Cytogenetics of double cross hybrids between Pennisetum americanum — P. purpureum amphiploids and P. americanum x Pennisetum squamulatum interspecific hybrids

Summary Pearl millet, Pennisetum americanum L. Leeke-napiergrass, Pennisetum purpureum Schum. amphiploids (2n=42) were crossed with pearl millet X Pennisetum squamulatum Fresen. interspecific hybrids (2n=41) to study the potential of germplasm transfer from wild Pennisetum species to pearl millet. These two interspecific hybrids were highly cross-compatible and more than two thousand trispecific progenies were produced from 17 double crosses. All doublecross hybrids were perennial and showed a wide range of morphological variations intermediate to both parents in vegetative and inflorescence characteristics. Some crosses resulted in sublethal progenies. Chromosomes paired mainly as bivalents (¯x15.88) or remained as univalents. At metaphase I, trivalents, quadrivalents, an occasional hexavalent and a high frequency of bivalents indicated some homeology among the genomes of the three species. Delayed separation of bivalents, unequal segregation of multivalents, lagging chromosomes, and chromatin bridges were observed at anaphase I. Although approximately 93% of the double-cross hybrids were male-sterile, pollen stainability in male-fertile plants ranged up to 94%. Seed set ranged from 0 to 37 seed per inflorescence in 71 plants under open-pollinated conditions. Apomictic embryo sac development was observed in double-cross progenies when crosses involved a pearl millet x P. squamulatum apomictic hybrid as pollen parent. These new double-cross hybrids may serve as bridging hybrids to transfer genes controlling apomixis and other plant characteristics from the wild Pennisetum species to pearl millet.     

Somatic hybrids between Solanum bulbocastanum and potato: a new source of resistance to late blight

 Solanum bulbocastanum, a wild, diploid (2n=2x=24) Mexican species, is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato. However this 1 EBN species is virtually impossible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum PI 245310 and the tetraploid potato line S. tuberosum PI 203900 (2n=4x=48) yielded hexaploid (2n= 6x=72) somatic hybrids that retained the high resistance of the S. bulbocastanum parent. RFLP and RAPD analyses confirmed the hybridity of the materials. Four of the somatic hybrids were crossed with potato cultivars Katahdin or Atlantic. The BC₁ progeny segregated for resistance to the US8 genotype (A-2 mating type) of P. Infestans. Resistant BC₁ lines crossed with susceptible cultivars again yielded populations that segregated for resistance to the fungus. In a 1996 field-plot in Wisconsin, to which no fungicide was applied, two of the BC₁ lines, from two different somatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late-blight epidemic. In contrast, under these same conditions the cultivar Russet Burbank yielded only 0.86 kg/plant. These results indicate that effective resistance to the late-blight fungus in a sexually incompatible Solanum species can be transferred into potato breeding lines by somatic hybridization and that this resistance can then be further transmitted into potato breeding lines by sexual crossing. Received: 27 October 1997 / Accepted: 11 November 1997     

Chromosome relationships between Lolium and Festuca (Gramineae)

With a view to eclucidating chromosome relationships between Lolium perenne (Lp), L. multiflorum (Lm) and Festuca pratensis (Fp), chromosome pairing in different diploid (2n=14), auto-allotriploid (2n=3x=21), trispecific (2n=3x=21), amphidiploid (2n=4x=28) and auto-allohexaploid (2n=6x=42) hybrids between them was analysed. At all these levels of ploidy there was very good chiasmate pairing between the chromosomes of the three species and, on the whole, there was little evidence of preferential pairing of the chromosomes of a particular species in the triploid, tetraploid and hexaploid hybrids. A critical test for this also came from the synaptic ability of the chromosomes of the single genome with those of the duplicated genome in the auto-allotriploids which formed predominantly trivalents with 2, 3 or even 4 chiasmata. Moreover, the homology between the Lp and Lm chromosomes seems strong enough to pass the discrimination limits of the B-chromosomes which do not suppress homoeologous pairing in the Lp LmLm triploid and LpLm diploid hybrids. — The triploids having two genomes of a Lolium species and one of F. pratensis had some male and female fertility which suggested genetic compatibility of the parental chromosomes resulting, presumably, in compensation at the gametic level. Also, the occurrence of comparable chiasma frequencies in the auto-allotriploids and trispecific hybrids showed that they were not markedly affected whether two doses of one genome and one of the other or all the three different genomes from the three species were present. From the trend of chromosome pairing in all these hybrids it is concluded that there is little structural differentiation between the chromosomes of the three species, no effective isolation barrier to gene-flow between them, and that they are closely related phylogenetically, having possibly evolved from a common progenitor. Taxonomic revision of the two Lolium species is suggested.     

Natural hybridization of Yezo and Sakhalin spruce in central Hokkaido,revealed by DNA markers with contrasting modes of inheritance

Yezo spruce (Picea jezoensis var. jezoensis) and Sakhalin spruce (Picea glehnii) occur across Hokkaido and co‐occur in some forest habitats. This leads to the potential for natural hybridization between these two species, which has been shown to occur at low frequencies. The purpose of this study was to identify these hybrids and their possible mating patterns, using various Pinaceae DNA markers with different modes of inheritance. The markers used were maternally inherited mitochondrial DNA (mtDNA), paternally inherited chloroplast DNA (cpDNA) and biparentally inherited nuclear microsatellites (nSSRs). Seven putative natural hybrids, four artificially‐crossed F₁ hybrids, four parent plants from each species, and two artificially‐backcrossed hybrids of putative natural hybrids and their parents were analyzed using the diagnostic DNA markers developed in this study. We found Yezo spruce and Sakhalin spruce to be distinct (J and G types, respectively), and the modes of inheritance held true for the two species, as was previously reported to be the case in Pinaceae. Four of the seven putative natural hybrids harbored J‐type cpDNA, G‐type mtDNA and J/G‐type nSSRs, indicating that natural F₁ hybrids are likely to arise from a G (female) × J (male) crossing. One natural hybrid harbored G‐type cpDNA, J‐type mtDNA and J/G‐type nSSRs, which implies that hybrids produced by J (female) × G (male) crossings occur at low frequencies. The two remaining hybrids harbored J‐type cpDNA and mtDNA with either J/G or J/J‐type nSSRs, suggesting that they may be F₂ hybrids resulting from backcrossing between an F₁ hybrid and a Yezo spruce.     

Demographic aspects of interspecific hybridization

Summary A demographic study was carried out on two closely related species of the isopods Jaera (albifrons) ischiosetosa and J. (a.) albifrons and their F ₁ hybrids. The results from the 16 possible combinations of crosses have permitted an analysis of the nature of the mechanisms assuring the isolation of the species studied. Although intraspecific crosses yield an immediate success, interspecific crosses in the absence of choice of mates progress only slowly during the course of weeks. The results of both crosses between hybrids and back-crosses turn out to be intermediate between those of intra- and interspecific crosses. The hybrids of the first generation are perfectly viable and their survival curves are identical to those of the parents. The fertility of parents in intra- and interspecific crosses is comparable, with the exception of the fragility of female descendants (heterogametic sex) in one direction of crossing. The fertility of the F ₁ hybrids, however, crossed either among themselves or with their parents, is quite noticeably decreased: the time needed to double the size of the population is 2.5 times longer for the hybrids than for the parents. This hybrid breakdown completes the pre-fertilization isolating mechanisms: partial ecological isolation, and especially ethological isolation, is practically total when a choice of mates exists. The two species studied, for which demographic parameters are quite close, were raised together for ten generations and yielded only exceptional hybrids with a frequency which does not exceed that found under natural conditions.     

Physiological significance of isoprenoids and phenylpropanoids in drought response of Arundinoideae species with contrasting habitats and metabolism

Physiological, biochemical and morpho‐anatomical traits that determine the phenotypic plasticity of plants under drought were tested in two Arundinoideae with contrasting habitats, growth traits and metabolism: the fast‐growing Arundo donax, which also is a strong isoprene emitter, and the slow‐growing Hakonechloa macra that does not invest on isoprene biosynthesis. In control conditions, A. donax displayed not only higher photosynthesis but also higher concentration of carotenoids and lower phenylpropanoid content than H. macra. In drought‐stressed plants, photosynthesis was similarly inhibited in both species, but substantially recovered only in A. donax after rewatering. Decline of photochemical and biochemical parameters, increased concentration of CO₂ inside leaves, and impairment of chloroplast ultrastructure were only observed in H. macra indicating damage of photosynthetic machinery under drought. It is suggested that volatile and non‐volatile isoprenoids produced by A. donax efficiently preserve the chloroplasts from transient drought damage, while H. macra invests on phenylpropanoids that are less efficient in preserving photosynthesis but likely offer better antioxidant protection under prolonged stress.     

Physical mapping of rDNA sites in possible diploid progenitors of polyploid Festuca species

Festuca species form a polyploid series but only two of the diploid species have been firmly proposed as progenitors of any polyploid. The number and distribution of rDNA sites on the chromosomes of F. scariosa (section Scariosae) and the four diploid species that comprise section Montanae are presented with their relative DNA amounts and key morphological features. Comparisons of the results with those of some polyploid Festuca species from section Bovinae published previously indicate that F. scariosa and F. altissima could be diploid progenitors of the polyploids. It is unlikely that any one of the other three Montanae species is a progenitor of these polyploids.     

Hybrid disadvantage in the larval foraging behaviour of the two neotropical species of <Emphasis Type="Italic">Drosophila pavani</Emphasis> and <Emphasis Type="Italic">Drosophila gaucha</Emphasis>

Flies from two populations of the Chilean endemic neotropical species Drosophila pavani and two populations of its sibling species Drosophila gaucha were crossed reciprocally to obtain intra- and interspecific hybrids. The developmental pathways of locomotor activity and feeding rate were analysed for eleven of twelve possible genotype groups. The hybrids showed reduced fitness indicated by a decrease in the measured traits. Hybrid disadvantage was strongest in interspecific hybrids, especially with respect to feeding behaviour. This evidence supports the contention that D. pavani and D. gaucha have evolved different coadapted gene pools controlling the developmental pathways for behavioural traits expressed during larval foraging; but genetic divergence affecting these behaviours has also taken place between locally adapted populations within each species.     

Durum wheat as a candidate for the unknown female progenitor of bread wheat: an empirical study with a highly fertile F<Subscript>1</Subscript> hybrid with <Emphasis Type="Italic">Aegilops tauschii</Emphasis> Coss.

Hexaploid bread wheat was derived from a hybrid cross between a cultivated form of tetraploid Triticum wheat (female progenitor) and a wild diploid species, Aegilops tauschii Coss. (male progenitor). This cross produced a fertile triploid F₁ hybrid that set hexaploid seeds. The identity of the female progenitor is unknown, but various cultivated tetraploid Triticum wheats exist today. Genetic and archaeological evidence suggests that durum wheat (T. turgidum ssp. durum) may be the female progenitor. In previous studies, however, F₁ hybrids of durum wheat crossed with Ae. tauschii consistently had low levels of fertility. To establish an empirical basis for the theory of durum wheat being the female progenitor of bread wheat, we crossed a durum wheat cultivar that carries a gene for meiotic restitution with a line of Ae. tauschii. F₁ hybrids were produced without using embryo rescue techniques. These triploid F₁ hybrids were highly fertile and spontaneously set hexaploid F₂ seeds at the average selfed seedset rate of 51.5%. To the best of our knowledge, this is the first example of the production of highly fertile F₁ hybrids between durum wheat and Ae. tauschii. The F₁ and F₂ hybrids are both similar morphologically to bread wheat and have vigorous growth habits. Cytological analyses of F₁ male gametogenesis showed that meiotic restitution is responsible for the high fertility of the triploid F₁ hybrids. The implications of these findings for the origin of bread wheat are discussed.     

Daphnia Galeata × D. Longispina Hybrids in Western Norway

We describe the occurrence of D. galeata×longispina hybrids in two lakes of western Norway. Parental species and interspecific hybrids were characterised by both nuclear and mitochondrial molecular markers. In one of the populations, hybrids were shown to dominate the population over several years. A few individuals in both populations were probably not F1 hybrids, but possibly backcrosses or F2 hybrids. Most (possibly all) F1 hybrids were of D. galeata maternal origin. In addition, interspecific hybrids could be identified based on morphological characters, which were intermediate between the parental species. Interspecific hybridisation between these two species is remarkable, since they are distantly related.     

CYTOLOGICAL CHARACTERIZATION OF PREMEIOTIC VERSUS POSTMEIOTIC DEFECTS PRODUCING HYBRID MALE STERILITY AMONG SIBLING SPECIES OF THE DROSOPHILA MELANOGASTER COMPLEX

In accordance with Haldane's rule, hybridizations between species of the Drosophila simulans clade produce fertile females but sterile males. In this study, a comprehensive characterization was undertaken on the six types of F₁ males that were the result of the crosses between D. simulans, D. sechellia, and D. mauritiana. With the use of light and electron microscopy, it was shown that while each particular hybrid genotype exhibited a specific sterility phenotype, these phenotypes fell into two distinct classes. The two hybrid genotypes that possessed D. mauritiana X-chromosomes contained spermatogenic defects that caused arrests in premeiotic spermatogenic stages. The other four F₁ hybrids possessed postmeiotic spermatogenic defects. Nonsynchronous cell divisions, underdeveloped mitochondrial derivative-axonemal associations, and microtubule abnormalities were common to all of these hybrids. Each particular postmeiotically defective hybrid genotype demonstrated characteristically distinct profiles in sperm bundle number in addition to characteristic spermiogenic arrests in the furthest developed spermatids. These results in species hybrids contrast with the absence of significant differences in spermatogenic characters between species of this clade. In addition, by utilizing an attached-X cross, we investigated the influence of maternal effects and cytoplasmic factors on the sterility of D. simulans F₁ hybrids and found none. However, we discovered a strain of D. simulans (2119) that caused a large shift in sterility from postmeiotic to premeiotic when crossed to D. sechellia. This suggests that D. simulans is polymorphic for genes involving premeiotic and postmeiotic sterility and that the two types of sterilities between species may have a simple genetic basis.     

Ecophysiology of first and second generation hybrids in a natural plant hybrid zone

Hybrids between related species vary widely in relative fitness, and that fitness can depend upon the environment. We investigated aspects of physiology that might influence fitness patterns in a plant hybrid zone. Seeds of Ipomopsis aggregata, I. tenuituba, F1 hybrids, F2 hybrids, and offspring of crosses between natural hybrids were planted into the relatively mesic site of origin for I. aggregata and the drier site for natural hybrids. We measured rates of photosynthesis (A _max), transpiration (E), instantaneous (A/E) and long-term (δ¹³C) indices of water use efficiency (WUE), and leaf nitrogen and carbon. We also examined correlations of these traits with plant size. Photosynthetic rate and A/E were higher in vegetative than flowering plants. WUE varied between sites and years, but differences among genotypic classes were spatially and temporally consistent. Instantaneous WUE was higher for F1 hybrids than for the average of the parental species, thereby showing heterosis. There was no evidence of hybrid breakdown, as WUE was no different in the F2 than the average across the F1 and parental species. Nor did WUE depend on cross direction in producing F1 progeny. Carbon isotope discrimination revealed higher long-term water use efficiency in I. tenuituba than I. aggregata. Leaf nitrogen was higher in I. tenuituba than I. aggregata, and higher in offspring of natural hybrids than in the F2. Results indicate heterosis for water use efficiency, with no hybrid breakdown. Heterosis in WUE may help to explain the relatively high survival of both reciprocal F1 hybrids in dry sites within the natural hybrid zone.     

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.     

Genome relationships between Hordeum vulgare L. and H. bulbosum L.

Interrelationships between H. vulgare (2x=14) and H. bulbosum (2x=14; 4x=28) were estimated on the basis of the karyotypes and the pairing behaviour of the chromosomes in diploid, triploid and tetraploid hybrids obtained with the aid of embryo culture. — A comparison of the karyotypes of the two species revealed similarities as well as differences. It was concluded that at least 4 or more of the chromosomes were similar in morphology and probably closely related. — Diploid and tetraploid hybrids are rarely obtained and their chromosome numbers tend to be unstable whereas triploid hybrids (1 vulgare + 2 bulbosum genomes) were stable and relatively easy to produce. In the diploid hybrid only 40% of the meiotic cells contained 14 chromosomes while the numbers ranged from 7 to 16 in other cells. All hybrids exhibited pairing between the chromosomes of the two species. Diploid hybrids had a mean of 5.0 and a maximum of 7 bivalents per cell in those cells having 14 chromosomes. Triploid hybrids from crosses between 2x H. vulgare and 4x H. bulbosum exhibited a mean of 1.5 and a maximum of 5 trivalents per cell. In a hexaploid sector found following colchicine treatment of a triploid the mean frequencies of chromosome associations per cell were: 5.5_I+8.0_II+0.7_III+3.7_IV+0.3_V+0.4_VI. One unstable 27 chromosome hybrid obtained from crosses between the autotetraploid forms had a mean of 1.1 and a maximum of 4 quadrivalents per cell. The chromosome associations observed in these hybrids are consistent and are taken as evidence of homoeologous pairing between the chromosomes of the two species. Interspecific hybridization between these two species also reveals that chromosome stable hybrids are only obtained when the genomes are present in a ratio of 1 vulgare2 bulbosum. Based upon the results obtained, the possibility of transferring genetic characters from H. bulbosum into cultivated barley is discussed.     

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.     

Host range of the European,rhizome-stem feeding scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), a candidate biological control agent for giant reed,Arundo donax (Poales: Poaceae) in North America

The armored scale Rhizaspidiotus donacis (Leornardi) was evaluated as a potential biological control agent of the invasive reed grass Arundo donax in North America. No-choice tests, native range field surveys and non-target host exposures were used to determine the fundamental host range of the scale collected from Caloma, Spain and Perpignan, France. Thirty-five species, including two genotypes of A. donax and seven ecotypes of Phragmites australis, along with closely related grasses, economic grasses and habitat associates were tested. In quarantine no-choice testing using releases of 200 crawlers per plant, normal development of R. donacis was observed on A. donax and A. formosana, with very limited survival to the adult stage on Spartina alterniflora and Leptochloa spp. In follow-up studies using 1000 crawlers per plant, 10 live adult females were found on Leptochloa virgata, and one adult female on Spartina alterniflora, but average adult female abundance per plant was (2580%) 26-times lower on L. virgata and over (39,090%) 100-times lower on S. alterniflora than on A. donax. Field surveys were conducted at five locations in Spain and France at which A. donax infested with R. donacis, co-occurred with two non-target species of concern and R. donacis was only found on A. donax. Six-month field host exposures in Spain using potted Leptochloa plants entwined with heavily infested A. donax confirmed that R. donacis is specific to Arundo under field conditions. Based on our results, the scale R. donacis appears to be specific to the genus Arundo and is unlikely to harm native or cultivated plants in the Americas.     

Hybridization and introgression in a mixed population of the intertidal seaweeds Fucus evanescens and F. serratus

The introduced Fucus evanescens (hermaphroditic) and the native F. serratus (dioecious) have been in secondary contact along the Danish coast of the Kattegat Sea for 60–100 years and dioecious hybrids have been observed at Blushøj for several years. Hybridization in Fucus is unusual because it appears to always involve a hermaphroditic and a dioecious parental pair. We determined the degree and spatial patterns of introgression for 286 individuals using 10 microsatellite loci and cpDNA. Hybrids accounted for nearly 13% of the population, yet parental species were well differentiated (F_ST = 0.633). The presence of F. evanescens chloroplasts in 100% of F₁ hybrids revealed asymmetrical hybridization. Fucus evanescens cpDNA was observed in 50% of introgressed and 5.4% of pure F. serratus, but no F. serratus cpDNA was found in F. evanescens. In contrast, nuclear DNA introgression was symmetrical with an equal amount (≈1.5%) of genes introgressed into each parental species. Survivorship and viability data suggest selection against hybrids in the hybrid zone.     

Experimental interspecific hybridization in Daphnia

Hybridization is a common phenomenon in Daphnia (Cladocera; Anomopoda); interspecific hybrids have been found between several species and hybrids are found in many European lakes. Although much information on the morphology, ecology and genetics of hybrids is available, little is known about the level of reproductive isolation among species or about the relative fitness of hybrids and parental species. In order to facilitate studies on differentiation and speciation processes and comparative experimental studies on hybrids and recombinant genotypes, we present the first successful laboratory crossing experiments of two different Daphnia species, D. galeata and D. cucullata. Males and sexual females from two D. galeata and two D. cucullata clones were reciprocally crossed, juveniles hatched from resting eggs and reared until maturity. Hatching and juvenile survival rates of hybrids were relatively low (12.1% and 24%, respectively). D. galeata and D. cucullata clones vary in their level of successful interspecific matings and in the number of subsequent offspring. In general, hybrid crosses between D. cucullata females and D. galeata males were more successful than reciprocal crosses.     

Genetic interactions between wheat and rye genomes in triticale

Summary Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents and the triticale derivatives were crossed in all possible combinations within each species group. Chiasma and univalent frequency of parents and hybrids were determined. The primary triticale lines had more univalents and less chiasmata per pollen mother cell than the corresponding wheat and rye parents together. The parental wheat F₁ exhibited negative heterosis for chiasma frequency whereas all rye hybrids had much higher chiasma frequencies than their inbred parents. Triticale F₁s generally showed lower chiasma frequencies and more univalents than their parents, but the degree of pairing failure was dependent upon which of the parental species within the triticale, wheat or rye, was in the heterozygous state. F₁s with heterozygous wheat genome only showed the least reduction in chiasma number (presumably caused by gene actions within the wheat genome), while F₁s with heterozygous rye genome showed high reduction in chiasma frequency and an increase in pairing failure (induced by negative interactions between the heterozygous rye and the wheat genome in triticale). A high correlation was found between the frequency of undisturbed pollen mother cells and the frequency of aneuploids in the subsequent generation. A higher number of aneuploids occurred in those populations which were heterozygous for the rye genome.     

Hybridization and asymmetric introgression between Cypripedium tibeticum and C. yunnanense in Shangrila County,Yunnan Province,China

Hybridization and introgression are thought to be important for speciation and adaptation in many plants. However, little is known about the hybridization and introgression among Cypripedium species. To investigate the evidence for hybridization and the pattern of introgression between Cypripedium yunnanense and C. tibeticum in Shangrila County, Yunnan Province, China, morphological characters and amplified fragment length polymorphism (AFLP) data for both the species and their putative hybrids were studied. Hand pollination was also performed to verify the crossability of the putative parents. Principal coordinate analysis based on morphological characters and the AFLP data suggested that the putative hybrids were true hybrids of these two Cypripedium species. Analysis with the NewHybrids software indicated that the putative hybrids were F1 generation individuals and backcrosses to C. yunnanese, but no F2 generation was found. Analysis with the Structure software demonstrated asymmetric introgression from C. tibeticum to C. yunnanense. We conclude that natural hybridization and introgression can occur between these two species and that in situ conservation of the parental species is required before fully assessing the evolutionary potential of hybrids.