Submitted to: American Journal of Potato Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/26/2002
Publication Date: 7/1/2002
Citation: LULAI, E.C. THE ROLES OF PHELLEM (SKIN) TENSILE STRENGTH-RELATED FRACTURES AND PHELLOGEN SHEAR-RELATES FRACTURES IN SUSCEPTIBILITY TO TUBER SKINNING INJURY AND SKIN-SET DEVELOPMENT. AMERICAN JOURNAL OF POTATO RESEARCH. 2002. V. 79 P. 241-248. Interpretive Summary: The skin covering potato tubers is often easily torn from the tuber surface during harvest. These skinning type wounds increase the spread of latent disease, rotting of potatoes during storage, and the development of blemishes that devalue or ruin the marketability of the potatoes. The skin (phellem) and related neighboring tissues (phellogen and phelloderm) collectively constitute the periderm. As the periderm matures, the tuber slowly becomes resistant to skinning injury; this process is frequently referred to as skin-set. Despite the costliness of the problem of skinning injury, very little is known about the physiology associated with the susceptibility to skinning or the physiological changes that cause skin- set. Recent microscopical research identified the phellogen as the distinct layer where periderm tissues separate upon skinning. In the current research, mechanical measurements of resistance to skinning injury are used to determine the role of skin tensile strength in skinning and in skin-set development. Relative tensile strength of the skin was found to play a minor role in the total resistance to skinning injury in immature and maturing tubers. Most important, the tensile strength of tuber skin did not measurably increase upon periderm maturation and therefor it does not play role in the economically important process of tuber skin-set development. These results: (1) unambiguously confirm that phellogen cell wall strengthening during periderm maturation confers skin-set development, (2)provide scientists with a clear direction for future research to hasten skin-set for the benefit of growers, processors and consumers, and (3) provide extension agents and members of industry with the correct basis for the economically important process of skin-set development.
Technical Abstract: The susceptibility of potato tubers to excoriation (idiom = skinning injury) during harvest is a widespread problem that results in costly disease, defects, and shrinkage. Little is known about the physiology associated with susceptibility and the development of resistance to skinning injury (skin-set) upon periderm maturation. The objective of this sresearch was to determine the role of phellem (skin) tensile strength in the susceptibility and the development of resistance to tuber skinning injury. The resistance to skinning injury was measured in potato tubers with immature and mature periderm. Separate physical measurements were obtained for the "total resistance to skinning" (total resistance = phellem tensile strength component combined with phellogen shear strength component) and for the "phellogen shear strength component." The "tensile strength component" was calculated from the difference of the two physical measurements. The results indicate that phellem tensile strength is a mino component in the total resistance to skinning. Phellem tensile strength appeared to be relatively constant for all time points for each cultivar and did not measurably increase upon periderm maturation; this indicates that phellem/skin tensile strength does not contribute to skin-set development. However, the phellogen shear strength component of total resistance to skinning injury did increase upon periderm maturation and was the determinant for the development of full resistance to skinning injury, i.e. full skin-set . The results were similar for all cultivars tested and provide a definite direction for future research on the biochemical changes and processes associated with phellogen cell wall strengthening (phellogen shear strength component) as a means of hastening skin-set development.