Non-specific symbiotic germination of Cynorkis purpurea (Thouars) Kraezl., a habitat-specific terrestrial orchid from the Central Highlands of Madagascar.

Orchids, particularly terrestrial taxa, rely mostly on basidiomycete fungi in the Cantharellales and Sebacinales that trigger the process of seed germination and/or initiate the full development of the seedling. During the course of development, orchids may associate with the same fungus, or they may enlist other types of fungi for their developmental needs leading to resilience in a natural setting. This study examined in vitro seed germination and seedling developmental behavior of Cynorkis purpurea, a terrestrial orchid from the Central Highlands of Madagascar. This species is mostly restricted to gallery forests in the Itremo Massif, in moist substrate between rocks bordering streams. The main objective was to understand the influence of diverse mycorrhizal fungi on seed germination and further development of C. purpurea. The study aims to compare symbiotic versus asymbiotic germination and seedling development with seeds and fungi collected from a 13-km(2) area in the Itremo region. Seeds collected from the wild were sown with diverse orchid mycorrhizal fungi (OMF) spanning 12 operational taxonomic units (OTUs) in three genera (Tulasnella, Ceratobasidium, and Sebacina) acquired from different habitats. Treatments were assessed in terms of the percentage of germinated seeds and fully developed seedlings against those in asymbiotic control media treatments. Overall, OMF significantly improved seedling development within the 12-week experiment period. Sebacina as a genus was the most effective at promoting seedling development of C. purpurea, as well as having the ability to enter into successful symbiotic relationships with orchids of different life forms; this new knowledge may be especially useful for orchid conservation practiced in tropical areas like Madagascar. A Sebacina isolate from an epiphytic seedling of Polystachya concreta was the most effective at inducing rapid seedling development and was among the five that outperformed fungi isolated from roots of C. purpurea. C. purpurea was found to be a mycorrhizal generalist, despite its specific habitat preference, highlighting the complex interaction between the plant, fungi, and the environment. The potential impact on conservation strategies of understanding the requirements for orchid seed germination and development by identifying and using OMF from diverse sources is discussed in detail.

Oryzalin-induced chromosome doubling in Rosa and its effect on plant morphology and pollen viability.

Shoot tips of the diploid rose Thérèse Bugnet were treated in vitro to oryzalin at concentrations of 5 and 15 microM. Tetraploid shoots were obtained in highest frequencies (40%) after exposure to 5 microM oryzalin for 14 days. Thin (1 mm) nodal sections were treated with 5 microM oryzalin and the highest frequency of tetraploids (66%) was obtained after exposure for only 1 day. The shorter exposure times required to induce chromosome doubling in thin nodal sections is attributed to the more efficient delivery of oryzalin to the meristem. Tetraploids were obtained from four diploid roses and hexaploids from two triploid roses. Chromosome doubling was accompanied by increases in thickness and a darker green colouration of the leaves and, in all diploid to tetraploid and one triploid to hexaploid conversion, the breadth/length ratio of leaflets was significantly increased. Internodes were longer in tetraploids than diploids but significantly shorter in hexaploids than triploids. The number of petals per flower in the tetraploid form of Thérèse Bugnet was double that of the diploid. Significant increases in pollen viability accompanied chromosome doubling of all four diploids and one of the two triploids.