Page 430 - Biosystems Engineering

Exogenous Bior egulators–Fruit Composition & Storability 407

and, consequently, an improvement in their storability. This was
69
proved for the first time by Stuivenberg and Pouwer in 1950. By
spraying apple trees with the cultivar “Notaris” with IAA, they
brought about a decrease in the number of apples with bitter pit. It is
interesting to note that this effect of IAA was achieved only when the
substance was applied between the end of June and the middle of
July (i.e., just after the natural fruit drop in June). Twenty years later,
61
in studies by Sharples, IAA delivered to the core of apples with the
cultivar “Cox’s Orange Pippin” was found to reduce the incidence of
core browning. IAA thus improved the keeping quality of apples, as
in the experiments by Stuivenberg and Pouwer. 69
Similar experiments were carried out by Looney, who used IBA
42
(indole butyric acid ) on the apple trees cultivar “Spartan.” Within
plants, this auxin gets converted to IAA. In one of three experiments,
the auxin IBA caused the amount of Ca in the skin to increase by
13 percent, and in the core by 28 percent. This reduced the decompo-
sition rate of apples. The effect of IBA was greatest when the apples
were treated with calcium chloride at the same time.
The auxin IAA delivered onto apples in a synthetic form does not
always cause an increase in their calcium content. According to
Bangerth, this happens in the case of apples that have a large number
2
of seeds. Apples of this kind can themselves produce auxins in
amounts necessary for Ca transport. This means that the additional
amount of auxins can have a toxic effect, destroying the seeds. This
was confirmed by the results of the experiments conducted by Wills
and Scott in 1974 in which injections of IAA into the seed core
77
speeded up the breakdown of apples. This effect was also shown by
the results of our experiments in which IAA was applied directly to
apples followed by an examination of the uptake and transport of a
Ca isotope through the parts of the tree consisting of fruits and
7
shoots. It was found that IAA deposited on the apples of the cultivar
“Double Red McIntosh,” which had a large number of seeds,
decreased the uptake of the Ca isotope by whole parts of the trees, but
the apples treated with IAA in general maintained higher levels of
calcium than the untreated ones.
The role of seeds in the acquisition of calcium by fruits was dem-
onstrated by the low levels of the element in parthenocarpic (seedless)
fruits found following the use of GA or GA . Bangerth’s experiments 2
3 4+7
indicated that seedless fruits—both apples and pears—contained
less Ca than those with seeds. Griggs et al. demonstrated that seed-
36
less fruits respond to the delivery of exogenous auxins in a different
way than seed-containing fruits do. In seedless fruits, the exogenous
auxin, particularly when used in combination with gibberellins, can
replace the endogenous auxin produced by the seeds. This can result
in an increase in the Ca content of the fruits and an improvement in
their storability.