Page 432 - Biosystems Engineering

Exogenous Bior egulators–Fruit Composition & Storability 409

example, when other parts of the tree are less active or after repeated
applications of gibberellins at high concentrations over a long period
resulting in a holding back of the ripening process. It was probably
for that reason that GA reduced the incidence of internal breakdown
3
19
in “Jonathan” apples in Clijsters’s experiments. It has repeatedly
been shown that GA used just before or just after the harvest improves
3
the keeping quality of apples. Among other things, GA reduced the
3
incidence of breakdown and core browning in studies by Scott and
Wills and Sharples. When used at those times, the gibberellin mod-
60
61
ified the calcium distribution in fruit during storage, making the
fruit more resistant to physiological diseases.
In orchards, the gibberellins GA are often used on their own or
4+7
in combination with benzyladenine in order to reduce russeting and
to improve the shape and size of apples. In Looney’s experiments, 43
these substances, used only once or twice in the period from petal
fall to 5 weeks after flowering, always decreased the level of calcium
in apple flesh, on average by 25 percent, and increased the incidence
6
of fruit breakdown in storage. In our experiments, GA reduced
4+7
the keeping quality of apples of the cultivar “Starkrimson.” Particu-
larly badly affected was the keeping quality of apples treated with
these substances at high concentrations. Similar effects were shown
by the gibberellins GA in the experiments by Greene et al. These
34
4+7
researchers demonstrated that as the concentration of the gibberel-
lins was increased, the calcium content of apples decreased. This
could have been caused by the reduced number of seeds as well as
by the large increase in apple size. The gibberellins A used in com-
4+7
bination with benzyladenine reduced calcium uptake by apples
treated with daminozide and adversely affected their storability.
Similar effects of GA and BA were observed in our experiments, in
4+7
which they were used on daminozide-treated “McIntosh” apple trees
(unpublished data).
15.1.3 Retardants Are Also Bioregulators
Use of retardants was very popular in the 1980s. They were used in
orchards very often. There is, therefore, a lot of information on the
effects of retardants on the storability and mineral composition of
fruits. According to Faust and Miller, retardants affect calcium
26
uptake by fruits as a result of a direct influence on the transport of
IAA, or indirectly by reducing fruit size, limiting competition among
shoots, or changing root weight.
Retardants are antigibberellins. They reduce the levels of gibber-
ellins in shoot tips. They can also impair the diffusion of auxinlike
substances from shoot tips. As a result, the transport of Ca to fruits
can be weakened. The direct effect of retardants on Ca uptake was
demonstrated by experiments in which these preparations caused a
drop in calcium levels in fruits and deterioration in their storability.