蘭科植物是全世界數量最多且分布最廣的開花植物之一，目前已知約有超過30,000 個物種。由於蘭花具有迷人的外觀與多種應用價值，近年來在全球市場中的交易量正逐年提升，並在 2019 年創下高達約 2.15 億美金的產值，其中蝴蝶蘭的銷售額就占總值的 80%。為了因應消費市場需求，蘭花業者栽培出不同花朵大小的蝴蝶蘭逐漸成為育種的趨勢。然而，植物疾病造成蝴蝶蘭產值損失高達 30%，因此培育出具有特定花朵大小以及能抵禦黃葉病的品種便成為育種者的首要目標。為了瞭解這兩者的相關性，本研究使用 203 個蝴蝶蘭商業品種作為實驗材料，並以造成蘭花黃葉病 (yellow leaf disease) 的茄型鐮胞菌 (Fusarium solani) 為病原體來源。首先以疾病嚴重指數 (disease severity index) 量化 203 商業品種的抗病能力後，再與該商業品種的花朵大小進行相關性分析 (correlation analysis)。接著藉由 8 個簡單重複序列 (simple sequence repeat) 所建立的親緣關係樹 (phylogenetic tree)進行抗性 (resistant) 與感性 (susceptible) 品種的集群分析(cluster analysis)，並透過主成分分析 (principal component analysis) 得知在商業品種的遺傳背景中，影響花朵大小與黃葉病抗性的蝴蝶蘭原生種。此外，由於 TCP4 參與植物的花朵發育以及加強植物面對生物性逆境 (biotic stress) 的抗性，因此檢視蝴蝶蘭的 3 個 TCP4 直系同源 (orthologous) 基因，包括PeCIN6、PeCIN7 及 PeCIN8 ，在極度抗性與極度感性品種之間的表現量差異。研究結果顯示，203 個商業品種由於來源不同，且針對抗性或感性商業品種而言，無法從親緣關係樹發現明顯的集群現象，僅以 8 個 SSR 分子標誌無法鑑別品種間遺傳背景的複雜度。然而根據花朵大小與 DSI 的相關性分析指出，當花朵越大時，對於黃葉病的抗性越弱；反之則越強。而 PCA 結果顯示，以小蘭嶼蝴蝶蘭 (P. equestris) 或矛舌蝴蝶蘭 (P. pulcherrima) 作為親本會產生具有花朵小且抗性佳的子代；相反地，以白蝴蝶蘭 (P. amabilis) 與臺灣蝴蝶蘭 (P. aphrodite) 作為親本會產生具有花朵大但抗性差的子代。根據基因表現量的結果得知，在同時比較 3 個極度抗性 (A7403、A11294 和 A2945) 及 3 個極度感性 (A10670、A6390 與 A10746) 的品種，只有 PeCIN8 在極度抗性的表現量是明顯高於極度感性的品種。此結果也與先前文獻的結果一致，即 TCP4 在高表現量時會抑制花朵發育卻能促進抗性增加。總結本研究的結果，花朵大小與黃葉病抗性之間存在高度的相關性，以及造成該性狀表現的 PeCIN8 相關基因。本研究的結果可提供未來育種者在考量到感染黃葉病的風險時，可以根據此研究結果挑選特定原生種作為親本，或是調控 PeCIN8 的表現量來孕育出符合消費者需求的蘭花品種。

Orchidaceae, containing more than 30,000 species, is one of the most abundant and widely distributed flowering plants. Due to its fascinating floral morphology and versatile applications, its output values in the global market have been increased in recent year. In 2019, it set an output value of 215 million U.S. dollars, of which the sales of Phalaenopsis accounted for 80% value. In addition, in order to meet the consent of consumers, breeding of Phalaenopsis with different flower sizes has gradually become a trend for orchid breeders. However, plant-related disease has caused 30% lost in the production value of Phalaenopsis. Therefore, breeding cultivars with specific flower size as well as resistance to yellow leaf disease has become the primary goal. To understand the correlation between the flower size and resistance to yellow leaf disease, this study used 203 Phalaenopsis cultivars as experimental materials, and Fusarium solani, which causes yellow leaf disease in orchids, was the source of the pathogen. First, the disease severity index (DSI) was used to assess the disease resistance of all cultivars, and then correlation analysis was performed between DSI and flower size of corresponding cultivars. The results indicated that larger flowers have weaker resistance to yellow leaf disease, while smaller flowers have stronger resistance. The complexity of genetic background was observed by phylogenetic tree using 8 simple sequence repeat (SSR) markers. In addition, the genetic background of all cultivars was checked using OrchidWiz, followed by performing principal component analysis (PCA). With P. equestris or P. pulcherrima as breeding parents, the offspring tend to have small flowers and good resistance. In contrast, with P. amabilis or P. aphrodite as breeding parents, the offspring tend to have large flowers but poor resistance. Previously, TCP4 gene has been reported to participate in the development of flower and improve the resistance to biotic stress. Thus, the differential expressions of three TCP4 orthologous genes, including PeCIN6, PeCIN7 and PeCIN8 were analyzed between the highly resistant and the highly susceptible cultivars. PeCIN8 showed significantly higher expression in the 3 extremely resistant (A7403, A11294, and A2945) than the 3 extremely susceptible (A10670, A6390, and A10746) cultivars, suggesting that PeCIN8 may be causal for flower size and resistance to yellow leaf disease. In conclusion, high correlations between flower size and resistance to yellow leaf disease were identified in Phalaenopsis orchids, and it is possible that PeCIN8 gene regulates these two traits in the extremely resistant/susceptible cultivars. These results can be applied to Phalaenopsis breeding programs for breeding the resistant cultivars against yellow leaf disease infection. Alternatively, the expression of PeCIN8 can be regulated to breed Phalaenopsis cultivars for resistant lines to meet consumers’ needs.

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