The objectives of this study were the detection and identification of biotic or abiotic stress factors which could be associated with the symptoms of dieback, severe leaf necrosis, and various chlorosis of citrus trees grown under screenhouse at Mediterranean Agronomic Institute of Bari. Virus infections were excluded because annual assays are carried out by IPM staff whereas tests were carried out to detect pathogenic viroids, fungi and bacteria. Growing media, salinity and pH were studied. To evaluate light deficiency, the old fiberglass cover sheet of the screenhouse was partially substituted with a polyethylene cover sheet. Irradiance and photosynthetic activity were measured by spectroradiometer. No pathogenic fungi or bacteria were isolated from the tested plants.
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HSVd was detected only in few tested clementine plants whereas mandarin-like species showing evident symptoms did not react to any viroid tested. Old growing media were associated with symptomatic plants, whereas plants in new growing media didn’t show symptoms. No symptoms were observed under the new polyethylene cover sheet, although, Photochemical Reflectance Index (PRI) of these plants shows a significant increase in photosynthetic activity. Therefore, we can assume that the symptoms observed are possibly correlated with light deficiency and growing media quality.
