Changes of water status, elastic properties and blackspot incidence during storage of potato tubers

The black-spot bruise susceptibility of potato tubers after mechanical load may change during prolonged storage. Both an increase and a decrease of the occurrence probability of this defect with storage duration have been reported. Increasing blackspot Susceptibility has often been related to declining tissue turgor and/or increasing tuber water losses. In the presented study the relationship between elastic properties. water status and blackspot incidence of potato tubers, and its variation during 8 month of storage has been investigated. Tubers of the cultivars 'Afra' and 'Milva' differing in their starch content were stored at 4-5 degrees C in boxes in a practical storage room and in a climate chamber at 4-5 degrees C and 97-100% relative humidity. Ill spite of a pronounced, mainly water loss-related mass reduction ('Afra': 3.1%, 'Milva': 2.7%) during 5 1/2 months in high humidity storage the tuber turgor remained almost stable or even increased under both storage conditions. This turgor maintenance which guarantees vitality of the cells despite the observed water losses may result from elastic adjustment as indicated by a strongly increasing intrinsic volumetric elastic modulus of the inner tuber tissue. The apparent quasi-static modulus of elasticity and the dynamic stiffness of the intact whole tubers from practical storage decreased for both varieties. The blackspot susceptibility of both varieties was Subject to strong fluctuations during the duration of storage and no clear relation to any of the measured parameters for water status and elastic properties was identified. In contrast to the general notion blackspot Susceptibility was not higher for 'Afra' than for 'Milva' despite the higher starch content of the former.