Studies On Genetic Diversity Among Main Sweetpotato Germplasm Resources In China

As an important material of industry,new energy resource,food and forage crop in the world, sweetpotato(Ipomoea batatas(L.) Lain.),is desired to increase starch yield in breeding.For the realization of high-starch yield varieties of sweetpotato in the early generation of directional selection,shorten the breeding cycle,in this study,48 main sweetpotato germplasm resources in china were assessed genetic diversity by using SRAP markers,and researched the correlation among starch yield,morphological traits and the activity of starch synthesis key enzymes in different periods.It was also discussed that germplasm resources classified based on yield,starch content and based on starch yield,respectively.The main results showed as follows:1.The results of cluster analysis which based on yield and starch content were not consistent with the practical classification,while the results of cluster analysis which based on starch yield were well consistent with the practical classification.2.The cluster results of morphological traits in 100 days after planting had the highest relevancy with the ones of starch yield in different periods.Among these morphological traits in 100 days after planting,starch yield was in highly significant negative correlation with plant branch, and in highly significant positive correlation with dry matter rate.No significant correlation existed between among starch yield and maximum length of vine,the number of root tubers per plant or the fresh weight of root tubers per plant.Because of the highly significant correlation with starch yield, plant branch and dry matter rate in 100 days after planting could be used as an important morphological index of early selection in sweetpotato high-starch yield breeding.3.The cluster results of the activity of starch synthesis key enzymes in 50 days after planting had the highest relevancy with the ones of starch yield in different periods.Among these activity of enzymes in 50 days after planting,starch yield was in negative correlation with AGPase,and in positive correlation with SS and SPS,but the correlation have not reached significant level. Because of the lowly correlation with starch yield,the activity of AGPase,SS and SPS could not be used as a physiological index of early selection in sweetpotato high-starch yield breeding. 4.An optimized SRAP reaction system for sweetpotato genome was established by this experiment.10μl reaction system contains 1.25μl 10×PCR Buffer,0.4μl 25mM MgCl₂,0.2μl 10mM dNTPs,0.5μl 50ng/μl forward primers,0.5μl 50ng/μl reverse primers,1.0μl 50ng/μl DNA template,0.1μl 5U/μI Taq DNA polymerase,6.05μl ddH₂O.An optimized PCR reaction procedure for SRAP analysis was also established.The temperature profile used for PCR was 94℃for 5min, followed by 5 cycles of 94℃for 1min,35℃for 1min,72℃for 2min,then 35 cycles of 94℃for 1min,50℃for 1min,72℃for 2min,and was terminated with a 5min DNA extension step at 72℃.5.29 out of the 37 primer pairs random selected were polymorphic among the 48 sweetpotato germplasms,the polymorphism ratio of primers was 78.4%,and 126 polymorphism bands were obtained,4.3 polymorphism bands per primer pairs in average.These results demonstrated that SRAP had much higher polymorphism in the tested sweetpotato resources.6.Based on the cluster analysis according to the SRAP markers,the genetic distance of the different germplasms was from 0.037 to 0.601.As the genetic distance was 0.46,48 germplasms were classified into six main groups,which included one complex group and five independent ones, and the complex group could be classified into seven subgroups.Most cultivars(lines) which had genetic relationship with Okinawa 100,Nancy Hall and Xushu 18 were classified into the same group.The cluster result was consistent with the pedigree of these varieties.The genetic differences among sweetpotato germplasms had not necessary relation with geographic origin.7.Relevancy analysis was carried out among the cluster results of starch yield,SRAP markers, morphological traits and the activity of starch synthesis key enzymes,and the results showed that the cluster results of SRAP markers had the highest relevancy with the ones of starch yield.