| In recent years, with the development of biomass energy industry, the use of ethanol, biomass diesel oil instead of part of the traditional gasoline and diesel has become a trend, providing a huge space for the progress of the living material fuel and the extraction of raw materials supply. Switchgrass, which is regarded as biological energy plant, is rich in cellulose and hemicellulose in the cell wall, and these two compositions are the main sources for transforming energy grass into ethanol. In addition, switchgrass is becoming a focal energy crop according to its low moisture and ash content.The of tetraploid to octoploid may lead to emergence of new features and phenotypes, such as phenotypic gigantism, the influence onthe structure of lignocellulose, drought resistance, resistance to diseases and pests, providing germplasm resoureces for screening and breeding more excellent switchgrass varieties. In this research, we analyzed the genetice variation between tetraploid and octoploid Alamo switchgrass by means of phenotypic traits, molecular markers, and MSAP methylation pattern.1.First of all, seven indexes of stem diameter, flag leaf length, leaf width, plant height, tiller number, dry weight and fresh weight were compared between 68 different polyploidy Alamo switchgrass. The results:there was highly significant defference in the stem diameter, plant height, flag leaf width and tiller number of these two ploidies (p< 0.01); the flag leaf length showed significant difference(p<0.05); the stem diameter, plant height, flag leaf width and length of tetraploid were less than those of octoploid, but tiller number was more. butthere was no significant difference between fresh weight and dry weight (p> 0.05). Variation analysis results showed phenotypic variation existed between individuals with various levels of ploidy, the tetraploid average variation coefficient was 39.56%, the octoploid average variation coefficient was 33.91%.2. For the study of the genetic relationship and genetic diversity between two different switchgrass ploidies, EST-SSR, IT-ISJ were used to analyze 68 switchgrass individuals with various levels of ploidy. The results showed that in tetraploid, EST-SSR and IT-ISJ diversity index I was 0.2145 and 0.2145, respectively, while the I was 0.2071 and 0.3955 in octoploid. For the whole switchgrass population, EST-SSR and IT-ISJ diversity index was 0.2716 and 0.5226. Tetraploid and octoploid switchgrass could be divided into two categories by EST-SSR and IT-ISJ, indicating that there were genetic variation between these two ploidies; EST-SSR marker genetic differentiation index was 26.75%, IT-ISJ markers was 16.55%, indicating that there were abundant genetic diversity among and within switchgrass ploides, and genetic variability within ploides was better than that among ploides.3. Methylation Sensitive Amplification Polymorphism (MSAP) was used to analyze methylation patterns of 68 switchgrass individuals with various levels of ploidy. The results showed that more than 20000 methylation sites were detected with 18 primer pairs, most of which were non-methylation sites. In tetraploid, methylation rate, total methylation rate, half methylation rate were 19.37%,12.28%,7.09%, respectively, which were higher than those of octoploid (18.03%,12.55%,5.47%, respectively). The results showed that in tetraploid and octoploid, methylation patterns were given priority to total methylation. The apparent genetic differentiation coefficient (GST) of tetraploid was 0.0197; while the GST of octoploid was 0.0226. Switchgrass methylation gene Shannon diversity index was 0.3096, the tetraploid Shannon index was 0.3157, the octoploid was 0.3026, showing that there was high methylation diversity among and within tetraploid and octoploid switchgrass. |
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