EXPERIMENTAL HYBRIDIZATION OF XANTHIUM STRUMARIUM (COMPOSITAE) FROM ASIA AND AMERICA. I. RESPONSES OF F1 HYBRIDS TO PHOTOPERIOD AND TEMPERATURE

Responses to photoperiod and temperature were compared for hybrids between Asiatic plants in the indigenous strumarium morphological complex and plants in five American complexes: oviforme, italicum, chinense, cavanillesii, and pennsylvancium. The F₁ hybrids between Hong Kong plants and various American plants showed intermediacy in photoperiodic response; however, the hybrid night requirement was more similar to that of the American parent. The Hong Kong plants are difficult to evaluate photoperiodically but showed a night length requirement of 9.25–9.50 hr. Day-neutral plants from India in the strumarium complex produced day-neutral F₁ hybrids in crosses with most American plants having night requirements less than 10 hr. The F₁ hybrids involving the day-neutral Indian plants and either Indian or Australian chinense plants showed a night requirement of 8.25–8.75 hr. The chinense parental plants had apparent critical nights of 10.25–10.50 hr. Crosses between the day-neutral Indian plants and Mexican plants with apparent critical nights of 10.75–11 hr produced F₁ hybrids requiring nights of 8.75–9.00 hr. The various hybrids tended to show the broader temperature tolerances of the American parents. The ripeness-to-flower (maturity) responses of seedlings tended to show the genetic controls of the parent with the faster developmental rate. The hybridization evidence suggests that photoperiodic responses are quantitatively controlled and inherited independently of morphology and ripeness-to-flower responses. The populations of India are highly diverse and probably reflect recombinations of photoperiodic and temperature responses between indigenous day-neutral plants and photoperiodic chinense plants introduced from North America.     

Photoperiodic reactions in conifer species

In Picea abies seedlings the critical night length for bud-set was determined for provenances from different latitudes, longitudes and altitudes within the natural range of the species. The clinal variation of this character was demonstrated. Inheritance studies indicated that this character is controlled by many genes with predominantly additive effects. In seedlings of Pinus sylvestris and Pinus contorta, growth cessation and bud-set took place in all light regimes, thus, even under continuous illumination. A photoperiodic optimum for height growth was determined. The photoperiodic influence on such characters as recurrent flushing of shoots, needle growth, dry matter production and frost resistance was demonstrated for northern and southern populations of the two Pinus species. Shorter nights were needed to induce a particular photoperiodic response in the northern populations as compared with those from the south. The importance of reliable phenological characters for assessing frost hardiness in provenance and progeny trials by means of early tests, is discussed.     

Inheritance of photoperiodic response in the bird cherry aphid, Rhopalosiphum padi

Abstract. The photoperiodic induction of presexual females (gynoparae) and males of the aphid Rhopalosiphum padi (L.) was examined in single clones collected from different latitudes (N clone from Blair Atholl, 56.5N 3.1W; C clone from Leeds, 53.5N 1.4W and S clone from Exeter, 50.4N 3.3W). Critical night lengths (CNLs) for gynopara and male production (CNLs: 50% of maximum production) and inter-clonal differences, defined by the different forms of progeny produced at a single discriminating night length (12 h 30 min), were measured at 16 ± 1C. The aphid clones differed in CNL and in the morphs produced at the discriminating night length. These differences were used to investigate the inheritance of the photoperiodic response. In crosses between clones the photoperiodic response showed considerable overall variation. The variation in CNLs indicated that the photoperiodic response was unlikely to affect the overwintering success after long-distance movement of clones from one latitude to another.     

The Cessation of Apical Growth in Latitudinal Ecotypes and Ecotype Crosses of Salix pentandra L

Apical growth cessation in seedling progenies of three latitudinalecotypes and ecotype crosses of Salix pentandra L. was investigatedunder controlled growth conditions and out-of-doors. The southernecotype (59° 40' N) was characterized by late growth cessationunder short day conditions, short critical photoperiod for growthcessation, and high light sensitivity; the northern ecotype(69° 39' N) by rapid growth cessation, long critical photoperiod,and low light sensitivity. The geographically intermediate ecotype(64° 28' N) had an intermediate photoperiodic response.The hybrid progenies were, however, closer to the southern thanto the northern parent ecotype indicating a tendency to favourinheritance of southern characters. Fluctuating temperatures(21 °C/9 °C and 18 °C/9 °C) induced growth cessationin the northern ecotype but not in the other ecotypes or ecotypecrosses with the exception of a few plants of the intermediateecotype and of two hybrid progenies. The time course of apicalgrowth cessation in various progenies grown out-of-doors at69° 39' N was similar to that observed under SD conditionsexcept that the differences between the northern ecotype andthe other ecotypes and crosses were greater.     

Sex‐linked inheritance of diapause induction in the butterfly Pieris napi

Many temperate insects survive harsh environmental conditions, such as winter, by entering a state of developmental arrest. This diapause state is predominantly induced by photoperiod. The photoperiod varies with latitude and has led to local adaptation in the photoperiodic induction of diapause in many insects. To understand the rapid evolution of the photoperiodic threshold, it is important to investigate and understand the underlying genetic mechanisms. In the present study, the genetic basis of photoperiodic diapause induction is investigated in the green‐veined white butterfly Pieris napi (Lepidoptera, Pieridae) by assaying diapause induction in a range of conditions for a Swedish and Spanish population. Furthermore, the inheritance of diapause induction is assessed in reciprocal F1 hybrids and backcrosses between the two populations. The southern population shows a clear photoperiodic threshold determining diapause or direct development, whereas the northern populations show a high incidence of diapause, regardless of photoperiod. The hybrid crosses reveal that the inheritance of diapause induction is strongly sex‐linked, and that diapause incidence in the genetic crosses is highly dependent on photoperiod. This emphasizes the importance of assaying a range of conditions in diapause inheritance studies. The results indicate a strongly heritable diapause induction with a major component on the Z‐chromosome, as well as a minor effect of the autosomal background.     

Photoperiodic control of dormancy in Sedum telephium and some other herbaceous perennial plants

The environmental control of dormancy and flowering of the herbaceous perennial Sedum telephium was studied in controlled environments. Short photoperiods induced growth cessation and the formation of resting buds in both seedlings and mature plants, whereas long photoperiods resulted in immediate growth activation of dormant buds. No chilling was required for dormancy release, even in plants induced to dormancy and maintained at high temperature (21°C) for more than 3 months. The critical photoperiod for dormancy release was about 15 h, a minimum of four long-day (LD) cycles (24 h) being required. The true photoperiodic nature of this response was ascertained by night interruption experiments. Flowering of S. telephium was found to have an obligatory LD requirement, with no requirement for vernalization. The critical photoperiod and minimum number of inductive cycles for floral induction were the same as for dormancy release. Dormancy release by long days was also obtained in preliminary experiments with three other herbaceous perennials. The eco-physiological significance of photoperiodic control of dormancy is discussed, and it is concluded that the mechanism ensures stability of winter dormancy, even under conditions of climatic warming.     

诱导小麦-天兰偃麦草-黑麦三属杂种花粉植株的研究

以法国六倍体小黑麦为母本,分别与普通小麦(Triticum aestivum)和天兰偃麦草(Elytrigia intermedia of Agropyron glaucum)的杂交后代中的中间类型3号和5号杂交。由此获得的三属杂种F_1性状介于亲本之间,兼有三属亲本类型的特征,呈中间类型。用马铃薯-Ⅱ培养基培养三属杂种F_1的花药,诱导花粉愈伤组织。将所获得的愈伤组织转入190-2培养基进行分化,已成功地诱导出一批三属间杂种花粉植株,并用Giemsa显带技术鉴定花粉植株的染色体组组成。     

Shoot Apical Meristems of Picea sitchensis Seedlings Accelerate in Growth Following Bud-set

First-year seedlings of Picea sitchensis were induced to setbuds by transferring them from long days (17 h) to short days(10 h at 20 °C, 12 h night at 12 °C). After 20 shortdays, the seedlings stopped growing in height, the shoot apicaldomes began enlarging and the transverse growth rates of theshoot apical dome tissues increased. For about 25 days thereafterprimordia were produced faster within the developing buds thanat the apices of seedlings which had been kept in long daysto prevent bud-set. Accelerated primordia production after bud-setenables the largest possible buds to be formed during the frost-freeperiod before winter. Picea sitchensis, apical meristem, bud-set     

Associations of genes encoding allozymes peroxidase and superoxide dismutase in poplar and spruce species

Summary Isozymes of peroxidase (PER) and superoxide dismutase (SOD) were analyzed in vegetative buds or very young leaves of seven species and two interspecific hybrids of Populus, in progenies of seven controlled crosses of three Populus species, and in needles of five Picea species and one putative hybrid. One to three PER, and one or two SOD zones of activity were observed. Electrophoretic mobility (EM) and banding phenotypes of isozymes of one PER locus were identical to those of one SOD locus in vegetative buds of five Populus species and hybrid. In leaves of the four Populus species and hybrid and progenies of controlled crosses, EM and phenotypes of isozymes of two PER loci were identical to those of two SOD loci. In Picea species, EM of isozymes of the only SOD locus was somewhat similar but not identical to that of one PER locus, and isozyme phenotypes of all individuals at the SOD locus were not identical to those at a PER locus. Chi-square tests verified the single-gene Mendelian control of the segregating allozyme variants at each of Per-L1 and Sod-1 in the three Populus species. The results of joint two-locus segregation tests indicated a very tight linkage and no recombination between Per-L1 and Sod-1 in three Populus species. Genes coding for isozymes of one or two PER loci are either presumably the same as, or very tightly linked to, the genes coding for isozymes of one or two SOD loci in the Populus species.     

Inheritance patterns of photoperiodic diapause induction in Leptinotarsa decemlineata

Photoperiod is a reliable indicator of season and an important cue that many insects use for phenological synchronization. Undergoing range expansion insects can face a change in the local photoperiod to which they need to resynchronize. Rapid range expansion can be associated with rapid photoperiodic adaptation, which can be associated with intense selection on strongly heritable polygenic traits. Alternatively, it is proposed that, in insects with an XO sex‐determination system, genes with large effect residing on the sex chromosome could drive photoperiodic adaptation because the gene or genes are exposed to selection in the sex carrying only a single X‐chromosome. The present study seeks to understand which of these alternatives more likely explains the rapid photoperiodic adaptation in European Colorado potato beetles Leptinotarsa decemlineata Say. Diapause induction is assessed in beetles from a northern and a southern population, as well as from reciprocal hybrid crosses between the northern and southern population, when reared at an intermediate length photoperiod. The crosses within population display the expected responses, with the northern and southern populations showing high and low diapause propensity, respectively. The hybrids show intermediate responses in all studied traits. No clear difference in the responses in hybrids depending on the latitudinal origin of their father or mother is detected, even though partial paternal line dominance is seen in the responses of male beetles in one hybrid cross. These results therefore indicate that, in L. decemlineata, photoperiodic diapause induction is strongly heritable, and has an additive polygenic autosomal background.     

Inheritance of photoperiodic induction of larval diapause in the Asian corn borer Ostrinia furnacalis

The Asian corn borer Ostrinia furnacalis (Guenée) enters facultative diapause as fully‐developed larvae in response to short‐day conditions. As a consequence of geographical variation in photoperiodic response, moths from Nanchang (28°46′N, 115°50′E) enter diapause in response to short day‐lengths (D strain), even at the high temperatures whereas moths from Ledong (18°47′N, 108°89′E) exhibit almost no diapause under the same conditions (N strain). In the present study, crosses between the two strains are used to evaluate the inheritance of diapause under different photoperiods at temperatures of 22, 25 and 28 °C. The moths, both reciprocal crosses and backcrosses, show a clear long‐day response, similar to that of the D strain, suggesting that the photoperiodic response controlling diapause in this moth is heritable. However, the critical day‐length for induction of diapause is shorter in hybrids than in the D strain. The N strain also shows a short‐day photoperiodic response at the lower temperature of 22 °C, indicating that the N strain still has the capacity to enter a photoperiodically‐induced diapause, depending on the rearing temperature. The incidence of diapause in all crosses is highest with D strain fathers or grandfathers and lowest with N strain fathers or grandfathers, indicating that the male parent has significantly more influence on the incidence of diapause of subsequent progeny than the female. The results obtained from all crosses under LD 12 : 12 h or LD 13 : 11 h photocycles at 25 °C show that inheritance of diapause in O. furnacalis does not fit an additive hypothesis and that the capacity for diapause is transmitted genetically in the manner of incomplete dominance.     

Influence of the female flowering environment on autumn frost-hardiness of Picea abies progenies

Two experiments were designed to test possible effects of photoperiod and temperature during microsporogensis to anthesis on early autumn frost-hardiness of Picea abies progenies. Pollen lots were produced in phytotron rooms and used in crosses in a seed orchard. No biologically important differences in progeny performance were evident either between high and low temperature or between long and short-day treatments, and no significant interaction between photoperiod and temperature was found. In a third experiment, however, an effect of the environment during female flowering was obtained. Crosses performed in early spring (March) inside a heated greenhouse (short day, high temperature) produced progenies which were less hardy than their full-sibs reproduced from crosses indoors (long day, high temperature) and outdoors (long day, low temperature) in May. The most hardy siblings originated from the late-spring outdoor crosses. These results indicate that some stages in reproduction during female flowering, such as female meiosis, pollen tube growth, syngamy, early embryogenesis and embryo competition, may be sensitive to temperature and/or photoperiodic signals which can be transmitted to the progeny. We suspect that the altered performance of the progenies could be due to an activation of a regulatory mechanism affecting the expression of genes controlling adaptive traits. Both the present and earlier results have implications for the genetic interpretation of provenance differences in Norway spruce.     

Dormancy release in beech buds (Fagus sylvatica) requires both chilling and long days

Chilling and daylength requirements for dormancy release and budburst in dormant beech ( Fagus sylvatica L.) buds have been studied in cuttings flushing in controlled environments after different durations of outdoor chilling. Non-chilled buds sampled in mid October required long days (LD) only for budburst. Buds chilled until March still required LD for normal budburst, whereas buds sampled in November and December were unable to sprout regardless of daylength conditions and would do so only after a substantial period of chilling. Four ecotypes of distant latitudinal and altitudinal origin responded very similarly with a typical quantitative photoperiodic response. In fully chilled shoots sampled in March only 13 to 40% budburst took place in 8-h SD and only after three times as long time as in continuous light. It is concluded that this dual dormancy control system ensures optimum winter stability in trees under conditions of climatic warming. In the closely related Carpinus betulus L. budburst was unaffected by daylength.     

Investigating Incipient Speciation in Arabidopsis lyrata from Patterns of Transmission Ratio Distortion

Our understanding of the development of intrinsic reproductive isolation is still largely based on theoretical models and thorough empirical studies on a small number of species. Theory suggests that reproductive isolation develops through accumulation of epistatic genic incompatibilities, also known as Bateson–Dobzhansky–Muller (BDM) incompatibilities. We can detect these from marker transmission ratio distortion (TRD) in hybrid progenies of crosses between species or populations, where TRD is expected to result from selection against heterospecific allele combinations in hybrids. TRD may also manifest itself because of intragenomic conflicts or competition between gametes or zygotes. We studied early stage speciation in Arabidopsis lyrata by investigating patterns of TRD across the genome in F₂ progenies of three reciprocal crosses between four natural populations. We found that the degree of TRD increases with genetic distance between crossed populations, but also that reciprocal progenies may differ substantially in their degree of TRD. Chromosomes AL6 and especially AL1 appear to be involved in many single- and two-locus distortions, but the location and source of TRD vary between crosses and between reciprocal progenies. We also found that the majority of single- and two-locus TRD appears to have a gametic, as opposed to zygotic, origin. Thus, while theory on BDM incompatibilities is typically illustrated with derived nuclear alleles proving incompatible in hybrid zygotes, our results suggest a prominent role for distortions emerging before zygote formation.     

The Application of Fluorescence In Situ Hybridization in Different Ploidy Levels Cross-Breeding of Lily

21 crossing were conducted between Asiatic Lily with different ploidy levels, the results showed that the interploidy hybridization between diploid and tetraploid lilies was not as successful as intraploidy hybridization. Regardless of male sterility, triploid lilies could be used as female parents in the hybridization which the progenies were aneuploidy. 3x×4x crosses could be cultured more successfully than 3x×2x crosses. 45S rDNA was mapped on the chromosomes of seven Lilium species and their progenies using fluorescence in situ hybridization (FISH). FISH revealed six to sixteen 45S rDNA gene loci, and normally the sites were not in pairs. The asymmetry indexes of LA (Longiflorum hybrids × Asiatic hybrids) hybrids was higher than Asiatic hybrids, the evolution degree was LA hybrids > Asiatic hybrids. 45S rDNA distributed variably on chromosome 1-10 and 12 among Asiatic hybrids. Chromosome 1 had invariable sites of 45S rDNA in all Asiatic hybrids, which could be considered as the characteristic of Asiatic hybrids. LA hybrid ‘Freya’ had two sites of 45S rDNA on one homologous chromosome 5, and also it could be found in the progenies. The karyotype and fluorescence in situ hybridization with 45S rDNA as probe were applied to identify the different genotypes of 9 hybrids. Typical chromosomes with parental signal sites could be observed in all the genotypes of hybrids, it was confirmed that all the hybrids were true.     

Genetic information from progeny trials: a comparison between progenies generated by open pollination and by controlled crosses

When conifer progenies generated by open pollination are assessed in field tests, it is usually assumed that all progenies of the same mother are true half-sibs. This assumption may be invalid, leading to overestimation of additive genetic variation and heritability and to biased breeding values. From one Scots pine (Pinus sylvestris) and one Norway spruce (Picea abies) seed orchard, containing 28 and 36 parent clones, respectively, progenies generated by open pollination (OP) and by controlled crosses (CC) were planted in adjacent trials at two to three sites in southern Sweden. The tree height and diameter at breast height were measured, and genetic parameters based on these traits were estimated for OP and CC progenies separately, in order to enable comparisons. Narrow-sense heritability estimates for Scots pine and Norway spruce OP progenies (in the ranges 0.04–0.13 and 0.15–0.38, respectively) did not differ significantly from CC estimates (0.07–0.12 and 0.23–0.30), suggesting that OP-based heritability values were not overestimated to any great extent. Similarly, genetic correlations between OP and CC progenies were in the ranges of 0.87–0.88 and 0.74–0.77 for Scots pine and Norway spruce, respectively, being significantly lower than unity only in the case of Norway spruce. OP-based breeding values for both species should therefore correspond well with those predicted from CC progenies, albeit not perfectly for Norway spruce. In conclusion, the assumption of true half-sibs for OP progenies was not violated to the extent that genetic parameter estimates or breeding value predictions were seriously biased.     

TEMPERATURE EFFECTS AND GENOTYPE-BY-ENVIRONMENT INTERACTIONS IN HYBRIDS: HALDANE'S RULE IN FLOUR BEETLES

When males of the flour beetle, Tribolium castaneum, are crossed to females of its close relative T. freemani, the sex ratio of the hybrids is female biased, owing in part to hybrid male mortality. Morphological abnormalities are also frequent in the surviving hybrid males, but not in the hybrid females. The finding that the heterogametic sex (male) is more adversely affected in interspecific crosses than the homogametic sex is consistent with Haldane's rule, which predicts that hybrid dysfunction should emerge as an indirect byproduct of divergent adaptation to differing environments. If so, environmental effects and genotype-by-environment interactions (GEI) should characterize the expression of Haldane's rule and interspecific hybrid traits in general. We used two wild-collected populations of T. castaneum (from Infantes, Spain, and Madagascar) to investigate the effects of environmental variation on the expression of Haldane's rule. Males from each population were mated to several T. freemani females and the half-sibling hybrid progenies were reared across a series of temperature regimes. For both populations, we found that hybrids raised at higher temperatures exhibited a more extreme expression of Haldane's rule: The hybrid sex ratios were more biased toward females and hybrid males had a much higher incidence of morphological abnormalities. The average response to temperature, the norm of reaction for Haldane's rule, varied between the two populations, and we found considerable and significant GEI for both hybrid traits within both populations. The evolutionary implications of these findings are discussed in the context of speciation arising as an indirect effect of local adaptation.     

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.     

Inheritance of the photoperiodic response controlling imaginal summer diapause in the cabbage beetle, Colaphellus bowringi

Adults of the cabbage beetle Colaphellus bowringi display a summer diapause in response to the exposure of their larvae to long photoperiods. In the present study, the inheritance of the photoperiodic response controlling summer diapause in C. bowringi by crossing a high diapause strain (D strain) with a laboratory selected nondiapause strain (N strain) was investigated under different photoperiods at 22, 25 and 28 °C. The beetles in both reciprocal crosses and backcrosses showed a clear short-day response for the induction of diapause at all temperatures, similar to that of the D strain, suggesting that photoperiodic response of this beetle is heritable. The diapause incidences in the progeny from all the crosses under LD 15:9 or LD 12:12 at 25 °C suggest that genetic and genetic-environmental interactions are involved in diapause induction. The incidence of diapauses in F₁ progeny was significantly lower than that in the D × D strain but significantly higher than that in the N × N strain, indicating that the diapause capability is inherited in an incomplete dominant manner. The incidence of diapause was greater among the offspring of hybrid females when those females had a D strain mother or grandmother rather than a N strain mother or grandmother, indicating that maternal effects on diapause induction are stronger than paternal effects. The laboratory selected nondiapause strain also showed a short-day photoperiodic response at a low temperature of 22 °C, indicating that the photoperiodic photoreceptor and photoperiodic clock still function in the nondiapause strain.     

The behaviour and coupling of the photoreceptor and hour-glass photoperiod timer at low temperature in the aphid Megoura viciae

In Megoura viciae photoperiodic time is measured during the scotophase by an hour-glass mechanism which is temperature compensated within the range 6–20°C. At lower temperatures the clock “loses time”, running at about half the normal rate at 0°C. The present experiments, based on the analysis of critical night lengths, showed that for short periods of scotophase chilling (4h or less) the same diminished rate is maintained irrespective of the position of the low temperature period within the scotophase. This occurs despite the known changes in spectral sensitivity of the photoreceptor. With longer periods of chilling (>6h) a normal critical response was not observed unless several hours of darkness intervened between the end of the chilling period and the temperature-modified critical night length. This is interpreted as a “recovery” process involving the photoreceptor but not the hour-glass. Additional data indicated that the sequence of changes in the photoreceptor, including the early resetting phase, is closely coupled to the progression of the timer even when photosensitivity is temporarily impaired by low temperature.