Abstract Huanglongbing, a highly destructive disease of citrus species, is associated with a fastidious, gram-negative, phloem-limited bacteria (Candidatus Liberibacter spp.). In Florida, the causative agent of Huanglongbing (HLB) is C. Liberibacter asiaticus (CLas) and it is transmitted by the insect vector, Asian citrus psyllid (Diaphorina citri Kuwayama). Previous investigations have revealed systemic infection of CLas with an erratic and uneven distribution of pathogen in tree phloem. However, previous investigations did not consider the potential impact of plant vegetative growth on presence/absence of CLas in planta. Our objectives were to determine: 1) the effect of vegetative growth of Citrus sinensis (L.) Osbeck cv Valencia on detection of CLas in mature leaves, and 2) the impact of CLas inoculation frequency on progression of CLas titer in citrus leaves through the first year of infection. Temporal dynamics of CLas detection were associated with vegetative flush growth. Surprisingly, there was no difference in CLas titer detected between plants exposed to infected vectors for a one-time 7 d inoculation access period, as compared with plants exposed to continuously breeding CLas-infected insects over the course of an entire year of plant infection. Our results suggest that the CLas bacterium is transported through phloem during annual movement of carbon compounds needed for vegetative plant growth, including transportation from roots to mature leaves. These results highlight the importance of vegetative growth on temporal dynamics of CLas in citrus, and suggest a critical role of the sink-source interaction on presence/absence of CLas in leaves.

中文翻译：

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柑橘 cv Valencia 成熟叶片中 Candidatus Liberibacter asiaticus 滴度的时间动态与营养生长相关

摘要 黄龙病是柑橘属物种的一种高度破坏性病害，与一种挑剔的革兰氏阴性韧皮部限制性细菌（Candidatus Liberibacter spp.）有关。在佛罗里达州，黄龙病 (HLB) 的病原体是 C. Liberibacter asiaticus (CLas)，它通过昆虫媒介亚洲柑橘木虱 (Diaphorina citri Kuwayama) 传播。先前的研究表明，CLas 的系统感染具有病原体在树木韧皮部中的不稳定和不均匀分布。然而，之前的研究没有考虑植物营养生长对植物中 CLas 的存在/不存在的潜在影响。我们的目标是确定：1​​) Citrus sinensis (L.) Osbeck cv Valencia 的营养生长对成熟叶片中 CLas 检测的影响，和 2) CLas 接种频率对柑橘叶中 CLas 滴度在感染的第一年进展的影响。CLas 检测的时间动态与植物性潮红生长相关。令人惊讶的是，与在整整一年的植物感染过程中暴露于连续繁殖 CLas 感染昆虫的植物相比，暴露于受感染载体的植物之间检测到的 CLas 滴度没有差异，为期 7 天的一次性接种访问期。我们的研究结果表明，CLas 细菌在营养植物生长所需的碳化合物的年度运动期间通过韧皮部运输，包括从根到成熟叶的运输。这些结果强调了营养生长对柑橘 CLas 时间动态的重要性，