Anatomy of Washington Navel Orange Rind in Relation to Water Spot

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Abstract
Localized edema of the mature rind is the first symptom of water-spot injury, which may or may not be followed by rind-cracking during winter rains in California. Epidermal wax coating consists of scales; the wax is secreted as rodlets through minute radial canals. The epidermis is structurally weak and liable to crack owing to the thinness of the cuticle of mature accessory cells and new epidermal cells. The lightly cutinized walls disintegrate readily in H2SO4. The albedo differentiates from meristematic tet-rakaidekahedral cells, and the mature open meshwork consists of 8-armed cells interconnected by plasmodesmata. The tendency of the epidermis to crack is evident in young fruits but incipient cracks are healed by concurrent cutiniza-tion. Rind weakness becomes critical at maturity when epidermal extension fails to keep pace with internal expansion. Resultant cracks may heal in dry weather, but in continued rain, remain open and admit fungal spores. Aqueous vital stains penetrate the mature rind readily and accumulate in the cell vacuoles of the accessory and certain other cells. Oil spraying has no visible effect on the structure of the fruit. No significant anatomical differences are observed between the Washington navel and other vars. less susceptible to water-spot.