Tristeza is an economically important disease of the citrus caused by Citrus tristeza virus (CTV) of genus Closterovirus and family Closteroviridae. The disease has caused tremendous losses to citrus industry worldwide by killing millions of trees, reducing the productivity and total production. Enormous efforts have been made in many countries to prevent the viral spread and the losses caused by the disease. To understand the reason behind this scenario, studies on virus distribution and tropism in the citrus plants are needed. Different diagnostic methods are available for early CTV detection but none of them is employed for in planta virus distribution study. In this study, a TaqMan RT-PCR-based method to detect and quantify CTV in different tissues of infected Mosambi plants (Citrus sinensis) has been standardized. The assay was very sensitive with the pathogen detection limit of > 0.0595 fg of in vitro-transcribed CTV-RNA. The assay was implemented for virus distribution study and absolute CTV titer quantification in samples taken from Tristeza-infected trees. The highest virus load was observed in the midribs of the symptomatic leaf (4.1 × 10⁷–1.4 × 10⁸/100 mg) and the lowest in partial dead twigs (1 × 10³–1.7 × 10⁴/100 mg), and shoot tip (2.3 × 10³–4.5 × 10³/100 mg). Interestingly, during the peak summer months, the highest CTV load was observed in the feeder roots (3 × 10⁷–1.1 × 10⁸/100 mg) than in the midribs of symptomatic leaf. The viral titer was highest in symptomatic leaf midrib followed by asymptomatic leaf midrib, feeder roots, twig bark, symptomatic leaf lamella, and asymptomatic leaf lamella. Overall, high CTV titer was primarily observed in the phloem containing tissues and low CTV titer in the other tissues. The information would help in selecting tissues with higher virus titer in disease surveillance that have implication in Tristeza management in citrus.

Tristeza 是由 Closterovirus 属Closteroviridae的Citrus tristeza病毒 (CTV) 引起的一种柑橘经济上重要的疾病。这种疾病杀死了数百万棵树，降低了生产力和总产量，给全世界的柑橘产业造成了巨大损失。许多国家已经做出了巨大的努力来防止病毒传播和疾病造成的损失。要了解这种情况背后的原因，需要对柑橘植物中的病毒分布和嗜性进行研究。有不同的诊断方法可用于早期 CTV 检测，但没有一种方法用于足底病毒分布研究。在这项研究中，一种基于 TaqMan RT-PCR 的方法来检测和量化受感染的莫桑比植物 ( Citrus sinensis ) 的不同组织中的 CTV 已被标准化。该测定法对体外转录的 CTV-RNA 的病原体检测限 > 0.0595 fg 非常敏感。该测定用于病毒分布研究和从受 Tristeza 感染的树木中采集的样本中的绝对 CTV 滴度定量。在有症状的叶片中脉中观察到最高的病毒载量（4.1 × 10 ⁷ –1.4 × 10 ⁸ /100 mg），在部分死枝中最低（1 × 10 ³ –1.7 × 10 ⁴ /100 mg），并且芽尖 (2.3 × 10 ³ –4.5 × 10 ³/100 毫克）。有趣的是，在夏季高峰期，与有症状叶片的中脉相比，在饲养根中观察到最高的 CTV 负荷（3 × 10 ⁷ –1.1 × 10 ⁸ /100 mg）。病毒滴度在有症状的叶中脉中最高，其次是无症状的叶中脉、饲养根、树枝皮、有症状的叶薄片和无症状的叶薄片。总体而言，主要在含有韧皮部的组织中观察到高 CTV 滴度，而在其他组织中观察到低 CTV 滴度。这些信息将有助于在疾病监测中选择具有更高病毒滴度的组织，这对柑橘的 Tristeza 管理有影响。