Mean Chromosome Association Research Articles

Comparison of 2,4‐D and dicamba treatments for embryo development and plant regeneration in crosses between Lolium multiflorum Lam. and Dactylis glomerata L.

AbstractWe compared the effects of 2,4‐dichlorophenoxy acetic acid (2,4‐D) and 6‐dichloro‐2‐methoxybenzoic acid (dicamba) treatments on embryo development and plant regeneration in crosses between Lolium multiflorum Lam. and Dactylis glomerata L. Two embryos (1.1% of pollinated florets) were obtained after 2,4‐D treatment for 2 days. They germinated on hormone‐free Murashige and Skoog (MS) medium containing 1 g L−1 yeast extract, 70 g L−1 sucrose and 6 g L−1 agar, and developed into green seedlings. Dicamba treatment for 2 days gave higher frequencies of embryo development (4.3% of pollinated florets) than did 2,4‐D treatment, but only one embryo (0.4% of pollinated florets) germinated on hormone‐free MS agar medium, and no seedling was obtained. These results show that 2,4‐D is more effective than dicamba at producing F1 hybrids on hormone‐free MS agar medium. The F1 plant was intermediate between the parents in height, inflorescence morphology and lower leaf appearance. The folding of leaves in young shoots and the number of glumes resembled those of D. glomerata. Anthers did not dehisce. The F1 plant was an aneuploid with 26 chromosomes. The mean chromosome association was 0.04 trivalents, 10.36 bivalents and 5.16 univalents at metaphase I in pollen mother cells.

RAPD and Cytogenetic Study in F1 and F2 of Interspecific Cross between Gossypium arboreum*Gossypium anomalum

An interspecific hybrid between G. arboreum×G. anomalum was obtained by pollinating previous day bagged flowers of G. arboreum genetic male sterile line MPKV GMS with pollen from wild G. anomalum.The chromosome constitution in all the plants of G. arboreum and G. anomalum were found to be normal while interspecific hybrid showed mean chromosome association 1.081I+10.479II+0.000III+0.990IV with normal sporads. Interspecific hybrid showed anomalous behavior of univalent and formation of single and double chromatin bridges both during fist and second meiotic division of meiosis. Meiotic chromosome association was observed in nine plants of F2 generation. The cytological studies showed that F1 and F2 generations were having irregular pairing and unequal separation of chromosomes. This led to pollen sterility in these generations. In F2 plants some good plants identified with higher pollen fertility and more number of bolls per plant. Selections from these plants can help to introgress desired characters from G. anomalum to G. arboreum. Random Amplified Polymorphic DNA (RAPD) analysis was employed to characterize the F1 interspecific hybrid of G. arboreum MPKV GMS×G. anomalum and its nine segregants. A total fifteen primers of 10 mer were screened of which eight were selected based on polymorphism of amplified fragments, amplification intensity and the presence of informative markers. Maximum 98 amplified fragments were resolved on the gel for parents, F1 and F2's with OPC-19 primers, whereas, minimum 25 fragments were seen with OPD-04 primer. Similarity coefficient based on DNA amplification using amplified RAPD primer was estimated. The values for genetic similarity ranged from 0.14 to 0.77.

Production and Fertility Restoration of an Interspecific Hybrid between Gossypium hirsutum L. and G. raimondii U.

Interspecific hybrids between 2 cultivated varieties (MCU 5 and MCU 7) of tetraploid cotton (Gossypium hirsutum) and diploid perennial species G. raimondii were synthesized. The resulting triploid F1s were pollen sterile and exhibited irregular meiosis with frequent formation of univalents and multivalents. Mean chromosome association of the triploid hybrids were 11.50 I+9.97 II+2.31 III+0.16 IV and 0.50 I+11.35 II+0.96 I. Successful synthesis of hexaploids involoving G. raimondii by doubling the genomes of the triploid hybrids with 0.1% colchicine and enhancement of fertility status in hybrids is reported for the first time. The mean chromosomal association of hexaploid hybrids were 4.05 I+26.91 II+4.45 III+1.23 IV+0.32 V and 1.26 I+25.81 II+1.18 III+5.19 IV respectively. The heterozygosity of triploid and hexaploid hybrids was also confirmed through SSR marker analysis. Further utility of the developed hybrids with respect to jassid resistance breeding in cotton is discussed.

Cytogenetic studies in Cyclamen persicum , C. graecum (Primulaceae) and their hybrids

Haploids, diploids and tetraploids of Cyclamen persicum (2n=x=24, 2x=48 and 4x=96), C. graecum (2n=84) and their interspecific hybrids (2n=45, 3x=66, 4x=90) were analyzed cytologically. The mean chromosome association per PMC at diakinesis or at metaphase I in meiosis was 23.29–23.39 I + 0.31–0.36 II in C. persicum (x), 0.17–0.23 I + 23.88–23.92 II in C. persicum (2x), 0.52–1.18 I + 46.39–46.78 II + 0.03–0.09 III + 0.41–0.48IV in C. persicum (4x) and 0.40–0.46I + 41.34–41.63 II + 0.02 III + 0.07–0.21IV in C. graecum. The mean chromosome association per PMC at diakinesis or at metaphase I was 0.47–0.62 I + 44.69–44.76 II in the hybrid (2n=90) of C. persicum (4x) × C. graecum, 38.48–42.50 I + 1.27–3.26 II in microspore-derived plants (2n=45) from the hybrid (2n=90) by anther culture and 26.22–26.67 I + 19.67–19.89 II in the hybrid (2n=66) of C. persicum (2x) × C. graecum. The results indicate that C. graecum is an autotetraploid, the hybrid (2n=4x=90) is an amphidiploid, the microspore-derived plant (2n=45) is a polyhaploid and the hybrid (2n=3x=66) is a sesquidiploid. Based on studies of meiosis, the ploidy levels and the origin of C. graecum and C. persicum are discussed in comparison with several species in the genus Cyclamen.

Chromosome Association and Giemsa C-banding of Meiotic Chromosomes in Interspecific Hybrid of Alstroemeria ligtu L. hybrid and A.pelegrina L. var. rosea, its Amphidiploid, and Sesquidiploid between the Amphidiploid and the Parents.

Alstroemeria ligtu L. hybrid (LH, 2n = 2x = 16), A. pelegrina L. var. rosea (PR, 2n = 2x = 16) and their interspecific hybrids (2n = 2x = 16, 3x = 24, 4x = 32) were analyzed cytologically. In the parental species, the mean chromosome association per pollen mother cell (PMC) at metaphase I in meiosis was 0.04 I + 7.98 II in LH and 0.08 I + 7.96 II in PR. Meiosis proceeded normally in these 2 species and pollen fertility was 98.4 % in the former and 94.9 % in the latter. These 2 species produced many normal seeds by self-pollination. The hybrid (2n = 16) showed partial chromosome association with a mean of 11.18 I + 2.41 II. Abnormal chromosome behavior such as the formation of bridges and micronuclei was observed frequently at anaphase I and II of PMCs or at the early uninucleate stage of microspores, which resulted in low pollen fertility (0.6 %). The hybrid did not produce any normal seeds when self-pollinated or backcrossed with either parent. In the amphidiploid (2n = 32), the mean chromosome association per PMC was 0.82 I + 15.59 II at metaphase I and pollen fertility was 86.3 %. Although the amphidiploid did not produce any normal seeds by self-pollination, it produced normal seeds by the reciprocal crosses with LH. The mean chromosome association in the sesquidiploid (2n = 24) of LH × the amphidiploid was 8.24 I + 7.85 II + 0.02 III and that of PR × the amphidiploid was 8.58 I + 7.66 II + 0.03 III. These sesquidiploids frequently showed chromosome bridges and micronuclei at anaphase I and II of PMCs or at the early uninucleate stage of microspores, and pollen fertility was 14.8 % in the former and 13.0 % in the latter. Although the two types of sesquidiploid did not produce any normal seeds by self-pollination, the former sesquidiploid produced normal seeds by the cross with LH. In LH, the Giemsa C-bands were observed in 7 out of 8 bivalents at metaphase I of PMCs and in 7-7 out of 8-8 chromosomes at anaphase I of PMCs, whereas no C-bands were observed in PR throughout these meiotic stages. These C-band patterns were detected at metaphase I of PMCs in the hybrid, the amphidiploid, and the two types of sesquidiploids.

Cytology and Morphology of Elymus hoffmanni (Poaceae: Triticeae): A New Species from the Erzurum Province of Turkey

Cytological and morphological characteristics of a proposed new species, Elymus hoffmanni Jensen & Asay, are described. This species is cytologically stable and is genomically similar to Elymus repens (L.) Gould (SSSSHH) (= Agropyron repens [L.] P. Beauv and Elytrigia repens [L.] Nevski) and the cultivar NewHy (SSSSHH), but morphologically different from E. repens. Elymus hoffmanni has longer leaves, shorter awns on the glumes, and less rhizome development, and it is taller than the cultivar NewHy. Elymus hoffmanni was crossed with E. repens and the cultivar NewHy hybrid wheatgrass (2n = 6x = 42). A natural hybrid between E. hoffmanni and the cultivar Hycrest crested wheatgrass (2n = 4x = 28, PPPP) was identified from open-pollinated progeny of E. hoffmanni. Meiosis of E. hoffmanni was characterized as an autoallohexaploids with a mean chromosome association of 1.63 I + 17.87 II + 0.35 III + 0.67 IV + 0.04 V per cell. Mean chromosome associations were 1.88 I + 19.12 II + 0.16 III 0.46 + IV per cell in the hybrids of E. repens x E. hoffmanni, 1.63 I + 19.43 II + 0.22 III + 0.31 IV + 0.01 V per cell in NewHy x E. hoffmanni hybrids, and 9.22 I + 12.74 II + 0.40 III + 0.02 IV in E. hoffmanni x Hycrest hybrids. Based on chromosome pairing in hybrids with E. repens and NewHy and its morphological uniqueness from E. repens, we propose E. hoffmanni as a new species originating from a primitive hybrid between E. repens and the bluebunch wheatgrasses (Pseudoroegneria spp.) of Turkey.

Chromosome Association and Fertility in the Hybrid of Cyclamen persicum Mill. and C. hederifolium Aiton and its Amphidiploid.

Chromosome association and fertility of the hybrids of C. persicum (2n=2x=48)xC. hederifolium (2n=34) and the amphidiploids were compared with their parental species. The mean chromosome association per PMC at metaphase I in meiosis was 0.13 I + 23.93 Iin C. persicum and 0.15 I +16.92 II in C. hederifolium. These parental species formed normal cells at telophase I and the tetrad stage, and produced viable pollen grains and seeds. On the other hand, the hybrids (2n=41) showed partial chromosome association with a mean of 35.39 I + 2.81 II . They formed abnormal cells at telophase I and the tetrad stage, which resulted in sterile pollen. The hybrids failed to set a seed by cross-pollination with fertile C. persicum pollen grains, suggesting female sterility. In the amphidiploids (2n=82), bivalents were formed at high frequency and the mean chromosome association was 0.51 1 +40.75II. Meiosis proceeded normally and fertile pollen grains were produced. These amphidiploids yielded viable seeds by self- pollination. These observations suggest that C. persicum and C. hederifolium are distantly related within the genus Cycl amen.

Intergeneric Hybrids between Aegilops squarrosa and Secale cereale and their Meiotic Chromosome Behaviour

Three hybrid plants with different combinations of D and R genomes were produced from crosses between Aegilops squarrosa (2×: and 4×) and Secale cereale (2× and 4×) using embryo culture. Production frequencies of mature hybrids, having the genomes DR, DDR and DDRR, were 2.0%, 5.2% and 2.2 %, respectively, of florets pollinated. Amphidiploids were obtained directly from the cross between tetraploid parents. The majority of their morphological features were intermediate between those of the parents but, as with rye, the rachis was tough. Diploid and triploid hybrids were completely seed-sterile, whereas the amphidiploid had an average self-fertility of 4.5 % with a range of 0 to 45 %. The somatic chromosome numbers of diploids, triploids and amphidiploids were 2n = 14, 21 and 28, respectively. At meiotic metaphase I, the mean chromosome associations were 0.01 III + 0.26 II + 13.4 I in diploids, 6.96 II + 7.1 I in triploids, and 10.5 II + 7.9 I in amphidiploids. In diploids, pairing between D and R chromosomes was observed in the form of end-to-end types without chiasmata. Homologous pairing between D chromosomes was predominant in plants having two sets of D genomes. Amphidiploids showed a diploid-like chromosome behaviour. Homoeologous pairing was not observed in either triploids or amphidiploids.

Cytogenetic Relationships between Paspalum dilatatum and P. cromyorrhizon, P. indecorum, and P. laxum

Paspalum cromyorrhizon Trin. (2n = 2x = 20), P. indecorum Mez (2n = 2x = 20), and P. laxum Lam. (2n = 6x = 60) were crossed with yellow-anthered dallisgrass, P. dilatatum Poir. (2n = 4x = 40), to determine their genome relationships. Meiosis was irregular in all hybrids examined. Twelve P. dilatatum x P. cromyorrhizon hybrids had a chromosome number of 2n = 3x = 30. The mean chromosome association of these hybrids was 25.50 I and 2.25 II per cell. Seven P. dilatatum x P. indecorum hybrids had 30 chromosomes. Their mean meiotic chromosome association was 23.45 I , 3.27 II , and 0.004 III per cell. Three P. dilatatum x P. laxum hybrids had 50 chromosomes. Their mean chromosome association was 44.76 I , 2.61 II , and 0.004 III per cell. In all hybrids, a majority of the bivalents were synapsed as rods. The P. dilatatum biotype in these crosses has the genome formula II JJ, and this study indicates that the other three species do not ...

Cytology and morphology of Pseudoroegneria deweyi (Poaceae: Triticeae): a new species from the foot hills of the Caucasus Mountains (Russia)

Cytological and morphological characteristics of a new species, Pseudoroegneria deweyi K. B. Jensen, from the Karachayevo-Cherkesskaya Avtonomnaya Oblast' Region of Russia are described. This species is cytologically stable, genomically similar to Pseudoroegneria tauri, highly fertile (cross-pollinating), and morphologically unique compared with most other species in the genus. Pseudoroegneria deweyi differs from other closely related species in the number of rachis nodes in the inflorescence. Pseudoroegneria stipifolia (2n = 2x = 14, SS) and Agropyron cristatum (2n = 2x = 14, PP) were used as male parents in crosses with P. deweyi. All three P. deweyi accessions studied were tetraploids (2n = 28) and behaved meiotically as allotetraploids with a mean chromosome association of 0.03 I + 13.30 II + 0.03 III + 0.26 IV per cell. In the hybrid P. deweyi × A. cristatum, average chromosome association was 5.92 I + 4.55 II + 1.83 III + 0.09 IV per cell, while the average chromosome association in P. deweyi × P. stipifolia was 4.98 I + 5.23 II + 1.73 III 0.04 IV per cell. Pseudoroegneria deweyi joins P. tauri as the only other known naturally occurring species with the genomic formula of SSPP. Cluster analysis of 21 morphological characters supports the inclusion of P. deweyi as part of the genus Pseudoroegneria rather than Agropyron. Key words: Agropyron, Pseudoroegneria, chromosome pairing, meiosis, Triticeae, new species.

Cytological Studies of Hybrids between Aneuploid and Eu-diploid Japanese Garden Iris(Iris ensata Thunb.).

Cytological studies of hybrids between the aneuploid variety “Ochibagoromo” (2n=25) and the eu-diploid variety “Shishinden” (2n=24) of Iris ensata were made. Among the hybrids (2n=24) examined, F1-1 and F1-2 exhibited normal associations (12 II), and the mean chromosome association per cell was 0.13 I+11.93 II for the former and 0.29 I+11.86 II for the latter, respectively. This indicates that one of three single chromosomes of “Ochibagoromo” has full homology for the second longest m chromosomes of “Shishinden”. On the other hand, F1-3 showed a fairly lower frequency for normal associations than the former two hybrids. The mean chromosome association per cell was 0.98 I+11.16 II+0.24 III. Consequently, this hybrid exhibited the lowest pollen fertility among F1 hybrids due to the irregularity in chromosome associations. Moreover, comparative karyotypic analysis between F1-1 and F1-3, and the meiotic data of F1-3 clarified that this irregularity was caused by structural changes of chromosomes such as translocation and deficiency. Finally, the origin and the development of the aneuploid varieties are discussed.

Genome Relationships between Tetraploid and Hexaploid Biotypes of Dallisgrass, Paspalum dilatatum

A sexual, yellow-anthered, tetraploid (2n = 4X = 40) biotype of dallisgrass, Paspalum dilatatum Poir., was crossed with an apomictic, purple-anthered, hexaploid (2n = 6X = 60) dallisgrass biotype from Uruguay to determine their cytological relationship and to establish the genomic composition of the hexaploid Uruguayan biotype. Forty-one intraspecific F1 hybrids were produced and 20 were studied cytologically. Nineteen plants had 50 chromosomes and one was aneuploid with 47 chromosomes. During metaphase I, the mean chromosome associations for 50-chromosome hybrids were 10.31I, 19.83II, 0.003III, and 0.003IV. The mean meiotic associations of the aneuploid hybrid were 7.12I and 19.94II. Most bivalents occurred as rings. These findings indicate that the biotypes have two homologous genomes. Based on the genome formula (IIJJ) of the yellow-anthered biotype, the 60-chromosome Uruguayan biotype has both the I and J genomes plus a third genome and its formula may be expressed as IIJJXX, where X is the third genome. The formula of the F1 hybrids is IIJJX. The chromosome number (2n = 5X = 50) and meiotic pairing behavior (20II + 10I) of these hybrids are similar to those of apomictic common dallisgrass. These results suggest that they may have the same genomic formula, but similarity of the X genomes in the Uruguayan and common biotypes has not been proven. If they are similar, apomictic common dallisgrass probably originated from a natural cross between the sexual yellow-anthered biotype or a closely related sexual tetraploid relative and the apomictic, hexaploid Uruguayan biotype.

Cytology, Reproductive Behavior, and Forage Potential of Hexaploid Dallisgrass Biotypes

During the past 25 yr, several different dallisgrass (Paspalum dilatatum Poir.) biotypes have been discovered, but little is known regarding their cytology and reproductive behavior. This study was undertaken to determine the cytology, method of reproduction, and fertility of three biotypes and the forage yield and quality of two of them. Two biotypes, Torres and Uruguaiana, were introduced from southern Brazil and the third, Uruguayan, was collected in Uruguay. All three are hexaploids with 2n = 6x = 60. The Torres biotype was meiotically irregular, with a mean chromosome association of 58.74 univalents and 0.63 bivalents per cell. Two accessions of the Uruguaiana biotype were studied; they had a mean meiotic chromosome association of 9.62 univalents, 25.17 bivalents, and 0.01 quadrivalents. Eleven accessions of the Uruguayan biotype were studied; their mean chromosome associations were 1.26 univalents, 29.28 bivalents, and 0.04 quadrivalents. It was proposed that the lack of chromosome pairing in the Torres biotype is genetically controlled. The genomic formulas of the Uruguaiana and Uruguayan biotypes are proposed to be AABBC1C2 and AABBCC, respectively. An examination of megasporogenesis and embryo sac development revealed that all three biotypes reproduce by apomixis, with apospory followed by pseudogamy. One Uruguayan accession was a facultative apomict with a small degree of sexuality. The forage yield potential and forage quality were determined for the Torres and Uruguayan biotypes, as well as for common dallisgrass. Torres produced less forage than the other two. Common dallisgrass produced less forage than the mean of the Uruguayan accessions in most environments. In vitro dry matter disappearance (IVDMD) differences among accessions were relatively small. Common dallisgrass did not differ in IVDMD from any of the Uruguayan accessions.

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

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.

Hybrid between durum wheat and diploid Thinopyrum bessarabicum

Gross morphological features and chromosome association of the first triploid intergeneric hybrid (2n = 3x = 21; ABJ genomes) between durum wheat, Triticum turgidum L. (2n = 4x = 28; AABB), and diploid wheatgrass, Thinopyrum bessarabicum (Savul. &Rayss) A. Löve (2n = 2x = 14; JJ), are described. Genome relationships are assessed in the presence of the pairing homoeologous gene, Ph1. The hybrid was intermediate in phenotype between the two parents. It inherited the tillering habit, perennial growth habit, and glaucous leaves and stems from the male Thinopyrum parent; spike density and awns of wheat were partially expressed. An average of 13.67% of the chromosome complement paired in metaphase I cells of the hybrid. Mean chromosome associations were 0.07 III + 0.03 ring II + 1.30 rod II + 18.13 I and 1.51 chiasmata per cell, with a mean arm-pairing frequency, c, of 0.107. Because chromosomes of the A and B genomes show very little pairing with each other in the polyhaploids of T. turgidum, it was inferred that most of the bivalents in the hybrid were formed between chromosomes of the A and J and (or) B and J genomes, a welcome feature from the breeding standpoint. Trivalent frequency, albeit low, further indicated intergenomic pairing among A, B, and J. Associations between wheat and Thinopyrum chromosomes may permit intergeneric transfer of genes, which may be accelerated by the use of the ph1c ph1c homoeologous pairing mutant of durum wheat.Key words: intergeneric hybrid, chromosome pairing, genome relationship, Triticum, Ph1 pairing regulator.

Embryo-callus-regenerated hybrids and their colchicine-induced amphiploids between Elymus canadensis and Secale cereale

Intergeneric hybrids recovered through plant regeneration from embryo callus culture and their colchicine-induced amphiploids were obtained from a cross of Elymus canadensis with Secale cereale (cv 'Gazeller'). The embryo-callus-regenerated F1 plants grew vigorously to maturity and regrew well after clipping, while the embryo-rescued F1 died of hybrid necrosis before maturity. Most of the morphological characters of the sterile F1 hybrids were intermediate between the parents, but tiller number and dry matter yield were higher than the parents. Amphiploids from these F1 plants had improved fertility but were less vigorous than the F1 plants. The predominance of univalents in the F1 and bivalents in the amphiploids indicated that the genomes S, H, and R were distinct. However, the occasional occurrence of multivalents reflected a random, intergenomic or intragenomic pairing. The mean chromosome associations of the F1 (2n=21, SHR), the C0 amphiploids (2n=42, SSHHRR), and the C1 amphiploid (2n=40) at metaphase I (MI) were 16.51I+2.05II+0.06III+0.02IV+0.02V, 2.20I+19.87II +0.02IV, and 7.10I+16.37II+0.04III+0.02IV, respectively. These amphiploids could be exploited as new germplasm for forage crop improvement by controlled introgression and backcrosses to the parents.

Karyotypes and chromosome association in aneuploid varieties of Japanese garden iris, Iris ensata Thunb

Karyotypes, chromosome association and pollen fertility of aneuploid varieties (2n=25), ‘Ochibagoromo’, ‘Matsusakatsukasa’ and ‘Isehomare’ in Iris ensata were analysed and compared with those of eu-diploid varieties (2n=24), ‘Shishinden’, ‘Kacho’ and ‘Asahimaru’. The somatic chromosome complement of the aneuploid varieties consisted of 11 pairs and 3 singles of chromosomes and that of the eu-diploid varieties 12 pairs of chromosomes. The singles of chromosomes in the aneuploid varieties had similarity with one another and with a pair of chromosomes in the eu-diploid varieties. The high frequency of normal association was present in the eu-diploid varieties, and this indicated that 12 pairs of chromosomes had full homology between each other. In contrast, the mean chromosome association per cell in an aneuploid variety ‘Ochibagoromo’ was 4.615I+10.067II+0.077III+0.005IV, indicating that the chromosome complement of this variety consisted of 11 pairs and 3 singles and that these singles had partial homology among them. The eu-diploid varieties exhibited high pollen fertility due to their regularity of chromosome association; the aneuploid varieties considerably lower fertility, i.e. 28.2% for ‘Ochibagoromo’, 31.8% for ‘Isehomare’ and 43.8% for ‘Matsusakatsukasa’. The primary cause for the low fertility of these varieties seemes to be the partial homology among 3 single chromosomes. Finally, the origin and the development of the aneuploid varieties were discussed.

A study on genomic relationships of Agropyron trachycaulum with Elymus scabriglumis, E. innovatus, and Hordeum procerum

Synthetic hybrids of Agropyron trachycaulum (2n = 4x = 28) with Elymus scabriglumis (2n = 6x = 42), E. innovatus (2n = 4x = 28), and Hordeum procerum (2n = 6x = 42) were produced through the embryo rescue technique, at relative frequencies of 7.1, 4.2, and 1.8%, respectively, of pollinated florets. The mean chromosome associations in two hybrids with E. scabriglumis was 11.71II + 1.47III + 0.15IV (mean chiasma frequency = 22.75), in one hybrid with H. procerum was 7.27II + 0.63III + 0.09IV (mean chiasma frequency = 10.20) and in a hybrid with E. innovatus was 2.8II (2.19 chiasma frequency). The data suggested two common genomes (S and H) with E. scabriglumis, one common genome (H) with H. procerum, and no common genome with E. innovatus. The evidence obtained suggested a SSHHYY genomic constitution for E. scabriglumis and two genomes different from SH for E. innovatus. The evidence also suggested that in H. procerum there may not be two related genomes present (derived from H. jubatum) as speculated in some earlier studies.Key words: intergeneric hybrids, Agropyron, Elymus, Hordeum, chromosome pairing.

Cytology of triploid and pentaploid hybrids of Elymus trachycaulus × Pseudoroegneria spicata and P. spicata ssp. inermis

Emasculated clones of tetraploid and octaploid Elymus trachycaulus crossed with Pseudoroegneria spicata yielded 69 triploids and 13 pentaploid hybrids. The triploid hybrids were morphologically intermediate between the parental species but the pentaploid hybrids resembled E. trachycaulus more closely than P. spicata. A very high degree of plant size variability (very weak to very vigorous) was observed among the 50 triploids that survived to maturity. The variability among the pentaploids, though apparent, was not high. Mean chromosome associations among the selected eight triploids varied from low multivalent formation at meiosis (7.60 I + 6.18 II + 0.24 III + 0.08 IV) to high multivalent-forming meiosis (7.28 I + 5.66 II + 0.32 III + 0.36 IV). The bivalent configurations in these triploids were attributed to homoeologous pairing between the S1 genome of P. spicata and S genomes of E. trachycaulus and the multivalents indicated intergenomal and intragenomal pairings. Mean chromosome associations of 5.22 I + 11.94 II + 1.97 III in 78.7% and 7 I + 14 II in 21.3% of the 150 cells were distributed among the three pentaploid hybrids. The low frequency of trivalents and the absence of multivalents higher than trivalent configurations suggest that homoeologous pairing was substantially reduced and there was no intergenomal and intragenomal pairing in these 2n = 35 x hybrids. Fourteen triploids and three pentaploid hybrids were produced from 4x and 8x forms of E. trachycaulus and P. spicata spp. inermis crosses. The triploids were intermediate between the parents but the pentaploids were more similar to E. trachycaulus. Mean chromosome associations in the triploids (6.020 I + 5.315 II + 0.554 III + 0.235 IV + 0.250 V + 0.048 VI + 0.03 VII) and in the pentaploids (3.50 I + 10.18 II + 3.54 III + 0.13 IV) indicated a very high degree of intergenomal and intragenomal pairing in the triploids; nevertheless, it was greatly reduced in the pentaploids. The Pseudoroegneria spicata ssp. inermis genome may have gene(s) that affect a high degree of intergenomal and intragenomal pairing in triploid hybrids with E. trachycaulus. However, in pentaploid hybrids (SS HH S2) the S and H genomes of E. trachycaulus in double dose seem to have restored its regular meiotic bahaviour, at least partially, and reduced homoeologous pairing as well as intergenomal and intragenomal pairing. Key words: Elymus trachycaulus, Pseudoroegneria spicata, regular meiotic behaviour, double dose, intergenomal pairing, intragenomal pairing.

Intergeneric Hybrids and Amphiploids between Pseudoroegneria spicata and Critesion violaceum

Diploid (2n = 14) Pseudoroegneria spicata ssp. inermis (genome formula, SS; formerly in Agropyron) was hybridized with diploid (2n = 14) Critesion violaceum (genome formula, HH; formerly in Hordeum). The hybrids (genome formula, SH) were morphologically intermediate to the parents. Mean chromosome associations of 7.28I, 3.11II, 0.16III, and 0.05IV were observed at metaphase I in 208 cells from four hybrids. Of the bivalents, 90% were rod configurations leading to a mean chiasma per arm of 0.269. The hybrids were completely sterile. The SSHH amphiploid derivatives were morphologically like the FI hybrids and were partially fertile, averaging 2.6 seeds per spike. At metaphase I, the amphiploids averaged 4.01I, 11.37II, 0.26III, 0.09IV, and 0.03V in 160 cells. Many progeny of the amphiploids were natural outcrosses to other species growing in the same field nursery. At least nine outcross hybrids occurred with Agropyron cristatum (2n = 14; genome formula, PP) and even more with Critesion brevisubulatum (2n = 28; genome formula, HHHH). These two hybrid combinations, whose identities were established on morphological and cytological grounds, were also analyzed at metaphase I. Data from hybrids, C0 and C1 amphiploids, and outcross hybrids led to the conclusions that (1) the S, H, and P genomes are distinctly different but contain some residual homologies, and (2) SSHH amphiploids are segmental alloploids.