Unilateral compatibility and genotypic difference in crossability in interspecific hybridization between Dianthus caryophyllus L. and Dianthus japonicus Thunb

Reciprocal interspecific crosses were carried out between six lines of Dianthus caryophyllus L. and one line of Dianthus japonicus Thunb. Although no seed was set when D. japonicus was used as the seed parent, six seedlings were successfully obtained from 2,380 immature ovules by applying the embryo-rescue technique. However, they showed seed parent-like morphology and no evidence for the hybridity by flow cytometry and RAPD analyses. When six lines of D. caryophyllus were used as seed parents, a total of 192 seedlings were successfully obtained without using the embryo-rescue technique. Among these seedlings, 12 out of 25 progenies obtained from the carnation line '98sp1651' were confirmed to be the hybrids. The remaining 13 progenies of this line, and the total 167 progenies obtained from the other carnation lines, had carnation-like morphology without any evidence of hybridity by flow cytometry and RAPD analyses. The progenies confirmed as hybrids had intermediate characters of the parents with respect to leaf width and flower size, but they had a uniform flower color, reddish purple, which was different from that of either parent. Since the hybrids obtained in the present study have some profitable characters such as vigorous growth in summer time, upright robust stem, broad leaves and early flowering, they are expected to be used for the breeding of carnation which is suitable for growing under the Japanese climate.     

Pollen genotype selection for a simply inherited qualitative factor determining resistance to chlorsulfuron in maize

Pollen genotype selection for genes expressed in both the haploid and diploid phases of the plant life cycle can lead to correlated responses detectable in the sporophyte. A pollen selection was conducted in two genetic backgrounds of maize (Zea mays L.) for chlorsulfuron resistance, conferred by the XA17 allele. Plants of two backcross (BC) lines segregating 1 (heterozygote, resistant) : 1 (homozygote, susceptible) for chlorsulfuron resistance were used as pollen donor. Selection treatment was applied during microspore development, and tassels were cut about 10 days before anthesis and placed into a liquid medium with or without 40 mg l^–1 of chlorsulfuron. Pollen was used to fertilize an unrelated susceptible genotype (tester). The resulting testcrosses (TC) were evaluated in the greenhouse by spraying seedlings with chlorsulfuron at 23 g ha^–1. Non-selected TC progenies derived from heterozygous BC plants showed a proportion of resistant and susceptible plants close to the expected 1:1 ratio, while non-selected TC progenies derived from homozygous BC plants showed susceptible plants only. Selected TC progenies derived from heterozygous BC plants showed a frequency of resistant plants ranging from 89% to 100%. BC plants homozygous for the susceptible allele, subjected to selection treatment, gave poor seed set, and no resistant plants were found in their TC progenies. Resistant TC plants obtained through pollen genotype selection were selfed, and the proportion of resistant plants was close to 3:1 in all selfed families, in accordance with the hypothesis that all of them inherited the XA17 allele through selection. In this study, pollen genotype selection was extremely effective, and its effect persisted in the second sporophytic generation. Received: 19 November 1999 / Accepted: 30 April 2000     

Use of <Emphasis Type="Italic">2n</Emphasis> gametes for the production of sexual polyploids from sterile Oriental × Asiatic hybrids of lilies (<Emphasis Type="Italic">Lilium</Emphasis>)

Sixteen Oriental and 12 Asiatic cultivars were crossed in 158 different combinations. A total of 708 F₁ hybrids were obtained from 86 of the different combinations of 15 Oriental and 11 Asiatic cultivars. Because the Lilium cultivars (2n=2x=24) used for the production of these hybrids belong to two different taxonomic sections—Archelirion (O) and Sinomartagon (A), respectively—the F₁ hybrids (OA) could be obtained only through embryo, embryo sac rescue, ovary slice or ovule culture. Most of the F₁ hybrids were highly sterile (did not produce viable n gametes) due to the failure of chromosome pairing. However, in a few cases F₁ plants were found that produced viable 2n pollen at variable frequencies. These 2n pollen grains were successfully used for the production of backcross progenies. Using genomic in situ hybridization we found intergenomic recombinant chromosomes in the sexual polyploid progenies. These results indicate that there are effective prospects for combining important horticultural traits from the two main groups of cultivars of lilies through sexual polyploidization.     

Assessing hybrid sterility in <Emphasis Type="Italic">Oryza glaberrima</Emphasis> × <Emphasis Type="Italic">O. sativa</Emphasis> hybrid progenies by PCR marker analysis and crossing with wide compatibility varieties

Interspecific crossing of the African indigenous rice Oryza glaberrima with Oryza sativa cultivars is hindered by crossing barriers causing 100% spikelet sterility in F₁ hybrids. Since hybrids are partially female fertile, fertility can be restored by back crossing (BC) to a recurrent male parent. Distinct genetic models on spikelet sterility have been developed predicting, e.g., the existence of a gamete eliminator and/or a pollen killer. Linkage of sterility to the waxy starch synthase gene and the chromogen gene C, both located on chromosome 6, have been demonstrated. We selected a segregating BC₂F₃ population of semi-sterile O. glaberrima × O. sativa indica hybrid progenies for analyses with PCR markers located at the respective chromosome-6 region. These analyses revealed that semi-sterile plants were heterozygous for a marker (OSR25) located in the waxy promoter, whereas fertile progenies were homozygous for the O. glaberrima allele. Adjacent markers showed no linkage to spikelet sterility. Semi-sterility of hybrid progenies was maintained at least until the F₄ progeny generation, suggesting the existence of a pollen killer in this plant material. Monitoring of reproductive plant development showed that spikelet sterility was at least partially due to an arrest of pollen development at the microspore stage. In order to address the question whether genes responsible for F₁ sterility in intraspecific hybrids (O. sativa indica × japonica) also cause spikelet sterility in interspecific hybrids, crossings with wide compatibility varieties (WCV) were performed. WCV accessions possess "neutral" S-loci (Sⁿ) improving fertility in intraspecific hybrids. This experiment showed that the tested Sⁿ-loci had no fertility restoring effect in F₁ interspecific hybrids. Pollen development was completely arrested at the microspore stage and grains were never obtained after selfing. This suggests that distinct or additional S-loci are responsible for sterility of O. glaberrima × O. sativa hybrids.Communicated by H.C. Becker     

INFLUENCE OF ENVIRONMENTAL FACTORS ON ORIGIN OF COLCHICINE-INDUCED TRUE-BREEDING DIPLOID MUTANTS IN SORGHUM

Sanders , Mary E., Clifford J. Franzke , and James G. Ross . (South Dakota State Coll., Brookings.) Influence of environmental factors on origin of colchicine-induced true-breeding diploid mutants in sorghum. Amer. Jour. Bot. 46(2) : 119-125. Illus. 1959.—Factors involved in the induction of true-breeding diploid mutants following colchicine treatment of sorghum seedlings (line ‘Experimental 3‘) were studied by growing untreated and treated seedlings in aseptic cultures under controlled conditions and examining mature plants and progenies for genetic changes. Factors found to increase rate of early growth and survival of treated seedlings are: use of agar media rather than quartz sand plus liquid media, presence of major minerals in the medium, and presence of up to 2% sucrose in the medium. The beneficial effect of sucrose is contingent upon the presence of major minerals. IAA from 0.01 p.p.m. to 0.1 p.p.m. increased rate of both root and top growth of treated seedlings during early development. Increased osmotic values of the medium increased early growth rate and survival of treated seedlings up to a concentration equivalent to 0.123 molar sucrose while early growth of control seedlings fell off with every increase in osmotic value. This shift in optimum osmotic value of the medium would seem to indicate an increase in the osmotic concentration of the tissues of colchicine-treated seedlings. Progeny tests of some of the treated plants from the culture experiments demonstrated that, out of 137, none were true-breeding diploid mutants. There were instances of polyploidy and minor changes, but the 2 treated plants which were the only obvious mutants gave progenies which segregated for many characters. Improved growing conditions for treated seedlings decreased the colchicine effect of induction of true-breeding diploid mutants as well as the colchicine effects of retarded seedling growth and decreased survival.     

Field Performance of Transgenic indica Hybrid Rice with Improved Cooking and Eating Quality by Down-regulation of Wx Gene Expression

High amylose content (AC) in rice endosperm is correlated with poor grain quality, particularly in indica hybrid rice. We have generated several homozygous transgenic parent lines of indica hybrid rice carrying an antisense Waxy (Wx) gene and demonstrated that the AC in seeds of these lines decreased dramatically. Two transgenic maintainer lines (L25B and L18B), derived from one of the key maintainer parents of an indica hybrid rice in China, Long-te-fu B (LTF-B), were selected and the antisense Wx gene was subsequently introgressed into the male-sterile counterpart, LTF-A, with the aim to generate improved indica hybrids. The indica hybrids derived from the selected transgenic male-sterile lines and restorer lines were tested for quality and agronomic performance under normal field conditions. Our results demonstrated that the reduction of AC in the homozygous transgenic maintainer lines stably passed down in five successive generations and the improved quality was also found in their relevant transgenic hybrids produced. The other two key characters of rice cooking and eating quality, the gel consistence (GC) and gelatinization temperature (GT), were also improved in the grains of both the transgenic maintainer lines and their relevant hybrids. In addition, no change was observed for most of the agronomic characters of the transgenic maintainer lines and the relevant transgenic hybrids. Although the grain weight of the transgenic line was reduced, the grain yield of the homozygous transgenic parent lines and the transgenic hybrids was similar when compared with that of the wild-type controls. These results suggest that transgenic approaches are an effective way to obtain rice lines with both improved qualities and high yield, especially for indica hybrid rice.     

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     

CYTOLOGICAL STUDIES OF NONTRUE–BREEDING MUTANTS IN SORGHUM OBTAINED AFTER COLCHICINE TREATMENT

Sanders , Mary E., and Clifford J. Franzke . (South Dakota State Coll.. Brookings.) Cytological studies of nontrue-breeding mutants in sorghum obtained after colchicine treatment. Amer. Jour. Bot. 49(9): 990–996. Illus. 1962.—Although pollen mother cells of nontrue-breeding mutant plants obtained after colchicine treatment of sorghum seedlings, line ‘Experimental 3,’ showed normal chromosome behavior (10 bivalents) at phases of meiosis I, some abnormalities were found at corresponding stages in first- and second-generation self-progeny plants of some of them. The most frequent chromosome irregularities were an increase over ‘Experimental 3’ in number of cells containing univalents, and mixoploid tissues with tetraploid and diploid cells. The higher polyploid groups (6n, 8n, 10n) also present in 2 plants might be related to their male-sterile condition rather than being an indication of the chromosome complement. Abnormalities in progenies suggest that some of the mutants might have been chimeras in which abnormalities were missed and raise the question whether chromosome changes are involved in the formation of the mutants in spite of the preponderance of normal diploid cells with 10 bivalents during prophase and metaphase of meiosis I. This could occur if sorghum contains a genetic mechanism which promotes bivalent rather than multivalent pairing. That such might be a possibility is indicated by the large numbers of bivalents and small numbers of multivalents found in polyploid cells or groups.     

Two new male-sterile mutants of Zea mays (Poaceae) with abnormal tapetal cell morphology

Two new recessive male-sterile mutants of Zea mays (Poaceae), or maize, were studied to identify the timing of pollen abortion and to examine the involvement of anther wall cell layers. The results of test crosses indicated that these mutants were not allelic with any known male-sterile mutants of maize. Light and transmission electron microscopy were used to compare pollen development in homozygous male-sterile mutants to that in fertile heterozygous siblings. In both mutants, microspores abort soon after release from the meiotic tetrad. However, the two mutations have strikingly different phenotypes. Large lipid bodies accumulate in the tapetal cells as the microspores vacuolate and die in the mutant ms25. Large vacuoles appear in both the tapetal cells and the young microspores as they begin to disintegrate in the mutant ms26. Because abnormal tapetal cell morphology is detected in both mutants, it is possible that both of these mutations affect the expression of genes in tapetal cells.     

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.     

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。     

Transmission of paternal chloroplasts in tobacco (Nicotiana tabacum)

Medgyesy et al. (1986, Mol. Gen. Genet. 204, 195–198) have described in Nicotiana plumbaginifolia and in an interspecific cross involving N. plumbaginifolia and N. tabacum a procedure for selecting cell lines derived from seedlings carrying paternal chloroplasts by taking advantage of a plastid-encoded mutation which confers resistance to streptomycin. We have extended their demonstration of occasional transmission of chloroplasts through pollen to the case of an intraspecific cross in N. tabacum. The line used as maternal parent, ITB19(sua), displayed a cytoplasmic male sterility due to the presence of a cytoplasm originating from N. suaveolens. The line used as paternal parent, SR1, was fertile and possessed mutant chloroplasts conferring resistance to streptomycin. From cell lines derived from 204 seedlings, three were regenerated into streptomycin-resistant buds. The plants derived from these three clones were male-sterile. Their progeny, after crossing with a wild type tobacco line, XHFD8, was resistant to streptomycin. Tests of resistance of the seedlings to tentoxin and restriction analyses of the chloroplast DNA indicated that two clones still had the maternal chloroplasts and were thus probably new streptomycin-resistant mutants, whereas the third one had acquired the chloroplasts of the paternal parent, but had retained the mitochondria of the maternal parent.Abbreviations cp-DNA chloroplast DNA - mt-DNA mitochondrial DNA - Np Nicotiana plumbaginifolia - Nt Nicotiana tabacum     

Chromosome elimination and fragment introgression and recombination producing intertribal partial hybrids from <Emphasis Type="Italic">Brassica napus</Emphasis> × <Emphasis Type="Italic">Lesquerella fendleri</Emphasis> crosses

The intertribal sexual hybrids between three Brassica napus (2n = 38) cultivars and Lesquerella fendleri (2n = 12) with the latter as pollen parent were obtained and characterized for their phenotypes and chromosomal and genomic constitutions. F₁ plants and their progenies mainly resembled female B. napus parents, while certain characters of L. fendleri were expressed in some plants, such as longer flowering period, basal clustering stems and particularly the glutinous layer on seed coats related to drought tolerance. Twenty-seven F₁ plants were cytologically classified into five types: type I (16 plants) had 2n = 38, type II (2) had 2n = 38–42, type III (3) had 2n = 31–38, type IV (5) had 2n = 25–31, and type V (1) had 2n = 19–22. Some hybrids and their progenies were mixoploids in nature with only 1–2 chromosomes or some chromosomal fragments of L. fendleri included in their cells. AFLP (Amplified fragments length polymorphism) analysis revealed that bands absent in B. napus, novel for two parents and specific for L. fendleri appeared in all F₁ plants and their progenies. Some progenies had the modified fatty acid profiles with higher levels of linoleic, linolenic, eicosanoic and erucic acids than those of B. napus parents. The occurrence of these partial hybrids with phenotypes, genomic and fatty acid alterations resulted possibly from the chromosome elimination and doubling accompanied by the introgression of alien DNA segments and genomic reorganization. The progenies with some useful traits from L. fendleri should be new and valuable resource for rapeseed breeding.     

The use of rootless mutants for the screening of spontaneous androgenetic and gynogenetic haploids in Nicotiana tabacum: evidence for the direct transfer of cytoplasm

Summary In crosses between a homozygous rootless mutant line of Nicotiana tabacum used as female and other Nicotiana tabacum lines, androgenetic haploids can be directly selected by their ability to form plantlets with a normal rooting system, whereas hybrid plants are killed few weeks after sowing. These androgenetic plants have the nucleus of the male parent into the cytoplasm of the female parent. In crosses where the homozygous rootless mutant line is used as a pollen donor, gynogenetic haploids can also be directly selected. Haploids can therefore be derived from male sterile plants using this approach. A generalization of this system for direct cytoplasm transfer and for the screening of spontaneous haploids in dicotyledons is proposed.     

Genetic and physiological variability among cultured cells and regenerated plants of Nicotiana tabacum

Summary Tobacco cell lines selected for resistance to picloram (4-amino-3,5,6-trichloropicolinic acid) and plants regenerated from these cell lines manifest several traits not shown by the parental strains. Genetics analyses of the regenerated plants have permitted the sources of this variability to be identified.Tricotyledenous seedlings appeared at a much higher frequency among the progeny of a heterozygous mutant plant (PmR1/+) regenerated from culture than they did among progeny of normal regenerated plants. In crosses with the regenerated heterozygous mutant plant and with homozygous progeny of this plant (PmR1/PmR1) the frequency of tricotyly was influenced more by the generation than by the genotype of the parent plant. Therefore, it is concluded that tricotyly is a physiological response to passage through cell culture.More than half of the picloram-resistant cell lines isolated were also resistant to hydroxyurea. Segregation of these two resistances was analyzed in progeny of crosses with regenerated plants. In all cases hydroxyurea-resistance was genetically stable and inherited as a single dominant nuclear mutation (designated HuR). In crosses with plants PmR1/+ and PmR7/+ the HuR and PmR mutations assorted independently. In contrast, the HuR mutation recovered from plant PmR6/+ was linked to the PmR6 mutation.     

Loss-of-function mutations and inducible RNAi suppression of Arabidopsis LCB2 genes reveal the critical role of sphingolipids in gametophytic and sporophytic cell viability

Serine palmitoyltransferase (SPT) catalyzes the first step in sphingolipid biosynthesis, and downregulation of this enzyme provides a means for exploring sphingolipid function in cells. We have previously demonstrated that Arabidopsis SPT requires LCB1 and LCB2 subunits for activity, as is the case in other eukaryotes. In this study, we show that Arabidopsis has two genes ( AtLCB2a and AtLCB2b ) that encode functional isoforms of the LCB2 subunit. No alterations in sphingolipid content or growth were observed in T-DNA mutants for either gene, but homozygous double mutants were not recoverable, suggesting that these genes are functionally redundant. Reciprocal crosses conducted with Atlcb2a and Atlcb2b mutants indicated that lethality is associated primarily with the inability to transmit the lcb2 null genotype through the haploid pollen. Consistent with this, approximately 50% of the pollen obtained from plants homozygous for a mutation in one gene and heterozygous for a mutation in the second gene arrested during transition from uni-nucleate microspore to bicellular pollen. Ultrastructural analyses revealed that these pollen grains contained aberrant endomembranes and lacked an intine layer. To examine sphingolipid function in sporophytic cells, Arabidopsis lines were generated that allowed inducible RNAi silencing of AtLCB2b in an Atlcb2a mutant background. Studies conducted with these lines demonstrated that sphingolipids are essential throughout plant development, and that lethality resulting from LCB2 silencing in seedlings could be partially rescued by supplying exogenous long-chain bases. Overall, these studies provide insights into the genetic and biochemical properties of SPT and sphingolipid function in Arabidopsis.     

I. THE EXPRESSION OF INSTABILITY IN N. TABACUM × N. PLUMBAGINIFOLIA

Moav , Rom (Hebrew U., Jerusalem), and D. R. Cameron . Genetic instability in Nicotiana hybrids. I. The expression of instability in N. tabacum × N. plumbaginifolia. Amer. Jour. Bot. 47(2): 87—93. 1960.—N. tabacum (n = 24) and N. plumbaginifolia (n=10) are distantly related species both from morphological and cytological points of view. Hybrids of these species with various genome dosages have exhibited somatic variegation when plumbaginifolia dominant characters were superimposed on an appropriate tabacum genetic background. Five loci were studied in this respect: Wh and Tg—for flower coloration; Ws—for chlorophyll production; Kl—for pollen abortion and Bs—for black shank resistance. All 5 were found to be unstable. Backcross progenies of the sesquidiploid hybrid (tbc-tbc-pbg) to tabacum showed a marked increase in intensity of variegation. This has been attributed to the breaking up of the plumbaginifolia genome into individual chromosomes. The evidence indicates that variegation was due to somatic chromosomal aberrations which probably characterized all the plumbaginifolia chromosomes. An hypothesis regarding the heterogeneity of F₁ hybrids of distantly related homozygous species is outlined and the occurrence of instability due to hybridization in other Nicotiana hybrids is discussed.     

Expression of unilateral incompatibility in pollen of Lycopersicon pennellii is determined by major loci on chromosomes 1, 6 and 10

Summary We have previously described gene introgression from the wild nightshade Solanum lycopersicoides into tomato (Lycopersicon esculentum) through the use of either diploid or sesquidiploid hybrids (the latter consisting of two genomes of L. esculentum and one genome of S. lycopersicoides). Both types of intergeneric hybrids display pollen sterility, but workable ovule fertility. Unilateral incompatibility prevents their direct hybridization with staminate L. esculentum. Pollen of a self-compattible form of the related wild species L. pennellii is compatible with pistils of L. esculentum x S. lycopersicoides hybrids. This trait was backcrossed from L. pennellii to L. esculentum in order to develop bridging lines that could be used to obtain progeny from the intergeneric hybrids and to study the inheritance of bridging ability. In progeny of L. esculentum x S. lycopersicoides hybrids pollinated with L. pennellii-derived bridging lines, preferential transmission of L. pennellii alleles was observed for certain isozyme and RFLP markers on chromosomes 1, 6 and 10. The skewed segregations suggest linkage to three major pollen-expressed compatibility loci. This was confirmed by observations of pollen tube growth, which indicated that compatibility with pistils of the diploid intergeneric hybrid occurred only in bridging lines at least heterozygous for the L. pennellii markers on chromosomes 1, 6 and 10. Compatibility with the sesquidiploid hybrid required only the chromosome 1 and 6 loci, indicating an apparent effect of gene dosage on expression of incompatibility in the pistil. In an F₂ L. esculentum x L. pennellii population, preferential transmission of L. pennellii alleles was observed for the same markers on chromosomes 1 and 10, as well as other markers on chromosomes 3, 11, and 12, but not 6. The chromosome 1 pollen compatibility locus maps to or near the S-locus, which determines S-allele specificity. The results are discussed in relation to existing genetic models for unilateral incompatibility, including the possible involvement of the S-locus.     

Compensating ability in pollen fertilization between group-6 and -7 homoeologous chromosomes of barley and wheat

By using alpha-amylase isozymes as markers for chromosomes of homoeologous groups 6 and 7, we analyzed the segregation of chromosome constitution in the progenies from crosses between double-ditelosomic or ditelosomic lines of hexaploid wheat cultivar 'Chinese Spring' (CS) as the female parent and double-monosomic F1 hybrids of CS x wheat-barley substitution lines for barley chromosomes 6H or 7H. From this analysis we estimated the transmission rate via pollen of barley chromosomes 6H and 7H in the double-monosomics and evaluated the compensating ability between barley and wheat chromosomes in homoeologous groups 6 and 7. The results indicated that both 6H and 7H showed their highest compensating ability for their respective homoeologous wheat chromosomes 6A (37.5% transmission rate) and 7A (39.4%), intermediate for 6D (34.1%) and 7D (29.6%), and lowest for 6B (26.6%) and 7B (22.6%) chromosomes.     

Specific Features of the Nuclear Genome Recombination in Backcross Progenies of Barley–Wheat Hybrids Hordeum vulgare L. (2n = 14) × Triticum aestivum L. (2n = 42)

The backcross progenies of the barley–wheat hybrids Hordeum vulgare L. (2n = 14) × Triticum aestivum L. (2n= 42) and two alloplasmic lines derived from them were studied using microsatellite markers of barley and wheat. The F₁ hybrids and first backcross plants BC₁ contained the genetic material of both cultivated barley and the cultivars of common wheat involved in developing of these hybrid genotypes. The genomes of BC₃, BC₄, and alloplasmic lines contained no microsatellite markers of the cultivated barley, whereas chromosomes of each homeologous group of common wheat were identified. In chromosomes of backcross progenies BC₃, BC₄, and alloplasmic lines yielded by backcrosses of hybrids and various common wheat cultivars, microsatellite markers of the parental wheat cultivars were shown to undergo recombination.