Huanglongbing (HLB) is the most devastating disease of citrus in Florida. HLB is caused by the phloem-inhabiting bacterium ‘Candidatus Liberibacter asiaticus’ (Las), which is transmitted by psyllid vector Diaphorina citri. The current management strategies of HLB are to control psyllids and eradicate infected plants. However, these management practices have not been able to stop the spreading of HLB (Duan et al. 2009). Alternative approaches are needed to control HLB. In previous studies we isolated multiple bacterial strains from roots of healthy citrus plants in HLB infected groves in Florida, which have the potential to enhance plant growth and suppress diseases (Trivedi et al. 2011). Recently, early infection of roots by Las leading to root decline was suggested to be important in HLB disease development (Johnson et al. 2012). We hypothesize that introduction of beneficial bacteria to roots of citrus plants could decrease root damage by promoting root growth and reducing Las infection and thus improve HLB management. To test this hypothesis, six beneficial bacteria were assessed for their plant growth-promotion ability; and three were found to be able to promote growth of both grapefruit and Arabidopsis (Col-0 ecotype) in greenhouse experiments, with increases in root length and weight, compared to mock treated plants. Thus, the three isolates were selected to evaluate the effect on Las infection in greenhouse assays. Details of the beneficial bacterial isolates, plant growth-promotion activity, and effect on Las infection will be discussed.

To decrease Candidatus Liberibacter asiaticus titer and increase the productive life of infected trees, thermal treatment of orange trees was proposed.  A moving greenhouse was developed to cover single trees during the summer of 2012.  Four trees (~ 2.5×2.5×2.5 m) were treated, one tree per day, during the months of September (trees T1 through T3) and October (tree T4).  From each tree, three symptomatic branches were sampled to determine microbial kill before (0 h) and at 2, 3, 4, and 5 h during the treatment.  Temperature distribution throughout the canopy and on the sampled branches was also recorded.  Maximal temperatures in the ranges 50 to 53 °C were reached at the top (2.4 m) of the canopy whereas at the bottom of the canopy (i.e., 0.6 m) maximal temperatures ranged from 36 to 43 °C.  Due to varied micro-meteorological conditions during the treatment, temperatures of the T1 through T4 sampled branches reached above 40⁰C for 217, 166, 35, 228 min, respectively.  For T1, T2 and T4 trees, average temperatures of the sampled branches reached above 45 °C for 87, 35, and 49 min or more.  Attempts to quantitatively determine microbial kill by determining percent live bacteria at selected time intervals during thermal treatment was unreliable due to the very uneven distribution of initial proportion of live-to-dead bacteria and analysis variability.  However, overall, after thermal treatments, live microbial populations decreased.  These findings indicate that adequate thermal treatment of trees required forced convection air flow and supplemental heating.