Evaluation of standard cultivars (‘Hamlin’, ‘Temple’, ‘Fallglo’, ‘Sugar Belle’, ‘Tango’, and ‘Ruby Red’) for HLB resistance/tolerance is underway. All trees exhibited symptoms of HLB and tested positive for CLas. Imidacloprid was applied quarterly to a subset of trees and significantly increased stem diameter compared to the non-treated trees but did not have a significant effect on tree height, disease severity, or Candidatus Liberibacter asiaticus (CLas) titer levels. There were significant differences in disease severity, stem diameter, and CLas titer between the varieties. ‘Fallglo’ had the lowest incidence and ‘Ruby Red’ the highest incidence of distinctive HLB mottling. The highest CLas titer levels in 2012 were observed in November and December, with ‘Sugar Belle and ‘Tango’ displaying the highest titer levels while ‘Fallglo’ and ‘Temple’ had the lowest levels. Despite the high titer CLas levels of ‘SugarBelle’, it had the greatest overall increase in diameter and was among the healthiest in overall appearance. Initial results indicate that compared to ‘Hamlin’, ‘Fallglo’ and ‘Temple’ appear to display field resistance to HLB while ‘SugarBelle’ appears to have significant tolerance. To generate plants with a range of CLas titer levels, bud-wood from nine varieties/genotypes, 3 putatively HLB-resistant (‘Temple’, ‘Gnarly Glo’, and ‘Nova’), 3 HLB-tolerant (‘Jackson’, FF 5-51-2, and Ftp 6-17-48), and 3 HLB-susceptible (‘Flame’, ‘Valencia’, and ‘Murcott’) were treated with various concentrations of penicillin and streptomycin. In April 2014, several treatments were repeated due to high bud mortality in December 2013. Treated buds were grafted onto sour orange rootstock. Once the new shoots are established, HLB symptoms and tree growth will be monitored on a monthly basis for a two-year period and compared to Liberibacter-infected and healthy standard varieties. Quantification of CLas titer levels will be conducted on a quarterly basis using real time PCR. Progress has been made on the development of HLB-resistant chimeras. Under in vitro conditions, etiolated hypocotyls from seedlings of Poncirus trifolata (‘Gainesville’, ‘Winter Haven’, and ‘Sacaton’) and ‘Hamlin’ were approach grafted. After the callus develops, a horizontal cut through the grafting union will be made and treated with growth regulators (gibberellic acid, .-napthaleneacetic acid, and 6-benzylaminopurine). Under greenhouse conditions, seedlings of ‘Carrizo’ were successfully approach grafted to ‘Hamlin’ and treated with growth regulators (as mentioned). The regenerated plants will be examined using LC/MS, which differentiates the parental layers based on unique chemical signatures. A method for the rapid identification of potential sources of HLB resistance is currently being developed. Seedlings of ‘Dancy’, ‘Hamlin’, and ‘Carrizo’ at the 3 to 5-leaf stage were exposed to HLB or non-HLB infected ACP feeding trials. Entire leaves, stem, and roots are being processed at 3, 6, 9, and 12 weeks after the initial feeding period. At the 3 week sample period differences in secondary metabolites of methanol extracts from HLB and non-HLB infected leaves was observed using LC/MS. Using real time PCR CLas was detectable in all parts of the seedlings, with the exception of the roots from ‘Carrizo’. ‘Dancy’ stems and leaves had the highest CLas titer levels.