Page 433 - Biosystems Engineering

410 Cha pte r F i f tee n

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For example, in the experiments by Schumacher et al., apples of the
cultivar “Grafsztynek” whose trees had been sprayed with damino-
zide had 20 percent less Ca and were affected by bitter pit more often
than apples from control trees of similar size and degree of ripeness.
12
In Poland, daminozide (SADH) often increased the incidence of core
browning in McIntosh apples. This also provides evidence for calcium
deficiency in those fruits or incorrect ratios of Ca to other elements.
Spraying such apples with or dipping them in calcium chloride
reduced the incidence of the disease. Also in Kallai’s experiments, 39
paclobutrazol (PB) decreased the calcium content of “Jonathan” apples
by as much as 28 percent, already 1 month after full bloom. As har-
vest time approached, the differences in the calcium content between
the treated and control apples became smaller. However, even at har-
vest the calcium content amounted to 11 percent.

15.1.4 Effect of Retardants on the Mineral
Composition of Fruits
The indirect effect of retardants on the mineral composition of apples
is related to a reduction in fruit size, among other things. A negative
correlation is known to exist between the Ca content of apples and
the apples’ diameter. It has repeatedly been shown that retardants
[SADH (daminozide; 1-N-(dimethylamino)succinamic acid), as well
as PB (paclobutrazol; 1-(4-chlorophenyl)-2-(1H-1,2,4-triazol-1-yl)-
penten-3-d)] decreased apple size, particularly after retardants had
been used at high concentrations. The decrease in size was often fol-
lowed by an increase in the calcium content of apples, which improved
59
their storability. In experiments by Schumacher et al., in which
daminozide reduced apple size by various degrees depending on how
it was used, the largest number of healthy apples without bitter pit
symptoms were found among the smallest apples. All the daminozide-
treated apples had a better keeping quality than the untreated con-
trol. The trees sprayed with daminozide only for 1 year produced
20 percent less fruit with bitter pit symptoms. The use of daminozide
for 2 years, however, reduced the number of apples with symptoms
of this disease by 34 percent, whereas the use of the retardant over
three consecutive years resulted in as much as a 75 percent reduction.
A small, 5 percent, reduction in apple size was found on the trees
where only the crown’s periphery was sprayed with daminozide.
Such a slight decrease in fruit size had the smallest effect on the inci-
dence of bitter pit. In this experiment, SADH was not very good at
retarding shoot growth.
The most frequent reason for changes in calcium content of fruit
following the use of retardants was the restricted growth of shoots
and, at the same time, reduced competition between them for mineral
nutrients. As it is known, large amounts of calcium are transported
in the spring when shoots grow very intensively. Young shoots are