Abschlussbericht Projekt: „Verminderung der ... - BLE

Discussion
Harvest date in comparison with BSI. Besides specific gravity also the length of the
vegetation period influenced tubers blackspot susceptibility of tubers. Also Corsini (1999)
and Thornton and Timm (1990) described that after a typically warm vegetative period
specific gravity as well as the maturity of tubers harvested at different stages of haulm maturity
were closely related to BSI. The time of interruption of the natural process of haulm
senescence must have important consequences for tuber properties at harvest and may provide
a possibility of adjusting the tuber response to impact as also previously described by
McGarry et al. (1996). Tubers were pre-harvested from relative immature haulms around
150 days after planting which corresponds to approximately 90 days after emergence.
Kolbe and Stephan-Beckmann (1997) stated that at this stage of tuber development until
harvest nutrient concentrations (P, K, Ca, Mg) and nitrogenous compounds differ only
slightly depending on growing conditions, which was also observed in this present study.
Despite the fact that nutrients as well as nitrogenous compounds are known to influence
blackspot susceptibility the presented results revealed no consistent relationship between
nutrient concentration and BSI of tubers. The concentrations of the organic acids namely
ascorbic, malic and citric acid are obviously higher in tubers harvested from premature
haulms compared to tubers harvested two weeks later as described by Kolbe and Stephan-
Beckmann (1997). This relative higher concentrations might decrease the pH-value and
inhibit enzymatic reactions (Pawelzik and Delgado 1999) leading to lesser blackspot development.
Nutrient concentrations in comparison with BSI. During both years of investigation
potatoes grew with an adequate supply of all essential nutrients because no nutrient deficiency
symptoms were detectable, while tuber quality parameters like starch concentration,
dry matter concentration and BSI were significantly different, which might be particularly
influenced by some nutrients. Only for K we observed a significant increase in the concentration
with increasing specific gravity of pre-harvested tubers in both years of investigation.
During these periods of tuber growth the function of K referred to starch synthesis
and dry matter accumulation for normal tuber development and yield response (Westermann
et al. 1994b). Within both tested periods of vegetation and storage there was no a
single nutrient whose concentration was continuously related to specific gravity and/or
BSI. Presented findings are comparable to results from Oswald et al. (1958), Dwelle et al.
(1977) and Corsini et al. (1999), who reported no effect of K on BSI presuming an adequate
K supply. This might particularly depend on type of fertilizer because KCl was able
to reduce BSI primary through the component Cl, which reduced the dry matter of tubers
grown in dry sandy soils (van Loon and van den Berg 2003/2004), while K 2 SO 4 (Maier et
al. 1986) and KNO 3 (Kumar et al. 2007) had no effect on BSI. Also P, Mg, Ca, Fe, B and
Se concentrations did not influence BSI permanently. In the case of P, Mg, Ca, Fe and B
presented findings agreed with studies from Scudder et al. (1950). Adequate fertilization
and irrigation ensured sufficient amounts of nutrients around roots and tubers and nutrient
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