Abschlussbericht Projekt: „Verminderung der ... - BLE

centrations may be a result of high numbers of starch granules which increase the potential
of mechanical deformation to membranes as a direct effect of impact (12).
BSI of stored tubers. During storage, tubers undergo several stages of dormancy. The
length of this period is controlled by genetic and environmental factors (29). At the end of
dormancy, tubers turn into a source organ providing growth of the developing sprout (30).
At that time, starch and protein degradation takes place and soluble sugars and amino acids
become available (31). Prolonged storage initiates aging and senescence. Both processes
are similar and the result of complex metabolic modifications. The senescence is characterized
among others by increased activity of membrane associated enzymes (e.g. phospholipases),
resulting in a release of membrane-bound PUFAs and their subsequent oxidation
can lead to the generation of ROS. ROS are able to peroxidise amyloplast membrane lipids
directly (31). Kumar & Knowles (31) observed a degeneration of amyloplast membranes in
relation to starch degradation during potato storage. Polyphenoloxydase (PPO) catalyses
melanogenesis and is mainly located in the amyloplast. A relation to increasing BSI could
be possible but direct relations were not reported. Lærke (12) pointed out that only few
membrane studies focused on tonoplast degeneration revealed a related increase in blackspot
susceptibility, where the tonoplast acts as physical barrier to pigment initiation. Therefore,
age and metabolic status of tubers depending on genetic and environmental factors
have an influence on the BSI of cultivars and tubers differing in their specific gravity during
storage.
Tubers differing in their DP. The determination of blackspot susceptibility via DP
showed a lower blackspot susceptibility of tubers harvested 2005 compared to tubers harvested
2006. The DP generally increased during storage. Relationships between BSI and
DP were significant but the correlation coefficient was relatively low. Performed DP tests
were suitable to recognize genotypic differences concerning blackspot susceptibility within
a vegetation period, while DP methods did not consider physical properties. The present
results show that the DP can not be used to compare blackspot susceptibility between different
cultivars and growing periods. With respect to the method colour changes after 24
hours of whole unpeeled homogenised tubers was measured. The colour may occur as a
mixture of actually originated melanin pigments and the cultivar characteristic tinct of
periderm and non-periderm tissue. These findings are confirmed by Lærke et al. (1), who
determined the DP of tubers in vivo using a colourimeter. Differences between BSI and DP
may be due to the fact that pigment formation after impact takes place in one to three days
in vivo but in only few minutes in vitro, which was also discussed by Lærke et al. (1) and
Matheis and Belitz (32). Despite the fact that the potato tuber is well aerated in vivo discolouration
may takes time because of a lack of oxygen.
Summarizing the data from vegetation and storage periods, blackspot susceptibility of the
studied cultivars is closely connected to BSI tests. However, the results revealed only a
weak relation between BSI and DP test.
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