Production,morphology, and cytogenetic analysis of Elymus caninus (Agropyron caninum) x Triticum aestivum F1 hybrids and backcross-1 derivatives

Summary Intergeneric hybrids were produced between common wheat, Triticum aestivum (2n=6x=42, AABBDD) and wheatgrass, Etymus caninus (Agropyron caninum) (2n=4x=28, SSHH) — the first successful report of this cross. Reciprocal crosses and genotypes differed for percent seed set, seed development and F₁ hybrid plant production. With E. caninus as the pollen parent, there was no hybrid seed set. In the reciprocal cross, seed set was 23.1–25.4% depending upon wheat genotype used. Hybrid plants were produced only by rescuing embryos 12–13 days post pollination with cv Chinese Spring as the wheat parent. Kinetin in the medium facilitated embryo germination but inhibited root development and seedling growth. The hybrids were vigorous, self sterile, and intermediate between parents. These had expected chromosome number (2n=5x=35, ABDSH), very little chromosome pairing (0.51 II, 0.04 III) and some secondary associations. The hybrids were successfully backcrossed with wheat. Chromosome number in the BC₁ derivatives varied 54–58 with 56 as the modal class. The BC₁ derivatives showed unusually high number of rod bivalents or reduced pairing of wheat homologues. These were sterile and BC₂ seed was produced using wheat pollen.     

Quantitative genetics of growth and development in Populus. I. A three-generation comparison of tree architecture during the first 2 years of growth

One approach to gain an insight into the genetics of tree architecture is to make use of morphologically divergent parents and study their segregating progeny in the F₂ and backcross (B₁) generations. This approach was chosen in the present study in which material of a three-generation pedigree growing side by side in a replicated plantation, was analyzed. The pedigree included Populus trichocarpa (T) and P. deltoides (D) parents, their F₁ and F₂ hybrids and their B₁ hybrids to the D parent. The trees were grown in the environment of the T parent and measured for the first 2 years of growth. Nine quantitative traits were studied at the stem, branch and leaf levels of tree architecture, in which the original parents differed. Strong F₁ hybrid vigor relative to the better parent (T) was expressed in growth and its components. Most quantitative traits in the F₂ and B₁ hybrids were intermediate between the T and D parents but displayed a wide range of variation due to segregation. The results from the analysis of variance indicated that all morphometric traits were significantly different among F₂ and B₁ clones, but the B₁ hybrids were more sensitive to replicates than the F₂. Broad-sense heritabilities (H ²) based on clonal means ranged from moderately high to high (0.50–0.90) for the traits studied, with H ² values varying over age. The H ² estimates reflected greater environmental noise in the B₁ than in the F₂, presumably due to the greater proportion of maladaptive D alleles in those hybrids. In both families, sylleptic branch number and length, and leaf size on the terminal, showed strong genetic correlations with stem growth. The large divergence between the two original parents in the traits studied, combined with the high chromosome number in Populus (2n=38), makes this pedigree well suited for the estimation of the number of quantitative trait loci (QTLs) underlying quantitative variation by Wright's biometric method (1968). Variation in several traits was found to be under the control of surprisingly few major QTLs: 3–4 in 2nd-year height and diameter growth, a single QTL in stem diameter/height ratio.     

Physiological root responses of iron deficiency susceptible and tolerant tomato genotypes and their reciprocal F1 hybrids

By using two tomato genotypes line 227/1 (Fe chlorosis susceptible) and Roza (Fe chlorosis tolerant) and their reciprocal F₁hybrid, some root morphological changes, pH changes of nutrient solution, reduction capacity of Fe^III and uptake and root-to-shoot translocation of ⁵⁹Fe were studied under controlled environmental conditions in nutrient solution with 3 different Fe supplies as Fe EDDHA (i.e., 10^–7 M, severe Fe deficiency; 10^–6 M, intermediate Fe deficiency; 10^–4 M, adequate Fe supply). Tolerant parent `Roza' was less affected by low Fe supply than susceptible parent `line 227/1' as judged from the severity of leaf chlorosis. Under both Fe deficient conditions there were no differences between the reciprocal hybrids concerning the appearance of chlorosis. Under intermediate Fe deficiency, reciprocal F₁ hybrids (`line 227/1 × Roza' and `Roza × line' 227/1) showed an intermediate chlorosis between tolerant and susceptible parents. However, under severe Fe deficiency the reciprocal hybrids were more chlorotic than the tolerant parent irrespective of which parent was the cytoplasm contributor. A decreased Fe supply during preculture enhanced Fe^III reduction capacities of the parents and reciprocal hybrids. Differences in the tolerance to Fe deficiency always were better correlated with Fe^III reduction capacity of the genotypes than the Fe deficiency-induced release of H⁺ ions. Under both Fe deficient conditions the tolerant parent Roza had a much higher Fe^III reduction capacity than the susceptible parent line 227/1. The reduction capacity of the hybrids `Roza × line 227/1' was very similar to the capacity of the parent Roza, but higher than the capacity of the hybrids `line 227/1×Roza' at both Fe-deficient conditions. Under both Fe deficient conditions tolerant parent had higher number of lateral roots than the susceptible parent. Among the reciprocal hybrids `Roza × line 227/1' possessed more lateral roots than the `line 227/1 × Roza' under both Fe deficient conditions. Low Fe nutritional status resulted in marked increase in root uptake of ⁵⁹Fe. At adequate Fe supply, reciprocal hybrids and their parents did not differ in uptake and root-to-shoot translocation of Fe. However, under Fe-deficient conditions uptake and root-to-shoot translocation of ⁵⁹Fe were significantly higher in the Fe chlorosis tolerant than the susceptible parent. Based on the reduction capacity of Fe^III and uptake and root-to-shoot translocation of Fe, the F₁ hybrids obtained from the cross in which the maternal genotype was Roza appeared to be more tolerant than when the maternal genotype was the susceptible line 227/1. Uptake and translocation ratio of the F₁ hybrids obtained from `Roza × line 227/1' were similar to those of the parent Roza, but higher than the F<sub>1</sub> hybrids obtained from `line 227/1 × Roza', particularly under intermediate Fe deficiency. The results indicate that Fe^III reduction show a better relationship to Fe efficiency than Fe deficiency induced release of H⁺ ions. The inheritance of Fe deficiency tolerance of Roza seems not to be simple monogenic. It might be characterised by both, nuclear and extranuclear heredity. The intermediate responses of the reciprocal hybrids of the `line 227/1 × Roza' indicates that the Fe deficiency tolerance character of Roza is transferable by nuclear heredity. The better responses of the hybrids of `Roza × line 227/1' than the hybrids of `line 227/1 × Roza' may be due to maternal transmission from the parent Roza besides the nuclear transmission.     

Procedures for identifying S-allele genotypes of Brassica

Summary Procedures are described for efficient selection of: (1) homozygous and heterozygous S-allele genotypes; (2) homozygous inbreds with the strong self- and sib-incompatibility required for effective seed production of single-cross F₁ hybrids; (3) heterozygous genotypes with the high self- and sib-incompatibility required for effective seed production of 3- and 4-way hybrids.From reciprocal crosses between two first generation inbred (I₁) plants there are three potential results: both crosses are incompatible; one is incompatible and the other compatible; and both are compatible. Incompatibility of both crosses is useful information only when combined with data from other reciprocal crosses. Each compatible cross, depending on whether its reciprocal is incompatible or compatible, dictates alternative reasoning and additional reciprocal crosses for efficiently and simultaneously identifying: (A) the S-allele genotype of all individual I₁ plants, and (B) the expressions of dominance or codominance in pollen and stigma (sexual organs) of an S-allele heterozygous genotype. Reciprocal crosses provide the only efficient means of identifying S-allele genotypes and also the sexual-organ x S-allele-interaction types.Fluorescent microscope assay of pollen tube penetration into the style facilitates quantitation within 24–48 hours of incompatibility and compatibility of the reciprocal crosses. A procedure for quantitating the reciprocal difference is described that maximizes informational content of the data about interactions between S alleles in pollen and stigma of the S-allele-heterozygous genotype.Use of the non-inbred I_o generation parent as a known heterozygous S-allele genotype in crosses with its first generation selfed (I₁) progeny usually reduces at least 7 fold the effort required for achieving objectives 1, 2, and 3, compared to the method of making reciprocal crosses only among I₁ plants.Identifying the heterozygous and both homozygous S-allele genotypes during the I₁ generation facilitates, during subsequent inbred generations, strong selection for or against modifier genes that influence the intensity of self- and sib-incompatibility. Selection for strong self and sib incompatibility can be effective for both homozygous inbreds and also for the S-allele heterozygote, thus facilitating production of single-cross F₁ hybrids and also of 3-and 4-way hybrids.Department of Plant Breeding and Biometry paper No. 690     

Successful crosses between Festuca arundinacea Schreb. and Dactylis glomerata L.

Summary Five F₁ plants have been obtained after extensive crossing between different ecotypes or varieties of Festuca arundinacea Schreb. and Dactylis glomerata L. The success did not appear to depend on specific treatments (spraying with -aminocaproic acid or gibberellic acid or pre-pollination with killed pollen from the seed parent), but the crossability is limited to exceptional plants.F₁ hybrids showed characteristics of both the parents. In four hybrids various developmental disturbances were observed (low viability, aneusomaty, absence of development of inflorescences). Only one hybrid consistently showed 2n=35 chromosomes, good viability and growth, however, it was sterile. After clonal propagation, attempts for polyploidization were started.     

The genetic basis of host range inHeliothis virescens: larval survival and growth

Larval feeding was assayed in a generalist caterpillar (Heliothis virescens (F.)), a specialist caterpillar (Heliothis subflexa (Gn.)), their F₁ hybrids and a backcross withH. s. to gain a preliminary understanding of the genetic basis of host use inH. v. Plants used in these experiments were tobacco (Nicotiana tabaccum), cotton (Gossypium hirsutum), soybean (Glycine max) (hosts ofH. v.) and ground cherry (Physalis pubescens) (host ofH.s.). A feeding study ofH.v., H.s. and their reciprocal hybrids showed that, after the first eight days of feeding,H.v. had its highest survival and weight gain on soybean and had lowest survival and weight gain on its non-host,Physalis. H.s. had its highest survival and weight gain on its host plant,Physalis, and performed very poorly on the three non-host plants. The two F₁ hybrids were SV₀ (offspring ofH.s. female andH.v. male) and VS₀ (offspring ofH.v. female andH.s. male). The hybrids did not differ from each other, indicating no sex linkage or maternal effects, except that VS₀ had greater weight gain on tobacco than did SV₀. The hybrids, unlike their parents, survived well on all four host plants and their weight gain was intermediate on all four host plants. In a separate experiment the VS₀ hybrid was mated to the specialist to produce the VS₁ backcross. In contrast to the F₁, the backcross had significantly lower survival than the generalist on soybean, cotton, tobacco and weight gain was lower on soybean, cotton and tobacco but higher onPhysalis. Survival and weight gain on cotton and tobacco were inherited as partially dominant traits; onPhysalis there was overdominance for survival and complete dominance for weight gain; on soybean both survival and weight gain were additive. Survival on cotton,Physalis, soybean and tobacco and weight gain onPhysalis could not be completely explained by a model that included only dominance and additive effects. These traits may be influenced by epistatic and/or environmental effects.     

Inheritance of seed weight in Cucumis sativus (L.) var. sativus and var. hardwickii (Royle) Kitamura

Summary A series of experiments was conducted to determine the inheritance of seed weight in cucumber. Matings between a Cucumis sativus var. sativus (Cs) L. inbred line (USDA WI 1606; P₁) and a C. sativus var. hardwickii (Royle) Kitamura (Ch) collection (PI 215589; P₂) were made to produce seed of reciprocal F₁, F₂, and BC₁ families. Families were grown under field and greenhouse conditions, and seeds were extracted from fruit 55 to 60 days post-pollination. Seed of F₁ and F₂ families was obtained using the Cs inbred WI2808 (P₁₂) and the Ch collection LJ 90430 (P₁₀), and seed of F₁ families were produced using a North Carolina Design II mating scheme in which three Cs (P₃= GY-14; P₄=WI 1379; P₅=WI 1909) inbreds were used as maternal parents and seven Ch collections (P₂; P₆= PI462369; P₇=486336; P₈=LJ91176; P₉=273469; P₁₀= 2590430; P₁₁=PI187367) were used as paternal parents. Mean seed weights of F₁ progeny reflected the dominance of genes of the C. sativus var. sativus parent. Transformation to number of seeds per unit weight resulted in increased variance homogeneity within generations and a broad-sense heritability ranging between 26% to 56%. Additive and dominance effects were important in the expression of seed weight in P₁×P₂ progeny produced in the greenhouse and additive effects were important in field grown progeny resulting from P₁×P₂ and P₁₀×P₁₂ matings. The estimated number of factors or loci involved ranged between 10 to 13, depending on the method of calculation.     

Hybridization and fertility of hybrid derivatives of Solatium melongena L. and Solanum macrocarpon L.

Summary Eleven genotypes of Solanum melongena L. and one genotype tentatively identified as Solanum macrocarpon were reciprocally intercrossed. Three patterns of the crossability were determined: a) reciprocally crossable, b) reciprocally non-crossable, and c) unidirectionally crossable. In toto 524 F₁ interspecific hybrids were grown during one season under open pollination conditions in the field. A large proportion of the F₁ hybrids produced seed set. The highest degree of seed set was recorded in the reciprocal F₁ hybrid of S. melongena (cv. Burpee Hybrid) and S. macrocarpon (Acc. 21–73). In addition, a limited number of back-cross progeny have been produced. The germinating seeds produced an F₂ generation of which some recombinants showed a considerably higher degree of fertility than the F₁. This finding suggests the possibility of the transfer of genes for resistance to two-spotted spider mite from S. macrocarpon to S. melongena.This research was performed as part of NJAES Project No. 99201 (NE-9) supported by the New Jersey Agricultural Experiment Station and Regional Hatch Funds. Paper of the Journal Series of the New Jersey Agricultural Experiment Station. Please address reprint requests to Dr. C. Boyer     

Growth performance of hybrid families by crossing selfed lines of Betula pendula Roth

Hybrid breeding is an effective approach in many agricultural crops. In allogamous tree species severe inbreeding depression and long reproductive cycles generally prohibit its use. However, three generations of selfing in silver birch (Betula pendula Roth) were obtained by forcing trees to flowering under greenhouse conditions. Hybrids were produced by crossing first-, second and third-generation selfed lines. The effects of different levels of parental inbreeding on the growth performance of hybrid families were observed in a 9-year-old field progeny test. Also, provenance crosses were carried out between selfed lines from different parts of Finland and several other European countries. Observations of growth performance of the provenance hybrids were made in the same trial. The results indicated that the mean stem volumes were significantly different between classes of parental in breeding coefficients (F_P) (P<0.0001), and were positively correlated with F_P (r=0.9106, P<0.05). Within-family variation of the hybrid families decreased with an increase of F_P. The performance of the provenance crosses between parents at a relatively close distance did not depart significantly from the standard controls. However, when the cross distance was extended far to the south, hybrids grew faster, indicating either higher heterozygosity or an extended growth period.     

Genetic control of seed proteins in wheat

Summary Electrophoretic profiles of crude protein extracts from seed of F₁ hybrids and reciprocal crosses among diploid, tetraploid and hexaploid wheats were compared with those of their respective parental species. The electrophoretic patterns within each of three pairs of reciprocal crosses, T.boeoticum X T.urartu, T.monococcun X T. urartu and T.dicoccum X T. araraticum, were different from one another but were identical with those of their respective maternal parents. Protein bands characteristic of the paternal parents were missing in F₁ hybrid seed suggesting that the major seed proteins in wheat were presumably regulated by genotype of the maternal parent rather than by the seed genotype. However, in another three pairs of reciprocal crosses, T.boeoticum X T. durum, T.dicoccum X T.aestivum and T. zhukovskyi x T. aestivum, protein bands attributable to the paternal parents were present in the F₁ hybrid seeds indicating that the seed proteins were not always exclusively regulated by the maternal genotype. The expression of paternal genomes is presumably determined by dosage and genetic affinity of the maternal and paternal genomes in the hybrid endosperm. The maternal regulation of seed protein content is probably accomplished through the maternal control over seed size. The seed protein quality may, however, depend upon the extent of expression of the paternal genome.     

Crossing experiments of lettuce cultivars and species (Lactuca sect.Lactuca,Compositae)

The degree of relationships withinLactuca sativa and three wild relativesL. serriola, L. saligna, andL. virosa was studied by observing the performance, vigour and fertility of the F 1 hybrids obtained from crosses made in and between the four species. The crosses ofL. saligna ×L. virosa and the reciprocal crosses produced no hybrids.L. saligna andL. virosa are the least related of the four species.L. sativa ×L. serriola and the reciprocal crosses were successful and produced fertile hybrids These two species are genetically very closely related.L. saligna is known to produce, as a female parent, hybrids withL. sativa andL. serriola. Now the reciprocal cross was successful for the first time, so the unability to obtain hybrids in the past was based on the choice of accessions and not caused by unilateral incompatibility.L. virosa ×L. sativa and the reciprocal combination produced hybrids. The combinationL. serriola ×L. virosa produced hybrids with very limited fertility. In contrast to earlier reports (sterile hybrids) one combination of the reciprocal cross too produced hybrids with very limited fertility.—Some of theL. saligna ×L. sativa (and reciprocal) hybrids were found to look strikingly likeL. serriola. This adds evidence for the descent ofL. serriola andL. sativa:L. saligna also made part of the ancestral complex of the cultivated lettuce.     

Behavioral and electrophysiological responses of Helicoverpa assulta, H. armigera (Lepidoptera: Noctuidae), their F1 hybrids and backcross progenies to sex pheromone component blends

Two sibling species, Helicoverpa assulta and Helicoverpa armigera both use (Z)-9-hexadecenal and (Z)-11-hexadecenal as their sex pheromone components but in almost reversed ratios, 93:7 and 3:97, respectively. H. assulta and H. armigera males performed upwind flight in response to the H. assulta sex pheromone blend (93:7). H. armigera responded strongly to the H. armigera blend (3:97), whereas H. assulta males remained inactive upon exposure to this blend. Both species gave clear dose-dependent electrophysiological responses to (Z)-11-hexadecenal. However, (Z)-9-hexadecenal evoked strong dose-dependent electrophysiological responses in H. assulta males but not in H. armigera. The two male F₁ hybrids exhibited similar behavioral responses to two sex pheromone blends and electrophysiological responses to two pheromone components as H. armigera males. This indicated that H. armigera genes appear dominant in determining the behavioral response and electrophysiological responses. Behavioral and electrophysiological responses of backcrosses of male F₁ hybrids (H. armigera female × H. assulta male) with female H. assulta and H. armigera were close to that of H. assulta and H. armigera, respectively. However, backcrosses of female F₁ hybrids (H. assulta female × H. armigera male) with male H. assulta and H. armigera showed reduced behavioral responses but normal electrophysiological responses compared to males of the respective parental line.     

Natural hybridization between an outcrossing and a selfingPhlox (Polemoniaceae): The maternal species of F1 hybrids

Natural F₁ hybrids between the outcrossingPhlox drummondii and the predominantly selfingP. cuspidata were examined to ascertain the proportion of hybrid individuals mothered by each species. Species-specific restriction fragment patterns (both nrDNA and cpDNA) were established as markers, and synthetic hybrids of known parentage were utilized to determine that the chloroplast genome is maternally inherited. Of 89 mature natural hybrids examined, approximately two thirds were mothered byP. drummondii, the outcrosser. That the outcrosser should mother most hybrids is expected since it is dependent upon incoming pollen for fertilization, and hybrids may result when heterospecific pollen is received. The fact that the highly selfingP. cuspidata mothered nearly one third of the hybrids is surprising, and may be related to both pre-zygotic and post-zygotic factors. Which species mothers hybrids has important implications for the potential for introgression as well as its direction.     

New hybrids between Agropyron and wheat

Summary Intergeneric hybrids of Triticum aestivum (2n=42,AABBDD) with Agropyron ciliare (2n= 28,SSYY), A. trachycaulum (2n=28,SSHH), A. yezoense (2n=28,SSYY) and A. scirpeum (2n=28) are reported for the first time. F₁ hybrids of T. aestivum were also produced with A. intermedium (2n=42,E₁E₁E₂E₂Z₁Z₁) and A. junceum (2n=14,JuJu). All wheat-Agropyron hybrids were obtained by embryo rescue technique. Cultivars and reciprocal crosses differed for seed set, seed development and F₁ plant production. The F₁ hybrids were sterile. Attempts to obtain amphiploids were unsuccessful. However, backcross derivatives were obtained with wheat as the recurrent parent.The level of chromosome pairing in A. trachycaulum x wheat, A. yezoense x wheat and wheat x A. junceum hybrids provided no evidence of homologous or homoeologous pairing. Mean pairing frequencies in A. ciliare x wheat, wheat x A. scirpeum and wheat x A. intermedium hybrids indicated homoeologous or autosyndetic pairing. Ph gene was more effective in regulating homoeologous pairing in A. yezoense x wheat hybrids than in A. ciliare x wheat hybrid. Chromosome pairing data of BC₁ derivatives indicated that either some of the wheat chromosomes were eliminated or Agropyron chromosomes caused reduced pairing of wheat homologues.Contribution No. 82-653-J, Department of Plant Pathology, Kansas State Agricultural Experiment Station, Manhattan, Kan, USA     

Chloroplast DNA inheritance in theStellaria longipes complex (Caryophyllaceae)

Inheritance of chloroplast DNA (cpDNA) was examined in F₁ progenies derived from three crosses and three corresponding reciprocal crosses betweenStellaria porsildii andS. longifolia. Chloroplast DNA restriction fragments were analyzed using methods of nonradioactive digoxigenin-11-dUTP labeling and chemiluminescent detection with Lumi-Phos 530. Distinct interspecific restriction fragment polymorphisms were identified and used to demonstrate the mode of cpDNA inheritance. Mode of cpDNA inheritance differed among crosses. Two crosses in whichS. porsildii, SP2920-21, was the maternal parent exhibited three different types of plastids, maternal, paternal and biparental, among the F₁ hybrids, suggesting a biparental cpDNA inheritance and plastid sorting-out inStellaria.     

HYBRID FITNESS IN THE LOUISIANA IRISES: ANALYSIS OF PARENTAL AND F1 PERFORMANCE

The assumption of hybrid inferiority is central to the two models most widely applied to the prediction of hybrid zone evolution. Both the tension zone and mosaic models assume that natural selection acts against hybrids regardless of the environment in which they occur. To test this assumption, we investigated components of fitness in Iris fulva, I. hexagona and their reciprocal F₁ hybrids under greenhouse conditions. The four cross types were compared on the basis of seed germination, vegetative and clonal growth, and sexual reproduction. In all cases, the hybrids performed as well as, or significantly better than, both of their parents. These results suggest that F₁ hybrids between I. fulva and I. hexagona are at least as fit as their parents. The results of this study are therefore inconsistent with the assumptions of both the tension zone and mosaic models of hybrid zone evolution.     

Ontogeny of gene expression in Pomoxis (pisces: Centrarchidae)

The regulation of gene expression during embryogenesis was investigated in white and black crappie (Pomoxis spp.) and their reciprocal interspecific F₁ hybrids. The schedule of morphological development and the timing of isozyme expression were compared among the two species and both reciprocal maternal half-sibling F₁ hybrids. Although absolute rates of morphological development differed in response to incubation temperature, relative rates of morphological development (normalized to the onset of retinal pigment deposition) were similar among all crosses. Furthermore, these relative rates were similar to those previously documented for other centrarchid species. To assess differences in ontogenetic patterns of gene expression among the crosses, we examined expression for 39 enzymeencoding loci. Expression was not detected in the embryos for 16 loci due to low or nonexistent activity. Enzymatic activity from eight other loci were continuously detected throughout embryogenesis as a result of maternal enzyme in the egg. However, 15 loci initiated expression during the early development period investigated (fertilization through yolk sac absorption). We observed temporal variability in expression of these 15 loci among the crosses, either in the form of differential expression between parental species or as disturbances in the ontogeny of expression in interspecific hybrids. Such variability in expression suggests that some of the gene regulating mechanisms have diverged since Pomoxis species shared a common ancestral genome. © 1994 Wiley-Liss, Inc.     

Chilling and freezing stress in live oaks (Quercus section Virentes): intra- and inter-specific variation in PS II sensitivity corresponds to latitude of origin

Sensitivity to cold and freezing differs between populations within two species of live oaks (Quercus section Virentes Nixon) corresponding to the climates from which they originate. Two populations of Quercus virginiana (originating from North Carolina and north central Florida) and two populations of the sister species, Q. oleoides, (originating from Belize and Costa Rica) were grown under controlled climate regimes simulating tropical and temperate conditions. Three experiments were conducted in order to test for differentiation in cold and freezing tolerance between the two species and between the two populations within each species. In the first experiment, divergences in response to cold were tested for by examining photosystem II (PS II) photosynthetic yield (ΔF/F _m′) and non-photochemical quenching (NPQ) of plants in both growing conditions after short-term exposure to three temperatures (6, 15 and 30°C) under moderate light (400 μmol m⁻² s⁻¹). Without cold acclimation (tropical treatment), the North Carolina population showed the highest photosynthetic yield in response to chilling temperatures (6°C). Both ecotypes of both species showed maximum ΔF/F _m′ and minimum NPQ at their daytime growth temperatures (30°C and 15°C for the tropical and temperate treatments, respectively). Under the temperate treatment where plants were allowed to acclimate to cold, the Q. virginiana populations showed greater NPQ under chilling temperatures than Q. oleoides populations, suggesting enhanced mechanisms of photoprotective energy dissipation in the more temperate species. In the second and third experiments, inter- and intra-specific differentiation in response to freezing was tested for by examining dark-adapted F _v/F _m before and after overnight freezing cycles. Without cold acclimation, the extent of post-freezing declines in F _v/F _m were dependent on the minimum freezing temperature (0, −2, −5 or −10°C) for both populations in both species. The most marked declines in F _v/F _m occurred after freezing at −10°C, measured 24 h after freezing. These declines were continuous and irreversible over the time period. The North Carolina population, however, which represents the northern range limit of Q. virginiana, showed significantly less decline in F _v/F _m than the north central Florida population, which in turn showed a lower decline in Fv/F _m than the two Q. oleoides populations from Belize and Costa Rica. In contrast, after exposure to three months of chilling temperatures (temperate treatment), the two Q. virginiana populations showed no decline in F _v/F _m after freezing at −10°C, while the two Q. oleoides populations showed declines in F _v/F _m reaching 0.2 and 0.1 for Costa Rica and Belize, respectively. Under warm growth conditions, the two species showed different F ₀ dynamics directly after freezing. The two Q. oleoides populations showed an initial rise in F ₀ 30 min after freezing, followed by a subsequent decrease, while the Q. virginiana populations showed a continuous decrease in F ₀ after freezing. The North Carolina population of Q. virginiana showed a tendency toward deciduousness in response to winter temperatures, dropping 58% of its leaves over the three month winter period compared to only 6% in the tropical treatment. In contrast, the Florida population dropped 38% of its leaves during winter. The two populations of the tropical Q. oleoides showed no change in leaf drop during the 3-months winter (10% and 12%) relative to their leaf drop over the same timecourse in the tropical treatment. These results indicate important ecotypic differences in sensitivity to freezing and cold stress between the two populations of Q. virginiana as well as between the two species, corresponding to their climates of origin.     

Fertile somatic hybrids between Petunia hybrida and a wild species,Petunia variabilis

Somatic hybrid plants were regenerated following electrofusion between leaf mesophyll protoplasts of P. hybrida (2n = 14) and a wild sexually incompatible species, P. variabilis (2n = 18). The selection of hybrids was based on the hybrid vigour, expressed both in the growth of the callus and at the shoot formation stage, resulting from the combination of parental genomes. Calli exhibiting vigorous growth were selected, and upon transfer to regeneration medium gave rise to shoots. Four regenerated plants from three calli had morphological characteristics intermediate between those of the parents. The hybrid nature of these plants was confirmed by chromosome counts as well as isozyme and DNA analyses. They had amphidiploid chromosome numbers (2n = 32) and were fertile. Following self-pollination and backcrossing with P. variabilis, large numbers of F₂ and BC₁ seedlings were obtained.     

Cytological analysis of tetraploid hybrids between sweet potato and diploid Ipomoea trifida (H. B. K.) Don.

Summary Tetraploid F₁ hybrids between Ipomoea batatas, sweet potato (2n = 6x = ca. 90), and diploid (2n = 2x = 30) I. trifida (H. B. K.) Don. showed various degrees of fertility reduction. The present study aimed to clarify its causes by cytological analysis of meiotic chromosome behavior in the diploid and sweet potato parents and their tetraploid hybrids. The diploid parents showed exclusively 15 bivalents, and the sweet potato parents exhibited almost perfect chromosome pairing along with predominant multivalent formation. Their hybrids (2n = 4x= 57–63) formed 2.6–5.0 quadrivalents per cell, supporting the autotetraploid nature. The meiotic aberratios of the hybrids were characterized by the formation of univalents, micronuclei, and abnormal sporads (monad, dyad, triad, and polyad). The causes underlying these aberrations were attributed in part to the multivalent formation, and in part to a disturbance in the spindle function. Three hybrids showing serious meiotic aberrations were very low in fertility. The utilization of the sweet potato-diploid I. trifida hybrids for sweet potato improvement is described and, further, the role of interploidy hybridization in the study of the sweet potato evolution is discussed.