Academic literature on the topic 'Rhytidophyllum'

Abstract Thirty-five broadleaf evergreens which are evergreen in USDA cold hardiness Zone 7 were screened using leaf discs in the laboratory for Zone 6 (-20C) temperatures. Field data were collected from the plants in the field after two consecutive nights with lows of-20C. Correlations between lab and field scores were high, demonstrating the usefulness of leaf discs in initially screening broadleaf evergreens for evergreeness. The method allows for a more thorough sampling of a taxon and may therefore give better results than using a limited number of larger leaf samples, such as whole leaves. A number of the tested taxa should prove evergreen in Zone 6, including: Camellia oleifera Abel ‘Lu Shan Snow’, Viburnum L. Arrowwood ‘Conoy’, Viburnum rhytidophyllum Hemsl. ‘Cree’, and certain selections of Pyracantha M.J. Roem, Illicium anisatum L., Quercus acuta Thunb., Quercus myrsinifolia Blume and Daphniphyllum macropodum var. humile Miq.

The study of the evolution of abiotic niches can be informative regarding the speciation drivers in a given group. Yet, two factors that could potentially affect niche evolution have seldom been addressed concomitantly, which are biotic interactions and geographical isolation. In this study, we used as a model group the Antillean plant genera Gesneria and Rhytidophyllum (Gesneriaceae) to evaluate the effect of pollinators and geographical isolation on the bioclimatic niche. These genera possess species characterized by interspecific geographical isolation in different islands and are pollinated by different pollinators. Some species are pollinated by hummingbirds, other by bats, while some are more generalists and are pollinated by pollinators from both functional groups. After describing the bioclimatic niches of plant species, we measured niche overlap for species pairs and we fitted Brownian motion and Ornstein–Uhlenbeck (OU) evolution models with multiple evolutionary regimes to test for an effect of pollination strategy or geographical isolation on bioclimatic niche evolution of these plants. The analysis of niche overlap between plant species, which could not be corrected for phylogenetic relationships, showed that it was significantly influenced by pollination mode and island distribution. By contrast, the best fitting evolutionary model on niche optima and tolerance was always an OU model with a unique selective regime, suggesting that neither pollination strategy nor island isolation had an important effect on bioclimatic niches at a macroevolutionary scale. Instead, we conclude that bioclimatic niches of Antillean Gesneriaceae evolved under phylogenetic conservatism and hypothesize that this macroevolutionary pattern could result from adaptation to temporally variable climates in the Antilles.

Cotoneaster Medik. is a genus of ornamental landscape plants commonly affected by fire blight. Fire blight is a disease caused by the bacterial pathogen, Erwinia amylovora (Burrill) Winslow et al., that attacks a wide range of taxa in the apple subfamily (Maloideae; Rosaceae). To assess susceptibility of species and identify potential sources of resistance, we inoculated 52 taxa of Cotoneaster with E. amylovora. Disease severity was scored by percent shoot necrosis (lesion length/total shoot length). Disease screenings were conducted over 2 years and varying levels of susceptibility were observed. Some taxa were highly susceptible to fire blight and the disease resulted in whole plant mortality (C. rhytidophyllus Rehder & E.H. Wilson, C. rugosus E. Pritzel ex Diels, and C. wardii W.W. Smith). Other taxa repeatedly exhibited moderate to high levels of disease resistance [C. arbusculus G. Klotz, C. chungtinensis (T.T. Yu) J. Fryer & B. Hylmö, C. delsianus E. Pritzel var. delsianus, C. sikangensis Flinck & B. Hylmö, C. simonsii Baker, and C. splendens Flinck & Hylmö]. Ongoing studies are being conducted to determine if taxa with high levels of resistance under artificial inoculation will exhibit high levels of resistance in the field under natural disease pressure. Identifying sources of disease resistance will be useful for breeding programs to increase tolerance of these landscape plants with desirable horticultural characteristics to fire blight.

In Australia disease caused by Phytophthora cinnamomi can have devastating impacts on native vegetation, especially on plant species with restricted distributions. The identification of susceptible threatened species is a crucial first step in understanding disease aetiology and selecting appropriate management. In a glasshouse trial, plants of 16 rare and threatened New South Wales native species from 10 families were inoculated with the pathogen. Phebalium squamulosum spp. alpinum was included as a susceptible control. We found that three species are highly susceptible to the pathogen (Nematolepis rhytidophylla (Albr. & N.G.Walsh) Paul G.Wilson, Prostanthera marifolia R.Br., Pultenaea sp. ‘Genowlan Point’); four others (Hibbertia spanantha Toelken & A.F.Rob, Phebalium bifidum P.H.Weston & M.J.Turton, Plinthanthesis rodwayi (C.E.Hubb.) S.T.Blake, Pomaderris delicata N.G.Walsh & Coates) are likely to be susceptible based on symptoms. The remaining species had few or no plant deaths and no pathogen recovery from the roots. All of the species regarded as highly susceptible are known from single populations. Following these results, subsequent research will assess the efficacy of prophylactic treatment on highly susceptible threatened species, and test whether glasshouse tests are indicative of field responses. Other threatened species will also be tested for susceptibility.

Les adaptations florales à des pollinisateurs comme les changements de forme de la corolle entraînent souvent un isolement reproducteur et donc la spéciation. Malgré leur importance écologique, les mécanismes génétiques à l'origine de cette diversité de caractères sont encore mal compris, surtout en dehors des espèces modèles. L’objectif de mon projet de maîtrise était donc d'identifier les gènes impliqués dans la variation de la forme de la corolle entre deux espèces du genre Rhytidophyllum (famille des Gesneriaceae), qui ont des modes de pollinisation différents. La première, R. rupincola, a des fleurs tubulaires et est strictement pollinisée par les colibris, tandis que la seconde, R. auriculatum, a des fleurs plus ouvertes et est pollinisée par les colibris et les chauves-souris. Dans cette étude, nous avons fait une revue de littérature et utilisé une approche de transcriptomique comparative pour identifier des gènes candidats qui pourraient expliquer la variation de la forme florale entre R. auriculatum et R. rupincola. Nous avons ensuite testé leur association avec la variation de la forme de la corolle en utilisant la cartographie de loci de traits quantitatifs (QTLs) pour une population hybride F2. Les résultats ont montré que 7 des 29 gènes candidats étaient associés à 8 QTLs différents. La répartition et la fonction supposée de ces gènes suggèrent que la forme de la corolle est un trait complexe. Ce type d'étude est rarement entrepris chez des espèces non-modèles, mais il est important afin d'intégrer la génétique du développement floral dans une perspective évolutive.
Floral adaptations to specific pollinators like corolla shape changes often result in reproductive isolation and thus speciation. But despite their ecological importance, the genetic mechanisms behind this diversity of traits are still poorly understood, especially outside model species. Hence, our goal is to identify genes involved in corolla shape variation between two species of the Rhytidophyllum genus (Gesneriaceae family) from the West Indies, which is characterized by shifts in pollination modes during its evolution. The first one, R. rupincola, has a tubular corolla and is strictly pollinated by hummingbirds. The second one, R. auriculatum, has more open flowers and is pollinated by both hummingbirds and bats. We know from previous work that the variation in morphological floral traits between these species is explained by a few quantitative trait loci (QTLs) of moderate to small effect (Alexandre et al., 2015), but we still do not know which genes underly these loci. In this study, we surveyed the literature and used a comparative transcriptomic approach to identify candidate genes that could explain floral variation between R. auriculatum and R. rupincola. We then tested their association with corolla shape variation using QTL mapping for a F2 hybrid population. Results showed that 7 out of 29 candidate genes were included within 8 different QTL. The number, repartition and putative function of these genes suggest that corolla shape is a complex trait. This sort of investigation is rarely undertaken in non-model species, but is important to integrate developmental genetics with an evolutionary perspective.

Contexte : Gesneria et Rhytidophyllum (Gesneriaceae) sont deux genres de plantes Antillais aillant subi une forte diversification et qui présentent une forte variabilité de modes de pollinisation associés à des traits floraux particuliers. Les spécialistes des colibris ont des fleurs tubulaires rouges, alors que les spécialistes des chauves-souris et les généralistes présentent des fleurs campanulées de couleur pâle. La capacité d’être pollinisé par des chauves-souris (en excluant les colibris ou en devenant généraliste) a évolué plusieurs fois indépendamment au sein du groupe. Ces caractéristiques font de ces plantes un bon modèle pour étudier les relations entre l’évolution des modes de pollinisation et la diversification spécifique et écologique. Pour ceci, nous avons étudié les bases génétiques des changements de mode de pollinisation et les liens entre ces modes de pollinisations et la diversification des niches bioclimatiques. Méthodes : Nous avons réalisé une étude de QTLs pour caractériser les régions génomiques associées à la transition de syndrome de pollinisation entre une espèce à stratégie de pollinisation mixte (Rhytidophyllum auriculatum) et une espèce spécialiste des colibris (Rhytidophyllum rupincola). Nous avons parallèlement analysé les relations entre les changements de modes de pollinisation (dimension biotique de la niche écologique) et l’évolution des niches bioclimatiques chez ces plantes. Enfin, d’un point de vue théorique, nous avons testé l’effet de la fréquence et de l’amplitude des changements environnementaux sur les patrons d’évolution des niches écologiques. Résultats : L’étude des QTLs a montré que la couleur et le volume de nectar sont basés chacun sur un QTL majeur, alors que la forme de la corolle a une base génétique plus complexe. Par ailleurs ces différents QTLs ne sont pas liés physiquement dans le génome. L’analyse des niches bioclimatiques a montré que ces Gesneriaceae antillaises sont caractérisées par un conservatisme phylogénétique de niche bioclimatique (PNC) et que l’évolution de ces niches est indépendante des stratégies de pollinisation. Les plantes semblent aussi être relativement généralistes du point de vue de leur niche abiotique. Finalement, nous avons testé l’hypothèse selon laquelle l’adaptation à un environnement temporellement hétérogène pourrait expliquer à la fois le caractère généraliste des plantes et leur patron de PNC. Cette hypothèse s’est trouvée partiellement vérifiée. Conclusion : Si l’indépendance génétique des traits floraux a pu faciliter l’émergence des syndromes de pollinisation en réduisant les contraintes génétiques, il semble que la répartition largement chevauchante des colibris et des chauves-souris ne représente pas une opportunité écologique suffisante pour expliquer les évolutions répétées vers la pollinisation par les chauves-souris. En revanche, les perturbations environnementales causant régulièrement des déclins dans les populations de pollinisateurs pourraient expliquer l’avantage des plantes qui ont une stratégie de pollinisation mixte.
Background: Gesneria and Rhytidophyllum (Gesneriaceae) are two genera endemic to the Antilles that underwent an important diversification and that present a great vari- ability in pollination modes with regard to specific floral traits. Hummingbird specialists harbour red tubular flowers while bat specialists and generalists have campanulate (i.e., bell shaped) flowers with pale colours. Bat pollination (excluding or not hummingbirds) evolved multiple times independently in this group. These plants are thus a good model to study the relationship between the evolution of pollination mode and ecological and species diversification. To understand these relationships, we studied the genetic basis of pollination mode transition and the link between pollination mode and bioclimatic niches diversification. Methods: We performed a QTL analysis to detect genomic regions underlying the floral traits involved in the pollination syndrome transition between Rhytidophyllum auriculatum (a generalist species) and Rhytidophyllum rupincola (a hummingbird specialist). Also, we analysed the consequence of pollination mode transitions (which represent the biotic part of ecological niches) on bioclimatic niches evolution in Gesneria and Rhytidophyllum. Then, we tested whether environmental changes can result in patterns of phylogenetic bioclimatic niche conservatism through time. Results: The QTLs analysis showed that corolla colour and nectar volume are both based on one major QTL, while corolla shape is determined by a more complex genetic architecture involving several unlinked QTLs. These Antillean Gesneriaceae were found to have a pattern of phylogenetic (bioclimatic) niche conservatism (PNC) and their niche evolution was found to be independent from pollination strategies. Overall, the plants were found to have relatively widespread bioclimatic niches. Finally, we partially confirmed the hypothesis that adapting to temporally variable environment might cause both species generalization and PNC pattern. Conclusion: Genetic independence of floral traits might have facilitated pollination syn- dromes evolution by reducing genetic constraints. However, the overlapping distribution of hummingbirds and bats do not represent an ecological opportunity that could explain re- peated evolutions toward bat pollination. However, environmental perturbations causing regular pollinator populations collapses could explain the advantage for plants to favour generalist strategies.