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.     

SOMATIC EMBRYOGENESIS IN LONG-TERM CALLUS CULTURES OF ZEA MAYS L. (GRAMINEAE)

Long-term (1 yr), soft, embryogenic callus tissue cultures were established from excised immature embryos of a commercial cultivar of hybrid maize (Zea mays L.). Plant regeneration occurred by the formation of somatic embryos, and the regenerated plants were morphologically normal with 2n = 20 chromosomes. Such cultures may be useful for the isolation of mutants and the establishment of embryogenic cell suspension cultures.     

Metabolic robustness in young roots underpins a predictive model of maize hybrid performance in the field

Heterosis has been extensively exploited for yield gain in maize (Zea mays L.). Here we conducted a comparative metabolomics‐based analysis of young roots from in vitro germinating seedlings and from leaves of field‐grown plants in a panel of inbred lines from the Dent and Flint heterotic patterns as well as selected F₁ hybrids. We found that metabolite levels in hybrids were more robust than in inbred lines. Using state‐of‐the‐art modeling techniques, the most robust metabolites from roots and leaves explained up to 37 and 44% of the variance in the biomass from plants grown in two distinct field trials. In addition, a correlation‐based analysis highlighted the trade‐off between defense‐related metabolites and hybrid performance. Therefore, our findings demonstrated the potential of metabolic profiles from young maize roots grown under tightly controlled conditions to predict hybrid performance in multiple field trials, thus bridging the greenhouse–field gap.     

Numerical analysis of isozyme variation in Glycine tomentella

Isozyme variation among 114 accessions of the Glycine tomentella Hayata was analysed by single linkage cluster analysis and the unweighted pair group centroid method (UPGMC). The diploid accessions fell into six distinct, well defined groups, which conformed with differences in chromosome number (2n − 38 or 2n − 40) or in geographic origin. The majority of the tetraploid accessions belonged to a large, geographically widespread group, predominantly aneuploid (2n − 78) group. The remaining four tetraploid groups were distinct on the basis of morphology or geographic distribution. The validity of tetraploid isozyme groupings for reflecting subspecific differentiation was supported by the published reports of hybrid fertility. All of the nineteen crosses between isozyme groups have yielded sterile hybrids, whereas five crosses within groups have yielded fertile hybrids. The relationship between diploids and tetraploids was examined either as the similarity between individual accessions, or that between isozyme groups. These analyses indicated that each tetraploid group is closely related to only one or two of the diploid groups or subgroups.     

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.     

Production of somatic hybrids between frost-tolerant Solanum commersonii and S. tuberosum: characterization of hybrid plants

Somatic fusion of mesophyll protoplasts was used to produce hybrids between the frost-tolerant species Solanum commersonii (2n=2x=24) and dihaploid S. tuberosum (2n=2x=24). This is a sexually incompatible combination due to the difference in EBN (Endosperm Balance Number, Johnston et al. 1980). Species with different EBNs as a rule are sexually incompatible. Fifty-seven hybrids were analysed for variation in chromosome number, morphological traits, fertility and frost tolerance. About 70% of the hybrids were tetraploid, and 30% hexaploid. Chloroplast counts in stomatal guard cells revealed a low frequency of cytochimeras. The frequency of aneuploids was relatively higher at the hexaploid level (hypohexaploids) than at the tetraploid level (hypotetraploids). The somatic hybrids were much more vigorous than the parents, and showed an intermediate phenotype for several morphological traits and moderate to profuse flowering. Hexaploid hybrid clones were less vigorous and had a lower degree of flowering than the tetraploid hybrid clones. All of the hybrids were female fertile but male sterile except for one, which was fully fertile and self-compatible. Many seeds were produced on the latter clone by selfing and on the male-sterile clones by crossing. The somatic hybrid plants showed an introgression of genes for frost tolerance and an adaptability to cold from S. commersonii. Therefore, the use of these somatic hybrids in breeding for and in genetic esearch on frost tolerance and cold-hardening is suggested.     

OBSERVATIONS ON INTROGRESSION OF TRIPSACUM INTO MAIZE

Derivatives of a cross between diploid Zea mays L. and Tripsacum dactyloides (L.) L. (2n = 72) were compared cytologically and morphologically. The objective of this study was to detect introgression from Tripsacum to maize that might have occurred during seven backcross generations with maize. Thirty-three morphological characters were used to analyze variation among aneuploid (20Zm + 2Td), 20-chromosome recovered maize, and the recurrent maize parent plants. Aneuploid and maize checks were extreme types, with 20-chromosome hybrid derivatives being morphologically intermediate. Several recovered maizes clustered with aneuploid plants and these hybrid derivatives have the greatest chance of Tripsacum introgression. Many traits such as endosperm abnormalities, tassel seed, albinos, tunicate glumes, tassel-tipped ears, fasciated and branched ear, and male spikelets between rows of kernels were observed. Although the genetic basis of many traits is unknown, mutations, epistatic effects or expression of Tripsacum chromatin are possible causes. The number of abnormal and tripsacoid traits observed in 20-chromosome recovered maizes indicates genetic transfer from Tripsacum to the maize genome.     

Composition of Esterase and Peroxidase Isoenzyme Complex, Zein-2 Protein Fraction, and SDS-Protein Complex of Zea Mays L. × Tripsacum Dactyloides L. Hybrids and Parents

The patterns of esterase and peroxidase isoenzymes, subunits of zein-2 fraction and protomers of SDS-protein complex of Zea mays L. × Tripsacum dactyloides L. hybrids and their parents were compared. The study has been made to detect specific to Tripsacum isoesterases and isoperoxidases, zein subunits and SDS-protein protomers which could be used as markers for introgression of gene loci encoding these proteins from Tripsacum into hybrids of Tripsacum with Zea mays. Isoesterases and isoperoxidases as well protomers of SDS-protein complex specific to Tripsacum were detected in all hybrids analyzed. Zein subunits, specific to Tripsacum were detected in some of the analyzed hybrids which i that introgression frequency of the loci encoding proteins studied was different. Chromosome counts taken on the examined hybrids showed the addition of 9 – 13 Tripsacum chromosomes to maize chromosome complement.     

A cytogenetic and phenotypic characterization of somatic hybrid plants obtained after fusion of two different dihaploid clones of potato (Solatium tuberosum L.)

Summary Somatic hybrid plants of various ploidy levels obtained after chemical fusion between two dihaploid clones of potato Solanum tuberosum L. have been analysed by cytological, morphological and molecular methods. The hybrid nature of tetraploid and hexaploid plants and the genome dosage in hexaploid hybrids were confirmed by Giemsa C-banding. Tetraploid and hexaploid hybrids showed numerical as well as structural chromosome mutations. The latter occurred mainly in the nuclear organizing chromosome. The tetraploid hybrids were more vigorous than the dihaploid parents as demonstrated by an increase in height, enlargement of leaves, increase in the number of internodes, restored potential for flowering and increased tuber yield. The grouping of tetraploid somatic hybrids into various classes on the basis of leaf morphology revealed that plants with a full chromosome complement were more uniform than aneuploids. Many hexaploid somatic hybrids were also more vigorous than the dihaploid parents and could be grouped into two different classes on the basis of floral colour and tuber characteristics, the differences being due to their different dosage of parental genomes. Most of the tetraploid somatic hybrids showed pollen development halted at the tetrad stage as one of the parental clones contained a S. Stoloniferum cytoplasm. However, one tetraploid plant produced pollen grains with high viability. The chloroplast genome in the hybrid plants was determined by RFLP analysis. All of the hybrids had a cpDNA pattern identical to one parent, which contained either S. Tuberosum or S. Stoloniferum cpDNA. A slight preference for S. Tuberosum plastids were observed in hybrid plants. No correlation between pollen development and plastid type could be detected.     

Phytohormones in Seedlings of Maize Hybrids Differing in Their Tolerance to High Temperatures

The contents of phytohormones (IAA, ABA, cytokinins, and gibberellin-like compounds) were measured in shoots and roots of eight-day-old seedlings of two maize (Zea mays L.) hybrids differing in their tolerance to elevated temperatures. More tolerant seedlings initially contained more ABA and cytokinins, and the contents of these hormones changed less after a temperature increase than in seedlings of the sensitive hybrid. Hyperthermia induced a destruction of chloroplast lamellar structure in the leaf sheath cells of the sensitive but not of the tolerant hybrid.     

Seedling Growth of Zea mays at 13 {degrees}C: Comparison of a Corn Belt Dent Hybrid and a Hybrid Selected for Rapid Plumule Emergence at Cool Temperatures

When intact seeds of maize (Zea mays L.) were germinated andgrown in the dark at 13 °C, the plumule length at all timeswas significantly greater for a selected cool temperature toleranthybrid than for an elite Corn Belt Dent hybrid. On the otherhand, no significant differences were obtained for radicle growth.Virtually identical results were obtained when the hybrids weregrown as dissected embryos or as dissected embryonic axes onnutrient agar. Similar results were obtained when axial dryweights were measured rather than axial lengths. When dissectedembryonic axes were grown at a range of sucrose concentrations,growth parameters of the tolerant hybrids were always greaterthan that of the Corn Belt Dent. Key words: Zea mays L., Low temperature, Seedling growth     

Cytogenetic studies in the genus Zea

Summary The nuclear DNA amount and the heterochromatin content in species and hybrids of Zea were analyzed in telophase nuclei (2C) of the root apex of germinating seeds. The results revealed significant differences among taxa and also among lines and races of maize. The hybrids between Z. mays ssp. mays x Z. mays ssp. mexicana (2n=20), Z. diploperennis x Z. perennis (2n=30), and Z. diploperennis x Z.perennis (2n=40) showed DNA content intermediate between that of the parents. The number of chromosomal C-bands and the proportion of the genome comprising C-band heterochromatin were positively related to genome size. In the different lines and races of maize studied, there was a positive correlation between genome size and the interval from germination to flowering. Octoploid Z. perennis (2n=40) showed the smallest DNA content per basic genome and the smallest heterochromatic blocks, suggesting that the DNA lost by this species consisted mainly of repetitive sequences. Considering that the extant species of Zea are tetraploid (2n=20) and octoploid (2n=40) and that the ancestral diploids are extinct, any consideration of the direction (increase or decrease) of the DNA change would be entirely speculative. The extant species could be the product of natural and artificial selection acting on different genotypic and nucleotypical constitutions at the diploid and/or tetraploid levels.     

Establishment of somatic hybrid cell lines between Zea mays L. (maize) and Triticum sect,trititrigia MacKey (trititrigia)

Summary Somatic hybrid cell lines were constructed by the fusion of protoplasts isolated from cell suspensions of Zea mays L. (maize, 2n = 20) and Triticum sect, trititrigia MacKey (trititrigia, 2n = 35), a perennial hybrid of T. durum Desf. and Elytrigia intermedium (Host) Nevski. Iodoacetamide-inactivated protoplasts of maize were fused with trititrigia protoplasts, which were sensitive to the PEG/DMSO fusion treatment at high pH and high calcium. Based on physiological complementation, approximately 0.002% of the total protoplasts cultured following fusion treatment developed into cell colonies, and 79 lines of them, almost a half, were singled out and subcultured. Among the subcultured lines three were, in comparison with the parents, identified as somatic hybrids by their coupled XbaI restriction patterns of total DNAs probed with the ribosomal DNA of rice. Southern analysis of the digested total DNAs with a mitochondrial gene, atpA., from pea, or a chloroplast gene, trnK, from rice, revealed that all the hybrids carried only the organellar DNAs of trititrigia, which excluded the possibilities of a chimeric callus or any DNA contamination. Cytogenetically, one hybrid was mixoploid with a 2n of 46–67 in which chromosomal endoreduplication, characterized by the appearance of diplochromosomes, was occasionally observed. Its hybridity was reconfirmed by the fact that it bore the satellite chromosomes of both maize and trititrigia, which were distinguishable from each other by size. In contrast, the other two hybrids were aneuploids. The potential of gene transfer between Zea and Triticum species was thus conclusively established.     

Phenotypic differentiation of peripheral populations of Santolina rosmarinifolia (Asteraceae)

Phenotypic differentiation of two tetraploid (2n = 4x = 36, 36+1B, 36+2B) populations of Santolina rosmarinifolia geographically isolated from diploid populations was investigated. The karyotype was relatively homogeneous, meiosis was regular and pollen was fertile in both cytotypes. An autopolyploid or allopolyploid origin for tetraploid cytotypes is discussed. Overall, 80.82% of all variance in achene weight, time t₀, t₅₀ and t₉₀ of germination and accumulated germination rate was due to achene age at each ploidy level. Partition of the total phenotypic variance showed that there was extensive variation between ploidy levels. The mean of morphological characters was generally higher in polyploids. For diploid cytotypes, flower number, achene production and fruiting percentage were significantly higher than for tetraploid cytotypes. Cluster analysis indicated that the patterns of seedling morphology and development were similar in three diploid individuals and several tetraploids; the same analysis showed high similarity between diploid individuals of the natural populations, whereas tetraploid individuals showed high dissimilarity among themselves and with diploid individuals. Multiple correspondence analysis and logistic regression analysis indicated that qualitative characters contribute strongly to cytotype differentiation. The results support recognition of the tetraploid cytotypes at the subspecies level. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 650–668.     

Natural hybridisation in birch: triploid hybrids between Betula nana and B. pubescens

Hybridisation between diploid (2n=28) dwarf birch Betula nana L. and tetraploid (2n=56) downy birch B. pubescens Ehrh. has occurred in natural populations in Iceland. About 10% of birch plants randomly collected are triploid (2n=42) hybrids. Ribosomal gene mapping on chromosomes and genomic in situ hybridisation confirms the hybridity. However, the triploid hybrids are not morphologically distinct, i.e. they are not different from diploid and tetraploid birch plants that have intermediate morphology. The triploid hybrids have evidently played an important role in driving bi-directional gene flow between these two species. This paper reviews the extent of interspecific hybridisation in selected birch woodland populations and discusses the significance of natural hybridisation and introgression in birch.     

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

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

BREEDING SYSTEM OF A HYBRID BETWEEN A SEXUAL AND AN APOMICTIC SPECIES OF AMELANCHIER,SHADBUSH (ROSACEAE,MALOIDEAE)

Amelanchier bartramiana, which has been shown to be sexual and self-incompatible, and A. laevis, in which apospory and self-compatibility occur, grow in a mixed population in western Maine. Also present there is the putative interspecific hybrid, A. × neglecta. Principal components and canonical discriminant analyses of seven morphological characters from 96 parental and putative hybrid individuals substantiate morphological intermediacy of the hybrids. A Nomarski differential interference microscopy study of megasporogenesis and megagametogenesis in five hybrid plants shows a predominantly aposporous mode of reproduction, and controlled pollinations indicate that seed formation between A. bartramiana and A. laevis is possible and that the hybrids are self-compatible. The hybrids, which are tetraploids (n = ca. 34) like both parents in Maine, produce viable pollen and seed, but there is little evidence for backcrossing with either parent.     

MORPHOLOGICAL AND CYTOLOGICAL VARIABILITY IN TRIPSACUM DACTYLOIDES (GRAMINEAE)

A total of 235 accessions of Tripsacum dactyloides (L.) L. representing natural populations from 88 locations distributed throughout ten states of the United States were collected in the wild and studied morphologically and cytologically. Multivariate analysis of variance (MANOVA) was applied to 17 morphological characters recorded for 868 specimens from the 88 locations, which were further combined into 25 groups to facilitate analysis. Multivariate F ratios for six comparisons involving different groups were highly significant, indicating that the populations were significantly different on the basis of all 17 characters. Non-significant MANOVA F ratios for two comparisons between sympatric diploid and polyploid accessions showed them to be morphologically similar. Discriminant function (DF) analysis was employed to determine which characters contributed towards group discrimination. No one variable was found to distinguish between groups; rather, a combination of characters was necessary, and the combination changed with each comparison. Accessions were mainly either diploid (2n = 36) or tetraploid (2n = 72), with two triploids (2n = 54) reported from separate locations in Texas. Cytological data revealed that diploids and tetraploids occupy a more sympatric distribution than previously supposed. Morphological analysis suggested that diploids could not always be distinguished from polyploids on the basis of morphology alone, unless the appropriate characters were used. Information from cytological and morphological data showed Tripsacum dactyloides to be composed of many populations covering a wide range of variability, with each population possessing a characteristic combination of morphological attributes. It was concluded that T. dactyloides can be most meaningfully analyzed in terms of particular geographic regions, rather than attempting to elucidate natural relationships by correlating data from the entire United States.     

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.     

Production and characterization of fertile somatic hybrids of eggplant (Solanum melongena L.) with Solanum aethiopicum L.

Summary In order to produce fertile somatic hybrids, mesophyll protoplasts from eggplant were electrofused with those from one of its close related species, Solanum aethiopicum L. Aculeatum group. On the basis of differences in the cultural behavior of the parental and hybrid protoplasts, 35 somatic hybrid plants were recovered from 85 selected calli. When taken to maturity either in the greenhouse or in the field, the hybrid plants were vigorous, all rapidly overtopping parental individuals. The putative hybrids were intermediate with respect to morphological traits, and all of their organs were larger, particularly the leaves and stems. DNA analysis of the hybrids using flow cytometry in combination with cytological analysis showed that 32 were tetraploids, 1 hexaploid and 2 mixoploids. The hybrid nature of the 35 selected plants was confirmed by a comparison of the isoenzyme patterns of isocitrate dehydrogenase (Idh), 6-phosphogluconate dehydrogenase (6-Pgd) and phosphoglucomutase (Pgm). Chloroplast DNA (ctDNA) restriction analysis using Bam HI revealed that among the 27 hybrid plants analyzed, 10 had S. aethiopicum patterns and the 17 remaining hybrids exhibited bands identical with those of eggplant without any changes. All of the somatic hybrid plants flowered. Both parental plants had 94% stainable pollen, while the hybrids varied widely in pollen viability ranging from 30% to 85%. The somatic hybrids showed high significant variation in fruit production. Nevertheless, there was a tendency for low fertility to be associated often with S. aethiopicum chloroplast type and/or with an abnormal ploidy level, while good fertility was mostly associated with the tetraploid level and eggplant chloroplasts. Interestingly, 2 tetraploid somatic hybrid clones were among the most productive, yielding up to 9 kg/plant. As far as the fertility of the F₁ sexual counterpart was concerned, only 2 fruits of 50 g were obtained. Hybrid fertility in relation to phylogenetic affinities of the fusion partners is discussed.