Keith R. W. Hammett

Yellow pinks: interspecific hybridization between Dianthus plumarius and related species with yellow flowers

Abstract Interspecific hybridization was carried out with the aim of transferring yellow flower colour from yellow-flowered carnations (2 n =2 x =30) and Dianthus knappii (2 n =2 x =30) to a white-flowered cultivar of the garden pink, Dianthus plumarius (2 n =6 x =90). These hybrids were difficult to make but a small number were produced from both cross combinations. All the progeny from the crosses with carnations were pink but those from crosses with D. knappii were pale cream–yellow, with some variation in intensity between plants. Differences were observed in chromosome number between hybrids, which were either tetraploid, which is the expected situation, or pentaploid. Observations on pollen mother cell meiosis and pollen production in D. knappii revealed that the plants were producing unreduced (diploid) gametes at significant frequencies. Analysis of the flower pigments showed that the yellow flower colour of D. knappii resulted from the presence of high levels of flavone and flavonol glycosides whereas those of yellow carnations were chalcones. Thus, the F 1 hybrids with D. knappii were yellow because they contained the same pigments as D. knappii but the hybrids with the carnations were pink due to their ability to convert chalcones through to dihydroflavones and then to anthocyanins.

Karyotype analysis of the genus Clivia by Giemsa and fluorochrome banding and in situ hybridization

The karyotypes of species in the genus Clivia were analyzed by using Giemsa C-banding, fluorochrome staining, silver impregnation and in situ hybridization. Banded ideograms were established with computer aided image analysis. A chromosome number of 2n = 22 and a similar basic karyotype, based on relative chromosome length and arm ratio, was found in all the four species. There were clear differences in banding pattern between the species which allowed their karyotypes, and consequently the species, to be unambiguously identified. Apart from at the centromere, heterochromatin was mainly distributed on the short arms of the smaller chromosomes. Amounts of heterochromatin in C. miniata and C. gardenii were greater than in the other two species. The number of pairs of rDNA sites, identified by in situ hybridization, ranged from one to three.

Interspecific Hybridization between Lathyrus odoratus and L. belinensis

The recent introduction to cultivation of Lathyrus belinensis has enabled experimental crosses to be made with cultivars of the sweet pea L. odoratus. Lathyrus belinensis has flowers with yellow pigmentation, a color missing from cultivars of sweet pea. Chemical analyses revealed that three pigment types, carotenoid, flavonoid, and anthocyanin, are present in L. belinensis, which is easily identified as seedling leaves exhibit a diagnostic red pigment spot and pods are membranous and indehiscent. Like L. odoratus, L. belinensis is distinctly scented. A hybrid was established by means of embryo rescue. Karyotypes of the parental species are very similar, and meiotic pairing in the hybrid indicated considerable homology. The hybrid between L. belinensis and the cream-flowered L. odoratus cv Mrs. Collier showed reduced vigor and novel flower color. A chemical/biochemical rationalization for the observed color changes is presented. Light and scanning electron microscopy showed differences in petal surface features and the distribution of pigments within petals.

Pollination systems, hybridization barriers and meiotic chromosome behaviour in Nemesia hybrids

The ability of 13 Nemesia species (six annual and seven perennial) to sexually hybridize was investigated. Six of the perennial Nemesia species investigated were inter-fertile with one another. Two of the annual species, N. macroceras and N. strumosa, were inter-fertile. Thirty three crosses were successful and resulted in viable seeds. The analysis of meiotic chromosome behaviour in interspecific hybrids indicated that Nemesia chromosomes in different parental species were homeologous. No evidence of chromosome inversions or chromosome translocations was observed during meiosis in interspecific hybrids between the six perennial Nemesia species. In the hybrids produced between N. macroceras and N. strumosa, a quadrivalent was observed during meiotic metaphase I, indicating that these two species differ by a reciprocal translocation. A successful hybridization was made between N. anisocarpa (annual) and N. foetans (perennial), producing two triploid hybrids. In the unsuccessful crosses, pollen tubes were observed entering ovaries and ovules, suggesting that post-fertilization barriers were preventing sexual hybridization. Many of these crosses produced nonviable, shrunken, empty seeds, suggesting that endosperm breakdown and embryo abortion prevent interspecific hybridization in unsuccessful crosses. The manipulation of ploidy levels in N. fruticans and N. strumosa and tissue culture of N. strumosa × N. fruticans ovules failed to overcome post-fertilization barriers between these species.

Evaluating genetic relationships between and within Clivia species using RAPDs

Abstract RAPD markers were used to examine the genetic relationships between the four named Clivia species and the relationships among 32 accessions within C. miniata . The result suggested that C. miniata is closely related to C. gardenii , C. nobilis is distantly related to these two species and C. caulescens occupies an intermediate position. Five genetically distinct groups were found within C. miniata . The genetic variation between wild accessions and cultivars is relatively large. The hybrids sourced from Germany (“German hybrids”), C. miniata wild type cultivated in New Zealand and the popular Japanese cultivar “Daruma” appeared to have the same origin. The hybrid sourced from Belgium (“Belgian hybrid”) had a different origin. This study represents the first wide-ranging survey of molecular variation of the genus Clivia .

Floral pigmentation in two yellow-flowered Lathyrus species and their hybrid

Abstract The chemical nature of the floral pigmentation in the yellow flowered Lathyrus chrysanthus, L. chloranthus and their putative hybrid, is reported for the first time. Pigmentation in L. chrysanthus is predominantly flavonoid and in L. chloranthus predominantly carotenoid. The hybrid is midway between the two parents with respect to flavonoid levels, but closely similar to L. chrysanthus in its carotenoid level and in the nature of its flavonoids. Lathyrus chrysanthus accumulates a series of kaempferol, quercetin and isorhamnetin glycosides including the 3-glycosides, 3glucoside-7-rhamnosides and the further glycosylated 3-glucoside-7-gluco(1 → 4)rhamnosides and quercetin 3-rutinoside-7-rhamnoside. Co-occurring with these is a near complete parallel series of (minor) 3-galactoside analogues. New compounds reported include isorhamnetin 3-galactoside-7-rhamnoside, quercetin 3-glucoside-7-gluco(1 → 4)rhamnoside and its 3-galactosyl analogue. Lathyrus chloranthus accumulates the same series of 3-glucosides, together with the xylo(1 → 2)glucosides and a higher glycoside of the quercetin derivative. Isorhamnetin 3-xylo(1 →2)glucoside is new. The L. chrysanthus × L. chloranthus hybrid accumulates, in addition to the L. chrysanthus flavonoids, the new ‘hybrid’ compounds quercetin and isorhamnetin 3-xylo(1 → 2)glucoside-7-rhamnoside. These compounds are not found in either parent and apparently result from the interaction of the two parental biosynthetic systems.

THE BASIS OF YELLOW COLOURATION IN LATHYRUS APHACA FLOWERS

Abstract Flavonol glycosides which constitute 12.7% dry wt of the yellow petals of Lathyrus aphaca consist primarily of larycitrin and syringetin 3- O -

Interspecific hybridization and the analysis of meiotic chromosome pairing inDahlia (Asteraceae — Heliantheae) species with x = 16

The successful production of a large number of artificial hybrids betweenDahlia species based on x = 16 has allowed a detailed study of their genomic relationships. Chromosome behaviour in these artificial hybrids was extremely similar to that observed in parental species suggesting that there is a considerable degree of homology between the genomes of theseDahlia species. Using GISH it can be demonstrated that in these hybrids bivalent formation involved pairing only between parental genomes. The ability of GISH to differentiate between parental genomes in artificial hybrids was variable, indicating that molecular divergence of highly repeated sequences has accompanied the evolution of these species. However, the extent of chromosome pairing and chiasma formation in the hybrids does not reflect the differences that can be detected by GISH. Seyeral of the new hybrid combinations have resulted in horticulturally interesting plants.

The karyotype of Clivia mirabilis analyzed by differential banding and fluorescence in-situ hybridization

The karyotype of the recently described species Clivia mirabilis was analyzed by differential chromosome staining with Giemsa, chromomycin, and DAPI and by fluorescence in-situ hybridization with 5S and 45S rDNA probes. Like the other five Clivia species it was shown to have a unique karyotype, although its karyotype was similar in several respects to that of C. gardenii, differing in having only one pair of chromosomes with CMA bands compared with two pairs in C. gardenii and lacking any DAPI-positive bands. The evolutionary relationships of the species and their karyotypes are discussed.