Anatomy of Lettuce Tissue Affected by Three Physiological Disorders1

Abstract Anatomical studies of 3 physiological disorders of lettuce ( Lactuca sativa L., cv. Climax) i.e., russet spotting (RS), brown stain (BNS), and rusty brown discoloration (RBD) showed that these disorders differ in their location and sequence of symptom development. RS produces well-defined, localized, spot-like lesions that may start either in the epidermis or in the mesophyll. In advanced stages of RS, the vascular tissue may also show discoloration and the mesophyll cells collapse, resulting in pit-like depressions. BNS lesions are restricted to the epidermis and may cover a large area. All the cells in a given lesion become discolored, with greater discoloration intensity at the periphery rather than the center of the lesion. RBD symptoms start in the epidermis and in advanced stages expand to mesophyll cells. RBD affected areas exhibit a mosaic-like pattern of discoloration.