Proceedings of The World Avocado Congress III, 1995 57-60
EFFECT OF POLYAMINES, GIBBERELLINS AND OTHER GROWTH
REGULATORS ON THE FRUIT-SET
OF AVOCADO
Marianthi
H. Loupassaki
Mediterranean
Agronomic Institute of Chania
73
100 Chania, Crete, Greece
Ioannis
1. Androulakis
Subtropical
Plants & Olive Trees Institute
73100
Chania, Crete, Greece
Miltiadis D. Vasilakakis
Aristotle
Univ. of Thessaloniki
Division
of Plant Sciences
54006
Thessaloniki, Greece
Abstract
The polyamines Spermidine at
10-4M, Putrescine at 10-3M and 10-4M, Spermine at 10-4M and aminoxyacetic acid at
500 ppm were applied, at full bloom to whole trees or branches of Fuerte, in a young
six year-old avocado orchard in the area of Chania Crete to increase fruit-set.
In other trials Fuerte trees were sprayed with GA3 at 50, 100, 200,
400 ppm and 100 ppm applied four times at regular 10-day intervals. Further a
mixture of 200 ppm GA3 25 ppm BAP (benzylan-iinopurine) and 10 ppm
NAA (naphthaleneacetic acid) was applied to young trees of the cvs Hass and
Fuerte.
As it was found
gibberellic acid (50-400) ppm applied on Fuerte at full bloom increased
parthenocarpic fruits 40 to 80 times while four repeated, at weekly intervals,
sprays of 100 ppm of gibberellic acid increased parthenocarpic fruits more than
200 times. A mixture of 25 ppm BAP plus 10 ppm of NAA and 200 ppm GA sprayed at
bloom induced the setting of parthenocarpic fruits in both Hass and Fuerte.
Sper- midine or Spermine at 10-4M or 10-3M of Putrescine sprayed at bloom increased fruit- set
in Fuerte.
Additional index words: hormones, fruit drop, parthenocarpic fruits
1. Introduction
Avocado (Persea americana Mill)
is an established crop in many parts of the World but yields are often
unreliable. Gibberellins, benzylaminopurine, napthaleneacetic acid, polyarnines
and other growth regulators are reported to increase fruit set in apples
(Longhlin et al., 1984), olives (Androulakis 1987, Rugini et al, 1986),
pears (Crisosto et al.1986), grapes (Shaltuunt et al.1986) and other crops.
Stewart et al. (1951) reported that a 5% emulsion of kerosene containing
either 25ppm of the isopropyl ester of 2,4-D or 2ppm of butyl ester of 2,4,5-T did
not affect the yield of normal fruits of Fuerte but 2,4-D when applied in
April, increased the number of seedless fruits. Razeto et al., (1983)
found that one application of GA3 at 50ppm on Fuerte at the end of
blooming increased parthenocarpic fruits 100 times while in cv. Negra de la
Cruz sprayed at the beginning of bloom, the seedless fruits increased as up to
14 times.
Avocado is a recent import in
several areas of southern Greece and in Crete. All imported cultivars with the
exception of Hass, however, suffer from less than adequate productivity. Thus
the present work was carried out in order to study the effect of putrecine,
spermidine and spermine and of GA and other growth regulators on the fruit set
of the avocado.
2. Material and methods
In order to evaluate the
effect of polyamines (spermidine spermine purtescine), aminoxyacetic acid,
gibberellin and of a triple hormone
mixture (NAA, BAP, and GA3) on the fruit-set of avocado, three experiments were carried out on
young 6 years old avocado orchards in the villages Alikianou and Nerocourou of
the district of Chania, Crete. The first experiment comprised sprays with the
polyamines spermidine, spermine at 10-4M, putrescine at 10-4 and 10-3 M (prepared in a 0.01M buffer of tris- (hydroxymethyl)
amino methane adjusted to pH 7.1), Aminoxyacetic acid (AOA) at 500 ppm plus
water sprayed and untreated controls.
The second
experiment comprised four levels of GA3 (50, 100, 200 and 400 ppm) plus water sprayed and
untreated controls. The treatments were randomly allocated on tagged branches
bearing more than one hundred inflorescences, of six uniform young trees of
Fuerte on the 6th of April, using a small, hand-held sprayer.
Besides an additional (seventh) treatment consisting of repeated four times (6,
15 and 29 of April and on 6th of May) application of 100 ppm GA3 (on the same branches) was
included. In another (third) experiment whole Fuerte and Hass trees were
treated, at full bloom (6th of April) with a triple hormone mixture comprising 200 ppm GA3 25 ppm BAP
(benzylaminopurite), 10 ppm NAA (naphthalenacetic: acid) and giberellic acid at
200 ppm. Water sprayed controls were also included.
3.
Results and discusion
The first counts (fruits per 100
inflorescences) on the branches of Fuerte treated with polyamines and
aminoxyacetic acid (AOA) were inconsistent and no clear conclusion can be drawn
about the effect of these treatments on initial fruit set. (Table 1). The
counts of fruits, retained to the end of growing season, were more consistent.
Thus with the exception of
the lower concentration (10-4 M) of putrescine, polyarnines
increased (final) fruit-set by 77.9 to 88.7% whereas aminoxyacetic acid showed
a definite thinning action (Table 1, count on 5 Oct.). Higher fruit-set rates
by polyarnine sprays were also obtained in olives (Rugini et al. 1984),
apple (Costa et al., 1984) and in pear (Crisosto et al. 1984).
In the second experiment, initially, a sizable
number of, mostly parthenocarpic fruits were set in all the treatments
including the controls, the application of GA3, however, greatly enhanced the setting of
parthenocarpic fruits. As shown in Table 2a and 2b GA3 applied at
full bloom, increased 40 to 80 times the number of parthenocarpic: fruits of
the Fuerte while it did not affect the number of normal fruits.
Similar results were reported
by Stewart and Hield (1951) after spraying avocados with 25 ppm of 2,4 D in
April while Razeto and Longueira (1983) reported that a single application of
50 ppm of GA3 on the cvs Fuerte and Negra
della Cruz resulted in 100 and 14 times more parthenocarpic fruits than in the
control respectively. The concentration of the growth regulators and the timing
of the sprays seem to be critical. The mixture of hormones (25 ppm BAP plus 10
ppm of NAA and 200 ppm GA3 ) applied at full bloom to
whole Fuerte and Hass trees (third experiment) induced the setting of
parthenocarpic fruits in both (Table 3). The counts of fruits well after the intensive early fruit drop
(28th of September), i.e. when normal and parthenocarpic fruits were
well developed, showed
that parthenocarpic increased nearly 100 times in Fuerte. Besides Fuerte (known
to give pathenocarpic fruits readily), in the cv Hass in which under normal
conditions no parthenocarpic fruits are seen, on average 81.8, such fruits per
tree were counted in response to the treatment with the triple hormone mixture.
The parthenocarpic fruits obtained with the use of hormones in cv Fuerte had
similar pattern of development with those in the controls. Kotob and Schwabe
(1971), who applied a similar hormone mixture on apples however, obtained
parthenocarpic apples similar in size with the seeded ones. This difference in
the response to the hormone mixture might be due to the fact that a different
proportion of the hormones - constituents might be needed for avocado.
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