臺灣香檬開花行為與溫度對其生育之影響

Abstract

臺灣香檬 (Citrus depressa Hayata) 為臺灣原生柑橘，利用價值高，但相關研究甚少。本研究藉由觀察與比較臺北與屏東兩地區生長的臺灣香檬的抽梢與開花特性，再利用4種日夜溫處理，探討溫度對臺灣香檬抽梢、花芽形成與開花的影響。 觀察試驗於2017年一至九月於臺北地區及二至八月於屏東地區進行。臺北地區的臺灣香檬於一至四月陸續抽出一次梢，而後每2個月為1週期抽梢；屏東地區的臺灣香檬亦多次抽梢。臺灣香檬開花型態主要為純花梢(無葉單花梢)與帶葉花梢(多葉單花梢)，每節位可抽出1-4朵花。枝梢頂端3節多形成帶葉花梢，枝梢基部多形成純花梢，其中又以帶葉花梢的著果率較純花高。臺北地區之臺灣香檬於三月初可見花芽萌發，並在三月底至四月初開花，花苞發育時間隨著調查期溫度增加而縮短。屏東地區之臺灣香檬於二月時有一次明顯的花期，但在調查期間每月皆有植株開花，非正期花開花型態多為帶葉花梢。二月形成之正期花帶葉花梢的著果率高於純花之著果率。整理兩批次觀察結果，建立一套臺灣香檬的BBCH編碼，用以描述臺灣香檬的物候生長階段。 溫度試驗於生長期(2017年四至六月)及生長停滯期(2017年十二月至隔年一月)進行，將植株分別置入日夜溫30/25℃，25/20℃，20/15℃，15/13℃處理，並以自然環境作為對照。生長期進行溫度試驗之結果，臺灣香檬於日夜溫30/25℃與25/20℃處理1週後抽梢，日夜溫20/15℃與15/13℃處理7週後抽梢，顯示高溫可促進臺灣香檬抽梢。生長停滯期進行溫度試驗且同時進行石蠟切片觀察芽體分化。於2017年十二月的臺灣香檬枝梢其芽體已可見進入花芽分化前期，經30/25℃及25/20℃溫度處理3週後芽體則逆分化回營養芽，而20/15℃及15/13℃溫度處理3週後可見萼片原體的形成，處理7週後已觀察到花瓣原體形成。 綜合上述結果，低溫為影響臺灣香檬花芽分化之因子，高溫則會抑制其花芽分化，但由於於屏東地區不時花的花芽形成條件尚未明瞭，未來可嘗試利用其他影響柑橘開花的因子如乾旱處理，探討其它可促進臺灣香檬植株的開花機制。

Citrus depressa Hayata is one of indigenous citrus in Taiwan, are high value of use in Taiwan and Okinawa. However, there is few studies working on the flowering behavior about C. depressa. In this research, we investigated and compared the flushing and flowering chacteristic between the trees located in Taipei and Ping-Tung county. And then, we treat C. depressa with four day/night temperature, to understand the flushing, flower bud formation and flowering characteristics in C. depressa. Obsevration was conduct in Taipei during January to September and in Ping-tung during February to Agust. In Taipei, the first flushes of C. depressa were began to emerging during January to April, 2017, and then sprouting every two monthes in Taipei. Plants in Ping-tung also sprouted many times all around the year. The flowers type of C. depressa were generative shoot (no leaves with one flower) and mixed shoot (several leaves with one terminal flower), the flower come from axillary and multiple in one node. The terminal part of C. depressa flowering shoot formed more mixed shoot, basal part of flowering shoot formed more generative shoot. Mixed shoot of C. depressa had higher ratio of fruit retaining than generative shoot. We can see the flower bud visible in early March 2017, C. depressa started to anthesis in late March and early April in Taipwi. Flowering days of C. depressa shortens when the temperature increasing during flower bud development.C. depressa could sprout and flower several times all around the year, and there was a main flowering period in Ping-tung in February. C. depressa formed more mixed shoot on the off season flowering shoots, and had also had higher ratio of fruit retaining than generative shoots.The preliminary BBCH scale of C. depressa is established for reference to understand the flush and flower phenology characteristics in C. depressa. Temperature treatment were carried out in growth period and growth stagnation period of C. depressa (April to June and December to January.) C. depressa were treated with day/night temperature 30/25℃, 25/20℃, 20/15℃, 15/13℃ and natural environment as a control. In the growth period conducting temperature treatment, the plant in 30/25℃and 25/20℃sprouted after 1 week; the plant in 20/15℃and 15/13℃sprouted after 7 week. The result shows that temperature treatment high temperature can promote flushing. During growth stagnation period conducting temperature treatment, we used paraffin-sectioning to obeserve the bud differentiation of C. depressa. The ealy stage of flower bud differentiation had formed in early December, 2017. The flower bud dedifferentiated back to vegetative bud, after 3 weeks treatment in 30/25℃ and 25/20℃. The flower bud formed sepal primordia after 3weeks and formed petal primordia after 7 weeks in 20/15℃and 15/13℃. The result indicated low temperature should be the most critical factor that induced C.depressa flower bud formation, high temperature can inhibition flower bud formation. The off-season flower formationof C.depressa in Ping-tung were still unknown. In the future, we can try to use other factors that affect citrus flower intiation, such as water stress, to know the flowering behavior of C. depressa.