Abschlussbericht Projekt: „Verminderung der ... - BLE

despite the fact that temperatures during harvest and tuber water concentration were similar
in 2006 and 2007. Presented results correspond to findings of Herppich et al. (2004) indicating
that, at a given temperature, carrots show a lower toughness at a lower pressure potential.
When water uptake was restricted and increasing specific gravity indicated a higher dry
matter concentration due to a higher amount of starch granules accompanied with a lower
water concentration of tissues the tuber tissues became more elastic due to the lower pressure
potential and the decreased elastic modulus. The susceptibility to blackspot might
increase because of a reduced cell wall tension and/or a higher concentration of starch
granules as it was discussed by Bajema et al. (1998a) and Scanlon et al. (1998).
Blackspot susceptibility and water status of stored tubers. Processing industry demands
a permanent supply of potato tubers throughout the year. Therefore potato storage is essential
in which tubers may undergo pronounced physiological changes (Laza et al., 2001;
Scanlon et al., 1996). Despite the fact that these physiological changes of potato tubers
have been widely studied (Alvarez and Canet, 2002; Baritelle and Hyde, 2001; Lærke,
2001; Scanlon et al., 1996) information are still incomplete in which way low temperatures
might influence storage physiology.
In both years, tubers obviously accumulated osmotically active solutes which significantly
decreased the water potential without decreasing pressure potential during the entire storage
period. Within this process of osmotic adjustment (Galindo et al., 2004a) tissue sap
osmolality increased in average by more than 100 mmol kg -1 due to the hydrolysis of
starch to sucrose (Espen et al., 1999). This resulted in a decline in osmotic potential of 0.2
MPa and more. Osmotic adjustment may be a direct response to cold temperatures helping
to reduce the freezing temperature of the tissue sap, thus, increasing tuber frost resistance.
As a result of this process tubers may also stabilize or even increase their pressure potential
despite a decreasing water potential (Galindo et al., 2004b). Remained pressure potentials
during the entire storage indicated a steady membrane integrity, which was also not influenced
by osmotic adjustment during storage corresponding to findings from Olsen et al.
(2003/4). The absolute water concentration did not change during storage, while a decreasing
water concentration would have indicated enhanced respiration usually accompanied
with sprouting or senescence (Suttle, 2007 ), which was not observed in the present study.
The tubers obviously maintained their vitality during storage as also described by Galindo
et al. (2004b) and Heuer and Nadler (1998).
Blackspot susceptibility and tuber water status-synopsis. Observed variation in blackspot
susceptibility at similar pressure potentials might be attributed to non-aqueous constituents
of tissue. Both parameters are often reported to be positively correlated within
potato tubers (Baritelle and Hyde, 2003; Peters et al., 2005; Wrigth et al., 2005). Throughout
the whole shelf time of eight months blackspot significantly increased with the specific
gravity. Specific gravity is generally assumed to be a cultivar characteristic (Laboski and
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