Pentaploid Hybrids Research Articles

Use of Progenitor Species Germplasm for the Improvement of a Cultivated Allotetraploid1

The suitability of progenitor species germplasm as a source of genetic variation for the improvement of quantitatively inherited genetic traits in a cultivated allotetraploid species was investigated. Tobacco, Nicotiana tabacum L. cv. SC 58 was doubled with colchicine to the octoploid state and crossed with the diploid progenitor species N. sylvestris Speg. and Comes. The partially fertile pentaploid hybrid was selfed, or backcrossed one generation to SC 58, to increase fertility. Two cycles of a recurrent selection scheme using SC 58 as a tester parent were then followed to concentrate desirable germplasm from N. sylvestris in the species‐derived synthetic populations.The two synthetic populations (Syn I and Syn II), 58, S1 families, and testcrosses to SC 58 of plants in Syn I which were used to produce Syn II were evaluated in three environments for 11 agronomic and chemical constituents. Significant differences were detected among genetic entries for all characters measured except percent nornicotine in cured leaf, indicating that germplasm from the diploid species, N. sylvestris, had been introgressed into the N. sylvestris genome of tobacco. The potential value of this genetic variation is demonstrated by the fact that Syn I and Syn II yielded 7.7 and 12.9%, respectively, more cured leaf than SC 58. Thus, the breeding technique may be useful in broadening the genetic base for the improve. merit of quantitatively inherited characters in this cultivated species.

Notes on the cytogenetic structure of the cultivated oat Avena sativa (2n=6x=42)

The cytogenetic structure of the cultivated oat has been studied using aneuploids. The chromosome pairing observed in pentaploid hybrids between the tetraploid species A. magna and telocentric lines of A. sativa show that the occurrence of multivalents in the hybrid are in part due to chromosomal differentiation.

Selection for seed set in crosses of Avena sativa L. × A. Abyssinica Hochst.

‘Precoz’ oat line, discovered in a mass planting of wild oats in Colombia, is a tetraploid belonging to Avena abyssinica. It crossed easily with ‘Kyto’, but not with ‘Bacata’, both hexaploid oat cultivars. Pentaploid hybrid plants of Precoz × Kyto and Precoz × Bacata had 35 chromosomes, tended to have seven bivalents and 21 univalents at meiosis, and were completely sterile, Colchicine treatment of pentaploid F1 plants produced decaploid tillers from which five amphiploid seeds were obtained. Selection for high percentage of seed set in the third and fourth amphiploid generations of Precoz × Kyto gave fifth generation plants with 80–100% fertility. The chromosome numbers of these plants approximated the octoploid level. Some derivatives from crosses of third generation amphiploids with hexaploid cultivars had the hexaploid chromosome number and good fertility.

Tetrahaploids from colchicine-induced octaploid Solanum acaule subsp. Aemulans

Crosses between colchicine-induced octaploid Solanum acaule ssp. aemulans (2n=8x =96) with diploid S. tuberosum, Group Phureja, carrying a homozygous embryo marker, produced a high percentage of S. acaule tetrahaploids besides pentaploid and hexaploid F1 hybrids. These results are discussed in relation to the behaviour of autopolyploid and allopolyploid Solanum species, which basically differ in the occurrence of haploids and the ploidy level of F1 hybrids after pollination of both types of poly-ploids with Phureja.

CHROMOSOME RELATIONSHIPS BETWEEN TETRAPLOID (2n=28) AVENA MURPHYI AND SOME DIPLOID, TETRAPLOID AND HEXAPLOID SPECIES OF OATS

On combined evidence of cytology and morphology it is apparent that the newly discovered tetraploid Avena murphyi shares a common genome with the tetraploid A. magna. Lack of crossability and limited pairing in triploid hybrids involving A. murphyi indicate that none of the presently known diploid oats participated in the formation of A. murphyi. Meiotic behavior of A. murphyi × A. sativa pentaploid hybrids shows considerable homology between the chromosomes of the parents. The origin of the hexaploid oats is discussed in the light of the cytogenetic status of A. murphyi.

Sterility in the Interspecific Hybrids of <i>Dichanthium</i> (Willemet)

Seven hybrids were obtained from D. annulatum (2n=40)×D. aristatum, (2n=20), out of which four were pentaploids (2n=50), one was tetraploid (2n=40), and two were aneuploids (2n=41 and 42). Out of four hybrids obtained from D. annulatum (2n=40)×D. caricosum (2n=20), two were pentaploids, one was a triploid (2n=30), and the other aneuploid (2n=46). These hybrids showed meiotic irregularities like univalents and multivalents at metaphase I, bridges and laggards at anaphase I and II, and micronuclei in the quartets. Abnormal sporads were frequently observed in those hybrids. The aneuploid hybrid with 2n=42 chromosomes of the cross D. annulatum×D. aristatum, occasionally formed pentads. One of the two pentaploid hybrids of D. annulatum×D. caricosum presented unusually long chromosomes during meiotic division. The hybrids exhibited different degrees of pollen and seed sterility. The factors responsible for such sterility have been discussed.

Cytology of a pentaploid hybrid and genome analysis in Solanum nigrum L.

Cytology of a pentaploid hybrid (2n=60) produced by crossing an autotetraploid (2n=48) of a diploid “race” of Solanum nigrum L. as seed parent with the naturally occurring hexaploid S. nigrum (2n=72) was studied which showed approximately 24II+12I. Chromosome pairing in the gametic complement of the hexaploid was deduced to be 12II+12I and on this basis it is concluded that the natural hexaploid is an autoallohexaploid, which has three sets (genomes) of 12 chromosomes each, two of which are to a large extent homologous to each other. Theoretically the genomic formula can be tentatively written as AAAABB. Since the natural hexaploid does not show any quadrivalents between the four homologous A genomes, chromosome pairing appears to be restricted to bivalent formation by a special genetic mechanism. The probability that S. nigrum could be an autohexaploid, parallelling Pheleum pratense, has been discussed.

Fertility and Chromosome Behavior of a Derived Decaploid of Vaccinium1

Abstract Chromosome pairing in a derived decaploid, 2n=10×=120, (from a colchicine-treated, sterile pentaploid hybrid of Vaccinium ashei Reade × V. corymbosum L.) was chiefly bivalent. Multivalent associations were present in 5 of 16 cells scored at metaphase I, but only 23 chromosomes of the 1,920 observed were involved in multiple pairing. Most of the cells at anaphase I (33 of 35 observed) contained lagging chromosomes which appeared to be non-disjoined bivalents rather than univalents. The decaploid was selfed and crossed with hexaploid, tetraploid, and diploid species. The mean number of seedlings produced per flower pollinated for each ploidy level was low, ranging from 0.04 to 0.09. The mean seedling number produced per self-pollinated flower was considerably higher, 0.92. The percent of pollen which stained in propionocarmine was 8% for the pentaploid parent, 62% for the derived decaploid and 99% for plants of V. ashei and V. corymbosum used as standards for comparison.

INTERSPECIFIC CROSSES INVOLVING ALFALFA. V. MEDICAGO SAXATILIS × M. SATIVA WITH REFERENCE TO M. CANCELLATA AND M. RHODOPAEA

M. saxatilis M.B. (2n = 48) could be crossed with tetraploid (2n = 32) as well as with hexaploid (2n = 48) M. sativa L. Pentaploid (2n = 40) hybrids tended to give progeny with fewer than 40 chromosomes; progenies from the hexaploid F1 tended to stabilize at hexaploid level with some fluctuations around it. At meiotic AI the hexaploid F1 showed two to five laggards in 21% of cells observed, and at AII there were 45% cells with irregular chromosome separation. M. saxatilis could be easily crossed with M. cancellata M.B. Tri-species hybrids involving M. saxatilis and M. sativa on one hand and M. cancellata or M. rhodopaea Velen. on the other hand were obtained. It is assumed that M. saxatilis has the genomic constitution S1S1 XXXX where S1 denotes homologous chromosome sets closely related to those of M. sativa s.l. The X chromosome sets probably have been derived from M. rhodopaea.

Chromosome Segregation in Hybrids between Extracted AABB Tetraploids and Common Wheat Varieties

Chromosome segregation was studied in pentaploid hybrids resulting from crosses between extracted AABB tetraploids and varieties of common wheat. Varietal differences were observed in univalent elimination in the F2 progeny. No clear-cut association could be made between the differences in cytological behaviour that were observed in the various meiotic stages examined and the final outcome in terms of mean chromosome numbers in the progeny.

NEW EVIDENCE ON THE ORIGIN OF THE HEXAPLOID OATS.

The hexaploid oats, sub-section Denticulatae in Malzew's (1930) monograph, comprise three main morphological and ecological types. In the forms classed under A vena sterilis, the entire spikelet comprises the dispersal unit. This oat occupies primary habitats in the relatively warm parts of the Mediterranean basin, is also a common weed in cultivation and massively colonizes other man-made habitats in the Mediterranean agricultural belt. The second hexaploid type is A. fatua in which the spikelet disarticulates upon maturity and each floret serves as a seed dispersal unit. In contrast to A. sterilis, A. fatua is very rare in primary habitats and known mainly as a segetal plant. This oat is a very common weed in cereal fields in the relatively cooler parts of the Mediterranean region. The third type of hexaploid oats is an aggregate of cultivated forms grouped in A. sativa and A. byzantina. Despite the morphological and ecological differences, all the types in the hexaploid oats are interfertile and should be regarded genetically as races rather than as independent entities (Ladizinsky, 1968). The mode of origin and the species comprising the hexaploid oats have not as yet been completely solved. Bivalent formation in the meiosis strongly indicates that these oats are allopolyploids. Furthermore, by means of karyotype study Rajhathy and Morrison (1959) identified what they assumed to be the A, C, and D genomes of the hexaploid oats. Employing chromosome match, these authors related A to the As genome, the genome of all the diploid forms of series Eubarbatae, usually referred to as A. wiestii, A. hirtula and A. strigosa. Using the same technique, it is impossible to relate any known Avena diploid either as the contributor of the C genome or of D. Similarly, the tetraploid parent of the hexaploid oats has not yet been identified. Recently Murphy et al. (1968) described a new tetraploid oat A. magna which is morphologically very close to the hexaploid A. sterilis. Karyotype study of A. magna and the meiotic behavior of the pentaploid hybrid involving this oat and A. sterilis led Murphy et al. (1968) to believe that these two polyploids share only the As genome. This interpretation has also been accepted by Rajhathy and Sadasivaiah (1968). During the course of the present study we became aware of several morphological and cytological features which seem incompatible with the interpretation of Murphy et al. (1968), and Rajhathy and Sadasivaiah (1968). The aim of this paper is to present this evidence and subsequently to prove that the As genome is not present in A. magna and that this new tetraploid oat and the diploid-carrying As genome can be regarded as the progenitor of the hexaploid oat.

Hybrids Between Tetraploid and Hexaploid Crested Wheatgrasses1

SummaryDoubled‐diploid Agropyron cristatum (L.) Gaertn., 2n=28, and tetraploid A. desertorum (Fisch. ex Link) Schult., 2n=28, hybridized with hexaploid A. cristatum, 2n=42. Meiosis in the parent plants was typical of that in autoploids. Pentavalent associations, up to five per cell, in the 35‐chromosome hybrids indicated close homologies between parental genomes. Occasional higher multivalent associations and bridge‐fragment formations at anaphase I indicated some structural heterozygosity.All crested wheatgrasses—whether diploid, tetraploid, or hexaploid—apparently contain one basic genome that has undergone some structural rearrangements. It is recommended that crested wheatgrasses be regarded as one species with taxonomic differentiation at the subspecies and varietal levels.The pentaploid hybrids were surprisingly fertile and ranged from 0.54 to 4.32 seeds per spikelet under open pollination. Some hybrids were considerably more vigorous than either parent and may have value in a breeding program. Interploidy hybridization is recommended to crested wheatgrass breeders.

Cytogeography of Achillea Millefolium in Western Oregon

A cytogeographic study was made of the tetraploid and hexaploid forms ofAchillea millefolium L. in western Oregon in order to clarify their distributions, to determine whether pentaploid hybrids are present at zones of contact between the two, and to correlate environmental conditions with the presence of the tetraploid in the coastal areas of Coos and Curry Counties, Oregon. The distributional pattern of the two chromosome forms was found to be more complex than previously reported, involving overlapping of ranges, the occurrence of mixed populations, and the presence of disjunct populations of one form in areas occupied by the other. A naturally occurring pentaploid hybrid with meiotic pairing of 18 II’s and 9 I’s was found, which could not be distinguished morphologically from the presumed parents. The coastal tetraploid form in southwestern Oregon is limited to the Siskiyou Mountains. Plants of this area, especially those at its geographical margins, were observed to be producing a large number of viable, unreduced pollen grains. It is suggested that the North American hexaploid form originated by autopolyploidy from earlier existing tetraploids.

Meiotic Bahavior and Sterility in an Avena Pentaploid Hybrid: C.I.7232 (2n=28) ✕ Mesdag (2n=42)1

A 1959 report3 that the interploidy cross [Avena saliva L. var. ‘Black Mesdag’ (2n=42)] ✕ [derived‐tetraploid C.I.7232 (2n=28)] resulted in highly fertile F1 hybrids and derivatives generated considerable interest and skepticism because such behavior was contrary to that expected. This led the current authors to make the reputed cross and to determine the meiotic and agronomic behavior of F1 plants. All F1's possessed 35 chromosomes and were sell‐sterile, indicating that tetraploid C.I.7232 was not a parent of the earlier hybrids.

THE CYTOGENETIC STATUS OF AVENA MAGNA

The corresponding pairing behaviour of the chromosomes of A. magna and A. abyssinica was determined in triploid and pentaploid hybrids. Much higher overall pairing was found in the A. abyssinica than in the A. magna triploids indicating reduced homology between the A genomes of the diploids and A. magna and the absence of homoeology between the A genome and the second genome of A. magna. In contrast, pairing was much higher in the A. magna pentaploid than that of A. abyssinica. It was concluded that the second genome of A. magna is closely related to one genome other than the A of the hexaploids. On the ground of morphology, cross-compatibility and the pairing behaviour of chromosomes it was proposed that A. magna has the genomes AADD and that it is the putative ancestral tetraploid of the hexaploid species. This hypothesis can be tested by a synthetic allohexaploid derived from A. ventricosa and A. magna.

Chromosome Associations in Triploid, Tetraploid, and Pentaploid Hybrids of Avena magna (2n=28)1

Diploid Avena strigosa Schreb. and A. wiestii Steud., tetraploid A. abyssinica Hochst., and hexaploid A. sativa L. and A. sterilis L. were cross‐compatible with A. magna Murphy and Tcrrell All hybrids except the pentaploids were sterile. Partial homology of the A genome of the diploid species with one genome of A, magna was indicated by the chromosome associations observed in the triploid hybrids A. magna ✕ A. wiestii and A. strigosa ✕ A. magna. In the tetraploid hybrid, A. abyssinica ✕ A. magna, chromosome associations suggest that the two species have one or both genomes partially common. In the pentaploid hybrids, the frequencies and kinds of chromosome associations observed suggest that A. magna may have two genomes partially in common with two genomes of the hexaploid species, a common genome and the remaining genomes partially common, or two genomes partially in common with the three genomes of the hexaploids.

Intergeneric Hybrids between Allohexaploid (Hordeum depressum x H. compressum) and Autotertraploid Svalof Rye (Secale cereale)

A partially fertile pentaploid hybrid has been obtained from a cross between allohexapolid (Hordeum depressum x H. compressum) and autotetraploid Svalof rye (Secale cereale). The F1 hybrid was intermediate between the parents in most morphological characteristics with the BC1 plants more closely resembling the rye parent. Cytological observations through various chromosome associations indicated that some homology existed between the chromosomes of the two parents.

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.

THE EVOLUTIONARY SIGNIFICANCE OF NATURAL FRAGARIA CHILOENSIS × F. VESCA HYBRIDS RESULTING FROM UNREDUCED GAMETES

A natural nonaploid hybrid (2n = 63) from fusion of a reduced F. vesca male gamete with an unreduced F. chiloensis gamete, and a partially fertile natural hexaploid hybrid (2n = 42) from fusion of an unreduced F. vesca (2n = 14) male gamete with a reduced F. chiloensis (2n = 56) gamete were discovered in separate mixed colonies along with over 20 additional pentaploid hybrids (2n = 35). Plants of all hybrids aggressively compete with F. chiloensis. This relatively high percentage of hybrids from unreduced gametes may mean that they have higher survival value than pentaploids, since some evidence indicates that unreduced gametes may not function that often in successful F. chiloensis × F. vesca hybridization. The partial fertility of the hexaploid shows that intermediate fertile levels of ploidy need not be derived exclusively from lower ploidy species, and unreduced gametes from such hybrids should produce a high percentage of decaploid offspring in natural backcrossing to F. chiloensis. The successful functioning of unreduced vesca and chiloensis gametes in natural hybridization justifies the postulation that other euploid levels also may occur naturally, including triploids, tetraploids, decaploids, 12 ploids, and 16 ploids. Of these, the even multiples—tetraploids, decaploids, 12 ploids, and 16 ploids—should be at least partially fertile.