Proceedings
of The World Avocado Congress III, 1995 316 -320
EFFECTS
OF PRODUCTION LOCATION IN SOUTH-EAST QUEENSLAND ON POSTHARVEST QUALITY OF
‘HASS’ AVOCADO FRUIT
S. Vuthapanich A. Klieber P.J. Hofman
Dept of Plant Production University of Adelaide Department of Primary
University of Queensland Waite Campus, Adelaide Industries Queensland Gatton
College, Lawes South
Australia 19
Hercules St, Hamilton
Australia
Australia
Australia
A.W. Whiley D.H. Simons
Department
of Primary University of
Queensland
Industries Queensland Gatton College, Lawes
P.O.
Box 5083 SCMC Australia
Nambour, Australia
To test
the effects of locality and/or cultural practices on 'Hass' avocado quality,
fruit were harvested from orchards in different locations in south-east
Queensland, at 3 stages of maturity (approx. 24, 29 and 34% dry matter; DM).
Fruit were either ripened at 22ºC or stored at 7ºC for 3 weeks before ripening.
Days to maximum ethylene production (DMEP), fruit skin colour, postharvest
disease severity and fruit Ca concentrations varied between locations. Days to
maximum ethylene production declined, with increasing maturity in fruit from
most locations. Disease severity was low in early harvested fruit, but
increased in later harvested fruit. Poor internal quality (disease and hard flesh
around the seed) was found in late harvests from orchards in warmer climates.
Correlations between DMEP and % DM and DMEP and flesh Ca concentration, were
either non-significant, or negative and positive respectively, depending on
locality. These results indicate the potential effect of production locality
and/or cultural practices on fruit quality, but more detailed research is
required to identify major factors involved.
1. Introduction
Successful marketing of horticultural products requires predictability
and consistency of quality. Postharvest performance of fruit can be influenced
by both cultural and climatic factors (Monselise and Goren, 1987; Hofman and
Smith, 1994), and fruit mineral composition, particularly calcium, can play a
major role (Ferguson, 1980). An understanding of the effects of production
factors on quality will improve predictability of fruit response to postharvest
handling. This paper reports some of the effects of production locality and/or
cultural practices on postharvest quality of 'Hass' avocado fruit.
2. Materials and Methods
Five uniform 5 to 8-year-old
'Hass' avocado trees were selected from each of 5 commercial orchards in
south-east Queensland between latitude 25-27.5ºS (table 1). Twenty fruit of
250-300 g mass each were harvested in 1993 at early, mid and late maturity
(approx. 24, 29 and 34% flesh DM respectively) from the northern aspect at 1.5
to 3 m above ground and 0 to 0.5 m into the canopy, and immediately dipped in
0.55 mL L-1 prochloraz for 30 sec. For each harvest, 2 fruit per
tree were ripened at 22ºC under humidified, ethylene-free air in ventilated
containers, and the other 2 fruit per tree stored at 7ºC for 3 weeks before
ripening at 22ºC.
Days to eating soft was
judged by hand pressure. Respiration and ethylene evolution were measured by
gas chromatography. Fruit skin colour (1 = skin fully green; 9 = fully black),
chilling injury (0 = none; 1 = 0-25%; 2 = 25-50%; 3 = 50-75%; and 4 = >75%
of cut fruit flesh surface area with discolouration) and disease severity (0 =
none; 1 = 0-5%; 2 = 5-10%; 3 = 10-25%; and 4 = >25% of fruit surface area
affected) were recorded. Mineral concentration (by wet digestion and
inductively coupled plasma emission spectroscopy) and % DM were determined on
equatorial sections of fruit flesh.
3. Results
3.1 Days to maximum ethylene production
Days from harvest to maximum
ethylene production (DUEP) was significantly affected by production location
(figures I a & 2a). Days to maximum ethylene production was less in stored
fruit and generally less in more mature fruit, except those from the Sunshine
coast. There were significant negative correlations between % DM and DMEP in
unstored and stored fruit, but not in all locations (table 2). Fruit reached
eating soft about 5 days after maximum ethylene production, and days to eating
soft and DMEP was correlated in both unstored and stored fruit (r = 0.95**
& 0.58* respectively).
3.2 Fruit shape and skin colour
Fruit from cooler localities had higher length: diameter
ratio (table 1). Fruit skin colour at eating soft differed markedly between
locations (figures lb and 2b). More fruit developed a full dark skin colour
following storage than when ripened following harvest.
3.3 Internal quality
Postharvest diseases (mainly
anthracnose and stem end rot) were low in early- harvested fruit, but higher
(up to >25% of fruit surface area affected) in late-harvested fruit from
warmer regions, and in stored fruit (figures 1c and 2c). Fruit from warmer
regions developed poor internal quality (firm flesh near seed, germinated seed
and rancid flavour) in late harvests (data not presented). There was negligible
chilling injury following storage (data not presented).
3.4 Flesh Ca concentration
Flesh Ca concentration was
higher in fruit from the Sunshine coast than from other localities, and was
less in more mature fruit (figure I d). A positive relationship between fruit
Ca concentration and DN1EP was found in non-stored fruit from the Lockyer
Valley and Toowoomba, and in stored fruit from Maleny (table 2). Correlations
of r = 0.29* and 0.56** were obtained between Ca concentration and DMEP in
non-stored and stored fruit respectively, over all localities.
4.
Discussion
Significant effects of
production locality and/or cultural practices have been noted in many fruits
(e.g. Blaripied et al., 1987; Rowell, 1988). A reduction in shelf life with
increasing maturity has been observed in avocado by Cutting et al. (1992), and
in mango by Hofman et al. (1995). Strong correlations between avocado flesh Ca
concentration and days to ripe have been noted by Witney et al. (1990) and
Cutting et al. (1992), and
in other fruit (Hofman and Smith, 1994). However,
our results indicate that while fruit Ca plays a role, yet to be identified production
factors are also important in determining the dynamics of avocado fruit
ripening.
Skin colour of 'Hass' is an
important commercial consideration in Australia.
Consumers consider 'Hass' to
be ready to eat when skin is very dark to black (Ledger and Barker, 1995), but
the flesh is often over-ripe by this stage, and disease is likely to be more
severe. Hence a delay in skin colour development relative to flesh softening
may result in over-ripe fruit and a reduction in quality. The present results indicate
that skin colour can be affected by production factors and maturity, and cold
storage delays flesh softening to a greater extent than skin colour
development, so that fully coloured, but over-soft fruit are less likely. There
may be some potential to exploit this finding to better synchronise skin colour
and flesh softening.
Disease was the major factor
determining storage life in these experiments. The generally increased severity
in warmer production areas and in more mature fruit, may partially result from
a longer exposure time of fruit to inoculum with later harvests, and reduced
physiological "vigour" of fruit when grown in warmer climates and
when harvested later. However, disease severity can be influenced by
pre-harvest and postharvest practices, so that the effect of the above factors
can be minimised.
These results indicate the
potential effect of climate and production factors on 'Hass' quality. The trial
is currently being conducted over another season to evaluate climatic
influences. More detailed studies involving specific manipulation of cultural
practices are required to identify production factors that influence
postharvest quality.
Acknowledgment
This research was supported by
the Department of Primary Industries Queensland, Project 9313 of the Australian
Centre for International Agricultural Research, and the University of
Queensland Gatton College. We thank the growers involved in this trial for
access to orchards and supply of fruit.
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