Page 431 - Biosystems Engineering

408 Cha pte r F i f tee n

Higher levels of Ca in fruits and better storability are also caused
by other auxins, such as 2,4,5-T (trichlorophenoxyacetic acid), which,
71
in the experiments by Sharples, caused a reduction in the incidence
of low temperature breakdown and core browning in apples of culti-
var “Cox’s Orange Pippin,” and 2,4,5-TP (trichlorophenoxypropionic
acid), which in Stahly’s experiments, 66,67 when used at 20 mg/L
24 days after full bloom, produced higher levels of Ca, and also of K
and Mg, in “Golden Delicious” apples.
The most commonly used auxin in orchard production is NAA
(α-naphthalene acetic acid). In one of three experiments carried out
50
by Martin et al., NAA reduced the incidence of bitter pits and the
decomposition rate in “Merton” apples. These apples are also richer
in calcium and many other elements. NAA was found to enhance the
effectiveness of CaCl in preventing the breakdown of Cox’s apples. 48
2
NAA also reduced the severity of bitter pit in apples sprayed with
daminozide and ethephon. NAA, used in our experiments for fruit-
53
let thinning, increased the level of calcium in apples or had no effect,
probably in relation to the degree of crop reduction and the range of
40
12
the increase in apple size. In Link’s experiments, NAAm (amide of
naphthalene acetic acid), used for fruitlet thinning, affected the min-
eral composition of apples, just as NAA did in our experiments, but it
sometimes increased the incidence of bitter pit. NAA is commonly
74
used to prevent preharvest fruit drop. According to Wertheim, NAA
used in this way does not affect the storability of apples provided,
however, that the harvest date is right. In contrast, in the experiments
77
by Wills and Scott, NAA injected into the seed core at a concentra-
tion of 20 μmol increased apple breakdown.

15.1.2 Exogenous Use of Gibberellins
The effect of these substances on the mineral composition and
storability of fruits depend on the time of their application and their
concentration.
For example, parthenocarpic fruit obtained in Bangerth’s experi-
2
ments following the use of GA and GA at flowering time con-
3 4+7
66
tained less Ca. In Stahly’s experiments, GA used later (i.e., 24 days
3
after full bloom), did not change the Ca content of “Spartan“ apples.
42
In studies by Looney, where both gibberellin A and auxin IBA
3
were used, most of the apples affected by breakdown were found
after both these substances were used in combination. The best-
keeping apples were those treated with the auxin only. This proves
that the gibberellin eliminated the beneficial effect of the auxin and
lowered the level of calcium in apples treated with the auxin, although
it did not cause definite changes in the mineral content and storabil-
ity of apples by itself.
According to Wills and Scott, gibberellins can, under certain
77
conditions, enhance the process of attracting calcium by the fruit, for