Genome Formula Research Articles

Origin of Fragaria Polyploids. I. Cytological Analysis

The genomic relationships between modern Fragaria diploids (European and American F. vesca and F. viridis—2n = 14) and octoploids (F. virginiana and F. chiloensis—2n = 56) were investigated. This contrasts with previous studies where cultivars have represented the octoploids. Critical information on genomic pairing was obtained by comparing chromosome behavior of pentaploid hybrids with that of hexaploid hybrids (obtained by using a recent colchiploid of European F. vesca). Supporting data were also used from an F. chiloensis × Potentilla glandulosa hybrid (2n = 35). A revision of the AABBBBCC (Federova) genomic formula for the octoploids to AAA'A'BBBB is proposed based upon cytological evidence of homology between the AA and “CC” genomes. The phylogeny of the octoploids is postulated.

ORIGIN OF FRAGARIA POLYPLOIDS. I. CYTOLOGICAL ANALYSIS

The genomic relationships between modern Fragaria diploids (European and American F. vesca and F. viridis—2n = 14) and octoploids (F. virginiana and F. chiloensis—2n = 56) were investigated. This contrasts with previous studies where cultivars have represented the octoploids. Critical information on genomic pairing was obtained by comparing chromosome behavior of pentaploid hybrids with that of hexaploid hybrids (obtained by using a recent colchiploid of European F. vesca). Supporting data were also used from an F. chiloensis × Potentilla glandulosa hybrid (2n = 35). A revision of the AABBBBCC (Federova) genomic formula for the octoploids to AAA'A'BBBB is proposed based upon cytological evidence of homology between the AA and “CC” genomes. The phylogeny of the octoploids is postulated.

Cytological Relationships and Genome Structure of SomeFestucaSpecies

SUMMARYThe object of the present study was to gain additional information about the genomic structure of F. pratensis, F. arundinacea var. glaucescens, F. arundinacea (2 n = 42), F. Mairei and to confirm through chromosome pairing in these species and their interspecific hybrids the homologies suggested on karyotypic basis between their chromosome complements. Based on two sources of evidence (karyotype and meiosis of F1 progeny) genomic formulae to different species are assigned. 1. In the triploid hybrids involving F. pratensis X F. arundinacea var. glaucescens, chromosome pairing at M-I could be represented by a mean of 7.48I, 5.48II, 85III. In some cells as many as 19 chromosomes were associated. (a) This pairing is regarded as allosyndetic though some amount of intergenomic pairing was also observed.(b) Considering the karyotypic similarities between the satellited chromosomes of F. pratensis and some of those of glaucescens, and also the meiosis of their F1 progeny, the genomic constitution of prate...

SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS: III. AGROPYRON REPENS × TETRAPLOID AGROPYRON SPICATUM

Three hybrids of A. repens, 2n = 42, × A. spicatum, 2n = 28, and two reciprocal hybrids were obtained from emasculated and unemasculated crosses, respectively. The 35‐chromosome hybrids tended to be morphologically intermediate between the parent species but resembled A. repens more closely than A. spicatum. A. repens behaved cytologically as a segmental autoallohexaploid, and A. spicatum acted cytologically as an autotetraploid. Mean chromosome associations of 8.04 I, 12.72 II, 0.41 III, 0.06 IV, and 0.009 V were observed in 116 hybrid cells at metaphase I. Most chromosome pairing in the hybrids was attributed to autosyndesis. A. spicatum, A. repens, and their hybrids were represented by genome formulas of SSSS, R1R1X1X1X2X2, and SSR1X1X2, respectively. Hybrid fertility ranged from 0.02 to 0.69 seeds per spikelet.

Synthetic Hybrids of New World and Old World Agropyrons: III. Agropyron Repens X Tetraploid Agropyron spicatum

Three hybrids of A. repens, 2n = 42, × A. spicatum, 2n = 28, and two reciprocal hybrids were obtained from emasculated and unemasculated crosses, respectively. The 35-chromosome hybrids tended to be morphologically intermediate between the parent species but resembled A. repens more closely than A. spicatum. A. repens behaved cytologically as a segmental autoallohexaploid, and A. spicatum acted cytologically as an autotetraploid. Mean chromosome associations of 8.04 I, 12.72 II, 0.41 III, 0.06 IV, and 0.009 V were observed in 116 hybrid cells at metaphase I. Most chromosome pairing in the hybrids was attributed to autosyndesis. A. spicatum, A. repens, and their hybrids were represented by genome formulas of SSSS, R1R1X1X1X2X2, and SSR1X1X2, respectively. Hybrid fertility ranged from 0.02 to 0.69 seeds per spikelet.

Genome analysis of Mentha spicata L. (Genome analysis in the genus Mentha, Part 2).

Mentha spicata L. (including M. viridis L. and M. Iongifolia (L.) HUDS.) can be divided into 4 groups in accordance with the number of chromosomes. That is, there are strains with 24, 36, 48 and 54 chromosomes in the somatic cells. In the present study, we took up the strains with 24 and 48 chromosomes as the subject of genome analysis. The strains with 24 chromosomes are given the genome formula RR like M. rotundifolia (L.) HUDS. In the strains with 48 chromosomes, there are two kinds of genome constitution. One is presumed to have RRSS, the other is RRScSc, where S and Sc are partially homologous genomes. Genome constitution in M. spicata L. is found to have no connection with the hairiness of the mint plant, which BRIQUET used as a criterion for the classiflcation of species in the series ‘Silvestres’ ; nor does it have any connection with the crispness, of the leaves, though he established a special subspecies crispata BRIQ. in M. viridis L. and a special subspecies undulata BRIQ. in M. longifolia (L.) HUDS., based on this character. In two triploid hybrids RRS and RRSc, some trivalent chromosomes can be seen in meiosis, so it is presumable that S and Sc are not entirely independent of R, but certain relations seem toexist between them. We also think that R grenome evolved into Sc and Sc into S. On the basis of this presumption, we tried to construct a family tree of the Spicatae section which included M. spicata and M. rotundifolia, as was shown in the Fig. 6.

Cytogenetical Studies in the Interspecific Hybrid ofSetcreasea Brevifolia×S. Purpurea. II. F2and Backcrosses

SUMMARYCytogenetical studies were conducted in 8 backcrosses and 76 F2 plants of the interspecific hybrid Setcreasea brevifolia × S. purpurea.Wide range of morphological variation and different types of recombinations between the parental characters were recovered in the F2 progeny.Meiosis was observed to be irregular in the parents, F1, backcrosses and F2 plants analyzed. The irregularities observed were the presence of multivalents and univalents besides bivalents at metaphase I, lagging chromosomes and chromosome bridges with fragments at anaphase I & II and micronuclei at the dyad and tetrad spore stages. The frequency of trivalents was low in the backcrosses. Based on the chromosome associations at metaphase I, the probable genomic formulae were assigned to the materials studied.Relationships between S. brevifolia and S. purpurea were discussed in the present investigation. These species seem to be closely related with each other.

Morphology, Cytology, and Fertility of Synthetic Hybrids of Agropyron spicatum x Agropyron dasystachyum-riparium

Agropyron dasystachyum and A. riparium were readily cross-compatible with diploid, 2n = 14, and tetraploid, 2n = 28, forms of A. spicatum in natural and controlled crosses. The hybrids were morphologically intermediate between the parent species, and some hybrids bore a close resemblance to A. griffithsii. Diploid A. spicatum formed bivalents exclusively at metaphase I. Tetraploid A. spicatum behaved cytologically as an autoploid and formed an average of 8.28 II and 2.86 IV in 72 cells at metaphase I. Agropyron dasystachyum and A. riparium behaved as allotetraploids and formed 14 bivalents in 159 of 161 cells interpreted. Triploid hybrids of diploid A. spicatum x A. dasystachyum formed an average of 6.84 I, 6.95 II, and 0.08 III in 242 metaphase-I cells. Averages of 7.05 I, 4.69 II, 3.01 III, 0.61 IV, and 0.01 V were observed in 195 cells of tetraploid hybrids of A. riparium x tetraploid A. spicatum. Chromosome-pairing data indicated that one of the two A. dasystachyum or A. riparium genomes was closely homologous with the A. spicatum genome. Genome formulae of SS and SSSS were assigned to diploid and tetraploid A. spicatum, respectively. Agropyron dasystachyum and A. riparium were represented by a genome formula of S1S1XX, whereas the triploid and tetraploid hybrids were designated as SS1X and SSS1X, respectively. Several hybrids of A. riparium x A. dasystachyum contained 32 and 34 chromosomes. The origin of the additional chromosomes was not determined. The triploid hybrids were highly sterile, and only three seeds were produced on 25 hybrids under open-pollination. From 0%-50% stainable pollen was formed in the tetraploid hybrids, some of which produced several hundred seeds. The 32- and 34-chromosome plants were the most fertile hybrids. Introgressive hybridization apparently occurs in nature between tetraploid A. spicatum and A. dasystachyum or A. riparium.

SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS II. AGROPYRON RIPARIUM X AGROPYRON REPENS

Five hybrids were obtained from 12 seeds formed in 26 emasculated florets of A. riparium pollinated by A. repens. The hybrid plants were morphologically intermediate between the parents for vegetative and spike characteristics, although they resembled A. repens more closely than A. riparium. The 28‐chromosome A. riparium parent behaved cytologically as an allotetraploid and formed an average of 13.98 II and 0.04 I in 94 cells at metaphase I. An average of 20.27 II and 0.36 IV were observed at metaphase I in 55 cells of A. repens, which was designated as a segmental autoallohexaploid. The hybrids contained 35 chromosomes and averaged 6.75 I, 12.49 II, 1.05 III, 0.01 IV, and 0.01 V in 162 cells interpreted at metaphase I. Bivalent chromosome pairing in the hybrids was attributed to autosyndetic pairing of 2 A. repens genomes and allosyndetic pairing between 1 A. riparium genome and 1 A. repens genome. Multivalent chromosome associations were attributed to structural hybridity. A. repens and A. riparium apparently share a genome in common, and this genome is the one responsible for rhizomes in both species. A. riparium was given a genome formula of R2R2SS; whereas the A. repens genome formula was written as R1R1X1X1X2X2, and the hybrid genome formula was designated as R1R2X1X2S. The “S” genome of A. riparium was derived from A. spicatum, and the “R” genome is the genome shared by A. repens and A. riparium. The origin and distribution of the so‐called “X” genomes of A. repens remain unknown. The hybrids produced from 3 to 10% stainable pollen; however, no seed was set on the hybrids during 2 years in the field.

GENOME ANALYSIS OF AGROPYRON REPENS × AGROPYRON CRISTATUM SYNTHETIC HYBRIDS

Hexaploid A. repens, 2n = 42, and diploid A. cristatum, 2n = 14, were hybridized and gave rise to two 28‐chromosome reciprocal hybrids. Approximately 1% of hand‐emasculated florets of both parent species produced viable hybrid seed following controlled pollination. Early embryo abortion prevented greater hybrid seed set on A. repens, whereas failure of fertilization appeared to be the major cause of poor hybrid seed set on A. cristatum. Reciprocal differences in hybrid vegetative and spike morphology were striking. The A. repens × A. cristatum hybrid was vigorous, highly rhizomatous, and bore abundant spikes whose morphology was intermediate between that of the parent species. A. cristatum × A. repens hybrids were weak, non‐rhizomatous with frequently‐malformed spikes. Mean chromosome associations of 0.10 I, 20.10 II, and 0.43 IV were observed in 134 metaphase‐I cells of A. repens. Subsequent meiotic stages were regular except for occasional laggards and bridges at anaphase I and II. Metaphase‐I chromosome associations averaged 0.07 I and 6.97 II in 124 A. cristatum cells. Chromosome pairing in the hybrids was highly variable and averaged 11.45 I, 7.58 II, 0.44 III, and 0.02 IV per cell in 187 cells interpreted. From 5 to 14 laggards appeared in every hybrid cell at anaphase I. Bridges were observed in approximately 25% of the anaphase‐I cells. Similar irregularities were observed at anaphase II. Pollen viability was estimated as 3%, and the hybrids failed to set viable seed. On the basis of chromosome pairing in the species itself and in the hybrids, A. repens was designated as a segmental autoallohexaploid with a genome formula of the type A1A1A2A2BB. Although A. repens and A. cristatum chromosomes paired occasionally, the genomes of the 2 species were essentially non‐homologous. Some of the interpretational difficulties of genome analysis were discussed.

SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS. I. TETRAPLOID AGROPYRON SPICATUM × DIPLOID AGROPYRON CRISTATUM

Four interspecific hybrids of tetraploid A. spicatum × diploid A. cristatum ‘Fairway’ were obtained by controlled pollinations of emasculated and unemasculated spikes of A. spicatum. Most vegetative and spike characteristics of the hybrids were intermediate between those of the parent species. Tetraploid A. spicatum behaved cytologically as an autotetraploid, with mean chromosome associations of 0.09 I, 7.95 II, 0.03 III, and 2.98 IV being observed in 103 cells interpreted. The diploid A. cristatum was cytologically regular and formed 7 bivalents in 160 of 163 cells examined. Meiosis in the triploid hybrids was highly irregular, and these plants were completely sterile. Chromosomes of A. spicatum and A. cristatum differed sufficiently in size so that they could be distinguished in the hybrids. Seven bivalents and 7 univalents were formed in 90.5% of 262 cells interpreted at metaphase I. Mean chromosome associations of 6.87 I, 6.98 II, and 0.05 III were observed in the hybrids. Most chromosome pairing was due to autosyndesis of A. spicatum chromosomes, but A. cristatum chromosomes occasionally paired among themselves and with A. spicatum chromosomes. Tetraploid A. spicatum was considered to be an autotetraploid. On the basis of cytological evidence, A. cristatum, A. spicatum, and their interspecific hybrids were represented by genome formulae of AA, BBBB, and ABB, respectively.

HYBRIDIZATION STUDIES IN PERENNIAL ZINNIAS

Results of hybridization studies among the 6 species of subgenus Diplothrix (Zinnia‐compositae) are reported. Also included are analyses of chiasmata frequency in the parental species and 2 diploid hybrids. Pairing relationships and chiasmata frequency of the chromosomes in the hybrids of the diploid species indicate their genomes are homologous. Analyses of F2's of Z. juni‐perifolia X acerosa (2n) show that production of pigment in ray flowers, C, from Z. juniperifolia segregates as a simple dominant over colorless, cc, from Z. acerosa. Morphological studies of the hybrids produced to date indicate that the origin of the polyploid taxa has been more circuitous than simple hybridization followed by chromosome doubling. The genomic constitution of Z. juniperifolia is designated A1A1, that of Z. acerosa A2A2, and that of Z. oligantha A3A3. Morphological data and chromosomal pairing in the polyploid hybrids suggest that the tetraploid species should be tentatively assigned genomic formulae as follows: A1A1A2A2 or A1A1A3A3 for both Z. citrea, and Z. grandiflora, and A2A2A3A3 for 4n Z. acerosa.

SEGREGATION IN NEW ALLOPOLYPLOIDS OF GOSSYPIUM. V. MULTIVALENT FORMATION IN NEW WORLD X ASIATIC AND NEW WORLD X WILD AMERICAN HEXAPLOIDS

The New World tetraploid cottons, G. hirsutum and G. barbadense, are natural amphidiploids (genome formula, 2[AD]) combining species of the cultivated Asiatic (2A) and wild American (2D) groups of diploid cottons. Multivalent frequency, per cell, for 2 New World X Asiatic synthetic hexaploids, G. hirsutum X G. arboreum and G. barbadense X G. arboreum, is 6.68 and 7.80, respectively. Multivalents per cell for a series of New World X wild American synthetic hexaploids are: New World X G. harknessii, 3.65;— X G. armourianum, 3.96;— X G. aridum, 3.48;— X G. lobatum, 3.66; — X G. gossypioides, 1.13. The expected correlation between multivalent frequency and genetic segregation (e.g., high multivalent frequency = high recovery of recessives, and vice versa) for these hexaploids is realized for the near‐allopolyploids (New World X wild American) but only approximated for the near‐autopolyploid combinations, New World X Asiatic. This is explained on the basis that different homogenetic:heterogenetic bivalent ratios are expected in autopolyploids as compared to allopolyploids.

THE CYTOGENETICS OF GOSSYPIUM AND THE ORIGIN OF NEW WORLD COTTONS

It has long been accepted by students of the genus Gossypium that the New World cottons (G. hirsutum L., G. barbadense L., and G. tomentosum Nutt.) are natural amphidiploids combining an A genome from a taxon of the Asiatic diploid group and a D genome from a taxon of the American diploid group (Skovsted, 1937). Beasley (1940b) and Harland (1940) provided confirming evidence on the origin of the New World type by synthesizing amphidiploids from A x D hybrids that were similar in morphology and cytogenetically compatible with the natural amphidiploids. More recent research on the general question of the origin of New World cottons has been directed toward pinpointing the taxa that were involved in the original hybrid and to the problem of when and how they were brought together so that hybridization could take place. These two questions form the basis of this paper, and they will be treated in turn. Triploid hybrids of New World (genome formula, AD) x Asiatic (A) and New World x American (D) show 13 II and 13 I at metaphase I (MI) of meiosis (this evidence supported Skovsted's hypothesis of amphidiploid origin). But since each of the two AD x A triploids and all of the seven possible AD x D triploids show essentially the same number of bivalents at MI, there is little basis here for identifying the parents of the New World amphidiploid. A method described by Stephens (1950) and used extensively in this laboratory (see review in Phillips, 1962) takes advantage of the segregation frequencies of marker genes in synthetic allohexaploids to discern interrelationships among the A, D, and AD taxa. A brief summary of the results of these studies (Gerstel, 1956; Gerstel and Phillips, 1957; Phillips and Gerstel, 1959; Phillips, 1962) appears in table 1. The relationships indicated in the table show that G. herbaceum and G. arboreum are very closely related to the taxon that contributed the A genome to New World cotton and that G. raimondii is rather closely related to the contributor of the D genome. The gap in this picture is the absence of the cross AD x D3 from table 1. Neither G. klotzschianum Andersson (D3-K) nor G. davidsonii Kellogg (D3-D), which some students of the genus consider to be conspecific, can be successfully hybridized with any of the New World species, and they will form vigorous hybrids with only two other species in the genus (G. anomnalum Wawra and Peyr. and G. longicalyx Hutchinson and Lee). There is thus no direct genetical or cytological method for assessing the relative chromosome homologies of D3 and DnW (D genome of New World cotton). However, by means of a bridging-species hybrid, the D3 and DnW genomes have been brought together in the same hybrid and their homologies compared by assessing chiasma frequency. By comparing chiasma frequency in this hybrid with that of a similar hybrid combining D5 and D,wy 'Contribution from the Crop Science Department, North Carolina Agricultural Experiment Station, Raleigh, N. C. Published with approval of the Director of Research as Paper No. 1509 of the Journal Series and with approval of the Crops Research Division, Agricultural Research Service, U.S.D.A.; supported in part by Project S-1 of the Research and Marketing Act of 1946. Aided by grant G-14203 of the National Science Foundation. 2 The genome nomenclature used in this paper follows Beasley (1940a and 1942) and Brown and Menzel (1950 and 1952).

MORPHOLOGY AND CYTOLOGY OF SYNTHETIC HYBRIDS OF AGROPYRON TRICHOPHORUM X AGROPYRON CRISTATUM

Dewey, Douglas R. (Utah State U., Logan.) Morphology and (cytology of synthetic hybrids of Agropyron trichophorum X Agropyron cristatum. Amer. Jour. Bot. 50(10): 1028–1034. Illus 1963.—Three hybrids were obtained from controlled crosses of pubescent wheatgrass, A. trichophorum (2n = 42), and hexaploid crested wheatgrass, A. cristatum (211 = 42). The hybrids were intermediate between the parent plants for all vegetative and spike characteristics observed. Under open pollination, 2 of the hybrids set 2 seeds each, and the other hybrid produced 60 seeds. Meiosis in the parent plants was basically regular. Average motaphase‐I chromosome associations were 0.09 I, 20.56 II, 0.05 III, and 0.16 IV per cell in the A. trichophorum parent, which was described as a segmental autoallohexaploid. The hexaploid A. cristatum parent averaged 0.18 I, 7.44 II, 0.81 III, 2.86 IV, 0.08 V, and 2.11 VI per cell at diakinesis and was described as an autohexaploid. Chromosome pairing in the hexaploid hybrid averaged 5.08 I, 8.94 II, 4.33 III, 1.11 IV, 0.27 V, and 0.05 VI per cell. On the basis of chromosome pairing in the parent species and their hybrids, it was concluded that 1 of the A. trichophorum genomes was partially homologous with the 3 genomes of hexaploid A. cristatum. Genome formulae for hexaploid A. cristatum, A. trichophorum, and their hybrids were represented as AAAAAA, A1A1B1B1B2B2, and AAAA1B1B2 respectively.

Cytotaxonomy of Helianthus Ciliaris and Related Species of the Southwestern U. S. and Mexico

In and around cultivated fields, along roadsides, and in various drainage habitats of the southwestern United States, central and northeastern Mexico, one frequently encounters plants of Helianthus ciliaris DC., commonly called blue weed. In a comprehensive submonographic treatment of Ilelianthus, Watson (1929) considered H. ciliaris as a single, exceedingly variable species, pointing out, in particular, variation in leaf shape, size and pubescence. As a result of cytological, morphological, and population studies in Mexico and the southwestern United States, I have come to the conclusion that several species were included in this taxon as delimited by Watson. The several species are generally similar to H. ciliaris and share with it the ability of rapid vegetative propagation by slender rhizomes, slightly or heavily glaucous stems, and certain types of pubescence. Cytological study has ellucidated the situation in some respects. Heiser and Smith (1955 and unpubl.) have shown that the chromosome number of H. ciliaris is n = 34. They also have one plant from western Texas with X 51 which probably arose by chromosome doubling in a natural hybrid between H. citiaris and one of the related species with n 17 discussed later. Counts from several additional populations of H. ctliaris have all been n 34 (Table 1). leliantivus has a basic number of x -_ 17, and H. citiaris (n 34) would be considered a tetraploid on this base. However, the closely related genus Viguiera has taxa with n -8 and 17, and Heiser and Smith (1955) have suggested that Helianthus may be of polyploid origin. Microsporocytes at diakinesis in Heltianthus ctlitaris from several localities had several quadivalents per cell (Fig. 1). This suggests that H. ctliaris is a segmental allotetraploid, derived from taxa with segments of chromosomes homologous enough for heterogenetic pairing to occur, and the genomic formula C1C1C2C2 is appropriate. The predicted result from intergenomal crossing over is segregation for characteristics by which the parental types differ (Stebbins 1950). At one extreme in H. ciliaris, one finds leaf types that are somewhat pinnately lobed, pilose or hispid, and stems that are pilose or hispid. At the other extreme are plants with entire or almost entire leaves with both leaves and stems glabrous. This suggests two possible ancestral types, both of which can be matched by existing diploids. One probable ancestral type of H. ciliaris is H. arizonensis, a diploid (Table 1), found in west-central New Mexico and east-cenrtal Arizona. Plants of this species are generally shorter than those of H. ctliaris and have smaller heads, but the only qualitative character that has been found to separate the two thus far is the completely yellow disc corollas in H. arizonensis. The disc corollas of H. ciliaris are invariably red-tipped or sometimes completely red. The populations of H. arizonensis tend to be smaller and more scattered than those of H-. cittaris. The other possible ancestor of H. ciliaris, assuming that the tetraploid has

CYTOLOGY AND MORPHOLOGY OF A SYNTHETIC AGROPYRON TRICHOPHORUM × AGROPYRON DESERTORUM HYBRID

Dewey, Douglas R. (Utah State U, Logan.) Cytology and morphology of a synthetic Agropyron trichophorum × Agropyron desertorum hybrid. Amer. Jour. Bot. 50(6): 552–562. Illus 1963.—A single hybrid was obtained from controlled pollinations of more than 1,200 emasculated florets of A. trichophorum (n=21) with A. desertorum (n = 14) pollen. Vegetative and spike characteristics of the hybrid were intermediate between those of the parent species. The A. desertorum parent behaved cytologically as an autotetraploid, whereas A. trichophorum was best described as a segmental autoallohexaploid. Chromosome associations at metaphase I in the 35‐chromosome hybrid averaged 5.75 I, 8.94 II, 2.91 III, 0.59 IV, and 0.04 V. On the basis of chromosome pairing in the parent species and their interspecific hybrid, it is suggested that A. trichophorum and A desertorum share 1 or 2 partially homologous genomes. A. desertorum and A. trichophorum were assigned genome formulas of AAAA and A1A1B1B1B2B2, respectively; and the hybrid genome formula was represented as AAA1B1B2.

CYTOGENETICS OF TAGETES JALISCENSIS x T. ERECTA

Towner, Joseph W. (U. California, Los Angeles.) Cytogenetics of Tagetes jaliscensis X T. erecta. Amer. Jour. Bot. 49(10): 1064–1067. Illus. 1962.—Although Tagetes jaliscensis and T. erecta are morphologically very distinct, the F1 hybrid between them had normal meiosis (12 bivalents) and was fertile. Segregation in F2 was undisturbed for marker genes on 4 pairs of chromosomes. These facts suggest that T. jaliscensis, like T. erecta, is an A‐genome diploid (genome formula A2A2). From plant morphology, the A‐subgenome of amphiploid T. patula is regarded as more likely derived from T. erecta than from T. jaliscensis. In T. jaliscensis X erecta F2, disk corolla anthocyanin (R = red) from T. jaliscensis segregated as a simple dominant over the absence of anthocyanin from T. erecta. A chlorophyll defect was determined by duplicate factor recessives. Tubular ray flowers (tu = tubular) segregated as a simple recessive to normal flat rays in the interspecific F2 and in T. erecta.

HYBRIDIZATION BETWEEN AMPHIDIPLOIDS AND THE EVOLUTION OF POLYPLOIDS IN THE WHEAT(AEGILOPS-TRITICUM)GROUP

The polyploid species of the wheat group (genera A egilops and Triticum) are familiar as classical examples of evolution through amphidiploidy. The two genera have been a subject of extensive cytogenetic study by numerous workers (see reviews by Kihara, 1954, and Sears, 1948, 1959). The cytogenetic relations between the various diploid species in this group have been studied through interspecific crosses, and the polyploid species have been subjected to intensive genome analysis. On the basis of the cytological information gathered, Kihara ( 19 54) and Kihara et al. ( 19 59) established genomic formulae for the various A egilops species (table 1). Kihara concluded that the polyploid species of this group are typical allopolyploids and assumed that each polyploid species originated independently, as a result of an interspecific cross (or crosses) between two given diploid parental species followed by chromosome doubling. At present, the various polyploid species of the wheat group are generally regarded as well-established cases of such a mode of origin. The purpose of the present paper is to question the assumption of an independent evolution of the various polyploid species in the Aegilops-Triticum group. Evidence is presented to indicate that a considerable number of existing polyploids are genetically interconnected through hybridization and cannot be regarded to have evolved independently. The hypothesis is advanced that in addition to amphidiploidy, hybridization on the tetraploid level has played a decisive role in the evolution of the polyploid species. Tetraploid entities in the wheat group (as well as their modified genomes) are

SEGREGATION IN NEW ALLOPOLYPLOIDS OF GOSSYPIUM. IV. SEGREGATION IN NEW WORLD × ASIATIC AND NEW WORLD × WILD AMERICAN HEXAPLOIDS

PHILLIPS, LYLE L. (North Carolina State Coll., Raleigh.) Segregation in new allopolyploids of Gossypium. IV. Segregation in New World X Asiatic and New World X wild American hexaploids. Amer. Jour. Bot. 49 (1) : 51-57. 1962.-The New World tetraploid cottons, G. hirsutum and G. barbadense, are natural amphidiploids (genome formula, 2 [AD]) combining species of the cultivated Asiatic (2A) and wild American (2D) groups of diploid cottons. Genetic segregation for marker alleles in New World X Asiatic and New World X wild American synthetic hexaploids have been determined. Average segregation for several loci in New World X Asiatic hexaploids is close to the autoploid 5:1 ratio, ranging from 5.1 to 6.8:1. Average segregation for 3 loci (L, Rd, and Rj) common to a series of New World X wild American hexaploids is: New World X G. raimondii, 9.3:1;-X G. harknessii, 16.4:1;-X G. armourianum, 17.4:1;-X G. aridum, 20.3:1;-X G. lobatum, 21.4:1-X G. thurberi, 32.9:1;-X G. gossypioides, 66.5:1. These data are discussed, and the method by which they were derived is compared with other cytogenetical means of discerning phyletic interrelationships among Gossypium species. RECENT publications from this laboratory concerning the cytogenetics of cotton have included descriptions of segregation and multivalent formation in various tetraploid and hexaploid synthetic amphidiploids of Gossypium species (Gerstel, 1956; Gerstel and Phillips, 1957, 1958; Sarvella, 1958; and Phillips and Gerstel, 1959). Of the 6 genome groupings delimited by Beasley (1942), A, B, C, D, E, and AD, 4 (A, B, D, and AD) have been represented by the 7 species used in forming these polyploid hybrids. Inasmuch as the cultivated species, G. hirsuitum L. and G. barbadense L., are themselves amphidiploids combining species from the A and D groups, raw allopolydiploids involving A, D, and AD species have received special attention. The present report concerns the segregation of a number of AD X A and AD X D synthetic allohexaploids. METHODS AND MATERIALS-The New World tetraploid group (genome formula, AD) contains 2 cultivated species, G. hirsutum and G. barbadense, as well as a wild indigen of the Hawaiian Islands, G. tomentosum L. The marker stocks used from this group and the alleles they carry are listed as follows: