Characterization and Detection of Leaf Photosynthetic Response to Citrus huanglongbing from cool to hot Seasons in Two Orchards

摘要

Citrus Huanglongbing (HLB) poses a serious threat to citrus production. This research aimed to explore chlorophyll fluorescence imaging for characterizing the photosynthetic response to HLB-infected citrus leaves in different orchards and seasons. Chlorophyll fluorescence images of citrus leaves were acquired with an in-house chlorophyll fluorescence imaging system. It was found that sucrose and glucose accumulated earlier than starch in HLB-infected leaves, and a similar carbohydrate metabolic pattern was observed in HLB-infected leaves grown in different orchards from cool to hot seasons. The pathogen damaged the thylakoid structure of chloroplasts with a higher value of Fo. It decreased photosynthetic activity of the host by reducing the number of active photosynthetic centers and the maximum quantum yield of PSII (Fv/Fm) with lower values of Fv/Fo and Fv/Fm. Additionally, the pathogen modified the allocation of excitation energy in citrus leaves by reducing the actual quantum yield of PSII (0PSI1) due to an increase of non-regulated energy quenching (0NO), which indicated irreversible PSII damage before symptom development. Moreover, photosynthetic signatures com-bined with the random forest method were able to identify HLB in the asymptomatic stage with an overall accuracy of 91.8%. These results demonstrated the potential of chlorophyllfluorescence imaging for evaluating the photosynthetic response to HLB as well as disease diagnosis.