Skin set evaluation by skin shear measurements
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Skin set of tubers, an indication of maturity, is a major reason for desiccating potato vines (Solanum tuberosum L.). A hand-held torque meter was evaluated for measuring tuber skin resistence to shearing as a measure of skin set. To demonstrate practical use of the torque meter to growers, shear resistance must be related to tuber skinning. ‘Atlantic’ and ‘Snowden’ potato tubers were individually measured for skin shear resistance followed by skinning. A linear relationship between skin shear resistance and tuber skinning was observed. The regression equations were Torque (mN*m) = 354 - (1.4 * Percent Skinning) for Atlantic in 1995 and Torque (mN*m) = 404 - (2.2 * Percent Skinning) for Snowden in 1996. The objective measuring of shear resistance was directly related to the more subjective measuring of tuber skinning with an R-square of 0.83. In 1995, harvested Atlantic tubers from desiccated plants were measured for skinning and resistance to torque. Skinning decreased and torque resistance increased during the 3-wk period after the initial desiccation treatment. However, skinning remained unacceptable at one and two weeks after desiccation regardless of treatment. Three weeks after desiccation, tubers from diquat-treated plots showed acceptable skin set levels and a torque resistance over 325 mN*m, which the model indicated would give acceptable skin set. Unacceptable skinning and a low torque resistance, less than 310 mN*m, remained a problem with vine flailing. Data indicated that resistance to torque exerted by the torque meter was an accurate measurement of skin set for harvested tubers. However, model regressions for the two round-white chipping cultivars, Atlantic and Snowden, differed. The torque meter can be used in the field or office. A major difficulty was maintaining a constant pressure on the tuber skin while applying the torque.
Additional Key WordsPotato Solanum tuberosum cultivar Atlantic cultivar Snowden torque meter skin maturity skinning vine desiccation diquat flailing
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