Investigation of the stages of citrus greening disease using micro synchrotron radiation X-ray fluorescence in association with chemometric tools

Citrus greening has been considered the worst citrus pest since 2004, both in Brazil and in the United States of America. This disease has had serious consequences in agricultural production and highlights the urgent need for early diagnostic methods. This analytical study investigated the mineral constituents of healthy leaves and leaves infected with citrus greening (or Huanglongbing) using micro synchrotron radiation X-ray fluorescence (mu SR-XRF) scanning combined with chemometric tools. The information obtained using the mu SR-XRF spectra profiles and the chemometric tools allowed the construction of predictive models to identify healthy and infected trees with and without symptoms. The signals for K, Ca, Fe, Cu and Zn and the region of coherent and incoherent scatterings were relevant to the differentiation of the healthy and infected samples. The calibration model correctly classified up to 95-98% of samples, and the validation data correctly assigned 90% of samples with a 95% significance level.