In 2019, citrus production in Florida declined by more than 70%, mostly because of Huanglongbing (HLB), which is caused by the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas). Thermotherapy for HLB-affected trees was proposed as a short-term management solution to maintain field productivity. It was hypothesized that thermotherapy could eliminate HLB from affected branches; therefore, the study objectives were to show which time–temperature combinations eliminated CLas from woody tissues. Hardening, rounded Valencia twigs collected from HLB-affected field trees were treated in a steam chamber at different time–temperature combinations (50°C for 60 s; 55°C for 0, 30, 60, 90, and 120 s; 60°C for 30 s; and an untreated control). Three independent repetitions of 13 branches per treatment were grafted onto healthy rootstocks and tested to detect CLas after 6, 9, and 12 months. For the RNA-based CLas viability assay, three branches per treatment were treated and bark samples were peeled for RNA extraction and subsequent gene expression analyses. During the grafting study, at 12 months after grafting, a very low frequency of trees grafted with twigs treated at 55°C for 90 s and 55°C for 120 s had detectable CLas DNA. In the few individuals with CLas, titers were significantly lower (P ≤ 0.0001) and could have been remnants of degrading DNA. Additionally, there was a significant decrease (P ≤ 0.0001) in CLas 16S rRNA expression at 55°C for 90 s, 55°C for 120 s, and 60°C for 30 s (3.4-fold change, 3.4-fold change, and 2.3-fold change, respectively) in samples 5 days after treatment. Heat injury, not total CLas kill, could explain the limited changes in transcriptional activity; however, failed recovery and eventual death of CLas resulted in no CLas detection in most of the grafted trees treated with the highest temperatures or longest durations.

2019 年佛罗里达州柑橘产量下降 70% 以上，主要是因为黄龙病（HLB），这是由细菌' CandidatusLiberibacter asiaticus' (CLas)。建议对受 HLB 影响的树木进行热疗作为维持田间生产力的短期管理解决方案。假设热疗可以消除受影响分支的 HLB；因此，研究目标是显示哪些时间-温度组合可以消除木质组织中的 CLas。从受 HLB 影响的田间树木收集的硬化、圆形的瓦伦西亚树枝在蒸汽室中以不同的时间-温度组合进行处理（50°C 60 秒；55°C 0、30、60、90 和 120 秒；60° C 30 秒；和未经处理的对照）。每个处理 13 个分支的三个独立重复被嫁接到健康砧木上，并在 6、9 和 12 个月后进行测试以检测 CLas。对于基于 RNA 的 CLas 活力测定，每个处理处理三个分支，并剥去树皮样品用于 RNA 提取和随后的基因表达分析。在嫁接研究期间，在嫁接后 12 个月，在 55°C 下处理 90 秒和在 55°C 下处理 120 秒的树枝嫁接的树木中，极低频率具有可检测的 CLas DNA。在少数具有 CLas 的个体中，滴度显着降低（P ≤ 0.0001) 并且可能是降解 DNA 的残余物。此外，有一个显著减少（P在55°C≤0.0001）CLAS的16S rRNA表达为90秒，55℃120秒和60℃30秒（3.4倍的变化，3.4倍的变化，和 2.3 倍的变化，分别）在处理后 5 天的样品中。热损伤，而不是总 CLs 杀死，可以解释转录活性的有限变化；然而，CLas 的恢复失败和最终死亡导致在用最高温度或最长持续时间处理的大多数嫁接树中没有检测到 CLas。