Page 435 - Biosystems Engineering

412 Cha pte r F i f tee n

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to the soil in the experiments by Steffens et al. caused the calcium
content to increase only in the leaves of long shoots. It did not, how-
ever, have any effect on changing the amounts of Ca in fruits and
the leaves of dwarf shoots. This could have been caused by a marked
reduction in shoot growth, whereas fruit size decreased only slightly.
According to these researchers, in order to bring about physiologi-
cal changes in fruits, PB should be supplied directly to the fruits or
the dwarf shoots. Only foliar applications of the retardant produce
significant effects on the postharvest physiology of fruits, but the
retardation effect is then weaker compared with applications to the
soil.
Studies carried out in Korea indicate that the retardants PB and
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daminozide, as well as NAA, intensify Ca transport to the plant
mainly under conditions of a low calcium content of the soil.

15.1.5 Effect of Retardants on Calcium Uptake
Retardants affect the uptake of calcium by plants as a result of an
increase in root weight. The supply of carbohydrates to the roots has
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a significant function in Ca uptake by fruits because it stimulates
root growth. Carbohydrates increase the weight of young roots whose
nonwoody growth apices take up more calcium. The acquisition of
calcium is confined only to the root tips.
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As was shown by Steffens et al., retardants cause an increased
efflux of carbohydrates to the trunk and roots, and this favors the
development of numerous young roots, actively taking up calcium
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from the soil. In experiments by Curry and Williams, the weight of
roots following the use of PB was found to have doubled. However,
other retardants in the same conditions had only a slight effect on
root weight.
Retardants can increase the calcium content of above-ground
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plant parts because by retarding growth, they increase the propor-
tion of roots to top growth.
In orchard production, various applications have been found by
products in which ethephon is the active ingredient. For example,
these preparations are used in fruit growing to improve color devel-
opment in apples. Information on the fact that apples treated with
ethephon have a lower keeping quality and contain less calcium has
repeatedly been published. For that reason, during the period when
daminozide was available, the storability of apples treated with eth-
ephon was enhanced by using daminozide on the same trees. As a
result of the combined application of the two substances, apples
stored better and contained more calcium. 5
More and more often, synthetic cytokinins are used in fruit pro-
duction. One of them is benzyladenine (BA), the latest compound
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used for thinning apple fruitlets. According to Greene et al., this
compound can affect the calcium content of apples indirectly by