Studies On Rapid Propagation, Cryopreservation And Shade Tolerance Of Gesneriaceae

The Gesneriaceae family, with few exceptions, is chiefly warm-climate, found in tropical areas. This giant family of some 150 different genus, and approximately 3700 species, includes hundreds of handsome, often velvety-leaved plants with showy wheel-shaped, tubular, or bell-like flowers. The gesneriads are so variable in foliage, texture, growth, and flowering habits that one would have to be a specialist to realize that all were member of the same plant group.The western hemisphere—Mexico, the West Indies, Central and South America—offer the great wealth in species of gesneriads in cultivation today. Most important of this tropical American group are the Sinningias, the Columneas, and Episcias. Africa is not so rich on species, but from a rather small area in East Africa originate the various Saintpaulia, Which as the "African violet" is easily today the most admired little flowering plant in the home of West countries.1. Many curious gesneriads come from Asia; amongst them are Aeschynan, Chirita, Hemiboea, and Titanotrichum and so on. Fifty eight genuses, 463 species have been found in China, and there are 27 genuses could be found in China only. There are all belong to Cyrtandroideae. Lots of the gesneriads are rarely and endangered species, Iots of them are beautiful ornamental flowers. When the central distribution area of a species is destroyed by human activities, remaining portions of the populations along marginal areas of the distribution may not have habitat suitable to maintain the survival of the species. Rare and endangered plants usually have limited reproductive capacities and very slow growth rates. The use of in vitro culture can overcome these difficulties.This study deals with the methods for in vitro rapid propagation and conservation of gesneriads. Another purpose of this experiment is to search and demonstrate the high regenerative capacity of leaf tissue of gesneriads. We used C. heterotricha, C. longgangensis and H. subcapitata as the main materials. The contamination rate was greatly decreased by using a improved surface-sterilized technology and had more adventitious shoot fort-nation in MS medium supplemented with BA 0.1～3.0 mg1^-1, NAA 0.1 mg 1^-1, sugar 30 g 1^-1. When optimal levels of growth substances, particularly auxin and cytokinins, are utilized, many species of gesneriads could be generated from a single leaf. So far, about 16 species and more than 24 clones of Gesneriaceae plants have been conserved in vitro and propagated. A procedure for the in vitro regeneration shoots yia organogenesia or somatic embryos of gesneriads is described. Many species, such as C. heterotricha, C. spadiciformis, C. subrhomboides and S. speciosa, are all flowered.2. Based on the research on the in vitro tissue culture of Gesneriaceae, the author took five years to investigate the in vitro conservation of Gesneriaceae germplasm. The results were summarized as follows:(1) In vitro shoots were conserved for 4～5 years by subculture at normal temperature and by slow growth about 20 Gesneriaceae species.(2) Protocols of cryopreservation for 3 Gesneriaceae species have been studied. The results demonstrated the feasibility of cryopreservation for storage of Gesneriaceae leaf explants. The procedure of cryopreservation involved in the step: in vitro induction of leaf explants→drying the explants in the air→dehydration of explants in a concentrated vitrification solution→stored in liquid nitrogen→thawed in the air→reculture on MS medium. (3) Single factor tests were applied to optimize the procedure for cryopreservation of 3 Gesneriaceae species. A procedure has been developed which was as follows: leaf explants after subculture 20 d→drying the explants in the air (22℃～25℃) 3 d→loading of explants with 2 M glycerol and 4 M sucrose for 20 rain at room temperature (20～25℃)→dehydration of explants in a concentrated vitrification solution (PVS4) for 20 min at 0℃→plunge into liquid nitrogen directly→thawing in water bath at 40℃→unloading of explants with MS and 1.2 M sucrose for three times→reculture on MS medium.3. Many species of gesneriads have highly decorative values of both leaves and flowers. Some of gesneriads are endemic and endangered in China. They are excellent shade plants and almost none study were conducted on shade-tolerance of the Gesneriaceae plants.The effects of shade on the photosynthetic characteristics, chlorophyll fluorescence in leaves, chlorophyll contents, leaf anatomical structure and growth characters of C. spadiciformis, S. ionantha and C. longgangensis were determined under different light conditions (10％, 30％, 50％and 100％full light in greenhouse) within pots. The results showed Gesneriaceae plants had lowest compensation point (20μmol·m^-2·s^-1) and saturation point (600λmol·m^-2·s^-1). The net photosynthetic rate (P_n) was significantly higher in shade than in full light. Change characteristics of chlorophyll fluorescence, such as real quantum efficiency (PhiPSⅡ), non-photochemical quenching (NPQ)and so on, and the adaptability of 3 Gesneriaceae species were studied under different irradiance.Chlorophyll contents were increased and value of C_a/C_b was decreased with shading. Shading affected leaf anatomical character as well. 3 Gesneriaceae species have typically shade anatomical structure. Growth characters at different light intensities were significantly affected. With shading levels increasing, biomass of the plants' decreased.Light compensation points, light saturation points, chlorophyll contents and value of C_a／C_b can all be important index of shade-tolerance, leaf anatomical character had close relation with shade-tolerance. According to their photosynthetic responses to shade treatments, the shade tolerant ability of 3 Gesneriaceae species was in the order: S. ionantha＞C. spadiciformis＞C. longgangensis.Theory guides were provided of Gesneriaceae plants of their cultivation and propagation in greenhouse.