Effects of melatonin supplementation on the bacterial population of Ca. L. asiaticus in HLB-symptomatic detached leaves of Valencia sweet orange. A, Fully mature HLB-symptomatic detached leaves, with their complete petioles, were incubated in one of five concentrations of melatonin (0.05, 0.1, 0.2, 0.5, and 1 mm aqueous solution), in addition to the control (mock; Milli-Q water with 0 mm melatonin). A single leaf disc was collected from each leaf before the treatment (zero time) and at 24, 48, 72, and 96 hpt for Ca. L. asiaticus quantification. B, CT of reverse transcription quantitative PCR (RT-qPCR) for the detection of Ca. L. asiaticus in HLB-symptomatic detached leaves of Valencia sweet orange after treatment with different concentrations of melatonin. Data shown are means ± sd (n = 12). P < 0.05 indicates statistically significant differences among treatments, whereas P > 0.05 indicates no significant differences between them using Tukey’s HSD. C, Fit means model and quadratic polynomial regression analysis between exogenous melatonin concentrations and CT of RT-qPCR for the detection of Ca. L. asiaticus. Black dots represent the raw data (n = 6). The fit means line is presented as a solid line, while polynomial regression models are presented as dashed lines. The 95% confidence intervals for the estimated regression are gray shaded and edged by dotted lines. Regression equations, R2, R2adj, and P value based on the F test (P ≤ 0.05) were also obtained and are presented within the graph. D to I, Simple linear regression plots of hpt versus the CT of RT-qPCR for the detection of Ca. L. asiaticus in detached leaves after treatment with different concentrations of melatonin. White dots represent the raw data (n = 12). The fitted regression line is presented as a solid line, whereas the 95% confidence intervals for the estimated regression are gray shaded and edged by dotted lines. Regression equations, R2, R2adj, and P value based on the F test (P ≤ 0.05) were also obtained and are presented within the graphs.