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Poster: Biology & Disease Mgmt: Cultural Control


Canopy and root response of HLB-affected citrus trees to steam-generated thermotheray
N. Thapa (1), S. Commerford (1), R. Ehsani (1), E. Johnson (1), M. Dewdney (1) (1) CREC, University of Florida, U.S.A.

Thermotherapy is an old technique used to control plant pathogens. Citrus huanglongbing (HLB) threatens Florida’s multibillion dollar citrus industry and has no effective control measures. The phloem-limited bacterium, Candidatus Liberibacter asiaticus (Las), is the causal agent of HLB and infects both canopy and root system. Thermotherapy can reduce Las titer in infected trees and this study explores steam as a heat source for rapid treatment to extend the productivity of HLB-affected citrus trees. Optimum temperature-time duration is important to reduce Las titer without affecting tree productivity. A randomized split-plot design field trial was laid out with the main plots at 3-month intervals to determine optimum time-of-year to reduce Las titer and the subplots at 6 temperature-time combinations (58°C/15s; 58°C/60s; 58°C/90s; 58°C/120s; 60°C/30s and untreated control, UTC) with 3 replications per treatment. Four leaves/tree from 10 trees/rep were collected quarterly and tested for Las titer via standard qPCR. Roots were assessed for Las titer as roots are an untreated reservoir. Preliminary data show an overall reduction in titer a month after the July treatment. Las titer increased in all leaves, but more in the UTC than the treatments, whereas root Las titer was reduced more in treatments than the UTC. This may be due to change of phloem flow from root to the treated canopy along with Las. Seasonality may be critical for successful suppression of Las.