Studies On Genetic Stability And Cryopreservation Of Sweet Potato Germplasm

Sweet potato is a vegetative propagation crop, for its genotype is highly heterozygous. At present, sweet potato germplasm in China was mainly kept in the following three ways: in field, in vitro culture and greenhouse-plotting. For long time conserved sweet potato germplasm, different degrees of genetic variation may occur as the external environment changed. To compare the effectiveness and differences of in field and in vitro conservation, we detected 32 variaties of sweet potatoes' genetic stability by morphological marker, isozyme biochemical marker and DNA molecular marker. The result showed that both of field and in vitro culture could conserve sweet potato germplasm safely, and their conservation efficiency is similar. But as the conserve time prolongs, a few varieties may occur genetic variation. Also, we wanted to find feasible technologies to conserve sweet potato germplasm and methods to detect its genetic stability. So we studied the cryopreservation of sweet potato shoot tips at the same time. The main content and conclusions of this thesis are as follows:1. The effectiveness of germplasm conservation in filed genebank and in vitro genebankTo evaluate the effectiveness of sweet potato germplasm preservation, we have investigated their main agronomic traits for two consecutive years. The on-the-ground traits include color and shape of the top of leaves; stem color, plant type and so on. The underground traits are skin color and shape of storage root as well as a flesh color. The total number of investigated agronomic traits is 13. Survey results showed that the differences were mainly reflected in color, such as the color of top leaf, pigmentation of vein, pigmentation of basic leaf vein, skin color of storage root, flesh color. And most of them are different in the deep of color. Overall, most varieties show high genetic stability. The majority differences are resulted from in vitro conservation, and after the second year growth in field, the majority of the differences were disappeared. We reached the conclusions that the most variations during long-term in vitro conservation were temporary and could be recovered through being planted in field. Therefore, both field genebank and in vitro culture could conserve sweet potato germplasm effectively. However, some varieties also be changed under the two conservation measures due to long-term conservation.2. Comparing the effectiveness of sweet potato germplasm conservation between field genebank and in vitro genebankThere is no significant difference in morphological traits between materials conserved by field genebank and in vitro conservation after consecutive investigation. The difference detected by biochemical markers are mainly in the color of esterase band. Only a small number of esterase isozyme banding pattern difference appeared in some varieties. .ISSR analysis shows that the vast majority of the conserved materials are the same in banding pattern. At the same time, there is no remarkable relation in storage time and the varieties occurring variations. Therefore, combining the three levels test results of morphological, biochemical and molecular markers, we could reach the conclusions that filed genebank and in vitro culture could conserve sweet potato germplasm effectively and the differences between the two has nothing to do with the conservation time within the time in texted.3. Cryopreservation of sweet potato germplasmDroplet vitrification and encapsulation-vitrification metholds were used in cryopreservation of sweet potato shoot tips. By single-factor analysis of each step and factors of cryopreservation, including the shoot tips' culture method, materials' genotype, preculture method, types of plant vitrification solution(PVS), PVS exposure time and so on, an optimized cryopreservation program of sweet potato shoot tip was obtained. And then, the optimized program was used to cryopreserve of seven sweet potato varieties. It showed that PVS2 is better than PVS3, and droplet vitrification is method superior to encapsulation-vitrification method. Applied, the survival rate of sweet potato shoot tips after cryopreservation using the optimized program is up to 64 %, and the highest regeneration rate is 46%.