Importance of woody debris in seed germination of Tipularia discolor (Orchidaceae)

Concerns about declining populations of terrestrial orchids make it important to identify the environmental factors crucial to seedling recruitment. This study shows that seedlings of Tipularia discolor (cranefly orchid) primarily occur on decomposing wood. Extensive searches of decomposing logs and stumps in mature and successional forests revealed seedlings at 24 sites, of which 15 could be identified as originating from seven different deciduous trees and one conifer. Seeds were planted in natural habitats to test the hypothesis that germination requires decomposing wood. In one experiment, seeds were placed into soil at sites where adult plants were abundant; no germination resulted. In a second experiment, germination of seeds sown in ambient soil was compared with sowings in plots amended with decomposing wood collected from a stump where spontaneous seedlings grew. Germination was much more frequent in plots amended with decomposing wood. We conclude that germination of T. discolor is stimulated in substrates that contain decomposing wood; judging from the occurrence of spontaneous seedlings, wood from at variety of tree species offer a suitable substrate.     

Germination and growth ofErythrorchis ochobinesis (Orchidaceae) accelerated by monokaryons and dikaryons ofLenzites betulinus andTrametes hirsuta

Four sib-monokaryons and two reconstituted dikaryons of two basidiomycetes,Lenzites betulinus andTrametes hiruta, accelerated the seed germination ofErythrorchis ochobiensis, an achlorophyllous orchid. All isolates ofL. betulinus and three isolates ofT. hirsuta induced the development of plants from germinated seeds. Although three monokaryotic isolates ofT. hirsuta failed to induce the development of plants, the reconstituted dikaryons induced the development.     

中国兰科二新记录种

兰科植物资源调查是掌握地区兰科本底资料的基础,对研究兰科植物的地理分布和资源多样性具有重要意义.该文报道了分别产自中国西藏自治区墨脱县和巴宜区的石豆兰属(Bulbophyllum Thou.)中国分布新记录种——尼泊尔大苞兰(B.raskotii J.J.Verm.,Schuit.&de Vogel)和曲唇兰属[Pan...     

菌根真菌与兰科植物互作的组学研究进展

兰科植物因其具有丰富的物种多样性和重要的社会经济价值,多年来一直是植物学及生态学界的重点研究对象.菌根真菌对兰科植物的种子萌发、营养吸收和种群动态等多个方面都具有十分重要的作用,因而近年来受到越来越多的关注.探究菌根真菌与兰科植物互作的内在机制是目前兰科菌根研究的一大热点领域,同时也为兰科植物野生资源保护和种群恢复提供...     

Reproductive effort and floral photosynthesis in Spiranthes cernua (Orchidaceae)

This study examined the cost of reproduction and photosynthetic characteristics of the reproductive structures of Spiranthes cernua, an agamospermic, terrestrial orchid. Reproduction was frequent: two-thirds of the plants flowered at least 2 yr in a row and one-fourth of the consecutive-year runs were ~3 yr. Neither a significant decrease in leaf area nor a reduced likelihood of flowering was observed following 1 or 2 yr of inflorescence production. While there was a tendency for plants producing >16 flowers to have decreased size the next year, plants with the greatest number of flowers (31+) were the most likely to reproduce. Leaf and reproductive gas exchange were measured in the field. Low but positive rates of net photosynthesis were documented at all stages of inflorescence development. The average rates of photosynthesis for each stage were: leaves, 9.2 mmol CO2/m2s; inflorescence in bud, 3.7 mmol CO2/m2s; inflorescence in flower, 2.5 mmol CO2/m2s and infructescence, 0.2 mmol CO2/m2s. Based on diurnal gas exchange, the contribution of leaves and reproductive structures to seasonal carbon assimilation was 91.6 and 8.4%, respectively. The role of the inflorescence as a source and sink for carbon assimilation may lower the cost of reproduction and support frequent inflorescence production.     

Identification of mycorrhizal fungi from single pelotons of Dactylorhiza majalis (Orchidaceae) using single-strand conformation polymorphism and mitochondrial ribosomal large subunit DNA sequences

The mitochondrial ribosomal large subunit (Ls) DNA was used to identify the orchid mycorrhizal fungi found in roots of Dactylorhiza majalis. The gene was amplified using DNA extracted from single pelotons obtained from fresh and silica gel dried roots. Furthermore, sequencing a variety of well-characterized orchid isolates expanded the fungal database of the mitochondrial ribosomal LsDNA. Polymerase chain reaction product length variants present in D. majalis were sequenced and identified using the expanded database. These analyses revealed two different peloton-forming fungi in samples from D. majalis, which sometimes occurred together as a single two-taxa peloton within the same cortex cell. The first taxon belonged to the genus Tulasnella and the second taxon was distantly related to Laccaria.     

Specificity and preference of mycorrhizal associations in two species of the genus Dendrobium (Orchidaceae)

Dendrobium is a large genus of tropical epiphytic orchids. Some members of this genus are in danger of extinction across China. To investigate orchid mycorrhizal associations of the genus Dendrobium, plants from two Dendrobium species (Dendrobium officinale and Dendrobium fimbriatum) were collected from two habitats in Guangxi Province, China, and clone libraries were constructed to identify the mycorrhizal fungi of individual plants. A low and high degree of specificity was observed in D. officinale and D. fimbriatum, respectively. Phylogenetic analysis revealed that the majority of Dendrobium mycorrhizal fungi are members of the Tulasnellaceae, but, in some plants, members of the Ceratobasidiaceae and Pluteaceae were also found. In D. officinale, individual plants associated with more than three fungi simultaneously, and, in some cases, associations with five fungi at the same time. One fungus was shared by individual plants of D. officinale collected from the two habitats. In D. fimbriatum, only one fungal partner was found in each population, and this fungus differed between populations. The two species of Dendrobium sampled from the same habitat did not share any fungal taxa. These results provide valuable information for conservation of these orchid species.     

Seed dormancy patterns in Epipactis palustris (Orchidaceae): Requirements for germination and establishment of mycorrhiza

Some terrestrial orchid species, including Epipactis palustris (L.) Crantz, are considered extremely difficult to germinate and cultivate in vitro. Observations of orchids germinating in nature are very few, and the timing and requirements for seedling establishment are unknown for most species. Seeds of E. palustris were incubated in vitro with an appropriate fungus, but germination was poor unless several other conditions were also met: scarification of the testa in Ca(OCL)₂, an initial incubation for several weeks at 27°C, and a subsequent cold stratification for 8–12 weeks at 4–8°C, With these pretreatments, germnation responses exceeded 50% after incubation for 4 weeks at 20°C. Healthy protocorms with normal organ development were only produced by symbiotic culture following this lengthy seed preparation. The findings suggest that under natural conditions the seeds need some after-ripening, and the testa needs to be partially decomposed before germination. The requirement for chilling suggests that germination of seeds in situ occurs in spring.     

Temperature sensitivity of in vitro germination and seedling development of Dactylorhiza majalis (Orchidaceae) with and without a mycorrhizal fungus

Abstract. Symbiotic germination and development in vitro of Dactylorhiza majalis seeds with a strain of Rhizoctonia is very temperature dependent. Above an optimum at 23–25 °C there is a marked decline in germination percentage. Seeds that did germinate at higher temperatures had only little or no development of mycorrhiza, and developed few or no rhizoids compared with seedlings raised at optimal or lower temperatures. Six-week-old seedlings grown for additional 4 weeks on a range of temperatures had an optimal length increase at 23–24.5 °C mean temperature. At superoptimal temperatures (26 °C), the seedlings contained smaller starch reserves than those at lower temperatures and increased about as much in length as seedlings grown at 13 °C but much less than those grown at optimum. Temperature also influenced the differentiation of the leafy shoot, seedlings growing to a larger size before shoot initiation in the temperature range of optimal growth. Because of the small span between optimal and too-high temperatures, a careful assessment of temperature optimum will be necessary in any orchid/fungus relationship before judging the success of symbiosis. At optimal temperature, symbiotic germination gave a germination percentage about twice that using a good asymbiotic method. The increase in seedling length was about 45% per week in symbiotic culture compared with less than 30% in the asymbiotic culture.     

Postpollination nectar reabsorption in the African epiphyte Aerangis verdickii (Orchidaceae)

Nectar reabsorption in flowering plants seems to be a rare phenomenon and to our knowledge it has not been reported previously in the Orchidaceae. In this study we present data that show statistically significant differences in nectar sugar concentrations before and after pollination. Virgin flowers of the African epiphytic orchid Aerangis verdickii showed mean sugar concentrations in the nectar of 14.4 and of 18.3% in 1994 and 1995, respectively (sucrose mass by mass equivalent). Sugar concentration in nectar from naturally pollinated flowers had a mean of 3.2 and of 8.7% for the same period. In an experiment in the wild 60 flowers were protected against nectar theft by the ants. Half of those flowers were hand-pollinated. Control (virgin) flowers had nectar with a mean value of 13.8%, while flowers measured 48 h after pollination had a mean sugar concentration of 4.3%. The mean volume of nectar based on measurements of 23 virgin flowers from nine different plants was 19 uL. We estimated an average energy value for the nectar produced of 684 J per plant per season. At the study site, over 60% of the unmanipulated flowers were robbed of all their nectar by arboreal ants, Polyrachis spp. (Formicinae). The adaptive significance of nectar reabsorption for A. verdickii is probably a function of the environmental stresses to which it has been exposed and the relative costs of nectar production.     

Hybridization and introgression across different ploidy levels in the Neotropical orchids Epidendrum fulgens and E. puniceoluteum (Orchidaceae)

The hypothesis of gene flow between species with large differences in chromosome numbers has rarely been tested in the wild, mainly because species of different ploidy are commonly assumed to be reproductively isolated from each other because of instantaneous and strong postzygotic barriers. In this study, a broad‐scale survey of molecular variation was carried out between two orchid species with different ploidy levels: Epidendrum fulgens (2n = 2x = 24 chromosomes) and Epidendrum puniceoluteum (2n = 4x = 52 chromosomes). To test the strength of their reproductive barriers, we investigated the distribution of genetic variation in sympatric and allopatric populations of these two species and conducted crossing experiments. Nuclear and plastid microsatellite loci were used to genotype 463 individuals from eight populations across the geographical range of both species along the Brazilian coastal plain. All six sympatric populations analysed presented hybrid zones, indicating that hybridization between E. fulgens and E. puniceoluteum is a common phenomenon. Bayesian assignment analysis detected the presence of F₁ and F₂ individuals and also signs of introgression, demonstrating a high potential for interspecific gene flow. Introgression occurs preferentially from E. fulgens to E. puniceoluteum. Pure parental individuals of both species display strong genotype–habitat associations, indicating that environment‐dependent selection could be acting in all hybrid zones. This study suggests that hybridization and introgression are evolutionary processes playing a role in the diversification of Epidendrum and indicates the importance of investigations of hybrid zones in understanding reproductive barriers and speciation processes in Neotropical orchid species.     

Factors affecting fruit and seed production in Dactylorhixa maculata (Orchidaceae)

It has been argued that some of resources needed for fruit and seed production in terrestrial orchids originate from storage in underground biomass. Resources for female reproductive traits may also originate from current photosynthesis. Orchid mycorrhiza may also influence fruit and seed production. The extent to which current photosynthetic activity and nutrient uptake via mycorrhizal fungi affect fruit and seed production has only rarely been studied experimentally. This paper examines the importance of photosynthesis and mycorrhiza for fruit and seed production, leaf area and plant status in the next season for Dactylorhiza maculata (L.) Soó in two populations. Plants were hand-pollinated in two populations to assure successful fertilization. Photosynthesis in the main leaves and in the green parts of inflorescence was prevented and/or mycorrhizal function inhibited by applying thiabendazole to plants. None of the treatments affected relative capsule production, but all treatments resulted in significant decreases in capsule dry weight and the number of seeds produced. The fact that seed production remained high in spite of the experimental treatments indicates that resources stored in the underground corms were used in fruit development and seed production. Inhibition of photosynthesis decreased leaf area in the year following treatments, while the other treatments had no effect on subsequent growth.     

Light stimulation and darkness requirement for the symbiotic germination of Dactylorhiza majalis (Orchidaceae) in vitro

Germination percentage of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. (Orchidaceae) was increased by illuminating surface-sterilized, rinsed and incubated seeds with white light in 16 h photoperiods. Optimal exposures (10–14 days) raised germination from 40 to 75%. Longer light treatments resulted in reduced germination percentage and smaller seedlings. Only about 2% of the seeds could actually germinate in photoperiods; the germination of the rest was delayed by initial light and required about 14 days in constant darkness. Interruption of this darkness period with two consecutive photoperiods increased the germination percentage when the interruption occurred before day 8, but not when occurring later than that.     

Biphenanthrene from Stanhopea lietzei (Orchidaceae) and its chemophenetic significance within neotropical species of the Cymbidieae tribe

Orchidaceae are one of the largest families of flowering plants. In this work, the first phytochemical study of the non-flowering parts of the South American species Stanhopea lietzei (Regel) Schltr. is reported. It led to the isolation of nine compounds, including the rare dimeric compound 2,2′,7,7′-tetramethoxy-4,4′,6,6′-tetrahydroxy-(1,1′)-biphenanthrene (1). This compound was tested for the first time against HeLa human cancer cells, with IC₅₀ 16.9 ± 0.9 μg/mL. Biological assays against neotropical parasites, virus and other human cancer cell lines are also reported. Finally, the relevance of biphenanthrenes, flavonoids, and C-glycosylated phenolic compounds for chemophenetics relationships within neotropical species of the Cymbidieae tribe and Oncidiinae, Maxillariinae, Cyrtopodiinae and Stanhopeinae subtribes was also discussed.