Page 434 - Biosystems Engineering

Exogenous Bior egulators–Fruit Composition & Storability 411

supplied with calcium and other nutrients first. The calcium content
of fruits depends on the ratio of fruit growth to shoot growth. Under
the conditions of greatly restricted shoot growth and a small reduc-
tion in fruit size, the Ca content of fruits increases. In experiments by
´
51
Miller and Swietlik, the effect of PB on the incidence of bitter pit and
the Ca content of fruit was found to decrease as the retarding effect on
shoot growth became smaller. The usually heavily cropping, but not
vigorously growing, trees supply sufficient amounts of nutrients to
growing fruits. The small number of leaves in that case restricts fruit
size and improves their calcium supply. Fruits from trees like that
usually keep well. As the axial shoots grow longer (e.g., from 12 to
55 cm), the incidence of bitter pit increases—from 0 to 60 percent in
experiments by Terblanche et al. 70
The most convincing evidence of the competition between shoots
52
and fruits for calcium was provided by Naumann. This researcher
followed the uptake of a calcium isotope by the fruits and shoots of
Cox’s Orange Pippin apple trees growing in pots under controlled
conditions. Calcium was supplied to the soil. In the case of untreated
control trees, Naumann found that most of the calcium was taken
52
up by the leaves of young shoots and much less was taken by the
fruits. The fruits were, to a large extent, affected by bitter pit. After
retardants were applied, shoot growth became weaker. At the same
time, the fruits took up more calcium and kept much better. Of a par-
ticularly good keeping quality were the apples treated with SADH.
However, 3-year-long experiments of Ludders and Fischer-Bolukbasi 45
indicated that the mineral content of apples treated with SADH
depended on the fruiting intensity of the apple trees; levels of Ca, Mg,
and N were higher in the fruits of abundantly fruiting trees.
In studies by Greene, 30,33 paclobutrazol deposited on the leaves
slowed down shoot growth, reduced apple size, and, at the same time,
increased the amounts of calcium in fruit flesh and limited the inci-
dence of diseases, even in the second year after treatment. However,
the total calcium content per fruit remained unchanged. Therefore,
the increase in Ca content was related to the reduction in fruit size.
At the same time, the total calcium content per tree increased. This
could have been caused by the shoots attracting less calcium. PB was
found to produce similar changes in the experiments by Elfving et
al., but only in the year of application. The preparation retarded
24
shoot growth and decreased fruit size in the next 3 years. Greene 31
tried to explain the divergent results with different environmental
conditions, cultivar-related differences, and different application rates
and times at which retardants were used. Only retardants applied at
the stage of intensive growth had an effect on the uptake of mineral
nutrients. When shoot growth was slowed down, the retardants
ceased to work.
The effect of PB on calcium acquisition by fruit depends on the
way the preparation is applied. The very same retardant, PB, applied