Natalia Tomas Marques has a PhD in Biological Sciences from the Classical University of Lisbon, Portugal. From 2004 until now is Assistant Professor at Faculty of Sciences of Universidade do Algarve. She is specialized in plant cell & molecular biology and in vitro culture. Her current research projects include Citrus tristeza virus (CTV)-citrus interaction, interaction of proteins encoded by Citrus tristeza virus to look for protein synergistic effects, studies on application of reflectance spectra in the visible/near infrared region to detect the CTV, performed in cooperation with Dr. Rui Guerra from Department of Physics of Universidade do Algarve.
Citrus plants are affected by Citrus tristeza virus (CTV), the most economically important viral disease. In this study we address the problem of identifying asymptomatic infected plants by multivariate analysis of reflectance and transmittance spectra of the leaves in the visible/near infrared region. Twenty young healthy and CTV infected Citrus macrophylla plants were assayed. Reflectance and transmittance spectra of selected leaves were acquired through a portable spectrometer, with measurements performed monthly over 10 months. The spectra study was complemented with biochemical analyzes and photosynthesis rate evaluation to estimate the condition of plants. In this communication we present the results conveyed by multivariate analysis of the spectra. Standard unsupervised classification methods such as Principal Component Analysis or clustering show promising results by yielding a correct separation of classes (infected vs. non-infected) for some of the months but not for others. We discuss optimization of the measurements directed at obtaining reliable results under field conditions.