13
& 14 FEBRUARY 2002
ABSTRACTS
SAAKV
NAVORSINGIMPOSIUM
13 &
14 FEBRUARIE 2002
Evaluation of new generation
fungicides for control of Cercospora
spot on avocado fruit
Riaan
Duvenhage
Merensky Technological Services
e-mail: riaand@hansmerensky.co.za
High
volumes of copper sprays cause build-up of copper in soils and can render soils
unfit for fruit production in future (such cases have already occurred in
Europe). Alternative chemicals were evaluated for control of Cercospora spot
and post-harvest diseases with the aim to replace or reduce copper sprays in
the future.
The experiments were carried
out at Westfalia Estate near Tzaneen and seven large Fuerte trees were used for
each treatment. Treatments were applied during the 1999/2000 season and Bion,
Flint, Ortiva, and Avogreen were selected for further evaluation. During the
2000/2001 season Bion, Lime sulphur and Ortiva gave good control when used in a
programme with copper oxychloride.
In future trials, Ortiva and
Lime sulphur will be evaluated for registration as well as ferric chloride,
chlorine dioxide and QAC as additives to low doses of copper oxychloride.
Institute
for Tropical and Subtropical Crops
e-mail: maritha@itsc.agric.za
Pepper
and Tar Spots of Hass and Pinkerton, both caused by Colletotrichum, have become increasing problems over the past five
years.
The trials
reported on were field evaluations of the standard sprays as also fungicides
from the strobin and triazole groups, which may be registered on avocados in
the future. A QAC sanitiser and the addition of ferric ions to copper sprays
were also tested. Spray timings were based on previous findings.
None of the
newer fungicide programs were better than the current standard copper or copper
alternated with Benlate programs. Newer fungicides are also considerably more
expensive.
AvogreenTM : Results of commercial trials
Ocean Agriculture (Pty) Ltd
e-mail: cornelia@oceanag.co.za
Commercial
AvogreenTM trials were conducted in different production areas and
on different Avocado cultivars. The biocontrol agent was applied according to
commercial spray schedules used for fungicide applications. Treatments included
benomyl or copper oxychloride sprays, alone or integrated with AvogreenTM,
and AvogreenTM alone. Trials were also conducted to determine the
influence of different modes of application and additives such as wetters and
mineral oils, on the efficacy of AvogreenTM. Bacillus population levels were monitored in the field at several
intervals by collecting leaves from random trees and following a standardised
analysing method. This information is necessary to predict the survival of the
antagonist in the field and to determine the optimum disease-reducing
concentrations of Bacillus necessary
to reduce incidence of Cercospora
black spot and other diseases. It provides information necessary to improve
biocontrol effectiveness through better formulation, adjustment of dosage and
spray scheduling. This information is also necessary to minimise wasteful
application of inoculum. Timing of antagonist application is of crucial
importance in biocontrol programmes and poor survival of the antagonist in the
field will result in inadequate disease control. Therefore, monitoring
antagonist survival is of prime importance to ensure effective disease control.
Testing of new rootstocks for
increased ‘Hass’ yields and resistance to root rot
Merensky Technological Services
e-mail:
sylviek@hansmerensky.co.za
Vegetatively propagated
rootstock selections grafted with Hass are evaluated for their root rot
tolerance and yield potential in an orchard heavily infested with Phytophthora cinnamomi. These are compared to the commercial
standard (Duke 7) and susceptible controls (Edranol seedling rootstocks). The
first orchard (established 1996) contains root rot tolerant rootstocks from
Israel, while the second orchard (established 1998) contains root rot tolerant
rootstock selections from Westfalia Estate.
A third orchard (planted in April 2000) contains 9 different rootstocks
including the South African selection ‘Bounty’ and two selections from the MTS
breeding program.
The annual tree health rating
(July 2001) showed that the tree condition in the first and the second orchards
had in general declined further, but not as severely as during the extremely
wet summer in 2000. The ranking order
of the rootstocks remained consistent during the period 1999 to 2001. In both orchards, a second crop was picked
in 2001. Rootstocks Merensky II,
Merensky III and V100 out-performed the Duke 7 rootstock in terms of yield and
root rot resistance.
How can
pruning and manipulation have a positive effect on fruit quality?
ARC-Institute
for Tropical and Subtropical Crops
e-mail:
Bram@itsg2.agric.za
The past few seasons have seen a significant occurrence of both grey pulp and black cold injury in South African export avocados. While the Pinkerton cultivar has been the most severely affected, grey pulp has also been evident in ‘Hass’ fruit arriving in Europe. The question is posed as to what is causing these difficulties with the export of South African fruit. Some role players regard the problems as being a result of an extended harvesting period and inappropriate plant nutrition. There is also the perception that the introduction of pruning and other manipulative tools may have led to sub-optimal orchard management, where other orchard practices have not been adapted to suit these new tools. In this paper, an attempt is made to understand the different management tools and their influence on fruit quality. The effect of pruning, the use of PGR’s and the influence of calcium sprays are discussed, as are preliminary results on the timing of N fertilizer applications or the removal thereof to increase fruit quality. The effect of these practices on both quality and yield stability are looked at.
Sunburn control on ‘Hass’ fruit
Therese Rossouw
Merensky
Technological Services
e-mail:
thereser@hansmerensky.co.za
ShadowTM,
a wettable powder used for sunburn control on various fruit and vegetables, was
applied as a double and a multiple treatment to ‘Hass’ fruit. After picking, fruit underwent the normal
packhouse treatment. However, Shadow residues were still present, especially on
fruit that received the multiple treatment. An increase of 20% clean fruit
(fruit without sunburn) was obtained with both Shadow treatments, compared to
the untreated control treatment. Scale insect numbers increased dramatically on
fruit treated with Shadow where 65 %
(double application) and 53 % (multiple application) of fruit were infested
with scale insects compared to only 22 %
in the untreated control treatment.
Sylvie
Kremer-Köhne
Merensky Technological Services
e-mail:
sylviek@hansmerensky.co.za
Six new Hass-like cultivars from California (Harvest, Gem, Jewel, Sir
Prize, Nobel, 8-22-5) and one Westfalia selection (Bonus) are evaluated. Top working started in 1996, and the third
crop was evaluated in 2001. Cultivars
Harvest and Gem matured at the same time as Hass. Both, Harvest and Gem, out-produced Hass and had good fruit
quality. Therefore further testing of these two cultivars is warranted and semi
commercial trials are recommended. All
the other cultivars tested either produced large fruit, did not colour up
and/or had a high incidence of physiological disorders. Their testing, therefore, was discontinued
after the 2001 season.
Further
refinement of ‘Pinkerton’ export parameters
ARC-Institute
for Tropical and Subtropical Crops
e-mail: bram@itsg2.agric.za
The
quality management research conducted on Pinkerton during the last three years
has rendered good results. In general, the internal quality of export
‘Pinkerton’ was found to be considerably better than in the past due to the
application of research results. Fruit maturity has been identified as the most
important quality determining parameter, but at the same time, aspects related
to orchard condition and tree management have also been noted as important. In
this respect, fruit Ca and N levels have been correlated with the two main
disorders, grey pulp and black cold injury. During the past season, the
recommended N and Ca norms were further refined. In addition, surveys were
conducted on the effects of tree age, fruit set and rootstock on fruit quality.
Tree age was found to be of particular importance and the quality problems were
found to diminish in older trees when correctly fertilized. The fruit set study
revealed some interesting trends. Earlier sets were found to be more
susceptible to grey pulp and less susceptible to black cold injury while the
reverse was true for the later sets. The fruit set distribution was spread in
younger trees but it considerably improved in older trees where 96% of the
fruit were found to be from the first set. Our initial results indicate
rootstock not to be of definite importance, but additional research is required
on this aspect.
Investigation into the use of methyl bromide fumigation as a
mitigating disinfestation treatment of fruit fly- and false codling
moth-infested avocados
Citrus
Research International (Pty) Ltd
e-mail:
ware@cri.co.za
Penetration
of the lucrative United States market has been one of the major aims of the
‘Haas’ avocado industry. However,
phytosanitary barriers are presenting a major obstacle and research has been
initiated in order to determine ways of satisfying the United States
authorities that fruit entering their markets do not pose a threat. After consultations with American experts it
was decided that the avocado industry needed to determine whether the methyl
bromide treatment currently authorised for Mediterranean fruit fly could be
extended to Natal fruit fly and Marula fruit fly. Unfortunately comparative testing demonstrated that Marula fruit
fly was the most tolerant of the three species. This meant that the existing protocol could not be used and a
Probit 9 level of confidence that the treatment was effective needed to be
established for this particular species.
The existing protocol for Mediterranean fruit fly did not produce the
desired level of control and a new treatment regime will have to be
established. Once treatment parameters
have been developed it will be tested against false codling moth.
False codling moth on ‘Hass’ avocado - a systems approach to quarantine
security
ARC-Institue
for Tropical and Subtropical Crops
e-mail: tertia@itsc.agric.za
False
codling moth, Cryptophlebia leucotreta
Meyrick (Lepidoptera: Tortricidae) is a pest of avocado and occurs in all
production areas. Most insect pests
have not reached their full potential of geographical distribution and
therefore most countries have regulatory agencies whose mission is to prevent
the introduction of exotic species. The
presence of false codling moth has resulted in embargos being placed on South
African avocados by quarantine authorities in countries such as the USA, thus
closing potentially valuable markets. Quarantine security is a term used by regulatory agencies to
indicate that important commodities that may contain exotic pests are safe for
entering into an importing country.
With the world-wide trend to move away from harsh fumigants and due to
the effect of physical treatments on product quality, interest has been renewed
to obtain sound biological information for establishing integrated systems
approaches to quarantine security.
The objective of this study is to evaluate a
systems approach to quarantine security for false codling moth on Hass
avocado. The evaluation includes (1)
proving poor host status, (2) proving low infestation levels in the field, (3)
monitoring population levels in the orchards and selecting orchards for
picking, (4) a program of insecticide application before harvest, (5) bagging
of fruit, (6) culling of fruit in the orchard and (7) cold storage after
harvest.
False codling moth does not complete its life cycle in Hass avocado fruit
on the tree. No development further
than first instar larvae was recorded.
False codling moth was monitored in 14 Hass orchards in two areas. Meothrin was applied 6 weeks before harvest
and caused > 89% mortality. Field
and laboratory studies proved that bags did not prevent infestation of fruit. Hass fruit infested with 1st, 3rd and 5th
instar larvae were placed in cold storage at 6°C for 4, 8,12, 16 to 24 days and
caused a reduction of larval survival.
Tans is slegs Bulldock (beta-cyfluthrin), ‘n piretroïed, geregistreer op avocado in Suid-Afrika vir die beheer van die suigbesieplaagkompleks, wat bestaan uit minstens vier verskillende Hemiptera-spesies. Dit is algemeen bekend dat piretroïedes breë-spektrum insekdoders is met ‘n relatiewe lang residuele nawerking, wat ‘n negatiewe invloed het op die natuurlike vyande van teiken en nie-teiken plae. Die gevolge hiervan kan wees dat die getalle van die nie-teiken plae kan styg wat dan lei tot verdere chemiese bespuitings, wat weer lei tot groter plaagversteurings. Insekdoders speel steeds ‘n baie groot rol in ‘n geïntegreerde benadering en geïntegreerde beheer is juis die kombinering van die voordelige eienskappe van beide chemiese en biologiese beheer van plae sonder om die aktiwiteite van die voordelige insekte te benadeel om sodoende plaaggetalle beter te beheer. Insekdoders is kragtige gereedskap om te gebruik teen plae en kan ‘n rol speel in geïntegreerde bestuursprogramme.
Agt
verskillende insekdoders in vier verskillende insekdodergroepe is as enkel en
dubbel bespuiting gedurende die 2001/02 seisoen ge-evalueer vir hulle
effektiwiteit teen die suigbesieplaagkompleks. Die reperkussie-impak op
nie-teiken plae (Hartvormige dopluis, Langstertwitluis en Teerooimyt) is ook
ge-evalueer.
As ‘n enkele bespuiting, was Asefaat (organofosfaat) net so effektief
soos die geregistreerde piretroïed-bespuiting, Bulldock. Alhoewel die
suigbesiebeheer deur Mercaptothion, Trichlorfon (albei organofosfate), Metomil
(oksim-karbamaat) en Endosulfan (organochlorien) as enkele bespuitings nie
betekenisvol (p = 0.01) verskil het van Asefaat en Bulldock nie, was die
vrugskade wel effens hoër. Veelvuldige bespuitings met hierdie insekdoders,
asook met Mevinphos en Dichlorfos, was egter net so effektief soos ‘n enkele
Asefaat of Bulldock bespuiting.
‘n
Styging in populasiegetalle van twee nie-teiken plae (hartvormige dopluis en
langstertwitluis) het voorgekom in beide die enkel en dubbel
Bulldock-bespuitings, wat die breëspektrum aktiwiteite van piretroïedes
bevestig. Die dubbel Metomil-bespuiting het daarenteen die getalle van die teerooimyt betekenisvol
verhoog. Bulldock en Metomil het dus die vermoeë om die biologiese beheerbalans
van nie-teiken plae te versteur. Nie een van die organofosfate of endosulfan
het ‘n verhoging in populasiegetalle veroorsaak van die nie-teiken plae nie,
wat moontlik ‘n aanduiding is van hulle versoenbaarheid in ‘n geïntegreerde
bestuursprogram.
Eco-friendly
insecticides for the control of sucking bugs in avocado orchards
The
pyrethroid, beta-cyfluthrin (Bulldock) is currently the only chemical
registered on avocado for the control of the sucking bug complex, which
consists of at least four Hemiptera species. Pyrethroids are broad spectrum
insecticides that are relatively persistent and can have a negative effect on
the natural enemies of target and non-target pests. This can result in an
increase in population of non-target pests, necessitating further use of
insecticides, which in turn can leader to even greater pest repercussions.
Insecticides, however, still play an important role in an integrated approach,
as integrated control makes use of chemicals together with biological control
in such a way that the affect on beneficial insects is kept to a minimum.
Eight
insecticides classified into four different insecticide groups were sprayed
either as a single or double application during the 2001/2002 season to
evaluate their efficacy against the sucking bug complex. The repercussion
impact on non-target pests (heart-shaped scale, long-tailed mealybug and tea
red mite) was evaluated.
A
single application of asephate (organophosphate) was as effective as the
registered Bulldock application. Although sucking bug control by single
applications of Mercaptothion, Trichlorfon (both organophosphates), methomyl
(oxime-carbamate) and Endosulfan (organochlorine) did not differ significantly
(p = 0.01) from single applications of asephate or beta-cyfluthrin, the level
of fruit damage in the former treatments was slightly higher. Multiple
applications of these insecticides, however, were as effective as single
asephate and beta-cyfluthrin applications.
Increased populations in two of the non-target pests (heart-shaped scale and long-tailed mealy bug) were observed in both the single and double beta-cyfluthrin treatments, thus confirming the broad-spectrum action of pyrethroids. The double methomyl application resulted in a significant increase tea red mite population. Beta-cyfluthrin and methomyl thus have the ability to upset the biological balance, causing increased pressure from non-target pests. Neither the Endosulfan nor the organophosphate treatments resulted in increased populations of non-target pests. This is possibly an indication of their suitability for use in an integrated management programme.
Supercritical fluid extraction of
natural products
Ben Botha
Department
of Chemistry and Physics, Technikon Pretoria
E-mail:
bothabm@techpta.ac.za
The existence of the critical point of a substance
was described as early as 1822 and the first experimental work involving carbon
dioxide was conducted in 1861. The last twenty years have seen an intense
interest in the use of supercritical fluids in extraction and separation
science.
Currently the most important established markets for
supercritical fluid extraction (SFE) are related to the processing of natural
products for application in the food-, nutraceutical-, pharmaceutical- and
cosmetic industries. It has been shown that SF extracted products are of
superior quality to that obtainable by solvent extraction. The different
organoleptic properties and the higher price associated with the extraction
unit, are the two most important reasons why these extracts are currently
restricted to certain niche markets. As a result of regulatory issues and
changing consumer preferences, research and development is currently being
carried out on applications of this technique. An increasing amount of
economically viable processes are becoming available and accepted worldwide.
To be able to compete in a global market it is
imperative that this technique be made available to and investigated by South
African industries. It must however be introduced on a holistic basis and
should also include factors like market trends, legislation and quality. It has
been proved that, submitted to the same constraints in terms of environmental
and consumer protection, a well designed and optimised SFE plant may often lead
to product prices similar to those obtained using classical processes.
The use of
CA storage, CO2 shock treatments and/or 1-MCP on ‘Hass’ and ‘Fuerte’
avocados
Leon Maré, A.B. Truter*, M.C. Dodd* & D.M.
Holcroft
Presented by: Marius Huysamer (e-mail: huysamer@maties.sun.ac.za)
Department of
Horticultural Science, University of Stellenbosch
*Transfresh Africa
With the increasing consumer demand for top quality avocado fruit,
storage and handling technologies are being reconsidered. ‘Fuerte’ avocados
were a) stored in controlled atmosphere (CA), b) stored in air (RA), or c)
treated with four carbon dioxide shock treatments over three time periods and
stored in RA. ‘Hass’ avocados were a)
stored in CA, with or without 1-MCP, b) stored in RA, with or without 1-MCP, or
c) treated with two carbon dioxide shock treatments for 48 hours and stored in
RA with or without 1-MCP. After storage, fruit were transferred to 20°C until
eating ripe to simulate shelf life. ‘Fuerte’ stored under RA following CO2
shock were generally firmer than the RA stored fruit without CO2
shocks, with CA stored fruit about 3 kg firmer (9.75 kg). ‘Hass’ treated with
CO2 shock and 1-MCP prior to RA storage, were generally firmer than
the RA stored fruit, with CA stored fruit about 2 kg firmer (12.2 kg). ‘Hass’ stored
under CA in combination with 1-MCP had a firmness value of 11.5 kg. ‘Fuerte’
stored under CA showed a lower incidence of pulp spot (0 %) and grey pulp (10.3
%), and slightly higher internal and external anthracnose (5.1% and 10.3 %, respectively) when compared to the RA
treatment. The 96 hours CO2 shock treated ‘Fuerte’ showed little
pulp spot, but had of the highest grey pulp (± 32 %), stem-end rot (± 16 %) and
vascular browning (± 45 %). ‘Hass’ stored in air showed the highest percentage
of sound fruit (91.3 %) while the 1-MCP treated fruit was 85.0 % sound. All
fruit showed significant rises in respiration and ethylene production on
removal from the storage temperatures to 20°C.
Maximum respiration for the ‘Fuerte’ ranged from 138 – 178 mg CO2.kg-1.h-1
while that of ‘Hass’ ranged between 56 – 90 mg CO2.kg-1.h-1.
Fruit stored in CA showed positive results compared to the CO2 shock
treated fruit. However, more work needs
to be done using CO2 shock treatments in combination with 1-MCP.
The
effects of wax coatings and storage temperatures on cold damage in ‘Fuerte’
avocados
Kelvin N. Fowler and
J P Bower
Horticultural
Science, School of Agricultural Sciences and Agribusiness, University of Natal
e-mail: BowerJ@nu.ac.za
Avocados exported from South Africa to distant markets require storage at
low temperature for long periods. Defects usually defined as chilling injury
often result. However, shipping at higher temperatures, does not always solve
the problem, and at times accentuates the external symptoms, accelerates fruit
ripening, and decreases shelf life. The role of water loss prevention,
particularly fruit coatings, was investigated for cv Fuerte. Fruits were coated
with a number of wax formulations or sealed in polyethylene bags, before storage
for 30 days at temperatures of 2 °C, 6 °C or, 8 °C. Fruit mass loss was
determined during storage and ripening at 20 °C, shelf life and appearance
evaluated. While temperature was significantly linked to chilling injury, there
was also a significant interaction with water loss at low temperature
suggesting the symptom is influenced by dehydration. Where fruit had been
treated to prevent water loss, little chilling injury occurred at 6 °C or 8 °C,
but was significantly correlated with water loss at 2 °C and appeared to change
the threshold temperature for chilling injury. Wax formulations played a
significant role in determining the extent of “chilling injury”. Carnauba based
waxes resulted in the best fruit quality, although micro perforated
polyethylene bags show potential provided anthracnose infection can be
controlled.
A preliminary analysis of posharvest fruit treatments for
maximising internal and external fruit qualities using cv Pinkerton
e-mail:
BowerJ@nu.ac.za
Previous work has indicated that low temperature storage may be
advantageous for maintaining internal fruit quality, but that external chilling
injury can result. External injury is modified by fruit coating. Efficient
fruit coatings may retard gaseous exchange as well as inhibit water loss, which
could lead to internal disorders. Uncoated fruit placed in polyethylene bags to
prevent water loss and subsequent external quality deterioration have shown
some promise. The purpose of the work was to investigate the potential for
packing individual fruit in micro perforated polyethylene bags, as well as
entire carton or pallet wrapping as opposed to waxing. Cultivar Pinkerton was
used due to the extreme sensitivity to adverse conditions usually resulting in
intense mesocarp blackening. Fruit treated with a standard wax formulation was
compared to fruit in individual micro perforated polyethylene bags and entire
cartons wrapped in a similar material. Fruits were stored at temperatures of 8
°C, 5,5 °C and 2 °C for 30 days, followed by ripening at 20 °C. Unwaxed fruit
showed the poorest external quality, while the individually wrapped fruit
stored at 2 °C had the best internal quality, plus softened the least during
storage, as well as had the longest days to soft after removal. While further
work needs to be done to confirm the results and determine the optimal degree
of micro perforation, it is concluded that fruit wrapping including full pallet
wrapping, in conjunction with low temperature shipping may be more suited to
the cultivar Pinkerton than present systems.
Tackling
the ‘Pinkerton’ problem
Zelda van Rooyen &
J.P. Bower
Horticultural Science, University of Natal
e-mail: BowerJ@nu.ac.za
It is no secret
that the Pinkerton cultivar as been receiving a lot of attention in the last
few years, unfortunately not much has been in a positive light. Although Pinkerton are heavy bearing green
skins, the development of intense mesocarp blackening after storage has
hindered the export this cultivar. Many
factors have been attributed to causing the disorder but few studies have been
conclusive. In this study the role of
post harvest shipping temperatures was investigated by storing fruit from
various areas at 8oC, 5.5oC and 2oC for 30
days and then allowed to ripen at 20oC. Following storage, membrane stability, internal blackening and
respiration rates were monitored. It
was found that temperatures below the recommended shipping temperature produced
the best quality fruit, i.e. 2oC.
This was supported by the membrane stability studies which found more
membrane collapse at the warmer temperatures of 8oC. Throughout the study carbon dioxide
evolution rates were seen to increase as fruit increased in maturity, perhaps
explaining why the lowest temperature treatment produced the best results as
respiration rates could be suppressed.
Fruit origin proved to have an effect on fruit physiology as differences
were observed in respiration rates between growers and provinces. Preharvest conditions are important as
growers within the same area showed marked quality differences. Future work will attempt to identify the
relevant preharvest factors starting with mineral and phenolic studies. Potassium and nitrogen levels are suspected
to play important roles.
1-Methyl cyclopropene (1-MCP): an alternative for controlled atmosphere
storage of South African export avocados
Institute for Tropical and Subtropical Crops
Email: frans@itsc.agric.za
In the past, the firmness of export avocados was maintained by reducing
the storage temperature during transport. More recently, controlled atmosphere
(CA) has been added to further reduce ripening during storage. This certainly
improved the chances of landing a hard fruit in Europe, but certain
physiological and monetary concerns remain. During the last 2 years we have
been evaluating the effectiveness of 1-methyl cyclopropene (1-MCP), an ethylene
inhibitor presently used in the cut-flower industry, on avocados. The trials
were done with all the major export cultivars and covered aspects such as
storage potential, respiration rate and fruit quality upon ripening. The
results were extremely positive and the manufacturer (Agrofresh inc., a Rohm
& Haas company, USA) is to file for registration of the product under the
trademark ‘SmartFresh’. Static container trials are planned for the 2002 season
and it is envisaged that 1-MCP will become available to the South African
avocado export industry during the 2003 season.
The
development of a strategy for the prevention of black cold injury in South
African export avocados
Frans Kruger, D. Lemmer & B. Snijder
Institute for Tropical and Subtropical Crops
Email: frans@itsc.agric.za
Black cold injury, like grey pulp, is initiated by a range of factors.
However, certain of the causative factors manifest in a reverse fashion. For
instance, more mature fruit are most susceptible to grey pulp while less mature
fruit, especially from later sets, are more affected by black cold injury. In
addition to maturity, aspects such as orchard temperature and the orientation
of the fruit with regard to the sun are also important. Unfortunately, it is
not possible to manipulate the latter two factors so as to reduce the risk of
black cold injury. At present, it would seem that the most promising
pre-harvest approach would be to improve the nutritional status, especially the
nitrogen and calcium content of the fruit. However, appropriate chemical
content parameters are considerably narrower for black cold injury than for
grey pulp. At present, the best post harvest approach to reduce black cold
injury is to increase the storage temperature. In this regard, a number of
techniques, aimed at retaining fruit firmness at higher storage temperatures
are presently being evaluated. These include storage in an ozone enriched
atmosphere, ethylene scrubbing, CO2 shock applications and 1-methyl
cyclopropene (1-MCP) treatments. Of these, 1-MCP shows the most promise.
Atmosphere refinement, and the effect of temporary gas
regime alterations on avocado quality after extended controlled atmosphere
storage
Steve Oosthuyse1 and Arthur Kemp2
1HortResearch
SA, email: hortres@pixie.co.za
2Transfresh
Africa, e-mail: arthur@transfresh.co.za
Fuerte avocado fruits that were highly predisposed to disease
colonization and disorder manifestation were used. The fruits were harvested in
November 2001, being very mature (pulp moisture content < 68%). The fruits
were treated and placed in cold storage within 36 hours of harvest. Prior to
storage, the fruits were waxed, sorted and packed. They were placed in cold
storage at 7 °C for 22 days, after which they were allowed to ripen fully for 4
days at 20 °C. The fruits were either stored without atmosphere adjustment
(control), or were stored under atmosphere. The following atmosphere regimes
were implemented, namely a refined atmosphere, where the carbon dioxide levels
always exceed that of oxygen (refined atmosphere), and an atmosphere
incorporating temporary alterations to the levels of carbon dioxide, oxygen and
nitrogen, and whose oxygen levels generally exceed that of carbon dioxide
(manipulated atmosphere).
Atmosphere storage was superior to conventional
storage in reducing the rate of softening and limiting the manifestation of
disease and internal disorders. On full ripening, 4 days after cold storage,
the fruits stored under atmosphere will still firmer. Disease suppression was
greatest following storage under the manipulated atmosphere, both immediately
and 4 days after cold storage. The atmosphere-treatments showed a similar
degree of suppression of physiological disorder manifestation, observed 4 days
after cold storage. The results of the present study indicate that the
adjustments to the conventional controlled atmosphere treatments hold a
significant benefit for avocado exported to Europe by sea.