Abschlussbericht Projekt: „Verminderung der ... - BLE

of potato tubers (Alvarez et al., 2000a; Bajema et al., 1998a; Lærke, 2001), elasticity and
specific gravity of potato parenchyma (Scanlon et al., 1998) and cold storage and impact
susceptibility of potato tubers (Bajema et al., 1998a, b). However, tissue water status of the
tuber is related to both its water concentration (e.g. water mass or water volume) and the
chemical potential of the water within cells (Galindo et al., 2004b; von Willert et al.,
1995). The latter is commonly described by the actual tissue water potential, which, itself
is determined by the respective osmotic (osmotic potential) and pressure component (pressure
potential or turgor) (Galindo et al., 2004b). Detailed information about the chemical
potential of water and impact susceptibility was given for carrot roots (Herppich et al.,
1999) and for radish tubers (Landahl et al., 2004) and particularly for potato tubers (Lærke,
2001).
The present investigation evaluates the chemical potential of water in potato tubers to provide
detailed measurements of changes in water status through time and to relate these
changes, if any, to blackspot susceptibility of potato tubers. This study is aimed to get a
more exact knowledge about blackspot development and may facilitate to develop optimal
techniques of handling and storage which help to obtain and to maintain the highest possible
product quality for the consumer.
Materials and methods
Material. Eight cultivars of table potatoes (Adretta, Afra, Gala, Granola, Lolita, Marabel,
Nicola and Renate) were grown near Dethlingen (Germany) by conventional farming
methods during two vegetation periods (2006 and 2007). To guarantee comparable results
only tubers with a similar size of 40 to 50 mm were chosen for the experiments. Analyses
were performed directly after harvest and after five and eight months, respectively, of storage
at 4°C and 95 % relative humidity. Prior to investigation tubers were sorted into six
classes of specific gravity from 1.095 kg L -1 , with 0.01 increments, by immersing
them into NaCl-solutions of different concentrations. Then, the tubers of each class
were split into two batches. Tubers of the first batch were used to determine their blackspot
index (BSI), those of the second batch were used to determine water concentration, water
potential, osmolality, osmotic potential, modulus of elasticity and pressure potential in the
stem end and the bud end of tubers, respectively.
Analyses. Blackspot index (BSI) of whole potato tubers of different specific gravities was
determined according to the method propose by the “Bundessortenamt” (BSA, Federal
Plant Variety Office, Germany). The tubers were cooled down to 4 to 5°C and mechanical
treated for 50 s in a vegetable washing machine with rotating drum (Flott 18 K, Flottwerk
H.J. Dames GmbH & Co. KG, Rotenburg a. d. F., Germany) with three replications. Each
replication consisted of an amount of tubers (Σ tuber ) adequate to a volume of 6 L. Subsequently,
treated tubers were stored at room temperature for 48 hours. For BSI determination
tubers were cut into halves length-wise and one half was evaluated visually using a
scale with four scores of discolouration. The score “No discolouration” indicated the lack
181