市場潛力柑橘品種對黃龍病的感病性評估與田間黃龍病現況調查

Abstract

柑橘作為臺灣產量最大的果樹，其經濟價值不容小覷。產期集中、品種單一化，是臺灣的柑橘產業長期以來的問題，而肆虐全世界的黃龍病一直是柑橘品質與產量的重要限制因子。農業試驗所的嘉義分所保存逾170個柑橘品種，並積極進行新品種的選育，其中不乏優良柑橘品種，儘管園藝性狀良好，其抗黃龍病的抗病能力卻是缺乏掌握的。有鑑於此，本研究選擇四種具有市場潛力的柑橘品種─臍橙、黃金茂谷、佛利蒙、與扁實檸檬，進行黃龍病之感病程度的測試，並與主流品種當中已知較感病的椪柑、桶柑還有已知較耐病的文旦、優利加檸檬相互比較。此外，本研究也測試不同的接種條件，對試驗結果的影響。四品種當中，黃金茂谷最感病，感染後葉片強烈黃化斑駁，且植株矮化程度高，臍橙與佛利蒙次之，扁實檸檬較耐病，罹病嚴重度低且菌量低，感病程度近似優利加檸檬。接種條件方面，雖然小植株與大植株在菌量增殖速度相差不大，但是小植株的發病速度普遍較快，此外矮小且分枝多的植株，其菌量分布較均勻。本研究也針對具市場潛力的品種，調查田間黃龍病的現況。罹病率方面，屏東的扁實檸檬與臺東的臍橙、佛利蒙的罹病率偏高，北部山區的佛利蒙、臍橙與黃金茂谷都沒有檢測到黃龍病，整體而言，罹病率與健康種苗的使用率無相關性。感染黃龍病的樣本中，多數都能檢測到原噬菌體，以T1原噬菌體單獨感染及T1+ T3原噬菌體複合感染的比例為主，有趣的是，不含任何已知原噬菌體的樣本，其菌量比較低。由於國內以往的黃龍病研究多半是針對市場的主流品種，缺乏新興品種或是非主流品種的學術研究資料，本研究針對上述四個具市場潛力的柑橘品種，提供黃龍病的試驗資料及田間危害現況，有助於未來推廣品種及田間管理能更加精準，因「品種」制宜。同時，本研究也累積臺灣本島的黃龍病生態資料，如噬菌體類型，為黃龍病菌系的演變提供資訊。

Citrus, as Taiwan's largest fruit tree crop, holds significant economic value. The concentrated harvest season and few citrus varieties supplied have been long-standing issues in Taiwan's citrus industry. The widespread Huanglongbing (HLB), also known as citrus greening disease, has been a crucial limiting factor for citrus quality and yield worldwide. Chiayi Agricultural experiment branch, Taiwan Agricultural Research Institute preserves over 170 citrus varieties and actively engages in breeding new varieties. While many of these varieties exhibit excellent horticultural traits, their susceptibility to HLB remains unclear. In light of this, this study aimed to select four citrus varieties with market potential, Navel, Ora, Fremont and Shiikuwasha, to test their susceptibility to HLB, and compared them with mainstream susceptible varieties such as Ponkan and Tankan, as well as resistant varieties like Wentan and Eureka Lemon. Additionally, this study also tested different inoculation conditions to assess their impact on the experimental results. Among the four varieties, Ora displayed the highest susceptibility to HLB, showing strong mottled yellowing on infected leaves and significant stunting. Navel and Fremont were the second, while Shiikuwasha exhibited greater disease tolerance, with lower disease severity and Candidatus Liberibacter asiaticus quantity, comparable to Eureka Lemon. In terms of inoculation conditions, although the rate of CLas proliferation did not significantly differ between small and large plants, small plants generally exhibited faster disease progression. Furthermore, shorter plants with more branches displayed a higher detection rate of CLas. This study also investigated the current status of HLB in the field for the selected market potential varieties. Disease incidence varied, with higher rates of Shiikuwasha in Pingtung and Navel and Fremont in Taitung. In the northern regions, Fremont, Navel and Ora showed no detectable presence of HLB. Overall, disease incidence did not correlate with the usage of the healthy seedlings. Among the HLB-infected samples, most contained prophages, with the highest proportion attributed to the T1 prophage alone or in combination with the T3 prophage. Interestingly, samples lacking any known prophage displayed lower CLas quantity. Given that previous HLB research in Taiwan mainly focused on mainstream market varieties, academic research data on emerging or non-mainstream varieties is scarce. This study provides valuable experimental and field data on HLB for the aforementioned four citrus varieties with market potential. This information will contribute to more precise field management and variety promotion, tailored to specific varieties. Additionally, this study collected ecological data on HLB in Taiwan, including information on prophage types, which offers insights into the evolution of CLas.