Crop model based QTL analysis across environments and QTL based estimation of time to floral induction and flowering in <Emphasis Type="Italic">Brassica oleracea</Emphasis>

Studying quantitative traits is complicated due to genotype by environment interactions. One strategy to overcome these difficulties is to combine quantitative trait loci (QTL) and ecophysiological models, e.g. by identifying QTLs for the response curves of adaptive traits to influential environmental factors. A B. oleracea DH-population segregating for time to flowering was cultivated at different temperature regimes. Composite interval mapping was carried out on the three parameters of a model describing time to flowering as a function of temperature, i.e. on the intercept and slope of the response of time to floral induction to temperature and on the duration from transition to flowering. The additive effects of QTLs detected for the parameters have been used to estimate time to floral induction and flowering in the B. oleracea DH-population. The combined QTL and crop model explained 66% of the phenotypic variation for time to floral induction and 56% of the phenotypic variation for time to flowering. Estimation of time to floral induction and flowering based on environment specific QTLs explained 61 and 41% of the phenotypic variation. Results suggest that flowering time can be predicted effectively by coupling QTL and crop models and that using crop modelling tools for QTL analysis increases the power of QTL detection.     

Effects of season and population size on pollination and reproductive output in a Mediterranean shrub

• Pollinator guilds may change throughout extended flowering periods, affecting plant reproductive output, especially in seasonal climates. We hypothesised a seasonal shift in pollinator guild and an autumn reduction in pollinator abundance, especially in small and sparse populations.
• We recorded pollinator identity, abundance and behaviour in relation to flower density from plant to population throughout the extended flowering of Ononis tridentata. We evaluated female reproductive output by recording pollination success and pre‐dispersal seed predation in eight populations of contrasting size and density. Offspring quality was also characterised through seed weight and germination.
• A diverse guild of insects visited O. tridentata in spring, while only Apis mellifera was observed in autumn. Visitation frequency did not vary seasonally, but the number of flowers per foraging bout was lower, and seeds were heavier and had a higher germination rate in autumn. Plant and neighbourhood flowering display were not related to pollinator visitation frequency or behaviour. However, the rate of fertilised ovules, seed set and autumn flowering display size were positively related to population density.
• The maintenance of pollination in autumn enhances the reproductive performance of O. tridentata due to higher quality of autumn seed, and to a large reduction in seed predator pressure. We also suggest that observed changes in pollinator behaviour could be one of the processes behind seasonal variation in seed performance, since geitonogamous crosses were less likely to occur in autumn.

     

Pre‐zygotic reproductive isolation between two synchronopatric Opuntia (Cactaceae) species in the Brazilian Chaco

• Opuntia (Cactaceae) is known for high rates of hybridization and ploidisation, resulting in the formation of new species. The occurrence of two sympatric and closely related species of Opuntia, O. elata and O. retrorsa, in Brazilian Chaco enabled us to test the hypothesis that pre‐zygotic reproductive isolation mechanisms operate in both species.
• We monitored the flowering period, as well as floral biology, and compared the morphological variation of floral structures through measurements, performed intra‐ and interspecific cross‐pollination tests, and recorded the guild of floral visitors and pollinators.
• Flowering was seasonal and highly synchronous. Floral biology exhibits similar strategies, and although floral morphology differs significantly in many of the compared structures, such morphological variation does not result in the selection of exclusive pollinators. Floral visitors and pollinators are oligolectic bees shared by both species. Opuntia elata and O. retrorsa are self‐compatible. While interspecific cross‐pollination (bidirectional) resulted in germination, the pollen tube did not penetrate the stigma.
• Opuntia elata and O. retrorsa are closely related; however, they are isolated and do not hybridise in Brazilian Chaco. We found that both have weak pre‐pollination barriers, but that they are strongly isolated by pollen–pistil incompatibility, i.e. post‐pollination barrier.

     

Unravelling the structure and function of the petal appendages in the tribe Schwenckieae (Solanaceae)

• The tribe Schwenckieae (Solanaceae) is characterised by the presence of appendages on the corolla, a diagnostic trait for the group. These appendages constitute a median distal projection of the three‐lobed petal and occur in the genera Melananthus and Schwenckia but are absent in Heteranthia.
• We investigated the micromorphology and anatomical structure of the appendages and lateral petal lobes of Schwenckia americana (two varieties), S. angustifolia, S. curviflora and S. novaveneciana, and Melananthus fasciculatus. We also performed histochemical tests to determine if the appendages are involved in the production of volatiles, acting as a fragrance secretory structure (osmophore).
• The appendages have a uniseriate epidermis, whose cells store phenolics and lipids. The parenchyma is starch‐rich just prior to anthesis in all species studied. The sensory test and anatomical analyses identified scent‐secreting tissues, not only in the appendages, but also in the lateral petal lobes, whose cells are papillose with a sculptured surface. The α‐naphthol p‐phenylenediamine (NADI) reaction detected volatile (essential oils) compounds in S. americana var. americana and S. americana var. angustifolia.
• We demonstrated the secretory tissues and the production of lipids in the corolla appendages of Schwenckia and Melananthus, which indicate their osmogenic function and probable scent emission to attract pollinators.

     

Olfactory versus visual cues in a floral mimicry system

 We used arrays of artificial flowers with and without fragrance to determine the importance of olfactory and visual cues in attracting insects to a floral mimic. The mimic is a fungus, Puccinia monoica Arth., which causes its crucifer hosts (here, Arabis drummondii Gray) to form pseudoflowers that mimic co-occurring flowers such as the buttercup, Ranunculus inamoenus Greene. Although pseudoflowers are visually similar to buttercups, their sweet fragrance is distinct. To determine whether visitors to pseudoflowers were responding to fragrance we performed an experiment in which we removed the visual cues, but allowed fragrance to still be perceived. In this experiment we found that pseudoflower fragrance can attract visitors by itself. In other experiments we found that the relative importance of olfactory and visual cues depended on the species of visitor. Halictid bees (Dialictus sp.) had a somewhat greater visual than olfactory response, whereas flies (muscids and anthomyiids) were more dependent on olfactory cues. We also used bioassays to determine which of the many compounds present in the natural fragrance were responsible for attraction. We found that halictid bees were equally attracted to pseudoflowers and to a blend containing phenylacetaldehyde, 2-phenylethanol, benzaldehyde and methylbenzoate in the same relative concentrations as in pseudoflowers. Flies, on the other hand, only responded to pseudoflower scent, indicating that we have not yet identified the compound(s) present in pseudoflowers that are attracting them. The ability of insects to differentiate pseudoflowers from true flowers by their fragrance may be important in the evolution of the mimicry system. Different fragrances may facilitate proper transfer of both fungal spermatia and pollen, and thus make it possible for the visual mimicry to evolve. Received: 3 January 1996 / Accepted: 13 August 1996     

High congruence of intraspecific variability in floral scent and genetic patterns in Gentianella bohemica Skalický (Gentianaceae)

Gentianella bohemica Skalický (Gentianaceae) is a critically endangered species endemic to the Bohemian Massif in the border region of Germany, Czechia and Austria. It consists of a restricted number of extremely scattered populations which are known to form distinct genetic groups. The objective of this work was to test for differences in the floral scent between Gentianella bohemica and Gentianella germanica and within these two species among populations, and to test for a correlation of scent and genetic similarity among the populations of G. bohemica. Floral scent was collected from the inflorescences/plants of eight flowering populations of G. bohemica and three populations of G. germanica using dynamic headspace methods, followed by GC/MS analyses. Both species emitted several aromatic and terpenoid compounds and multivariate analyses revealed differences in scent between the two species and within species among G. bohemica populations. Volatile components overlapped as expected for closely related species but floral scent was taxon-specific. Floral scent differentiation among G. bohemica populations was in high congruence with the genetic differentiation suggesting that scent differences among populations have a genetic basis and showing that scent is a suitable chemotaxonomic marker in this species.     

Flower Scent and Pollination in Selected Neotropical Palms

Abstract: The flower scents of 14 palm species were collected in the field in Ecuador and Puerto Rico by head-space adsorption and analysed by gas chromatography-mass spectrometry. Insect visitors were recorded in seven of the species in Ecuador. The floral scent of the different species was dominated by a variety of compounds, e.g., the fatty-acid derived 3-pentanone and the hydrocarbon series dodecane to pentadecane, the benzenoid compound 1,4-dimethoxybenzene, the isoprenoids ( E )-ocimene, myrcene, linalool, and ( E )-α-farnesene and the nitrogen-containing compound 2-methoxy- sec -butylpyrazine. Rather than mirroring the systematics of the studied palm species, the chemical composition of the floral scent reflected the pollination mode. The scent of beetle-pollinated species was characterized by large amounts of one or a few dominant compounds, whereas fly- and bee-pollinated species contained a mixture of several compounds in smaller total amounts. We suggest that specific scent compounds, as found in the beetle-pollinated species, have evolved as a response to pollinator preferences. The importance of olfactory cues in relation to visual cues is higher in beetle-pollinated species than in species pollinated by flies and bees.     

Floral meristems as a source of enhanced yield and quality of DNA in grasses

Floral meristems of Lolium and Festuca grasses give a 5- to 19-fold enhancement in yield of extracted DNA in comparison with leaves. Meristems also provide highly pure DNA samples. The method could be useful for applications in molecular genetics in many species of the Gramineae. Received: 14 April 1998 / Revision received: 8 June 1998 / Accepted: 10 July 1998     

Operculum development inEucalyptus clöeziana andEucalyptus informal subg.Monocalyptus (Myrtaceae)

Flowers ofEucalyptus clöeziana have two clearly distinct perianth whorls. The small free parts of the outer (calycine) whorl cease growth early and are lost from the flower; the parts of the inner (corolline) whorl become continuous laterally by confluence of growth centres and form an operculum in the mature flower. The stamens are inserted on a circumfloral buttress (staminophore) that is homologous to the adaxial corolline component inAngophora and the bloodwood andEudesmia eucalypts. Flowers ofMonocalyptus have only one perianth whorl, which is opercular. The stamens are similarly inserted on a circumfloral buttress. Developmental study does not provide conclusive evidence for either a calycine or corolline determination of theMonocalyptus operculum, but comparison with other eucalypt groups, includingE. clöeziana (the sister taxon), predicts an essentially corolline composition.     

Aspects of floral structure and phenology in the genusConophytum (Mesembryanthemaceae)

The complex floral structure in the southern African genusConophytum (Mesembryanthemaceae; 77 spp.) is described in detail and assigned to three basic floral types, two of which can be divided into two subtypes. Correlations between structural features and phenological patterns are demonstrated and discussed in the family context as well as in relation to the systematic subdivision of the genus.