Abschlussbericht Projekt: „Verminderung der ... - BLE

Discussion
No significant tuber position-dependent differences in water potential, osmolality, osmotic
potential, pressure potential or in the modulus of elasticity could be detected in the present
study. In contrast, Bajema et al. (1998b) reported lower tissue elasticity and consequently a
higher impact susceptibility for stem ends compared to bud ends of ‘Russet Burbank’ and
‘Atlantic’ tubers. Due to the fact that larger cells, thicker cell walls and interrupted starch
packing of cells of the stem end enhanced their susceptibility to blackspot (Lærke, 2001),
while affecting tissue water status (von Willert et al., 1995). Olsen et al. (2003/4) measured
a relative lower turgor at stem end compared to the bud end of tubers of ‘Shepody’. This
relationship was not observed in the present study.
Blackspot susceptibility and water status of tubers after harvest. In both years 2006
and 2007 tubers with a specific gravity lower than 1.095 kg L -1 showed significantly higher
water potential after harvest, than after short-term or long-term storage. According to Suttle
(2007) this result indicated that freshly harvested tubers were well hydrated despite, soil
water was not longer available, while transpiration water losses of tubers were generally
high a rapid decline of respiration might take place delaying metabolic processes (Galindo
et al., 2004a; Suttle, 2007), whereby water was preserved. The concentration of stored
macromolecules (starch and proteins) remained constant or decreased only slightly thus
providing a sufficient resource of nutrients and carbohydrates for sprout development. This
promptly declined metabolism in analysed tubers maintained their vitality.
The vitality of tubers is influenced by their pressure potential since its loss will inhibit
sprouting (Galindo et al., 2004a). The pressure potentials found in harvested tubers ranged
between 0.25 and 0.45 MPa and are thus very similar to those reported for potatoes of
‘Maries Piper’ (0.36 MPa; Alvarez et al., 2000a), ‘Katahdin’ (0.36 MPa; Brusewitz et al.,
1989), ‘Russet Burbank’ and ‘Shepody’ (0.26 MPa; Laza et al., 2001), and ‘Dali’ and
‘Oleva’ (0.43 MPa and 0.44 MPa, respectively; Lærke, 2001). This indicates only a minor
difference between our measured pressure potentials and those reported in literature. Storey
(2007) proposed that pressure potential may vary between different potato cultivars
differing in their specific gravity. Tuber pressure potential was highly affected by the state
of plant development or senescence, defoliation and the activity of water uptake by the root
system (Storey 2007). However, analysed tubers (Fig. 1) were grown at similar conditions
in the same field and planted and harvested at once displaying similar pressure potentials.
Furthermore the modulus of elasticity of well-watered and turgid, freshly harvested tubers
did not differ significantly (Tab. 1, 2). This corresponds to results given by Alvarez and
Canet (2002) who found a generally reduced variability of tissue elasticity (Young’s
modulus) measurements at high pressure potentials.
Nevertheless, a decreasing pressure potential may further increase blackspot susceptibility
as reported by Lærke (2001). Tubers harvested in 2007 revealed significantly lower pressure
potentials and higher blackspot susceptibility compared to tubers harvested in 2006,
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