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POSTERS: Cultural control

Determining the viability of Candidatus Liberibacter asiaticus (CLas) via RNA-based assay and grafting results
Naweena Thapa - University of Florida. Megan Dewdney- University of Florida, Evan Johnson- University of Florida

Florida citrus production has declined 70% in recent years, due to Huanglongbing (HLB), caused by CLas. Thermotherapy on HLB-affected trees was proposed as a short-term management solution to maintain field productivity. With the hypothesis that thermotherapy could eliminate CLas from affected branches, the objectives were to show which time-temperature combinations killed CLas in woody tissues. Just hardened, rounded Valencia twigs, collected from HLB-affected field trees, were treated in a steam chamber at 50C-60s, 55C-0s, 55C-30s, 55C-60s, 55C-90s, 55C-120s, 60C-30s and an untreated control (UTC). Three independent repetitions of 13 branches/treatment were treated, grafted onto healthy rootstocks, and tested for CLas DNA after 6, 9, and 12 months. For the expression analysis of CLas, 3 branches/treatment were used, bark samples were collected, and stored at -80C for RNA extraction. At 12 months after grafting, leaf samples from branches treated at 55C-90s, and 55C-120s had significantly lower CLas titers (p ? 0.0001), when detected, possibly remnants of degrading DNA. Additionally, CLas 16S rRNA expression significantly decreased at 55C-90s, and 60C-30s (7.5 and 11.5-fold change, respectively; p ? 0.0001) in samples 5 days post-treatment. Heat injury, not direct CLas kill, could explain limited changes in transcriptional activity; however, failed recovery and eventual death of CLas could result in no detection in most grafts at severe treatments.