Chromosome association and fertility in hybrids of Iris laevigata Fisch. x I. ensata Thunb.

Summary Chromosome association at MI of PMCs in hybrids of I. laevigata x I. ensata was examined and compared with that of parental species. The mean chromosome association per cell in the parental species was 0.02_I+11.99_II for I. ensata (Kachô, 2n=24), 0.11_I+15.94_II and 0.15_I+15.92_II for I. laevigata (Yukidôrô and wild type, 2n=32), respectively. On the other hand, the mean chromosome association per cell in the hybrids (2n=28) was 20.22_I+3.88_II+0.0046_IV for Yukidôrô × Kachô and 20.92_I+3.54_II for wild type × Kachô. Thus, the hybrids indicated a low homology between I. ensata and I. laevigata, and did not exhibit pollen and seed fertility. The utility of the hybrids was discussed.     

Cytogenetic analysis of interspecific hybrids in genus Citrullus (Cucurbitaceae)

Investigations on interspecific crossability in two species of the genus Citrullus were studied based on their morphology, chromosome pairing and pollen fertility in their hybrids resulting from 12 combinations(including reciprocals). These have been utilized for tracing the phylogenetic relationship between the taxa and factors responsible for their differentiation. A collective evaluation of data on cross compatibility,morphology, chromosome association and pollen fertility indicated a close phylogenetic relationship between the species C. colocynthis (wild2n = 22) and C. vulgaris (cultivated 2n = 22). Significant differences for crossability and pollen fertility were observed between hybrids of C. colocynthis × C. vulgaris and reciprocals. Meiotic analysis of F₁ hybrids revealed that these two species are freely crossable and provide normal chromosome association, involving an average of 9 to maximum 11 pairs of chromosomes. This indicated the possibility of high recombination and thereby genetic introgression of desirable traits. As both the species are of economic significance, breeding strategies can be developed for the genetic improvement of these species. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lilium x ‘Black Beauty’—a potential bridging hybrid in Lilium

Summary Lilium Black Beauty, a rare intersectional hybrid previously reported sterile, was re-examined for pollen and ovule fertility. No pollen tubes were detected following incubation of styles pollinated with Black Beauty pollen. However, embryos varying in size from small globular to long boat-shaped and only rarely associated with endosperm, were found in 0.1–1.0% of the ovules in Black Beauty pistils pollinated with Oriental or Aurelian division lilies. Aseptic extraction and culture of these embryos on a nutritive medium resulted in growth, germination, and plantlets. It is apparent that with embryo culture, Black Beauty has unique value as a species bridge in that it accepts pollen of both Oriental and Aurelian lilies, two of the major commercial lily divisions.Scientific Journal Series Paper Number 9197 of the Minnesota Agricultural Experimental Station.     

New interspecific hybrids in the genus Agropyron

Summary Fifteen species from the genus Agropyron were crossed together. Fourteen of the crosses did not produce fruits. Twenty crosses produced varying numbers of caryopses. Of the fruits produced, 22% contained no embryos. For a variety of reasons it was possible to obtain only 2 plants from the remaining 140 embryos. The crosses which yielded viable plants were between A. trachycaulum cv. Primar (2n=28) and A. intermedium cv. Chief (2n=42) as well as between A. trachycaulum from Lethbridge (2n=28) and A. desertorum cv. Nordan (2n=28). The somatic chromosome numbers for the hybrids are 37 and 28. respectively. Studies of vegetative plant character are presented.     

Meiotic behavior in interspecific hybrids between Brachiaria ruziziensis and Brachiaria brizantha (Poaceae)

The meiotic behavior of two half-sib interspecific tetraploid (2n = 4x = 36) promising hybrids, a sexual and an apomictic one, from crosses B. ruziziensis and B. brizantha, was evaluated. Although chromosome paired predominantly as bivalents, a few tri- and quadrivalents were recorded. Results suggest that B. brizantha and B. ruziziensis are closely related and genetic recombination is expected in hybrids. Introgression of specific target genes from B. ruziziensis into B. brizantha and vice-versa may be foreseen. However, abnormalities such as irregular chromosome segregation, chromosome stickiness and abnormal cytokinesis reported in these hybrids affect pollen fertility. More than 65% of pollen grains are sterile. Since the distinctive cytological feature of these hybrids is abnormal cytokinesis, this fact suggests that both parental genomes are unable to coordinate their activities with regard to this cytological phenomenon. Deployment of such hybrids in the process of developing varieties is discussed.     

Cytogenetics of interspecific hybrids in the genus Capsicum L.

Summary Crosses between a wild species C. chacoense and three cultivated species of chili pepper viz. C. annuum, C. frutescens and C. chinense yielded hybrids when C. chacoense was the seed parent but the reciprocal crosses were unsuccessful. C. chacoense × C. annuum F₁ hybrids were partly fertile and therefore an F₂ population could be raised; the other two F₁ hybrids were totally sterile. Chromosome pairing in the F₁ plants resulted largely in bivalents and a few multivalents and univalents. The genomes of the four species share large homologies and the role of chromosome structural changes in genome differentiation is suggested. Hybrid sterility is the major reproductive isolation mechanism.     

Comparison of different pollen viability assays to evaluate pollen fertility of potato dihaploids

Summary The main obstacle in breeding potato (Solanum tuberosum L.) dihaploids is the severe limitation of male fertility. To determine pollen viability assays that correlate well to fertility in crosses, results of five different pollen viability assays were compared by correlation analysis with fruit and seed set characters in test crosses, and to pollen tube growth in situ (PL-test). The methods used were: staining the pollen cells with carmino acetic acid (CAA-test); in vitro pollen germination (PG-test); and detection of pollen staining rates after incubation with fluoresceine diacetate (FDA-test), 2-3-5-triphenyle tetrazolium chloride (TTC-test), and 5-bromo-4-chloro-3-indolyle--galactoside (X-Gal-test).The results of test crosses and pollen tube growth in situ correlated with the results of all other assays with the following ranking, from highest to lowest: enzyme activity assays (X-Gal-test, FDA-test, TTC-test), in vitro pollen germination (PG-test), and pollen staining by CAA. The newly developed X-Gal-test for monitoring -galactosidase activity showed the least variation of all assays investigated. Thus, this highly reproducible simple procedure is recommended for male fertility screening.Abbreviations B/F Berries obtained per 100 flowers - CAA Carmino acetic acid - FDA Fluoresceine diacetate - PG Pollen germination rate in vitro - PL Pollen tube growth in situ - S/B Seeds per berry - S/F Seeds per pollinated flower - TTC 2-3-5-triphenyle tetrazolium chloride - X-Gal 5-bromo-4-chloro-3-indolyle--galactoside     

Cytology and pollen grain fertility in creeping bentgrass interspecific and intergeneric hybrids

Creeping bentgrass (Agrostis stolonifera L. or A. palustris Huds.) is a highly outcrossing allotetraploid species. It can form hybrids with a number of other Agrostis species and Polypogon genus. However, cytology and pollen grain fertility of the creeping bentgrass interspecific and intergeneric hybrids are not well known. In this research, chromosome pairing behaviors during meiosis I in F₁ and pollen viability of F₁ hybrids, as well as seed set rate and seed germination rate of backcrosses were studied in hybrids between creeping bentgrass, and other bentgrass species and three species of Polypogon genus. Abnormal chromosome pairing, laggard chromosomes, and premature segregation in F₁ hybrids were found. Pollen viability ranged from 1.6 to 48.5% amongst F₁ hybrids, significantly lower than that of the parents (85.5–94.1%). Some hybrids produced pollens of different sizes within the same anther. Seed set following backcrosses using F₁ hybrids as the male parent and creeping bentgrass as the recurrent parent was significantly lower than their parents. The study of chromosome paring behaviors and progeny fecundity are important in utilizing the alien genes to improve bio-stress and abio-stress resistance, and in assessing the potential transgene risks of creeping bentgrass.     

Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. Ex Fr. II. Meiosis in F1 hybrids and back crosses to C. Arabica

Summary Melosis was studied in Coffea arabica, in induced tetraploid C. canephora, in their F₁ hybrid (arabusta hybrid) and in backcross generations of the hybrid with C. arabica as recurrent parent. Irregularities were observed, consisting of univalents (especially in the arabusta hybrid), multivalents (especially in tetraploid C. canephora) and uneven distribution of chromosomes at first anaphase. Chromosome distribution was improved by backcrossing. Meiotic irregularities wer negatively correlated with pollen fertility.     

Fertility restoration of hybrids between Solanum melongena L. and S. aethiopicum L. Gilo Group by chromosome doubling and cytoplasmic effect on pollen fertility

Reproductive fertility traits were studied in the reciprocal hybrids of the eggplant(Solanum melongena L.) and S. aethiopicum L. Gilo Group, and in synthetic amphidiploids to discover whether fertility in these reciprocal hybrids was restored by chromosome doubling. Isozyme and RAPD analyses confirmed hybridity of the hybrids and amphidiploids. Analyses of chloroplast and mitochondrial DNAs confirmed that the cytoplasm of each of the hybrids and amphidiploids was from the maternal parent. Pollen sterility of S. melongena × S. aethiopicum Gilo Group [F₁ (Mel × Aet)] was restored by chromosome doubling, while the reciprocal hybrid S. aethiopicum Gilo Group ×S. melongena [F₁ (Aet × Mel)]and its amphidiploid did not produce any pollen grains; their microspores degenerated without being released from tetrads. Hence the cytoplasm of S. aethiopicum Gilo Group seems to beresponsible for their pollen-non-formation type sterility of the hybrid. Both the F₁ hybrids did not set any fruits by either selfing or backcrossing, while their amphidiploids set fruits after pollinating with pollen from the amphidiploid of F₁ (Mel × Aet). Seeds obtained from both the amphidiploids germinated normally. Chromosome doubling has been effective in restoring fertility of the hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pollen fertility among BC2 offspring of Impatiens interspecific hybrids of New Guinea and Indonesian ancestry

BC_T2 seedlings, derived from the cross Tangeglow (I. hawkeri Bull. × I. aurantiaca Teysm.) × 7851-1 (I. hawkeri Bull. × I. platypetala Lindl.) with 7851-1 as recurrent parent, were tested for presence of pollen fertility. Of 59 BC₂ seedlings, 11 were capable of in vitro pollen germination and also of effecting fertilization and subsequent seed set as pollen parent when crossed with Tangeglow as the seed-parent tester. The Spearman's rank correlation coefficient [r_s] of + 0.63 indicated a moderately good correlation of seedling ranking, based on pollen germination percent in vitro and seed set in vivo. Pollen germination of the 11 pollen-fertile BC₂ seedlings varied from a mean low of 4% to a mean high of 41%. The 3 highest pollen-germinating BC₂ seedlings also had the highest seed sets, but siblings showed a wide range in pollen-germinating ability. The best pollen germination for a seedling was 8% in the BC₁ and 41% in the BC₂. Pollen fertility in the BC₂ is discussed in relation to using interspecific hybridization in an Impatiens breeding program. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. ex Fr. I. Fertility in F1 hybrids and backcrosses to C. Arabica

Summary The interspecific (C. arabica × tetraploid C. canephora) F₁ hybrid showed a low but highly variable fertility. An almost complete restoration to normal fertility was observed in individual trees of BC₁ and BC₂ generations with C. arabica as recurrent parent. From a comparison of various tests of fertility, it was found that pollen viability is a satisfactory measure of fertility.     

Heterosis for symbiotic nitrogen fixation in Phaseolus interspecific hybrids

Summary Interspecific hybrids of Phaseolus vulgaris and Phaseolus acutifolius or Phaseolus filiformis have been evaluated for evidence of heterosis for symbiotic nitrogen fixation activity. Hybrids showing composite leghemoglobin profiles were selected for comparison. Rooted cuttings from hybrids and their respective parents were used to estimate nitrogen fixation (acetylene reduction) rates and to determine nitrogen accumulation during the growth period. Some hybrids of Phasolus vulgaris × Phaseolus acutifolius and Phaseolus vulgaris × Phaseolus filiformis had significantly (P<0.01) higher nitrogen fixation rates and in the latter case, accumulated more total nitrogen, than either parent. The interspecific hybrids also showed more complex leghemoglobin profiles than either parent.     

Expression of barley yellow dwarf virus and Russian wheat aphid resistance genes in and fertility of spring wheat × triticale hybrids and backcross lines

Summary The Barley Yellow Dwarf Virus disease (BYDV) and the Russian wheat aphid (RWA) Diuraphis noxia (Mordvilko) have caused significant losses to wheat and barley in several areas of the world. Important sources of resistance to both BYDV and RWA have been found in Triticale. Different generations of interspecific wheat x Triticale crosses were produced and the progenies were screened for BYDV and RWA tolerance. Plants with equal chromosome numbers showed different levels of fertility. A significant correlation was observed between pollen fertility and seed set in primary florets (r=0.57). In generaL, pollen fertility, seed set and the number of euploid plants (2n=42) increased from one generation to the next. The expression of BYDV tolerance varied from population to population. Additive effects were predominant in F₁ and some backcross populations. A dominant effect of rye tolerance genes was also observed in few populations. A monogenic trait or a quantitative (polygenic) character would not agree with the observed segregation patterns. The heritability of this oligogenic tolerance was quite different between populations and in many populations the tolerance genes were only partially expressed. Some transgressive segregation for tolerance and sensitivity was demonstrated. The genes controlling tolerance to RWA in Triticale lines, Muskox 658 and Nord Kivu were not expressed in advanced lines resistant to BYDV. This indicates that tolerance genes for BYDV and RWA in these lines are located on different chromosomes.     

Relationships between African species of the genus Cucumis L. Estimated by the production,vigour and fertility of F1 hybrids

Summary The production, vigour, and fertility of F₁ hybrids between nine African species of the genus Cucumis L. were studied as a measure of the relationships between the species. Hybrid plants were obtained from 29 out of the 72 possible cross combinations. Two F₁ hybrids died as seedlings, and 27 hybrids were raised to maturity. Pollen production and stainability varied greatly amongst these hybrids, as did fruit and seed set following self pollination and backcrossing with either parental species. The fruit shape of the hybrids was always intermediate between that of both parental species.Two species appeared to be closely related: C. prophetarum L. and C. anguria var. longipes A. Meeuse. Most other species produced highly to moderately fertile F₁ hybrids with at least one other species. C. metuliferus Naud. produced only sterile hybrids with C. zeyheri Sond. 2x. The results sustain the recent taxonomic classification of the genus (Jeffrey, 1980).     

Production of interspecific hybrids between Glycine max and G. tomentella through embryo culture

Summary Interspecific hybrids have been obtained in an incompatible cross between Glycine max and G. tomentella through the in vitro culture of hybrid embryos. The percentage of successful pod setting in the crosses averaged 12.8% but there were marked differences depending on the soybean cultivar used as the female parent. Hybrid embryos at globular to heart stages were extracted from the embryo sac 15–25 days after pollination and cultured in vitro. Hybrid plants were successfully obtained by culturing the embryos on B5 medium supplemented with 0.1 mg/l IBA followed by culture on B5 medium supplemented with 0.1 mg/l TBA plus 0.25 mg/l 2-iP. The F1 plants resembled the wild male parent in growth form, but had an intermediate leaf shape between that of the parents.     

A test of the mentor pollen technique in the genus Ipomoea

Summary A major barrier to hybridization of some Ipomoea species is located at the stigma-style interface. In 5 interspecific combinations examined with the aid of fluorescence microscopy, pollen was found to germinate and penetrate the stigma surface without, however, passing into the style. In the cross I. hederacea x 1. purpurea, pollen tubes were observed in the style and capsules were set, but no full seeds were produced. Attempts to facilitate hybridization among Ipomoea species using mentor pollen-foreign pollen mixes were unsuccessful.     

Cytology and digoxin production in hybrids between Digitalis lanata and D. grandiflora

Summary Digitalis lanata is the only commercial source of the cardiac glycoside digoxin. It is an outbreeder and displays considerable variation. An attempt to increase uniformity was made by making D. lanata × D. grandiflora diploid hybrids and from these produce allotetraploid hybrids using colchicine treatment. Such tetraploid plants would be homozygous. Tetraploid hybrids were shown to contain digoxin but at lower levels than in D. lanata. Progeny of selfed tetraploid hybrids were significantly more uniform than D. lanata grown from commercial seed, but were considerably less vigorous.     

Phylogenetic relationships in Lens species and their interspecific hybrids as measured by morphological characters

Phylogenetic relationships of 15 genotypes of the genus Lens and 7 of their interspecific hybrids were determined by morphological (quantitative and qualitative) characters. The first multivariate analysis was conducted on quantitative characters and second analysis was conducted on qualitative characters. In the first analysis on the basis of two canonical variates, accessions of Lens nigricans, L. odemensis and L. culinaris ssp. orientalis grouped together, while L. ervoides and L. culinaris ssp. culinaris formed two different groups. The second analysis yielded different results based firstly on two canonical variates where L. nigricans and L. culinaris ssp. culinaris formed two separate groups but the other three (sub)species clustered together when the third canonical variate was included. L. odemensis separated from this larger group and formed a separate group. The phylogenetic relationships of parents and their hybrids have also been discussed. This revised version was published online in July 2006 with corrections to the Cover Date.