D3265: Spectral evaluation of citrus plants infected with “Candidatus Liberibacter asiaticus” transmitted by Asian citrus psyllid

Huanglongbing (HLB) is the most destructive disease that affects the citrus orchards, being transmitted by a vector insect, Diaphorina citri Kuwayama (Hemiptera: Psyllidae). The disease does not have curative methods, therefore, rapid and accurate sampling methods are needed for the early detection of the disease in the field, even before the symptoms are visible. In view of this, there were spectral evaluations of healthy plants and infected plants (Citrus sinensis L.) with “Candidatus Liberibacter asiaticus” (CLas) until the visual appearance of symptoms. As a result, it was possible to determine ranges of bands that demonstrated significant differences in relative reflectance between treatments consisting of healthy and infected plants, from the first days of evaluation, when the plants infected with CLas were still in the asymptomatic stage of the disease. From the second week of evaluation, spectral differences were detected in the Red-edge region (660 – 750 nm) until the last week of evaluation. From the sixth week, spectral differences between healthy and symptomatic plants were observed in bands close to the visible region (520 – 680 nm). Therefore, we conclud that it is possible to detect spectral differences in the leaves of citrus infected by CLas before the onset of symptoms, making it feasible to use hyperspectral sensor for monitoring the disease. Our results indicate the need for more advanced studies in the future to validate the use of hyperspectral sensors for the management and detection of HLB in citrus orchards, contributing to the integrated management of pest and disease.