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Cytology of Fibrous Roots from Citrus Blight-Affected Trees

Citrus blight is an economically important decline disease of citrus in various areas of the world. The cause of citrus blight is unknown, but transmission via root grafting has been demonstrated. Root tissue from fibrous roots of citrus blight-affected and healthy citrus trees were compared. Amorphous plugs of the type previously observed in the trunk xylem and large roots of blighted trees were also found in the fibrous roots. The plugs were yellow to light gold in color, gave a positive staining reaction for the presence of lignin, and were retained when kept overnight in water. With scanning electron microscopy the amorphous plugs appeared to be solid, occluding part or all of the vessel. These plugs have previously been implicated in the reduction of water transmission in blighted trees.