Abschlussbericht Projekt: „Verminderung der ... - BLE

Nutrient concentrations in potato (Solanum tuberosum) tubers in comparison
with their different susceptibility towards blackspot
Wulkow A 1 , Pawelzik E 1*
1 Quality of Plant Products Section, Department of Crop Sciences, University of Goettingen
Abstract
The blackspot index (BSI) was determined in potato tubers harvested at different stages of
haulm maturity and after storing tubers for several months. Pre-harvested tubers had a
lower BSI compared to tubers harvested two weeks later (main harvest) whereas the BSI of
stored tubers varied from year to year. The BSI increased when cultivar specific gravity
was relative high. However, the concentrations of K, P, Mg, Ca, Fe, B and Se were not
related to the BSI of tubers. Irrigation to attain optimum soil moisture conditions during
periods of vegetation enhanced nutrient sufficiency and reduced the potential damage inflicted
on tubers. Nutrient uptake was nearly complete when the majority of tuber growth
ends approximately 150 days after planting. Although extreme nutrient deficiency was not
observed nutrient concentrations of tubers particularly depended on nutritional interactions
influenced the BSI also.
Keywords: specific gravity, maturity, storage, fertilization, potassium, phosphorus,
magnesium, calcium, iron, boron, selenium
Introduction
Potato tuber are rich in parenchymatous tissue including water as a predominant component
and shows a lack of specialized thickened tissue (Peterson et al. 1985). This characteristic
determine tubers susceptibility towards various forms of external and internal damage
that occur after impact caused during commercial production, harvest and/or post-harvest
handling (Thornton and Timm 1990). In contrast to external damage, internal damage is
not visible before cutting or peeling the tuber. The symptoms of internal damage may or
may not include visible tissue fracture. If there is no visible fracture, damage sometimes
includes the development of floury-white regions in clear contrast to the cream background
of undamaged tissue finally resulting in the formation of grey and black coloured pigment
melanin. This symptom is usually referred to as internal bruising particularly termed
blackspot (McGarry et al. 1996). A major factor on the intensity of blackspot is the speed,
distance and type of impact as well as the genetic and environmental diversity. In general
tubers of a given cultivar or among cultivars subjected to a known impact do not express
the same degree of blackspot. This suggested that there is at least one component influencing
blackspot susceptibility among tubers (Thornton and Timm 1990). Dry matter has a
major influence on blackspot susceptibility, whereas dry matter primary depends on to the
starch concentration of tubers (Wulkow et al. in preparation) and, therefore, it is highly
variable. Even the alternation of the water concentration influences blackspot susceptibility
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