichita hybrid were cultured. Different parts of young spikelets of A. trachycaulum x CS F₁ and A. yezoense x Wichita F₁ 's were also cultured. Percent callus induction was lower in wheat than in the wheat-Agropyron hybrids or backcross derivatives. Percent callus induction from different organs in both hybrids was in the descending order of whole spikelet, spikelet without glumes, rachis, and glumes. No plants could be regenerated from calli of wheat and backcross derivatives except those of CS x A. intermedium combination. Callus induction in hybrids varied from 54 to 84% and plant regeneration from 14 to 31%. The regenerants required no vernalization. Variants including one with top-dense spikes and another with elongated spikelets were recovered. Out of eight A. trachycaulm x CS hybrid regenerants, one had anthers and stigma as opposed to neutral flowers of the original hybrid.     

Biochemical evidence of homoeology between Triticum aestivum and Agropyron intermedium chromosomes

Summary The alcohol dehydrogenase (ADH), phosphoglucose mutase (PGM), glucosephosphate isomerase (GPI), glutamic oxaloacetic transaminase (GOT), malate dehydrogenase (MDH), leaf esterases (ESTL), leaf acid (ACPH) and endosperm alkaline (PHE) phosphatases, leaf peroxidases (PERL) zymogram phenotypes of Triticum aestivum, Agropyron intermedium, Triticum aestivum — Agropyron intermedium octoploids and six Agropyron intermedium chromosome additions to Triticum aestivum and two ditelocentric addition lines were determined. It was found that the six disomic chromosome addition lines and one ditelocentric chromosome addition line could be distinguished from one another and from the other possible lines on the basis of the zymogram phenotypes of these isozymes. The structural gene Acph-X1 was located on Agropyron chromosome L1, the genes Got-X3 and Mdh-X2 on chromosome L2, the gene Gpi-X1 on chromosome L3, the genes Adh-X1, Pgm-X1 and Phe-3 on chromosome L4, gene Perl-1 on chromosome L5 and the gene Estl-2 on chromosome L7 and chromosome arm L7d2. These gene locations provide evidence of homoeology between Agropyron chromosomes L1, L2, L3, L4, L5 and L7 and the Triticum aestivum chromosomes of homoeologous groups 7, 3, 1, 4, 2 and 6, respectively.     

New hybrids between Agropyron and wheat

Summary Intergeneric hybrids of Triticum aestivum (2n=42,AABBDD) with Agropyron ciliare (2n= 28,SSYY), A. trachycaulum (2n=28,SSHH), A. yezoense (2n=28,SSYY) and A. scirpeum (2n=28) are reported for the first time. F₁ hybrids of T. aestivum were also produced with A. intermedium (2n=42,E₁E₁E₂E₂Z₁Z₁) and A. junceum (2n=14,JuJu). All wheat-Agropyron hybrids were obtained by embryo rescue technique. Cultivars and reciprocal crosses differed for seed set, seed development and F₁ plant production. The F₁ hybrids were sterile. Attempts to obtain amphiploids were unsuccessful. However, backcross derivatives were obtained with wheat as the recurrent parent.The level of chromosome pairing in A. trachycaulum x wheat, A. yezoense x wheat and wheat x A. junceum hybrids provided no evidence of homologous or homoeologous pairing. Mean pairing frequencies in A. ciliare x wheat, wheat x A. scirpeum and wheat x A. intermedium hybrids indicated homoeologous or autosyndetic pairing. Ph gene was more effective in regulating homoeologous pairing in A. yezoense x wheat hybrids than in A. ciliare x wheat hybrid. Chromosome pairing data of BC₁ derivatives indicated that either some of the wheat chromosomes were eliminated or Agropyron chromosomes caused reduced pairing of wheat homologues.Contribution No. 82-653-J, Department of Plant Pathology, Kansas State Agricultural Experiment Station, Manhattan, Kan, USA     

Populations composed entirely of hybrid colonies: bidirectional hybridization and polyandry in harvester ants

In eusocial Hymenoptera, haplodiploid life cycles, obligate sterile castes, and polyandry may facilitate selection for hybridization. We analyzed a broad hybrid zone between the ecologically distinct seed‐harvester ants Pogonomyrmex occidentalis (Cresson) and Pogonomyrmex maricopa (Wheeler) using mitochondrial (mt)DNA sequence data, eight morphological markers, and 14 random amplified polymorphic DNA (RAPD) markers. Average mtDNA sequence divergence among parental species was 11.34%, indicating secondary contact. RAPD markers were significantly correlated with morphological variation, confirming the interspecific hybrid origin of all morphologically putative hybrid colonies. A morphological hybrid index indicates an abundance of both F₁ hybrids and parental morphotypes within colonies. Individual character frequencies plotted against distance show coincident and concordant clines, suggesting little to no introgression. The structure of the hybrid zone is two‐fold. Within the western region, stark reversals in character frequencies coincide with overt soil differences, indicating a mosaic hybrid zone structure. The eastern region is a riparian habitat where four adjacent populations were composed entirely of hybrid colonies. These habitat associations suggest that hybrid worker genomes permit dispersal into intermediate environments that select against one or both parental species. The present study suggests that, in addition to retaining reproductive compatibility, ecologically distinct species of ants may generate hybrid colonies maintained by environmental selection. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 320–336.     

Production and cytogenetic analysis of BC1, BC2, and BC3 progenies of an intergeneric hybrid between Triticum aestivum (L.) Thell. and tetraploid Agropyron cristatum (L.) Gaertn.

Summary Intergeneric hybrids between Triticum aestivum cv Chinese Spring and Agropyron cristatum 4x (2n= 5x=35, ABDPP genomes) with a high level of homoeologous meiotic pairing between the wheat chromosomes were backcrossed 3 times to wheat. Pollination of the F₁ hybrid with Chinese Spring resulted in 22 BC₁ seeds with an average seed set of 1.52%. Five BC₁ plants with 39–41 chromosomes were raised using embryo rescue techniques. Chromosome pairing in the BC₁ was characterized by a high frequency of multivalent associations, but in spite of this there was no evidence of homoeologous pairing between chromosomes of wheat and those of Agropyron. All of the plants were self sterile. The embryo rescue technique was again essential to produce 39 BC₂ plants with chromosome numbers ranging from 37 to 67. The phenomenon of meiotic non-reduction was also observed in the BC₃ progenies. In this generation male and female fertility greatly increased, and meiotic pairing was fairly regular. Some monosomic (2n=43) and double monosomic (2n=44) lines were produced. Analysis of these progenies should permit the extraction of the seven possible wheat-Agropyron disomic addition lines including those with the added chromosomes carrying the genes involved in meiotic non-reduction and in suppression of Ph activity.     

Meiotic configuration and chromosome number in some Iranian species of Elymus L. and Agropyron Gaertner (Poaceae: Triticeae)

Chromosome numbers and analyses of meiotic metaphase I are reported for the following taxa: Agropyron cristatum subsp. incanum (2n= 42), A. cristatum subsp. pecttnatum (2n=28 – 33), Elymus elongatus subsp. ponticus (2n= 69, 70), E. hispidus var. hispidus (2n= 41 43), var. podperae (2n= 42) and var. villosus (2n= 41, 42), E. libanoticus (2n= 14), E. pertenuis (2n= 28, 28+1B), E. repens (2n= 42), E. transhyrcanus (2n= 40–42), E. hispidus var. villosus x E. cf. repens (2n= 42). Chromosome numbers only are reported for the following taxa: E. gentri (2n= 41, 42), E. nodosus subsp. dorudicus (2n= 28), and E. elongatiformis (2n= 56, 57). The haploid genomic constitution SP is reported for Elymus pertenuis. Variable chromosome numbers (2n= 28–32) were observed in the meiotic metaphase I within single anthers of Agropyron cristatum subsp. pectinatum, and the supernumerary chromosomes in this taxon are assumed to have originated from crosses with hexaploids. Partial elimination of these supernumerary chromosomes probably occurs during archesporial mitotic divisions or at an early stage in the meiotic cycle. A hybrid, morphologically intermediate between E. hispidus and E. repens, was obtained from a seed of E. hispidus collected in the field. The meiotic metaphase I configuration in this E. hispidus hybrid suggests that the pollen parent may itself be a hybrid or hybrid derivative of E. repens x E. hispidus.