Developmental Anatomy and Features of the Exocarp as Related with Fruit Skin Disorders in ‘Niitaka’ Pear Fruit

Abstract

Causal process and characteristics of three physiological disorders on ‘Niitaka’ pear fruit was analyzed through an anatomical approach. Anatomical differences in the skin layers suffered from surface-stain, skin-blackening, and peeling-off disorders were observed and analyzed using microphotography. The skin layer of surface-stain fruit was 11.6 μm thicker than that of sound fruit. The thicker skin layer of surface-stain fruit seemed to be resulted from the formation of two or three cork cell layers. In contrast, the fruit skin of skin-blackening suffered fruit was 95.8 μm thinner than that of sound one. The thinner skin layer of skin-blackening fruit was induced by the collapse of the hypodermal layer. The third disorder, peeling-off symptom was characterized by a newly developed decorking layer beneath the cork cell layer. The developmental process of decorking leading to peeling-off consisted of reactivation of phellogen, vertical elongation of phellogen cells, and physical force up to the cork layer. The term, decorking was first suggested to describe anatomical process of peeling-off disorder.