醋栗番茄柱頭外突性狀變異調查

Abstract

柱頭外突性狀影響番茄的交配模式，突出於雄蕊管之柱頭降低自花授粉的機會。現今的番茄栽培種多為自交，不再具有柱頭外突特徵。本研究收集了235個醋栗番茄 (Solanum pimpinellifolium) 種原，調查雄蕊長度、雌蕊長度、柱頭外突長度與雄雌蕊長度比，共四個與柱頭外突相關的性狀。外表型調查結果顯示高達92%的品系雌蕊長於雄蕊，並且柱頭外突平均長度約為1 mm，表示大多數品系具有柱頭外突特徵。由於雄蕊長度與雌蕊長度兩性狀之外表型分布呈雙峰分布，柱頭外突長度分布經Shapiro-Wilk檢定亦不符從常態分布，因此嘗試將資料分布轉換。經Yeo-Johnson轉換法能夠將柱頭外突長度轉換為近似常態分布，此常態分布為遺傳關聯性分析之前提假設。 將來自安地斯山脈的醋栗番茄種原進一步依其採集的地理位置劃分為厄瓜多、北祕魯、南祕魯三個次族群，其中柱頭外突長度最長以及雄雌蕊比例最低的為北祕魯次族群，厄瓜多次族群次之，柱頭外突表現最不明顯的則是南祕魯次族群；至於柱頭外突相關外表型之變異程度，平均而言則是厄瓜多次族群最高，北祕魯次族群以及南祕魯次族群相對較低。此外，我們發現柱頭外突長度與地理位置分布具有一定之關聯性，厄瓜多南部至祕魯北部有最明顯的柱頭外突現象，祕魯中南部次之，厄瓜多北部則是幾乎不具柱頭外突特徵。柱頭外突外表型隨地理位置改變之趨勢與前人所提出的番茄兩階段馴化路徑相似，因此我們推測番茄的柱頭外突性狀或許隨著野生番茄的馴化歷程逐漸演化為不外突。

The stigma exsertion trait affects the mating system of tomatoes. Stigma protruding the stamen tube reduces the chance of self-pollination. Most of the modern tomato cultivars are self-pollinated, and no longer have the stigma exsertion feature. In this study, 235 accessions of currant tomato (Solanum pimpinellifolium) were collected to investigate the four traits related to exserted stigma, including stamen length, pistil length, stigma exsertion, and stamen-pistil ratio. Results of the phenotypic investigation showed that up to 92% of the accessions had pistils longer than stamens, and the average length of stigma exsertion was about 1 mm, indicating that most accessions were with the characteristics of exserted stigma. Since the distribution of stamen length and pistil length showed bimodal patterns nor did the distribution of stigma exsertion follow the normal distribution by Shapiro-Wilk test, we tried to transform the data distribution. The Yeo-Johnson transformation method can transform the stigma exsertion into an approximately normal distribution which is the assumption for genetic association analysis. The currant tomato accessions from the Andes were further divided into three subpopulations according to the geographical location: Ecuador, northern Peru, and southern Peru. Among these three subgroups, the subgroup northern Peru had the longest exsertion length and the lowest stamen-pistil ratio, the subgroup Ecuador was second, and the subgroup southern Peru exhibited the least exserted stigma behavior. As for the degree of variation of the traits related to exserted stigma, the variation within the subgroup Ecuador was the highest on average, and the variation within the subgroup northern Peru and the southern Peru was relatively lower. Furthermore, we found that there existed a certain correlation between stigma exsertion and geographical distribution. The most prominent stigma exsertion pattern was from the accessions of southern Ecuador to northern Peru, the second was the accessions of central Peru to southern Peru, and the accessions of north Ecuador showed almost no exserted stigma. For the reason that the tendency of stigma exsertion to change with geographical location is similar to the two-stage domestication route of tomato proposed by previous studies, we speculate that the stigma exsertion of tomato may gradually evolve into non-exsertion along with the domestication of wild tomato.