不同柚類品種對柑橘萎縮病毒莖陷系統之感病性分析

Abstract

臺灣主要栽培文旦柚，這使得採收和銷售盛期都集中在中秋節，進而導致了產銷失衡的問題。柑橘萎縮病對柚類植株的影響非常大，尤其是柚類莖陷強毒系統，而且不同柚類品種表現出不同的感病程度。透過溫室實驗，評估了不同柑橘萎縮病系統抗感病性的反應。本研究選擇了四種柚類品種進行實驗，包括文旦、麻豆紅柚、白柚和泰國西施柚。這些柚類品種分別接種了兩種不同的柑橘萎縮病柚類莖陷病毒系統：（1）柑橘萎縮病柚類莖陷TC-1强毒系統；（2）柑橘萎縮病柚類莖陷TC-5弱毒系統。透過即時定量RT-PCR技術每月追蹤病毒複製的情形，並觀察接種後的病徵表現。結果顯示，所有的柚類品種皆可被柑橘萎縮病柚類莖陷TC-1强毒系統和TC-5弱毒系統感染。單獨接種柑橘萎縮病柚類莖陷TC-1强毒系統時，麻豆紅柚與白柚出現了嚴重的病徵，包括植株矮化、葉片變小、莖部凹陷、節間縮短以及樹勢衰弱。然而，在文旦和西施柚植株則未出現嚴重的病徵，植株的整體健康狀態良好，但莖部仍可見凹陷病徵。再者，在單獨接種柑橘萎縮病柚類莖陷TC-5弱毒系統時，所有柚類品種皆未出現嚴重病徵，植株的生長狀態接近健康植株狀況，僅有極輕微的莖陷病徵可見。當柚類複合感染TC-1强毒系統和TC-5弱毒系統時，同樣是麻豆紅柚和白柚出現嚴重病徵，經病毒量比較後證明兩者之間並無顯著差異。此外，本研究以白柚和西施柚進行交叉保護實驗，首先使用TC-5弱毒系統進行初次感染，然後接種挑戰的TC-1强毒系統。結果顯示，交叉保護處理組的四棵白柚植株中，有兩棵植株病徵變得更加劇烈，如出現葉脈木栓化和嚴重莖部凹陷病徵。然而，交叉保護處理組的西施柚則無出現嚴重病徵。此項研究首次提供柑橘萎縮病柚類莖陷弱毒系統對柚類品種進行交叉保護的重要資訊。

In Taiwan, the predominant cultivation of Wentan pomelo leads to a concentrated harvest and sales period during the Mid-Autumn Festival, resulting in a production imbalance issue. Citrus Tristeza Virus, especially pomelo stem-pitting strain, can significantly impact on pomelo trees. Various levels of severe strains of Citrus Tristeza Virus (CTV) pathogenicity are exhibited among different pomelo cultivars. Wentan, Matou HongYu, Peiyu, and Xishi pomelo were chosen for experimentation presented in this thesis. These pomelo cultivars were individually inoculated in the greenhouse with two distinct CTV strains: (1) the severe TC-1 strain and (2) the mild TC-5 strain. Monthly monitoring of virus replication using real time RT-PCR, along with an evaluation of symptom expression post-inoculation were employed. Both CTV strains can infect all pomelo cultivars. When the pomelos were individually inoculated with the severe TC-1 strain, Matou Hongyu and Peiyu pomelo displayed severe symptoms, including growth reduction, leaves atrophy, stem pitting, shorter internodes, and diminished tree vigor. In contrast, the severe symptoms did not occur in Wentan and Xishi pomelo. Despite the presence of slight stem pitting, these pomelos remained in a healthy condition. Regarding susceptible rating, the pomelo cultivars can be ranked as follows: Peiyu, Matou Hongyu, Wentan, and Xishi pomelo, with Peiyu being the most susceptible cultivar. Furthermore, when individually inoculated with the mild TC-5 strain, all pomelo cultivars exhibited little to no symptoms, with their growth closely resembling that of healthy plants. Only slight stem pitting symptoms were observed. In cases of co-infection with both the severe TC-1 strain and the mild TC-5 strain more pronounced symptoms were found in Matou Hongyu and Peiyu pomelo. However, the comparative viral load analysis showed no significant difference between these two strains. Cross-protection experiments were also conducted on Peiyu and Xishi pomelo. Initially, the mild TC-5 strain was inoculated into the plants to induce plant immunity. Subsequently, the severe TC-1 strain was introduced to test the effectiveness of the mild strain’s protection. Based on the results, two of the four Peiyu pomelo seedlings subjected to cross-protection treatment exhibited intensified symptoms, which includes leaf vein corking and severe stem pitting. Conversely, no severe symptoms were observed in the Xishi pomelo seedlings undergoing the same treatment. These findings provide valuable insights into cross-protection strategies for enhancing the resistance of pomelo cultivars against CTV infection.