CYTOLOGY OF MAIZE-TRIPSACUM INTROGRESSION

The American Maydinae genera Zea and Tripsacum cross readily when not isolated from each other by gametophytic barriers, and it has been suggested that intergeneric introgression played a role in the evolution of maize. Four Zea chromosomes pair with members of at least one basic genome of tetraploid Tripsacum, and in hybrids involving octaploid Tripsacum all 10 chromosomes of the basic maize genome frequently compete successfully in synapsis with Tripsacum chromosomes. Hybrids that combine 36 Tripsacum and 10 maize chromosomes are female fertile. When they are pollinated by maize their offspring have 36 Tripsacum and 20 maize chromosomes, or again have 36 Tripsacum and 10 maize chromosomes, but the 10 Zea chromosomes are contributed by the new pollen parent. Later backcross generations also include plants with 36 Tripsacum and 12, 14, 16, or 18 maize chromosomes. Individuals with 2n = 56 produce an abundance of offspring with 18 Tripsacum and 20 maize chromosomes when backcrossed with maize. Further backcrossing results in elimination of Tripsacum chromosomes, and eventually plants with 2n = 20 Tripsacum-contaminated maize chromosomes are obtained. Two generations of selfing restore full fertility to these 2n = 20 plants and eliminate all obvious traces of Tripsacum morphology.     

COUNTERFEIT HYBRIDS BETWEEN TRIPSACUM AND ZEA (GRAMINEAE)

Diploid (2n = 36) Tripsacum australe Cutler and Anderson var. hirsutum de Wet and Timothy, T. cundinamarce de Wet and Timothy, T. dactyloides (L.) L. var. dactyloides and var. meridonale de Wet and Timothy, and T. laxum Nash were crossed with Zea mays L. (2n = 20) as the pollen parent. True hybrids combine the cytologically nonreduced genome of Tripsacum (36 chromosomes) with the haploid (10 chromosomes) or more rarely diploid (20 chromosome) genome of Zea. Maternal offspring with 2n = 36 Tripsacum chromosomes commonly result from parthenogenetic development of cytologically nonreduced eggs. Some individuals with 2n = 36 Tripsacum chromosomes, however, resemble true hybrids in phenotype. These counterfeit hybrids incorporated Zea genetic material into their Tripsacum genomes without true fertilization having taken place. Offspring of counterfeit hybrids that were grown to maturity resembled their mothers in phenotype, and must have originated parthenogenetically. It is proposed that counterfeit hybrids are also produced in nature, and that this process contributes to origins of variation in gametophytic apomicts, and perhaps also in sexually reproducing species.     

Retroelement genome painting: cytological visualization of retroelement expansions in the genera Zea and Tripsacum

Divergence of abundant genomic elements among the Zea and Tripsacum genera was examined cytologically and a tool kit established for subsequent studies. The LTR regions from the CRM, Huck, Grande, Prem1, Prem2/Ji, Opie, Cinful-1, and Tekay retroelement families were used as FISH probes on mitotic chromosome spreads from a "trispecies" hybrid containing chromosomes from each of three species: Zea mays (2n = 20), Z. diploperennis (2n = 20), and Tripsacum dactyloides (2n = 36). Except for Tekay, which painted both Zea and Tripsacum chromosomes with nearly equal intensity, the retroelement probes hybridized strongly to the Zea chromosomes, allowing them to be distinguished from those of Tripsacum. Huck and Grande hybridized more intensely to maize than to Z. diploperennis chromosomes. Tripsacum genomic clones containing retroelement sequences were isolated that specifically paint Tripsacum chromosomes. The retroelement paints proved effective for distinguishing different genomes in interspecific hybrids and visualizing alien chromatin from T. dactyloides introgressed into maize lines. Other FISH probes (180-bp knob, TR-1, 5S, NOR, Cent4, CentC, rp1, rp3, and alpha-ZeinA) could be simultaneously visualized with the retroelement probes, emphasizing the value of the retroelement probes for cytogenetic studies of Zea and Tripsacum.     

The genome organization and diversification of maize and its allied species revisited: evidences from classical and FISH-GISH cytogenetic analysis

The present review summarizes our classical and molecular cytogenetic investigations in the genus Zea. The results obtained from the meiotic behavior analysis of Zea species and hybrids, confirm the amphiploid nature of all species in the genus, with a basic number of x = 5 chromosomes. All species with 2n = 20 are diploidized allotetraploids, whereas Z. perennis (2n = 40) is an allooctoploid with four genomes somewhat divergent from one another. These analyses also revealed the existence of postzygotic reproductive isolation among Zea species. Our studies using genomic in situ hybridization (GISH) provide evidence about the evolutionary relationships among maize and its allied species, and reveal remarkable genomic divergences. Particularly, knob sequences were not completely shared between taxa previously considered to be closely related. Our data strongly suggest that the teosinte Z. mays parviglumis is not the only progenitor of cultivated maize. Introgression of Tripsacum into cultivated maize cannot be discarded.     

ORIGIN OF TRIPSACUM ANDERSONII (GRAMINEAE)

Tripsacum andersonii Gray (Gramineae) is a species with 2n = 64 chromosomes. Chromosome behaviour during meiosis of microsporogenesis suggests that the species combines three homologous haploid Tripsacum genomes of x = 18 (54 chromosomes), and an alien haploid genome of x = 10 chromosomes. Cytogenetic studies indicate that T. andersonii originated as a hybrid between a species of Tripsacum (2n = 36) and a species of Zea (2n = 20). Comparative morphology and flavonoid chemistry fail to identify the Zea species involved in this intergeneric hybrid. Chromosome morphology suggests that it was either Z. mays L. subsp. mays (domesticated maize) or subspecies mexicana (Schrad.) Iltis (annual teosinte). The Tripsacum parent probably was T. latifolium Hitchc. of Central America. It resembles T. andersonii in vegetative morphology. Tripsacum maizar Hernandez et Randolph and T. laxum Nash, which resemble T. andersonii in flavonoid chemistry, are eliminated as possible parents on the basis of growth habit and the morphology of their hybrids with maize.     

A complete set of maize individual chromosome additions to the oat genome

All 10 chromosomes of maize (Zea mays, 2n = 2x = 20) were recovered as single additions to the haploid complement of oat (Avena sativa, 2n = 6x = 42) among F(1) plants generated from crosses involving three different lines of maize to eight different lines of oat. In vitro rescue culture of more than 4,300 immature F(1) embryos resulted in a germination frequency of 11% with recovery of 379 F(1) plantlets (8.7%) of moderately vigorous growth. Some F(1) plants were sectored with distinct chromosome constitutions among tillers of the same plant and also between root and shoot cells. Meiotic restitution facilitated development of un-reduced gametes in the F(1). Self-pollination of these partially fertile F(1) plants resulted in disomic additions (2n = 6x + 2 = 44) for maize chromosomes 1, 2, 3, 4, 6, 7, and 9. Maize chromosome 8 was recovered as a monosomic addition (2n = 6x + 1 = 43). Monosomic additions for maize chromosomes 5 and 10 to a haploid complement of oat (n = 3x + 1 = 22) were recovered several times among the F(1) plants. Although partially fertile, these chromosome 5 and 10 addition plants have not yet transmitted the added maize chromosome to F(2) offspring. We discuss the development and general utility of this set of oat-maize addition lines as a novel tool for maize genomics and genetics.     

Biochemical systematics and evolution ofzea,tripsacum and related genera

Antibody systems were produced in rabbits by immunization with antigen systems from seed ofZea mays, Z. mexicana andTripsacum dactyloides. Antigen systems were generally ranked in the following order using Zeaantibody systems: Zea > Tripsacum > Elyonurus ≈ Bothriochloa > Coix ≈ Manisuris > Andro-pogon ? Triticum. Tripsacum antibody systems also ranked these antigen systems in a similar order except that Tripsacum > Zea, and Manisuris ≈ Bothriochloa ≈ Elyonurus. Some Tripsacum species produced anomalous results. Serology suggests that Zea and Tripsacum should be placed together in the subtribe Tripsacinae of the tribe Andropogoneae: the tribe Maydeae is probably an unnatural assemblage. Tripsacum and Zea have probably evolved from ancestors with affinities to the subtribes Rottboellinae and Bothriochloeae of the tribe Andropogoneae. The high degree of serological correspondence shown by Elyonurus to Zea suggests a close common ancestry, but Manisuris appears no more similar to Tripsacum than do other genera of the Rottboellinae and Bothriochloeae. By polyacrylamide gel electrophoresis, no differences were found between maize and teosinte from Mexico and north Guatemala. Teosinte from south Guatemala consistently lacked bands present in both maize and Mexican teosinte but shared no greater similarity to Tripsacum and cannot therefore be considered as tripsacoid. The high degree of band homology between maize and Mexican teosinte supports a parental relationship and it is suggested that Mexican teosinte represents the germ plasm from which maize was domesticated. Neither electro-phoretic nor serological results supported the hypothesized hybrid (viz. Zea x Manisuris) origin of Tripsacum.     

Production and characterization of maize chromosome 9 radiation hybrids derived from an oat-maize addition line

In maize (Zea mays L., 2n = 2x = 20), map-based cloning and genome organization studies are often complicated because of the complexity of the genome. Maize chromosome addition lines of hexaploid cultivated oat (Avena sativa L., 2n = 6x = 42), where maize chromosomes can be individually manipulated, represent unique materials for maize genome analysis. Maize chromosome addition lines are particularly suitable for the dissection of a single maize chromosome using radiation because cultivated oat is an allohexaploid in which multiple copies of the oat basic genome provide buffering to chromosomal aberrations and other mutations. Irradiation (gamma rays at 30, 40, and 50 krad) of a monosomic maize chromosome 9 addition line produced maize chromosome 9 radiation hybrids (M9RHs)-oat lines possessing different fragments of maize chromosome 9 including intergenomic translocations and modified maize addition chromosomes with internal and terminal deletions. M9RHs with 1 to 10 radiation-induced breaks per chromosome were identified. We estimated that a panel of 100 informative M9RHs (with an average of 3 breaks per chromosome) would allow mapping at the 0. 5- to 1.0-Mb level of resolution. Because mapping with maize chromosome addition lines and radiation hybrid derivatives involves assays for the presence or absence of a given marker, monomorphic markers can be quickly and efficiently mapped to a chromosome region. Radiation hybrid derivatives also represent sources of region-specific DNA for cloning of genes or DNA markers.     

萝卜与甘蓝属间杂种基因组原位杂交分析

用基因组原位杂交方法（Genomic in situ hybridization, 简称GISH）研究了萝卜( Raphanus sativus,2n=18,RR)和甘蓝（Brassica oleracea , 2n=18, CC）属间杂种F1减数分裂过程。结果表明杂种体细胞染色体组成为RC,2n=18,但花粉母细胞有三种不同类型：1. RC,2n=18, 终变期染色体平均配对构型为14.87Ⅰ+1.20Ⅱ+0.04Ⅲ+0.06Ⅳ, 染色体配对主要发生在萝卜和甘蓝染色体之间, 后期Ⅰ9条萝卜染色体主要以5/4和6/3的分离比移向两极, 所形成配子的染色体数目和组成均不平衡,配子败育; 2. RRCC,4n=36, 终变期染色体形成18个二价体,后期Ⅰ染色体均衡分离,形成RC不减数配子;3. RRCC缺体,4n=30－34, 少数萝卜染色体丢失,形成的配子具有全套的甘蓝染色体和部分萝卜染色体。     

Cytological and molecular characterization of oat x maize partial hybrids

In cereals, interspecific and intergeneric hybridizations (wide crosses) which yield karyotypically stable hybrid plants have been used as starting points to widen the genetic base of a crop and to construct stocks for genetic analysis. Also, uniparental genome elimination in karyotypically unstable hybrids has been utilized for cereal haploid production. We have crossed hexaploid oat (2n=6x=42, Avena sativa L.) and maize (2n=2x=20, Zea mays L.) and recovered 90 progenies through embryo rescue. Fifty-two plants (58%) produced from oatxmaize hybridization were oat haploids (2n=3x=21) following maize chromosome elimination. Twenty-eight plants (31%) were found to be stable partial hybrids with 1–4 maize chromosomes in addition to a haploid set of 21 oat chromosomes (2n=21+1 to 2n=21+4). Ten of the ninety plants produced were found to be apparent chromosomal chimeras, where some tissues in a given plant contained maize chromosomes while other tissues did not, or else different tissues contained a different number of maize chromosomes. DNA restriction fragment length polymorphisms (RFLPs) were used to identify the maize chromosome(s) present in the various oat-maize progenies. Maize chromosomes 2, 3, 4, 5, 6, 7, 8, and 9 were detected in partial hybrids and chromosomal chimeras. Maize chromosomes 1 and 10 were not detected in the plants analyzed to-date. Furthermore, partial self-fertility, which is common in oat haploids, was also observed in some oat-maize hybrids. Upon selfing, partial hybrids with one or two maize chromosomes showed nearly complete transmission of the maize chromosome to give self-fertile maize-chromosome-addition oat plants. Fertile lines were recovered that contained an added maize chromosome or chromosome pair representing six of the ten maize chromosomes. Four independently derived disomic maize chromosome addition lines contained chromosome 4, one line carried chromosome 7, two lines had chromosome 9, one had chromosome 2, and one had chromosome 3. One maize chromosome-8 monosomic addition line was also identified. We also identified a double disomic addition line containing both maize chromosomes 4 and 7. This constitutes the first report of the production of karyotypically stable partial hybrids involving highly unrelated species from two subfamilies of the Gramineae (Pooideae — oat, and Panicoideae — maize) and the subsequent recovery of fertile oat-maize chromosome addition lines. These represent novel material for gene/ marker mapping, maize chromosome manipulation, the study of maize gene expression in oat, and the transfer of maize DNA, genes, or active transposons to oat.Joint contribution of the Minnesota Agricultural Experiment Station and USDA-ARS. Scientific journal series paper No. 21 859 of the Minnesota Agricultural Experiment Station. Mention of a trademark or proprietary product does not constitute a guarantee or warranty by the USDA-ARS or the University of Minnesota and does not imply approval over other products that also may be suitable     

Ribosomal Gene Structure, Variation and Inheritance in Maize and Its Ancestors

We have examined the structure of nuclear genes coding for ribosomal RNAs in maize and its wild relatives, the teosintes and Tripsacum. Digestion of the rDNA (genes coding for 18S, 5.8S and 26S RNAs) with 15 restriction endonucleases (with six base pair recognition sites) yields essentially a single map for the approximately 10,000 repeat units within an individual plant or species. Both length and site variation were detected among species and were concentrated in the intergenic spacer region of the rDNA repeat unit. This result is in agreement with patterns of rDNA change observed among wheat and its relatives (Triticeae), and among vertebrate species. Digestion of these nuclear DNAs with BamHI and subsequent hybridization with a 5S RNA gene-specific probe allowed determination of the size of the 5S gene repeat unit in maize, teosintes, and Tripsacum. Groupings in the genus Zea were characterized by distinct repeat unit types five Tripsacum species examined shared a 260 base pair major repeat unit type. Additionally, several other restriction endonuclease cleavage patterns differentiated among the 5S DNAs within the genus Zea. The rDNA and 5S DNA restriction site variation among the species can be interpreted phylogenetically and agrees with biochemical, karyotypic, and morphological evidence that places maize closest to the Mexican teosintes. For both gene arrays, contributions from each parental genome can be detected by restriction enzyme analysis of progeny from crosses between maize and two distantly related teosintes, Zea luxurians or Zea diploperennis, but certain teosinte arrays were underrepresented in some of the hybrids.     

MORPHOLOGY OF SOME MAIZE-TRIPSACUM HYBRIDS

Diploid (2n = 20) and tetraploid (2n = 40) Zea mays L. were crossed with diploid (2n = 36) and tetraploid (2n = 72) Tripsacum dactyloides (L.) L. to produce a series of hybrids combining different numbers of haploid genomes from each parent. Eight hybrid groups and three parental groups were studied morphologically. Twenty-nine quantitative characters were recorded for each sample. Data were analyzed by univariate analysis of variance, multivariate analysis of variance, and discriminant function analysis, in an attempt to evaluate hybrid differences objectively and determine which morphological characters contribute statistically to group separation. The overall MANOVA F test was significant, establishing the presence of real differences between the hybrids; discriminant function analysis indicated that the percent of paired pistillate spikelets/cupule in the lateral inflorescence was the main variable which differentiated hybrids. Duncan's Multiple Range Tests for significant differences between means were applied to five variables contributing maximally to group discrimination, using the appropriate univariate ANOVAs. Pronounced maize-like attributes of backcross hybrids, as compared with corresponding F₁'s possessing similar genome constitutions, gave possible evidence of gene transfer between Zea mays and Tripsacum during backcrossing to maize.     

CYTOGENETIC STUDIES OF ALLOTETRAPLOID HYBRIDS OF MAIZE AND PERENNIAL TEOSINTE

Shaver , Donald L. (Brookhaven Natl. Lab., Upton, New York.) Cytogenetic studies of allotetraploid hybrids of maize and perennial teosinte. Amer. Jour. Bot. 49(4): 348–354. Illus. 1962.—Euchlaena perennis (4n), “perennial teosinte,” was less fertile when pollinated with 4n Zea mays than when selfed. Cross fertility between the 2 genera was influenced by the particular maize stock involved. Chromosome numbers varied from 36 to 43 in a population of 4n maize maintained by interpollination without regard to chromosome number. In the 4n intergeneric hybrid, nearly every chromosome number from 29 to 44 was found. The expression of the perennial growth habit varied with the proportion of perennial teosinte germ plasm present. Triploid hybrids with 2 perennial teosinte genomes and 1 maize genome were usually perennial. Tetraploid hybrids having 2 genomes of each parent were usually not fully perennial. Tetraploid hybrids with only 1 perennial teosinte genome had no perennial tendency but had a strong tendency to tiller. As compared with autotetraploids of maize having the same genetic markers, intergeneric hybrids showed a highly significant degree of preferential segregation for each of the 12 marker genes studied. In the opinion of the author, these data may represent the best available measure of the relationship of maize to teosinte, and are considered to support the proposal of Reeves and Mangelsdorf that maize and teosinte are congeneric.     

Glutamate Oxaloacetic Transaminase and Malate Dehydrogenase Isozymes of Zea mays L. × Tripsacum dactyloides L. Hybrids and Parents

Electrophoretic patterns of glutamate oxaloacetic transaminase (Got) and malate dehydrogenase (Mdh) of Zea mays L. × Tripsacum dactyloides L. hybrids and their parents have been compared. The results suggested that Got and Mdh isozymes may be used as markers for genic regions on 5 S and 6 L maize chromosomes and for linkage groups D and L on T. dactyloides chromosomes, syntenic to genic regions on 5 S and 6 L maize chromosomes. The latter have a regulatory effect on fertility and on the apomictic mode of reproduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rapid amplification and fixation of new restriction sites in the ribosomal dna repeats in the derivatives of a cross between maize and Tripsacum dactyloides

Some of the derivatives of a cross of maize (Zea mays L.) × Tripsacum dactyloides (L) L (2n = 72) have abnormal development leading to strange and striking morphologies. The Tripsacum chromosomes in these “tripsacoid” maize plants (with Tripsacum-like characteristics) were eliminated and the maize chromosomes were recovered through repeated backcrossing to maize. As an initial attempt to analyze the DNA alterations in tripsacoid maize, we have detected a few restriction site changes in the ribosomal DNA repeat of these plants (Hpa II, Bal I, Sst I, Mbo II, and Sph I) and a new Sph I site was mapped to the spacer region between the 26S and 17S genes. Several possible mechanisms for the generation of a new restriction site are discussed, and we propose that the transient presence of Tripsacum genome during the backcrossing in some way induced a rapid amplification and fixation of new restriction sites in a relatively short period of time.     

Cytological and molecular evaluation of the reproductive behavior of Tripsacum andersonii and a female fertile derivative (Poaceae)

Research was conducted to characterize the reproductive behavior of the highly sterile Tripsacum andersonii Gray and its viable progeny through breeding, cytological, and molecular studies. Four progeny were obtained from open-pollinated seeds of clones (M-34445, M-34450 and M-34455) of T. andersonii maintained at the USDA-ARS National Germplasm Repository, Miami, Florida. One of the progeny had 64 chromosomes, which is typical of T. andersonii, and probably resulted from apomictic reproduction. Karyotypes of the other three progeny indicated a tetraploid Tripsacum genomic constitution (2n = 4x = 72) plus a haploid set of Zea (1n = 1x = 10) chromosomes. Two of these progeny were completely sterile, whereas one (95-51) produced ～5% seed set when crossed with diploid (2n = 36) T. dactyloides (L.)L. The partially fertile 95-51 produced four progeny, one with 2n = 72 (elimination of 10 Zea chromosomes), two with 2n = 82 (apomictic reproduction) and one with 2n = 100 (sexual polyploidization). Polymerase Chain Reaction - Random Amplified Polymerase DNA analysis verified that T. andersonii accessions from seven countries were genetically uniform, and that its progeny were derived through apomixis and sexual polyploidization. This analysis also confirmed that chromosome elimination, apomixis, and sexual polyploidization reproductive behaviors occur in the T. andersonii derivative 95-51.     

Aberrant microspore development in hybrids of maize x Tripsacum dactyloides.

Cytogenetic investigations of meiosis in hybrids between maize and Tripsacum have been well documented; however, the inherent problem of male and female sterility has not been addressed either on a genetic or cytogenetic level. The purpose of this cytological study was to identify some of the probable causes of male sterility in maize x Tripsacum dactyloides hybrids. Disturbances in pollen development of maize x T. dactyloides hybrids, derived from both diploid (2n) and tetraploid (4n) Tripsacum sources, were commonly observed. Anomalies in the development of the microspore apparently occurred because of a failure of the chromosomes to congregate at the metaphase plate, development of a tripolar spindle, and failure of cytokinesis at the first and second meiotic divisions. Phenotypic features of abnormal microspore development were the maturation of large pollen grains, "Siamese" pollen grains, the occurrence of variable invaginations, and a nuclear budding-type behavior. These abnormalities were not observed in the 56-chromosome amphidiploid or the 38-chromosome backcross generations.     

Chromosome control of apomixis in maize-gamagrass hybrids

The results of long-term studies on the transmission of the mode of asexual reproduction through seeds to maize from gamagrass, a closely related wild plant, performed in the Laboratory of Plant Cytology and Apomixis are summarized. The first apomictic hybrids between Zea mays and Tripsacum dactyloides were obtained in this laboratory more than 40 years ago and have been maintained until the present time. Cytogenetic studies on the hybrids have shown that at least nine chromosomes of the wild parent are necessary for the expression of asexual reproduction through seeds. In addition, the genes controlling two elements of apomixis (apomeiosis and parthenogenesis) have been found to be inherited independently from each other.     

Malate Dehydrogenase, Alcohol Dehydrogenase, and 6-Phosphogluconate Dehydrogenase Isozymes of Zea mays L. × Tripsacum dactyloides L. Hybrids and Parents

Electrophoretic patterns of malate dehydrogenase (Mdh), alcohol dehydrogenase (Adh), and 6-phosphogluconate dehydrogenase (Pgd) of Zea mays L. × Tripsacum dactyloides L. hybrids and their parents were compared. The components of enzymes specific to T. dactyloides may be used as markers to identify the following T. dactyloides chromosomes in the hybrids: Tr 16 (Mdh 2 and Pdg 1), Tr 7, and/or Tr 13 (Adh 2). The isozymes of Mdh 2 are supposed as a possible biochemical marker to evaluate the introgression of genes, determining an apomictic mode of reproduction from T. dactyloides (localized on Tripsacum 16 chromosome) into Z. mays. The isozymes may be used as markers for the identification of maize chromosomes 1 and 6 in the hybrids as well. Chromosome count taken on the examined hybrids showed the addition of 9 to 13 chromosomes of T. dactyloides to maize chromosome complement.     

Meiotic restitution in wheat polyhaploids (amphihaploids): a potent evolutionary force

Polyploidy is well recognized as a major force in plant speciation. Among the polyploids in nature, allopolyploids are preponderant and include important crop plants like bread wheat, Triticum aestivum L. (2n = 6x = 42; AABBDD genomes). Allopolyploidy must result through concomitant or sequential events that entail interspecific or intergeneric hybridization and chromosome doubling in the resultant hybrids. To gain insight into the mechanism of evolution of wheat, we extracted polyhaploids of 2 cultivars, Chinese Spring (CS) and Fukuhokomugi (Fuko), of bread wheat by crossing them with maize, Zea mays L. ssp. mays. The derived Ph1-polyhaploids (2n = 3x = 21; ABD) showed during meiosis mostly univalents, which produced first-division restitution (FDR) nuclei that in turn gave rise to unreduced (2n) male gametes with 21 chromosomes. The haploids on maturity set some viable seed. The mean number of seeds per spike was 1.45 +/- 0.161 in CS and 2.3 +/- 0.170 in Fuko. Mitotic chromosome preparations from root tips of the derived plantlets revealed 2n = 42 chromosomes, that is, twice that of the parental polyhaploid, which indicated that they arose by fusion of unreduced male and female gametes formed by the polyhaploid. The Ph1-induced univalency must have produced 2n gametes and hence bilateral sexual polyploidization and reconstitution of disomic bread wheat. These findings highlight the quantum jump by which bread wheat evolved from durum wheat in nature. Thus, bread wheat offers an excellent example of rapid evolution by allopolyploidy. In the induced polyhaploids (ABD) that are equivalent of amphihaploids, meiotic phenomena such as FDR led to regeneration of parental bread wheat, perhaps a simulation of the evolutionary steps that occurred in nature at the time of the origin of hexaploid wheat.