The effect of a natural plant extract and synthetic plant growth regulators on growth, quality and endogenous hormones of Actinidia chinensis and Actinidia deliciosa fruit : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Horticultural Science at Massey University, New Zealand
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Date
2009
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Massey University
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Abstract
Kiwifruit are of huge economic importance for New Zealand representing 29
percent of total horticultural exports. Fruit size is the biggest determinant of
what consumers are willing to pay, and there is also a positive relationship
between consumer preference for flavour and percentage dry matter. The two
main cultivars exported from New Zealand are Actinidia chinensis ‘Hort 16A’
(gold kiwifruit) and A. deliciosa ‘Hayward’ (green kiwifruit). Under current
commercial practice the only product allowed for use on kiwifruit to increase
fruit size in New Zealand is Benefit®. Benefit® has been shown to induce
different results when applied to A. chinensis and A. deliciosa, whereas
synthetic plant growth regulators such as the cytokinin-like substance N-(2-
chloro-4-pyridyl)-N’-phenylurea (CPPU) have been found to promote similar
increases in fresh weight of fruit in both cultivars. Final fruit size is determined
by both cell division and cell enlargement. It was been shown that fresh weight
can be increased in both of the major Actinidia cultivars even though their
physiology differs. Hormonal control of fruit size in relation to cell division and
cell enlargement phases of fruit growth was studied in both A. chinensis and A.
deliciosa.
CPPU was applied to both cultivars in a growth response experiment where
fruit were collected throughout the growing season. The objective of this
experiment was to create growth curves, to compare and contrast the effect on
A. chinensis and A. deliciosa, and to provide material for hormone analysis.
Application of CPPU was found to significantly increase the fresh weight of
both A. chinensis and A. deliciosa fruit (46.98 and 31.34 g increases
respectively), and alter the ratio of inner and outer pericarps of A. chinensis
fruit. CPPU and Benefit® were applied individually and together to both
cultivars. It was found that only A. chinesis fruit were affected by the
application of Benefit®; fresh weight was increased by 26.38 g, and percentage
dry matter was significantly reduced. There was a statistically significant (p <
0.05) interaction between CPPU and Benefit® when applied to A. chinensis.
3,5,6-trichloro-2-pyridyloxyacetic acid (3,5,6-TPA) was applied to A. deliciosa
on two application dates at three concentrations and was found to decrease
fresh weight of fruit, but significantly increase percentage dry matter regardless
of application date or concentration. Lastly CPPU and 1-naphthalene acetic
acid (NAA) were applied to A. deliciosa at two application dates and in all
combinations. Application date affected the response to both a low
concentration of CPPU and NAA. A synergistic interaction was observed when
CPPU was applied early plus NAA late (CPPU early (4.53 g increase) plus
NAA late (13.29 g) < CPPU early plus NAA late (33.85 g).
Finally endogenous hormone content was studied. Methods were developed
and tested for the simultaneous analysis of both indole-3-acetic acid (IAA) and
cytokinins. Freeze dried fruit were purified using Waters Sep-pak® cartridges
and Oasis® columns then IAA was quantified by high pressure liquid
chromatography. Preliminary results indicate a correlation between application
of CPPU and endogenous IAA, high concentrations of IAA correlated well with
periods of rapid fruit growth particularly for CPPU treated fruit.
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Keywords
Kiwifruit, Fruit growth, Fresh fruit weight