Relationship between parental chromosomic contribution and nuclear DNA content in the coffee interspecific hybrid C. pseudozanguebariae×C. liberica var ‘dewevrei’

 F₁ hybrids were obtained between two coffee species with the same chromosome number (2n=22) but with different nuclear DNA contents [C. pseudozanguebariae (PSE) 2C=1.13 pg and C. liberica var ‘dewevrei’ (DEW) 2C=1.42 pg]. G2 hybrids were obtained by open-pollination of the F₁ hybrids. Genomic in situ hybridisation (GISH) and flow cytometry were used on six F₁ hybrids and seven G2 hybrids to determine their parental chromosomic contribution and their nuclear DNA content (qDNA), respectively. GISH efficiently identified chromosomes from both species. F₁ hybrids had a qDNA intermediate between that of the parental species and contained the expected 11 chromosomes from each species. There was a linear relationship between the number of PSE chromosomes and the nuclear DNA content, which indicates that flow cytometry can be used to give a rough estimate of the parental chromosomic contribution in G2 hybrids. Received: 1 August 1997/Accepted: 25 August 1997     

A comparison of Hordeum bulbosum-mediated haploid production efficiency in barley using in vitro floret and tiller culture

Summary A high efficiency of Hordeum bulbosum-mediated haploid production in barley has been achieved using a floret culture technique in which florets pollinated with Hordeum bulbosum are cultured on modified N₆ media containing 0.5 mg/l kinetin and 1.2 mg/l2,4-D. Cultures were maintained at 25 °C with a 16 h photoperiod for 9 days before embryo rescue. In a comparison of haploid production efficiency using five F₁ hybrids from winter x winter and winter x spring barley crosses, 41.6 haploid plants/100 florets pollinated were produced using floret culture. Using detached tiller culture, 13.5 haploid plants/100 florets pollinated were produced. Higher efficiencies achieved with floret culture are attributed to the formation of larger, differentiated embryos. Such embryos lead to higher frequencies of plant regeneration. The F₁ from a winter x winter cross was inferior in haploid production compared to F₁s from winter x spring crosses. No genotype x technique interaction was observed.Oregon Agricultural Experiment Station Technical Paper No. 8653     

GENOMIC RELATIONSHIP OF GUAYULE WITH PARTHENIUM SCHOTTII

F₁ hybrids obtained from crosses between the rubber-bearing species, Parthenium argentatum Gray (commonly known as guayule), and P. schottii Greenman ex Millspaugh and Chase, a nonrubber-producing species from southern Mexico, were morphologically variable. They were generally intermediate between the two species with respect to leaf size, head size, number of disk florets per head, and the length of the peduncles. Like the parental species, the hybrids had 2n = 36 chromosomes. They averaged 14.56 bivalents, 3.92 univalents, 0.56 trivalents, and 0.32 quadrivalents, indicating a high degree of homeology between the genomes of the two species. The observation of one quadrivalent at diakinesis in 32% of the PMCs and the frequent occurrence of a bridge accompanied by a fragment at late anaphase I of the F, hybrids suggested that the two species differ in a reciprocal translocation and a paracentric inversion. The ease of hybridization, the partial fertility of the hybrids, and their high degree of chromosome pairing indicate that P. schottii and P. argentatum are closely related in spite of their distinct morphological features and geographical distributions. This close relationship provides an opportunity to transfer genes from P. schottii to guayule for desirable characteristics, such as high biomass production and resistance to Verticillium dahliae Kleb, by means of interspecific hybridization.     

Cytology of inbreds and f 1 hybrids of pearl millet

Summary The meiotic behaviour of chromosomes was studied in four inbred lines and their F ₁ hybrids of P. typhoides. The inbred lines showed a decrease in mean chiasma frequency when compared with the population plants, but differed from one another in their mean chiasma frequencies. Together with the decrease in mean chiasma frequency the inbreds showed variation in mean chiasma frequencies. The inbred lines showed a number of meiotic abnormalities such as extra chromosomes, extra fragments, desynapsis, persistent nucleoli and differential condensation of chromosomes. The F ₁ hybrids of these inbreds exhibited heterosis for chiasma frequency. All the F ₁'s had mean chiasma frequencies higher than the means of the respective participating parents. The F ₁'s, however, differed in the degree of heterosis exhibited. In the F ₁ hybrids, the variation in mean chiasma frequency, both between plants and between PMC's within plants, was significantly lower than that of the inbred lines. The effect of environment was studied in the inbred lines and their F ₁ hybrids. The mean chiasma frequencies of the inbred lines were significantly lower, and the variation in mean chiasma frequencies was greater, in the stress season. The mean chiasma frequencies of F ₁'s did not show any significant differences between the two seasons. The F ₁'s exhibited less variation in mean chiasma frequency than the inbred lines, showing that F ₁'s were developmentally more stable. The F ₁'s did not show any meiotic abnormalities in either season.     

Karyotypes and serum transferrin patterns of hybrids between Asian and Oceanian black rats,Rattus rattus

Karyotypes and serum transferrin patterns were examined in Asian and Oceanian black rats (R. rattus). Japanese R. r. tanezumi and Malayan R. r. diardii had 2n=42, but Australian and New Guinea R. r. rattus showed 2n=38 chromosomes. F₁ hybrids between Japanese and Australian rats and Malayan and New Guinea rats had 2n=40 chromosomes which consists of the two genomes of both parents. Although various matings between the F₁ hybrids were made, only one F₂ male rat with 2n=39 chromosomes was obtained. The F₁ hybrids seem to be semisterile. Parental transferrin phenotypes were TfR in Japanese rats and TfCD in Oceanian rats. F₁ hybrids examined showed TfRD in both male and female and one F₂ hybrid had TfR type transferrin. Based on the above investigations, it is suggested that Asian and Oceanian black rats are geographically isolated and evolved different chromosomal and serum transferrin characteristics, but the sexual isolation of the two groups is incomplete at the present time.Contribution No. 826 from the National Institute of Genetics, Japan. Supported by a grant-in-aid from the Ministry of Education of Japan (Scientific Expedition in 1968, No. 8801 in 1969 and No. 9001 in 1970).     

Chromosomal inheritance of parental rDNAs distribution pattern detected by FISH in diploid F1 hybrid progeny of Cobitis (Teleostei,Cobitidae) species has non-Mendelian character

This study was conducted to describe the major and the minor rDNA chromosome distribution in the spined loach Cobitis taenia (2n = 48) and the Danubian loach Cobitis elongatoides (2n = 50), and their laboratory-produced diploid reciprocal F₁ hybrid progeny. It was tested by fluorescence in situ hybridisation (FISH) whether the number of 28s and 5s rDNA sites in the karyotypes of diploid hybrids corresponds to the expectations resulting from Mendelian ratio and if nucleolar organiser regions (NOR)were inherited from both parents or nucleolar dominance can be observed in the induced F₁ hybrid progeny. Ten (females) or twelve (males) 28s rDNA loci were located in nine uniarm chromosomes of C. taenia. Two of such loci terminally bounded on one acrocentric chromosome were unique and indicated as specific for this species. Large 5s rDNA clusters were located on two acrocentric chromosomes. In C. elongatoides of both sexes, six NOR sites in terminal regions on six meta-submetacentric chromosomes and two 5s rDNA sites on large submetacentrics were detected. The F₁ hybrid progeny (2n = 49) was characterised by the intermediate karyotype with the sites of ribosome synthesis on chromosomes inherited from both parents without showing nucleolar dominance. 5s rDNA sites were detected on large submetacentric and two acrocentric chromosomes. The observed number of both 28s and 5s rDNAs signals in F₁ diploid Cobitis hybrids was disproportionally inherited from the two parental species, showing inconsistency with the Mendelian ratios. The presented rDNA patterns indicate some marker chromosomes that allow the species of the parental male and female to be recognised in hybrid progeny. The 5s rDNA was found to be a particularly effective diagnostic marker of C. elongatoides to partially discern genomic composition of diploid Cobitis hybrids and presumably allopolyploids resulting from their backcrossing with one of the parental species. Thus, the current study provides insight into the extent of rDNA heredity in Cobitis chromosomes and their cytotaxonomic character.     

The effect of B chromosomes on meiotic and pre-meiotic spindles and chromosome pairing in Triticum/Aegilops hybrids

Diploid populations of Aegilops mutica and Aegilops speltoides containing B chromosomes have been used as male parents in crosses with aneuploid genotypes of Triticum aestivum to investigate the effect of B chromosomes on meiotic homologous and homoeologous chromosome pairing. F₁ hybrids of T. aestivum/Ae. mutica and T. aestivum/Ae. speltoides segregated into four classes with regard to the degree of meiotic chromosome pairing, irrespective of the presence of B chromosomes. The B chromosomes do not introduce factors altering the level of pairing other than that due to the natural allelic and gene variation occurring in the diploids. Similarly no reduction in pairing of homologous chromosomes was observed in genotypes in which pairs of homologues co-existed with B chromosomes. However, a significant drop in chiasma frequency was observed in F₁ hybrids of T. aestivum × Ae. mutica with B chromosomes and T. aestivum × Ae. mutica nullisomic for wheat chromosome 5D with B chromosomes, in temperature regimes of 12° C. No asynapsis occurred in similar hybrids in the absence of Mutica B chromosomes at low temperatures. The low-temperature sensitive phase lies early in the pre-meiotic interphase. In this instance the Mutica B chromosomes are interacting with specific gene loci of the A chromosomes. Synaptic pairing has been observed between A and B chromosomes in Ae. mutica. A high frequency of pollen mother cells with twice the number of chromosomes was observed in hybrids in the presence of Mutica B chromosomes due to failure of spindle formation at the last pre-meiotic mitosis. Meiotic spindle irregularities occurred in hybrids containing Speltoides B chromosomes. Hybrids of Ae. speltoides + B's X Ae. mutica + B's displayed the mitotic and meiotic spindle abnormalities introduced by the presence of the B chromosomes of each parent.     

CHROMOSOME DIFFERENTIATION IN SEVERAL SPECIES OF MELILOTUS

Shastry , Sishta V. S., William K. Smith , and Delmer C. Cooper . (U. Wisconsin, Madison.) Chromosome differentiation in several species of Melilotus. Amer. Jour. Bot. 47(8) : 613–621. Illus. 1960.—Two species of the section Eumelilotus (M. alba and M. officinalis), 2 of Micromelilotus (M. messanensis and M. segetalis), 2 F₁ hybrids (M. officinalis × M. alba and M. messanensis × M. segetalis), 2 autotetraploids (M. alba and M. officinalis), and 1 allotetraploid (M. officinalis × M. alba), were utilized during the course of this investigation. The 4 species and F₁ hybrids have 16 somatic chromosomes and the tetraploids have twice that number (32). The 2 Eumelilotus species are completely isolated because of seed failure after cross pollination. The F₁ hybrid (M. officinalis × M. alba), obtained elsewhere by the use of embryo-culture techniques, was intermediate between the parents in certain morphological characters and was ca. 75% pollenfertile whereas the parents approached complete fertility. No structural differences between the chromosomes were evident at pachytene. Disturbances which led to the reduced fertility occurred at later stages of meiosis. The Micromelilotus species are cross compatible, but the F₁ hybrid (M. messanensis × M. segetalis) is highly sterile. Despite chromosome structural differences of various types evident at pachytene, bivalents regularly occur at metaphase I. Irregular distribution of the chromosomes at later stages of meiosis leads to high sterility. Species which readily cross but produce a hybrid of very low fertility are likely to compound chromosomal structural differences, because of abnormalities in meiosis, in contrast with species that are completely incompatible.     

ARTIFICIAL HYBRIDIZATION OF RUBBER-BEARING GUAYULE WITH COLD-TOLERANT PARTHENIUM LIGULATUM

ABSTRACT Caespitose and cold-tolerant plants of Parthenium ligulatum (Jones) Barneby (Asteraceae) from a native population in the Uinta Basin, Utah, were uprooted, potted, and transferred to a greenhouse in California. Approximately two years after transfer, the plants flowered and subsequently were crossed to diploid guayule (Parthenium argentatum Gray), the rubber-bearing species, native to the state of Durango, Mexico. Only female guayule × male P. ligulatum crosses produced F₁ hybrids. Only crosses involving guayule as female parent and F₁ plants as male parents produced backcross (BC,) plants. Hybrid plants were variable with respect to their growth habit, inflorescence, and leaf shape. Both parents and F₁ hybrids had 2n = 36 chromosomes. Unlike the parents, however, meiosis was irregular in the hybrids which showed a range of 0–5 and an average of 2.1 univalents at metaphase I. Hybrids averaged 0.87 laggards at anaphase I and 0.83 micronuclei at the tetrad stage. The crossability of guayule and P. ligulatum, the high degree of chromosome pairing of the F₁ hybrids, and the production of BC₁ plants indicate that the two species are related in spite of their distinct morphological and ecological differences. This study suggests that the cold-tolerance trait of P. ligulatum may be transferred to guayule through interspecific hybridization followed by backcrossing. The development of cold-tolerant guayule cultivars is expected to expand the areas of guayule production beyond that of the Chihuahuan desert and similar climates.     

NATURAL AND ARTIFICIAL HYBRIDS OF HELIANTHUS MAXIMILIANI X H. GROSSESERRATUS

Long , Robert W. (Ohio Wesleyan U., Delaware.) Natural and artificial hybrids of Helianthus Maximiliani × H. grosseserratus. Amer. Jour. Bot. 46(10): 687–692. Illus. 1959.—An investigation of the occurrence of natural hybridization in two perennial sunflowers, Helianthus Maximiliani and H. grosseserratus, was begun in 1950. Subsequently, artificial F₁, F₂, and first and second backcross generations were produced. Fertility and vigor were high in all these plants, but F₁ plants appeared to excel the others in these characteristics. Observations in the experimental garden were supplemented by examination of chromosomes in pollen mother cells, comparisons of herbarium collections, and study of wild populations. Evidence pointed to close genetic relationship of the species and to the occurrence of natural hybridization in areas of distributional overlap. In 1957 and 1958, field work in these areas resulted in the scoring of 18 natural populations, 3 of which consisted of both parental species plus putative F₁ hybrids. Two explanations are offered to account for the seeming absence of introgression. The results support the conclusion that natural hybridization leads to the establishment of F₁ hybrids and that introgression does not occur to any significant extent. Although both species display a high degree of interfertility, they are distinct morphologically. For this reason, it is advisable to maintain them as separate species.     

Intergeneric hybridization between Brassica napus and Sinapis pubescens,and the cytology and crossability of their progenies

The cytological possibility of gene transfer from Sinapis pubescens to Brassica napus was investigated. Intergeneric hybrids between Brassica napus (2n = 38) and Sinapis pubescens (2n = 18) were produced through ovary culture. The F₁ hybrids were dihaploid and the chromosome configurations were (0–1) _III + (2–11) _II + (5–24) _I . One F₂ plant with 38 chromosomes was obtained from open pollination of the F₁ hybrid. Thirty-one seeds were obtained from the backcross of the F₂ plant with B. napus. Five out of seven plants had 38 chromosomes, and the pollen stainability ranged from 0% to 81.4%. In the B₂ plants obtained from the backcross of B₁ plants with B. napus, 66.7% of the plants examined had 38 chromosomes. S. pubescens may become a gene source for the improvement of B. napus.     

MORPHOLOGY,FERTILITY, AND CYTOLOGY OF AGROPYRON REPENS × AGROPYRON DESERTORUM F2'S

Dewey , Douglas R. (Crops Res. Lab., Agric. Expt. Sta., Logan, Utah.) Morphology, fertility, and cytology of Agropyron repens × Agropyron desertorum F₂'s . Amer. Jour. Bot. 49(1): 78–86. Illus. 1962.—An 82-plant population derived from F₁ hybrids of A. repens × A. desertorum included morphological types indistinguishable from the parent species as well as many intermediate forms. Most, if not all, of the F₂ population were products of backcrossing of F₁ hybrids to one of the parent species. Backcrossing of F₁ hybrids to A. repens and A. desertorum occurred with equal frequency. Fifty-four percent of the F₂ plants were completely sterile. Fertility in the F₂ population was related to the nature of the F₁ backcross. F₂ plants obtained from backcrossing to A. desertorum were more fertile than equivalent backcrosses to A. repens. Fertility in the F₂'s was concentrated in a few plants. Nine F₂'s accounted for 85% of the seed produced in the 82-plant population. The most fertile plant produced 441 viable seeds. Meiotic chromosome counts of 66 F₂'s ranged from 30 to 49 and averaged 36. Chromosome number was related to the direction of the backcross. Chromosome associations in all F₂ plants at metaphase I included many different combinations of univalents, bivalents and trivalents. Occasional pairing of A. repens and A. desertorum chromosomes were noted in some F₂'s. On the basis of morphology, fertility and chromosome pairing, genome formulae were assigned to the parent species. The genome formula of A. repens was given as BBBBCC and A. desertorum was designated as AAAA.     

HETEROSIS AND OUTBREEDING DEPRESSION IN INTERPOPULATION CROSSES SPANNING A WIDE RANGE OF DIVERGENCE

The intertidal copepod Tigriopus californicus was used as a model organism to look at effects of crossing distance on fitness and to investigate the genetic mechanisms responsible. Crosses were conducted between 12 pairs of populations spanning a broad range of both geographic distance (5 m to 2007 km) and genetic distance (0.2% to 22.3% sequence divergence for a 606-bp segment of the mitochondrial COI gene). For each pair of populations, three fitness components (hatching number, survivorship number, and metamorphosis number) were measured in up to 16 cohorts including parentals, reciprocal F₁, F₂, F₃, and first-generation backcross hybrids. Comparisons of each set of cohorts allowed estimation of within- and between-locus gene interaction. Relative to parentals, F₁ hybrids showed a trend toward increased fitness, with no correspondence with population divergence, and a decrease in variance, which in some cases correlated with population divergence. In sharp contrast, F₂ hybrids had a decrease in fitness and an increase in variance that both corresponded to population divergence. Genetic interpretation of these patterns suggests that both the beneficial effects of dominance and the detrimental effects of breaking up coadaptation are magnified by increasing evolutionary distance between populations. Because there is no recombination in T. californicus females, effects of recombination can be assessed by comparing F₁ hybrid males and females backcrossed to parentals. Both recombinant and nonrecombinant backcross hybrids showed a decline in fitness correlated with population divergence, indicating that segregation among chromosomes contributes to the breakup of coadaptation. Although there was no difference in mean fitness between the two backcross types, recombinational backcrosses showed greater variance for fitness than nonrecombinational backcrosses, suggesting that the breakup of parental gene ombinations within chromosomes has both beneficial and detrimental effects.     

SEMISTERILITY IN THE INTERSPECIFIC HYBRID MELILOTUS POLONICA × M. ALBA

Jaranowski , J. K. (Coll. of Agriculture, ul. Wojska Polskiego 71c, Poznan, Poland.) Semisterility in the interspecific hybrid Melilotus polonica × M. alba. Amer. Jour. Bot. 48(1): 28–35. Illus. 1961.—Interspecific hybrids between Melilotus polonica (n = 8) and M. alba (n = 8) are readily secured. The F₁ hybrids are intermediate between the parents and partially sterile with a mean percentage of 58.8 (ranging from 46.8 to 72.6) defective pollen grains. Six bivalents and a chain or ring of 4 chromosomes occur at diakinesis and metaphase-I of microsporogenesis. A crossshaped configuration characteristic of a reciprocal translocation is present at pachytene, indicating that one of the parents is homozygous for an interchange of relatively large section between two of the members of the chromosome complex. Chromosome bridges, lagging chromosomes, movement of the univalents to the same pole and precocious division of the univalents lead to aberrant chromosome distribution during the course of meiosis. Reduction in self-fertility indicates a corresponding aberrant distribution of chromosomes during megasporogenesis. Pollen sterility in the F₂ generation ranged from 24.8% to 72.5% with a mean value of 54.6%. Two plants in the F₂ generation which had relatively low pollen sterility proved to be aneuploids (2n + 1). Meiotic irregularities in the F₂ plants were comparable to those exhibited by the F₁ plants.     

Interspecific hybrids of Antheraea roylei and A. pernyi — a cytogenetic reassessment

Summary A rare case of interspecific hybridization between the Indian oak feeding silkworm Antheraea roylei (n=31) and Chinese oak feeding silkworm A. pernyi (n=49) yielding fertile and vigorous offspring is reported. The F₁ and the backcross (A. roylei X A. pernyi X A. pernyi male individuals of the above cross and the F₂₃ and F₃₂ male offspring derived from an earlier cross between another race of A. roylei (n=30) and A. pernyi (n=49) were cytogenetically analysed in order to study their chromosome dynamics. The F₁ hybrids showed 18 trivalents and 13 bivalents in the first meiotic prophase and metaphase. The backcross individuals possessed either 9 trivalents and 31 bivalents or 49 bivalents, in Metaphase I cells. The F₂₃ and F₃₂ individuals were karyotypically alike and exhibited 49 bivalents. The following conclusions were drawn from the above observations: (a) in spite of allopatry and karyotypic divergence in number, a high degree of homology exists between the chromosomal complements of the two species; (b) A. pernyi possibly evolved from A. roylei, during the course of which 18 chromosomes of the latter underwent fission to give rise to the 36 chromosomes of the former. This is demonstrated by trivalent formation and pairing affinities in F₁ hybrids; (c) selection has favoured the elimination of large A. roylei chromosomes which participated in trivalent formation in successive generations of inbred hybrids to establish a stable Karyotype like that of A. pernyi.     

A CYTOGENETIC STUDY OF A THREE-PAIRED RACE OF HAPLOPAPPUS GRACILIS

Haplopappus gracilis (Nutt.) Gray is an aneuploid species of Compositae of wide distribution in the southwestern U.S.A. and northern Mexico. Except for 2 types of supernumeraries, cytological samples from throughout its range have regularly shown 2 pairs of chromosomes. However, recent collections from a small area in south-central Arizona had 2n = 4, 2n = 5, and 2n = 6 in the same population. The 2n = 5 plants were hybrids between the 2n = 4 and 2n = 6 types. Both natural and artificial F₁ hybrids show preferential disjunction from a trivalent and produce genetically balanced gametes with n = 2 and n = 3. In backcrosses of the F₁ to n = 2 plants, a 1:1 ratio of 2n = 4 and 2n = 5 plants was obtained. The possible mechanisms for the evolution of n = 2 from n = 3 and vice versa are discussed.     

The pattern of polytene chromosome synapsis in Drosophila species and interspecific hybrids

The pairing of polytene chromosomes was investigated in Drosophila melanogaster, Drosophila simulans and their hybrids as well as in species of the D. virilis group and in F₁ hybrids between the species of this group. The study of frequency and extent of asynapsis revealed non-random distribution along chromosome arms both in interspecific hybrids and pure Drosophila species. It is suggested that definite chromosome regions exhibiting high pairing frequency serve as initiation sites of synapsis in salivary gland chromosomes.     

UNUSUAL CYTOLOGICAL PATTERNS IN MICROSPOROGENESIS AND POLLEN DEVELOPMENT OF EVOLUTIONARY SIGNIFICANCE IN THE MIMULUS GLABRATUS COMPLEX (SCROPHULARIACEAE)

Four populations of Mimulus glabratus var. utahensis Pennell from the Great Basin and seven of M. glabratus var. fremontii (Bentham) Grant from the New Mexico–Texas–northeastern Mexico area were intercrossed and their F₁ hybrids grown. Cytology and fertility of both the parental populations and the F₁ hybrids were studied. The following cytological abnormalities were observed in microsporogenesis: cytomixis, the stretching of one or more chromosomes from cell to cell; multipolar divisions, separation of the chromosome complement into two or more parts; unequal disjunction; spontaneous polyploidization; and the production of encapsulated pollen tetrads. Typically, these abnormalities were rare or not observed in the parents, were rare in the intravarietal hybrids, but were more common in the intervarietal hybrids. They were closely associated with, in fact were the probably causes of, barriers to gene exchange between these two diploid (n = 15) varieties. Thus, the apparent causes of barriers to gene exchange in intervarietal hybrids are the likely mechanisms for the evolution of aneuploidy and polyploidy so characteristic of the rest of the Mimulus glabratus complex.     

Transmission of chromosomes through the eggs and pollen of triticale × wheat F1 hybrids

Summary The substitution patterns of rye chromosomes in hexaploid triticale × wheat F₂ hybrids, along with the transmission patterns of rye chromosomes through egg cells and pollen when several of the F₁ hybrids were test crossed to triticale and wheat were investigated. The data indicated that the rye chromosome transmission through both the egg and pollen was random in number and in composition. The test crosses suggested that it was best to use wheat pollen for the transmission of rye chromosomes through the egg cells of the F₁ hybrids and triticale egg cells for the transmission of rye chromosomes through F₁ hybrid pollen. A deviation from random segregation in the F₂ and the transmission rate was observed for rye chromosomes 1R, 4R/7R, and 6R. The transmission rates of 1R and 6R varied depending on the direction in which the cross was made. The results also indicated that there was little or no compensation between the R- and D-genomes and that the chromosomes of these two genomes appeared to be transmitted independently of each other.     

Performance of aneuploid backcross hybrids between the crop Brassica napus and its wild relative B. rapa

• Crossings between the diploid wild Brassica rapa (AA , 2n = 20) and the tetraploid cultivar B. napus (AACC , 2n = 38) can readily be made. Backcrosses to the wild B. rapa (BC ₁) produce aneuploids with variable chromosome numbers between 20 and 29. How does survival and performance relate to DNA content of plants?
• Growth of the BC ₁ plants was measured in the lab. One plant in the F₁ self‐pollinated spontaneously and produced abundant F₂ seeds that were also examined. The number of C‐chromosomes was estimated from DNA values obtained with flow cytometry.
• Average DNA value of the BC ₁ was similar to that of the parents, which shows that C‐chromosomes do not reduce success of pollen or embryos. The average DNA value in the F₂ was 13% higher than in the F₁, suggesting that extra C‐chromosomes facilitated gamete success and/or embryo survival. Under both optimal and drought stress conditions growth and survival of BC ₁ hybrids was similar to that of B. rapa . No significant correlations existed between growth or survival and DNA value.
• Aneuploid plants were not inferior under the conditions of the growth room and may persist in nature. We discuss other factors, such as herbivory, that could prevent hybrid establishment in the field.