A novel intergeneric hybrid in the Triticeae: Triticum aestivum x Psathyrost achys juncea

Summary Two hybrid embryos of intergeneric origin between Triticum aestivum cv Fukuho (2n=6x=42, AABBDD) and Psathyrostachys juncea (2n=2x=14, NN) were successfully rescued. One hybrid plant had the expected chromosome number of 28 (ABDN), whereas the second plant had 35 chromosomes. The average meiotic chromosome pairing in the 35-chromosome hybrid was 21.87 univalents + 6.38 bivalents + 0.11 trivalents + 0.009 quadrivalents, which indicates that two copies of the N genome were present. Chromosome pairing in the 28-chromosome hybrid was low (1.35 bivalents), and pointed out the lack of homology between the wheat genomes and the P. juncea genome. These new hybrids showed some necrosis and chlorosis, which caused severe floral abortion in the plant that had 35 chromosomes. These problems became gradually less severe after 18 months.Contrib. no. 372     

Morphology and cytology of intergeneric hybrids involvingLeymus multicaulis (Poaceae)

The morphology and meiotic behaviour of pollen mother cells were studied in hybrids involvingLeymus multicaulis (2n = 28) ×Psathyrostachys huashanica (2n = 14),L. multicaulis ×P. juncea (2n = 14), andL. secalinus (2n = 28) ×L. multicaulis. Chromosome pairing was almost identical in theL. multicaulis ×P. huashanica, andL. multicaulis ×P. juncea hybrids, in which it averaged 7.30 univalents + 6.69 bivalents + 0.096 trivalents and 7.48 univalents + 6.75 bivalents, respectively. The meiotic pairing in the two hybrids indicated that oneL. multicaulis genome was closely homologous with theP. huashanica andP. juncea genomes. BothP. huashanica andP. juncea are possibly donors of oneL. multicaulis genome. Chromosome pairing in theL. secalinus ×L. multicaulis hybrid averaged 4.49 univalents + 11.71 bivalents + 0.02 trivalents, indicating that the genomes ofL. multicaulis andL. secalinus are to some degree homologous. However, they are sufficiently differentiated to insure species distinctness.     

Chromosome pairing relationships among the A,B, and D genomes of bread wheat

Summary Chromosome pairing and chiasma frequency were studied in bread wheat euhaploids (2n = 3x = 21; ABD genomes) with and without the major pairing regulatorPh1. This constitutes the first report of chromosome pairing relationships among the A, B, and D genomes of wheat without the influence of an alien genome. AllPh1 euhaploids had very little pairing, with 0.62–1.05 rod bivalents per cell; ring bivalents were virtually absent and mean arm-binding frequency (c) values ranged from 0.050 to 0.086. In contrast, theph1b euhaploids had extensive homoeologous pairing, with chiasma frequency 7.5–11.6 times higher than that in thePh1 euhaploids. They had 0.53–1.16 trivalents, 1.53–1.74 ring bivalents, and 2.90–3.57 rod bivalents, withc from 0.580 to 0.629. N-banding of meiotic chromosomes showed strongly preferential pairing between chromosomes of the A and D genomes; 80% of the pairing was between these genomes, especially in the presence of theph1b allele. The application of mathematical models to unmarked chromosomes also supported a 21 genomic structure of theph1b euhaploids. Numerical modeling suggested that about 80% of the metaphase I association was between the two most related genomes in the presence ofph1b, but that pairing under Ph1 was considerably more random. The data demonstrate that the A and D genomes are much more closely related to each other than either is to B. These results may have phylogenetic significance and hence breeding implications.This paper is dedicated to the memory of the late Ernest R. SearsCooperative investigations of the USDA-Agricultural Research Service and the Utah Agricultural Experiment Station, Logan, UT 84322, USA. Approved as Journal Paper No. 3986     

Reproduction and cytogenetic characterization of interspecific hybrids derived from crosses between Brassica carinata and B. rapa

The tri-genomic hybrid (ABC, 2n=27) between Brassica carinata (BBCC, 2n=34) and B. rapa (AA, 2n=20) is a unique material for studying genome relationships among Brassica species and a valuable bridge for transferring desirable characteristics from one species to the other within the genus Brassica. The crossability between B. carinata and B. rapa was varied with the cultivar of B. rapa. Hybrid pollen mother cells (PMCs), confirmed by morphological observation and molecular marker assay, could be grouped into 20 classes on the basis of chromosome pairing configurations. More than 30% of the PMCs had nine or more bivalents. Genomic in situ hybridization confirmed that two of the bivalents most likely belonged to the B genome. Nearly one-half of the PMCs had trivalents (0–2) and quadrivalents (0–2), which revealed partial homology among the A, B, and C genomes and suggested that there is a good possibility to transfer genes by means of recombination among the three genomes. The advantages of using the tri-genomic hybrids as bridge material for breeding new types of B. napus are discussed.     

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.     

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。     

Asynchronous meiotic rhythm as the cause of selective chromosome elimination in an interspecific <Emphasis Type="Italic">Brachiaria</Emphasis> hybrid

This paper reports the occurrence of chromosome elimination during microsporogenesis in an interspecific hybrid between a sexual diploid accession (SEX) of Brachiaria ruziziensis (2n=2x=18) and an apomictic tetraploid accession (APO) of B. brizantha (2n=4x=36). Meiosis was very abnormal in the triploid hybrid (2n=3x=27); we observed a distinct asynchrony from metaphase I to the end of meiosis. The APO and the SEX genomes did not show the same meiotic rhythm. When the former, with nine bivalents, was in metaphase I, the nine SEX univalents were not yet aligned; when the latter reached the plate, the APO genome was already in anaphase. In subsequent stages, the APO genome had reached the poles while the SEX was undergoing sister-chromatid segregation. As the SEX genome always remained temporally behind, it gave rise to one extra-nucleus in each pole. In the second division, the behavior was the same but anaphase II did not occur for the SEX genome, and only one extra-nucleus was observed in each cell in telophase II. Chromosome elimination for the SEX genome ranged from partial to total. The importance of these findings with respect to Brachiaria breeding programmes is discussed.     

Cytological studies on meiotic configurations of intraspecific aneuploids ofCarex blepharicarpa (Cyperaceae) in Japan

Chromosome configurations at meiotic metaphase I ofCarex blepharicarpa were determined for 245 individuals collected from 11 localities in the Chugoku District of Japan. Nine intraspecific aneuploids, 2n=26–33 and 41, were found. The most common diploid number was 29, and found in 73 individuals. No clear geographical pattern was suggested by a distribution of these aneuploids. A consecutive series of chromosome numbers from 2n=26 to 32 was found in two populations from Okayama Prefecture. At meiotic metaphase I, univalents and multivalents were found, and one to three trivalents were observed in each aneuploid. Heteromorphic chain trivalents comprising large, medium and small chromosomes were prevalent. Homomorphic trivalents, which are thought to be originated from chromosome duplications caused by unreduced gametes, were found in only one individual with 2n=41. The high frequency of heteromorphic trivalents in this species indicates that most aneuploidy probably results from fission and/or fusion of chromosomes.     

Supernumerary chromosomes in Tradescantia I. Meiotic behavior of three homologous isochromosomes

The meiotic behavior of three homologous iso-supernumerary chromosomes in an individual of Tradescantia ohiensis Raf. has revealed sevealed several interesting features. There is a high frequency of pairing-partner exchange within bivalents and trivalents. The mean chiasma frequency per chromosome is relatively high (1.046) for supernumerary chromosomes and is not significantly different from that of the much larger normal (A) chromosomes. The high frequency of trivalent and bivalent configurations would seem to suggest that the isosupernumerary chromosomes are premeiotically dispositioned to allow for full random pairing among all six homologous arms.     

The cytogenetics of a Triticum turgidum x Psathyrostachys juncea hybrid and its backcross derivatives

Psathyrostachys juncea (2n = 2x = 14, NN), a source of barley yellow dwarf (BYDV) virus resistance with tolerance to drought and salinity, has been successfully hybridized in its autotetraploid form (2n = 4x = 28, NNNN) as the pollen parent to durum wheat (Triticum turgidum L.). The 2n = 4x = 28 (ABNN) F₁ hybrid has a mean meiotic metaphase-I configuration of 20.29 univalents + 0.29 ring bivalents + 3.36 rod bivalents + 0.14 trivalents. Spike length, internode length, glume awn length and lemma awn length, as well as the general spike morphology of the F₁ hybrid, are intermediate with those of the two parents. Pollinating the ABNN F₁ hybrid has given backcross (BC)-I derivatives of an amphiploid (AABBNN) that expresses limited self-fertility. BC-2 derivatives have been obtained from these plants. Direct transfers of useful genes from Ps. juncea to wheat would require substantial genetic manipulation strategies. Both conventional and novel methodologies, which may complement each other, and so facilitate reaching an agricultural objective end point, are addressed.     

Tissue-culture-facilitated production of aneupolyhaploid Thinopyrum ponticum and amphidiploid Hordeum violaceum x H. bogdanii and their uses in phylogenetic studies

Summary An aneupolyhaploid (2n = 36) of the decaploid Thinopyrum ponticum and an amphidiploid (2n = 28) of Hordeum violaceum x Hordeum bogdanii were produced through anther and inflorescence culture, respectively. Meiotic associations in pollen mother cells at metaphase I of these plants were analyzed. The aneupolyhaploid arose by direct embryogenesis from a microspore without passing through a callus phase. The mean pairing frequencies of 2.67 univalents ⁺ 0.54 rod bivalents ⁺ 8.85 ring bivalents ⁺ 2.75 trivalents ⁺ 0.17 chain quadrivalents ⁺ 0.56 ring quadrivalents ⁺ 0.65 pentavalents in the aneupolyhaploid (2n = 36) best fit the 221 model. However, the frequent multivalents (up to five trivalents, or three quadrivalents, or four pentavalents in a cell) indicated that decaploid T. ponticum has five sets of closely related genomes representable by the genome formula J₁ J₁ J₁ J₂ J₂. Colchicine treatment of inflorescence-derived H. violaceum x H. bogdanii regenerants greatly enhanced the rate of chromosome doubling, and completely doubled regenerants could be isolated. The H. violaceum x H. bogdanii amphidiploid had a mean pairing pattern of 12.53 univalents ⁺ 5.57 rod bivalents ⁺ 1.97 ring bivalents ⁺ 0.07 trivalents ⁺ 0.03 hexavalents, indicating the presence of desynaptic gene(s) in the original diploiid hybrid. Therefore, the pairing frequency in that diploid hybrid was an under-estimate of chromosome homology between the parental genomes, and additional diploid hybrids are needed to assess the genome homology between H. violaceum and H. bogdanii. These two contrasting experiments demonstrated that tissue culture techniques are useful in altering the ploidy level to produce plant materials suitable for genome analysis and phylogenetic studies.Cooperative investigation of the USDA-ARS, Forage and Range Research Laboratory, Logan, UT 84322-6300, and the Utah Agricultural Experiment Station, Utah State University, Logan, UT 84322-4810. Approved as journal paper No. 3991     

Cytogenetics of a Hordeum vulgare x Elymus patagonicus hybrid (n=4x=28)

Summary Hordeum vulgare L. (2n=2x=14) was hybridized with Elymus patagonicus Speg. (2n=6x=42). The hybrid had 28 chromosomes, genomically represented as HSH₁H₂, and was perennial with a codominant phenotype. The chromosomes were meiotically associated as 19.6 univalents + 0.004 ring bivalents + 2.6 rod bivalents + 0.8 trivalents + 0.14 quadrivalents in 1,129 meiocytes, with a chiasma frequency of 4.77 per cell. The bivalent pairing presumably is an autosyndetic but modified expression of the H₁H₂ genomes of E. patagonicus, since ring bivalents were rare. This does not preclude the association of the H. vulgare H genome chromosomes with either H₁ and/or H₂ genomes of E. patagonicus to form bivalent or multivalent associations. A further evaluation of the genome homologies of H. vulgare, H. bogdanii, E. canadensis and E. patagonicus is proposed.     

The influence of rye cytoplasm on meiotic stability of tetraploid Secalotriticum

Chromosome pairing in tetraploid Secalotriticum was analysed. In the studied plants wheat chromosomes in PMCs during metaphase I showed a higher degree of pairing, in comparison to the rye genome. This is reflected in a very low frequency of univalents and a higher frequency of ring bivalents. The occurrence of wheat univalents was dependent on wheat mixogenome. In plants with an unstabilized fourth homoeologous group, a heteromorphic bivalent 4A-4B was observed in 39.9% of PMCs, whereas in plants with an unstabilized seventh homoeologous group, chromosome 7A-7B pairing was found in all analysed cells. Rye univalents were present in all plants studied. The highest mean frequency of univalents and rod bivalents, both in wheat and in rye genomes, were recorded in plants whose first homoeologous group contained chromosome 1A. The mean number of terminal chiasmata per chromosome amounted to 1.78 in the wheat genome and 1.36 in the rye genome. It may be concluded that the plasmagenes in Secalotriticum did not increase the meiotic stability of the rye genome and also did not stabilize plant fertility.     

Studies on male and female meiosis in Indian Allium

Male meiosis in autotetraploid Allium tuberosum (4×=32) is fairly regular, keeping in view its cytological status, with 81 percent of the chromosomes associated in quadrivalents and trivalents. About 5% of the cells have 32 univalents. Anaphase segregation is slightly irregular. While 48% of the pollen mitoses show 16 chromosomes, 87% of the mature pollen is viable as indicated by carmine or iodine staining. — Megaspore mother cells have 64 chromosomes associated in 32 bivalents at metaphase I. Anaphase segregation is normal. In three out of 56 cells studied multivalents, bivalents and univalents are observed as in male meiosis. — It is concluded that the species reproduces by pseudogamous parthenogenesis made possible by meiotic modification. This modification is almost perfect and almost completely specific for female meiosis. Slight effects are observed in male meiosis.     

Genomic constitution and variation in five partial amphiploids of wheat–<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis> as revealed by GISH,multicolor GISH and seed storage protein analysis

Genomic in situ hybridization (GISH) and multicolor GISH (mcGISH) methodology were used to establish the cytogenetic constitution of five partial amphiploid lines obtained from wheat × Thinopyrum intermedium hybridizations. Line Zhong 1, 2n=52, contained 14 chromosomes from each of the wheat genomes plus ten Th. intermedium chromosomes, with one pair of A-genome chromosomes having a Th. intermedium chromosomal segment translocated to the short arm. Line Zhong 2, 2n=54, had intact ABD wheat genome chromosomes plus 12 Th. intermedium chromosomes. The multicolor GISH results, using different fluorochrome labeled Th. intermedium and the various diploid wheat genomic DNAs as probes, indicated that both Zhong 1 and Zhong 2 contained one pair of Th. intermedium chromosomes with a significant homology to the wheat D genome. High-molecular-weight (HMW) glutenin and gliadin analysis revealed that Zhong 1 and Zhong 2 had identical banding patterns that contained all of the wheat bands and a specific HMW band from Th. intermedium. Zhong 1 and Zhong 2 had good HMW subunits for wheat breeding. Zhong 3 and Zhong 5, both 2n=56, possessed no gross chromosomal aberrations or translocations that were detectable at the GISH level. Zhong 4 also had a chromosome number of 2n=56 and contained the complete wheat ABD-genome chromosomes plus 14 Th. intermedium chromosomes, with one pair of Th. intermedium chromosomes being markedly smaller. Multicolor GISH results indicated that Zhong 4 also contained two pairs of reciprocally translocated chromosomes involving the A and D genomes. Zhong 3, Zhong 4 and Zhong 5 contained a specific gliadin band from Th. intermedium. Based on the above data, it was concluded that inter-genomic transfer of chromosomal segments and/or sequence introgression had occurred in these newly synthesized partial amphiploids despite their diploid-like meiotic behavior and disomic inheritance.     

Characterization of sexual progenies of male-sterile somatic cybrids between Brassica napus and Brassica tournefortii

Cytogenetic studies were performed on four male-sterile progenies derived from four different cybrids produced between Brassica napus and B. tournefortii using the donor-recipient protoplast fusion method. The objective of these studies was to characterize the nuclear constitution of the plants. Mitotic investigation revealed that three of the four male-sterile lines had 38 chromosomes, which is equal to that of B. napus. The fourth line, C6, had variable chromosome numbers, ranging from 39 to 42 in different plants. The meiotic behavior in each progeny varied distinctly. Of the plants having 38 chromosomes, fairly high chromosome pairing, on average 18.08 bivalents per cell, was detected at metaphase-I. However, univalents with an average of 1.39 per cell, and very low frequencies of trivalents and/or tetravalents, were also observed in the lines. These results revealed that male-sterile cybrid lines were obtained with 38 chromosomes and a relatively high level of chromosome-pairing ability, indicating their potential for establishing a stable male-sterile rapeseed line. Received:15 December 1998 / Accepted:30 January 1999     

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.     

The genus Argemone

Summary Crosses between three diploid (A. mexicana; A. subfusiformis; A. albiflora) and one tetraploid (A. ochroleuca) Argemone species were made. The F₁'s were cytogenetically analysed. All the triploid hybrids were sterile and did not set any seed. In the species there was predominantly bivalent pairing (14II; 28II) and high pollen and seed fertility. The F₁'s displayed different configurations, e.g. I, II and III, and pollen fertility was low; the capsules were shrunken and did not contain any seed.In the two combinations mexicana X ochroleuca and subfusiformis X ochroleuca, pairing was identical and both auto- and allosyndesis were observed. The number of univalents, bivalents and trivalents varied in the three combinations but the number of associations did not differ significantly. In the albiflora X ochroleuca combination as many as 13 trivalents were observed.In general a negative correlation was observed between univalents and chiasmata per cell. However, chiasma frequency and paired associations displayed a positive correlation.It is deduced that sufficient similarities existed between one of the ochroleuca and the three diploid species genomes; the remainder of the ochroleuca genome had homologous chromosomes. Apparently A. ochroleuca carried enough cryptic intergenomal homologies which ordinarily remained unexposed. In the hemizygous state however, as in the F₁'s, there was intergenomal pairing. In an attempt to resolve the conflict between homology and bivalent pairing in the species, a diploidizing genetic mechanism is envisaged. Alternatively an acute propensity to preferential pairing caused bivalent formation. Such a system or systems caused meiotic isolation of various genomes and instituted normal fertility. Furthermore, the segmental allotetraploid nature of A. ochroleuca is concluded. The cytogenetic relationship between mexicana and ochroleuca is appraised.     

Research on meiotic chromosome pairing in <Emphasis Type="Italic">Roegneria sinica</Emphasis> var. <Emphasis Type="Italic">media</Emphasis> evaluated using genomic in situ hybridization

The analysis of chromosome pairing during meiosis is important for understanding the relationships between different genomes. To evaluate the diversity of chromosome pairing behavior in the wild species of Roegneria sinica var. media Keng with St and H genomes in Triticeae (Poaceae), differences and similarities in the meiotic chromosome pairing behaviors of the two genomes in two populations of R. sinica var. media, were analyzed using genomic in situ hybridization. Chromosome pairing at meiotic metaphase I in the two populations of R. sinica var. media mainly formed bivalents, although several univalents, trivalents and quadrivalents also occurred. Chromosome pairings occurred mainly between homologous chromosomes. However, some non-homologous pairings were observed under natural conditions. No significant differences in karyotype were found between the St and H genomes. Chromosome pairing behaviors differed between and within the two populations. Genetic variation occurred mainly within populations (94.04 %), and variation was more abundant in one population than the other. The genomes St and H differed, but there was some relationship between the two genomes. These findings suggest that homoeologous pairing of chromosomes or exchanges occurred between different genomes of the wild species in Triticeae during evolution. The findings also provide conclusive cytological evidence for genetic variation within the wild species, which forms the basis of their genetic diversity.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.