Research On The Genetic Traits And Stress-Tolerance Of Tetraploid Cymbidium Hybrids

Cymbidium flowers possess high ornamental value for their exotic flowers, beautiful leaves. In recent years, with the improving appreciation ability of people, there are more and more requirements for Cymbidium flowers on the floral pattern and cultivation adaptability. Traditional chinese orchid owns small floral pattern, thick aroma and strong cold resistance, while tropical epiphytic orchid shows large floral pattern, no-aroma and poor cold resistance. Now there are a lot of reports on the research of interspecific hybridization and the chromosome doubling of the new hybrided varieties from chinese orchid and tropical epiphytic orchids. However, there is few report on the investigation of the genetic stability and stress resistance in the polyploid. In this study, the seedlings from Cybidium hybrids of C.faberi, and the tetraploid hybrids gained by colchicine treatment were analyzed. The genetic stability of tetraploid was determined after long-term tissue culture. The physiological and biochemical characters were valuated in diploid and diploid after exposed to high temperature stress and low temperature stress. New Cymbidium germplasm will be selected basing on the compare of above parameters.The major results were as followed:1. There were significant differences between diploid and tetraploid Cymbidium hybrids in terms of external morphology, stomatal density, guard cell size and chlorophyll content. In a summary, the tetraploid plants seemed robust and the leaves of tetraploid were wider, thicker, shorter, and deepener color than diploid, and the tetraploid also have a stronger rooting system. When diploid were compared to tetraploids T1, T2, the leaf length showed34.4%,30.6%increase respectively, the leaf width decreased41.3%and39.7%respectively, the leaf thickness decreased51.2%and63.4%respectively, leaf indexes increased53.7%,50.3%respectively. Diploid stomata densities were2.8and2.9folds over tetraploid T1, T2respectively, the stoma length ratios of diploid to tetraploid were1:2and1:2.1respectively, width ratios were both1:2.0, the total chlorophyll content of tetraploid T1, T2were1.5and1.6folds over diploid respectively. All above comparison parameters showed significant differences.2. Chromosome analysis indicated that chromosome number of diploid is2n=2x=40, while the tetraploid chromosome number is2n=4x=80, showing two times as much as that of diploids. Flow cytometry detection found diploid at about200, tetraploid at about400, suggesting the content of DNA of tetraploid was two times to that of diploid. On the whole, Chromosome analysis and flow cytometry detection gave out the same results.3. The physiological indices of diploid and tetraploid were compared. The results show that compare to diploid, tetraploid T1, T2showed54.8%and57.1%increase of soluble suger content,68.2%and68.5%increase of souble protein content, respectively. The tetraploid T1,T2leaf water content was both1.1folds, the root activity was1.7times,1.6times as that of diploid. All indexes indicated significant differences.4. The effects of heat and cold stress on plants physiological and biochemical characteristics were analyzed to assess the ability of heat resistance and cold resistance of the diploid and tetraploid. The results showed that high temperature stress or cold stress all decreased the chlorophyll content of both seedlings and tetraploids showed less decrease. The malondialdehyde (MD A) content was increased in both of plants and diploid increased more. The O2·-release rate was decreased in both of seedlings and decreased fast in diploid. The increasing ranges of leaf proline content, soluble sugar, soluble protein were all higher in tetraploid. After high temperature stress, the activity of catalase (CAT) and superoxide dismutase (SOD) increased, while decreasing ranges of POD activity was notable in diploids. Similarly, after cold stress, the activity of catalase (CAT) and superoxide dismutase (SOD) were also increased, and the increasing rate in tetraploid was higher. On the other hand, peroxidase (POD) activities went through a short-time increase then declined sostenuto and the reduction rate was lower in tetraploid seedlings. Our data suggests that tetraploids are stronger than diploids in heat and cold resistance.