以農藝性狀與簡單重複性序列評估高粱種原之遺傳歧異度

Abstract

高粱 (Sorghum bicolor (L.) Moench) 為全球第五大禾穀類作物，起源於非洲 熱帶地區。由於高粱具有高度的耐旱性與適應環境的能力，對半乾旱地區是重要 的糧食作物，除此之外，也用於飼料、掃帚、釀酒與生質酒精，用途相當廣泛。 評估高粱種原的遺傳歧異度對於高粱的遺傳育種有其必要性，是以，我們從外表 型性狀和DNA 分子標幟基因型著手進行探討。本研究高粱材料包括來自農委會 農業試驗所作物種原中心、臺灣大學農藝學系和由臺灣各地田野採集之高粱種原， 共計93 個品系。其中，以48 個高粱品系於民國102 年第二期作種植臺灣大學農 業試驗場，田區設計採完全隨機設計，每品系5 個重複，並進行株高、分蘗數、 穗長、抽穗日數和穗數等五個性狀之調查。試驗結果發現株高表現介於25 - 204 公分；分蘗數目為0 - 8 個；抽穗時間則介於59 - 195 天；穗數介於1 - 23 個；穗 長介於6 - 44 公分，由上述調查結果可明顯看出這些高粱品系之遺傳歧異度相當 大。進一步以外表型資料進行分群分析，結果發現所蒐集之高粱品系呈現高度之 遺傳歧異，臺灣蒐集與飼料釀酒用的高粱則大致歸為同一類群。其次，另以53 個簡單重複性序列 (simple sequence repeat, SSR) 分析93 個高粱種原的基因型， 平均每個分子標幟可偵測到14.4 個對偶基因數目，其中多態訊息含量 (polymorphic information content, PIC) 介於0.206 – 0.922，平均PIC 值為0.709。 進一步分析93 個高粱品系親緣關係，兩兩之間的Nei’s 遺傳距離(genetic distance) 介於0.055 – 0.983，顯示品系間的相似度差異很大。而由親緣樹圖分群 結果可分為三大群，臺灣各地收集來的種原大致落在第二大群之一個小群，而飼 料用之高粱品系大多分在第三大群，此外，屬於野生型的擬高粱與強生草皆分在 第一大群中。主座標分析 (principal coordinate analysis, PCoA)，亦有相似之歸群 結果，擬高粱與強生草位於第三範圍，而第六範圍之高粱品系皆為臺灣蒐集系。 最後，本研究以STRUCTURE 軟體分析93 個高粱種原之族群結構，模擬結果將供試高粱種原分為八個次族群，臺灣收集之高粱大致分在兩個次族群內，表示其 遺傳背景相似程度高，而大多高粱屬 (Sorghum) 之種原也分在同一次族群內， 然仍含有混合型之個體。總而言之，本研究結果顯示SSR 分子標幟之多型性程 度很高，對於探勘具有發展潛力之高粱種原相當有幫助，而參試之高粱種原間的 遺傳歧異度不論透過外表型性狀或分子標幟分析，均顯示有相當大的差異存在。 因此，期望經由本研究之分析結果，能提供未來進行高粱育種改良工作中，選擇 雜交親本之參考應用，奠定高粱的遺傳研究以及育種改良等研究之基礎。

Sorghum (Sorghum bicolor (L.) Moench) is the fifth most important cereal crop in the world. Sorghum is an important staple food for people who live in semi-arid regions because of its drought tolerance and high ability of environmental adaptation In addition, it can be used as forage, feed crop, broom, and bio-ethanol production. As a result, sorghum is a multipurpose crop. Assessing the genetic diversity of sorghum germplasm is essential to breeding programs. We investigated the collected sorghum accessions by evaluating phenotypes in the field and genotypes of DNA marker, simple sequence repeat (SSR). The sorghum germplasm were obtained from 1) National Plant Genetic Resources Center; 2) Department of Agronomy, National Taiwan University (NTU); and 3) fields in all parts of Taiwan. We planted 48 sorghum accessions according to complete random design (CRD), five replicates for each sorghum accessions, in the experimental farm at NTU in fall 2013. Then we measured five important traits, including plant height, tiller number, panicle length, heading date, and panicle number. The results showed that plant height was ranged from 25 to 204 cm; tiller number was ranged from 0 to 8; heading date was ranged from 59 to 195 days; panicle number was ranged from 1 to 23; and panicle length was ranged from 6 to 44 cm. These results implied that sorghum accessions highly diversified at the morphological level. The sorghum accessions demonstrated high level of genetic diversity based on the cluster analysis by phenotype data. The Taiwan collected accessions were clustered together, and so as the forage and waxy sorghum. Furthermore, a total of 53 SSRs were used to evaluate genetic diversity of 93 sorghum germplasm. Averagely, 14.4 alleles were detected per locus, and the polymorphic information content (PIC) value ranged from 0.206 to 0.922 with a mean of 0.709,indicating high discriminating ability of SSR markers used. The Nei’s genetic distance ranged was from 0.055 to 0.983, implying that the substantial difference among the sorghum accessions. The sorghum germplasm were divided into three clusters based on the phylogeny tree using neighbor-joining. The Taiwan collected accessions were in a subgroup of the second cluster; the forage sorghum accessions were in the third cluster. Moreover, S. propinquum and S. halepense were all in the first cluster. The result of Principle Coordinate analysis was largely identical to phylogeny analysis for which S. propinquum and S. halepense were belonged to the third range and the Taiwan collected accessions belonged to the sixth range. According to STRUCTURE analysis, sorghum germplasm were divided into eight subpopulations. Taiwan collected accessions were separated into two different subpopulations, indicating that the genetic background among Taiwan collections were similar to each other; on the other hand, the germplasm of Sorghum genus were grouped in one subpopulation, though admixtures were observed. In summary, the levels of polymorphism of SSR markers used in this study were very high, and it might help explore some sorghum germplasm with potential. Either through agronomic trait or marker analysis, the genetic diversity among the collected sorghum germplasm was highly diverse. This study established the fundamental of sorghum genetic reseach and provided useful information to sorghum breeding programs.