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					                        PACKER NEWSLETTER
Volume 88                                                                                                        September 2007

            Editor: Peter Taverner
            Waite Research Precinct
            GPO Box 397
            Adelaide 5001
            Phone 08-83039538

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                                                                          water loss from fruit. The gradual progression toward
             Citrus rind disorders                                        age-related damage should be accounted for in any
                                                                          marketing schedule. However, a problem occurs when
             associated with advanced                                     symptoms occur on fruit unexpectedly and rapidly.

             age, water stress and                                        Stem-end rind breakdown (SERB) in oranges often
                                                                          appears 6-7 days after harvest (McCormack and
             other non-chilling factors.                                  Grierson 1965). SERB is associated with low humidity
                                                                          storage between harvest and waxing, and 2 days
             Peter Taverner                                               exposure under these conditions can result in the later
             SARDI                                                        expression of SERB on ‘Valencia’ oranges. SERB
             Unseasonably dry conditions and advanced maturity in         affected fruit have dark blemishes, appear aged, and are
             fruit suggests that caution should be taken when             more prone to decay.
             choosing markets for fruit, especially late in the season.   SERB is characterised by epidermal and sub-epidermal
             Unfortunately, water allocations are likely to remain low    cell collapse and subsequent darkening of collapsed
             for the foreseeable future, and the consequences for         areas around the stem-end of the fruit. The most
             quality and storage life of citrus fruits are unclear.       distinctive feature is a narrow band of undamaged tissue
             The following is a discussion of some of the                 around the calyx. This area would be less prone to water
             physiological disorders associated with advanced age,        loss due to a lack of stomata and thicker cuticular wax
             water stress and other non-chilling factors.                 (Albrego 1972). Aging damage on citrus is
                                                                          symptomatically similar to SERB, but does not tend to
             Age-related and stem-end rind breakdown                      have this halo of undamaged tissue.
                                                                          Recommendations for the prevention of SERB relate to
             Age-related blemish occurs in citrus after long storage,
                                                                          minimising water losses from fruit, particularly
             and probably expresses due to a combination of cell
                                                                          immediately after harvest. Harvested fruit should be
             weakness with advancing rind maturity and progressive
                                                                          shaded in the orchard and protected from drying winds.
                                                                                                                          Continued on page 2
           1          Citrus rind disorders associated with advanced
                      age, water stress and other non-chilling factors.

           2          Market Access using complementary methods -
                      combining postharvest oil with high pressure

South Australian Research and Development Institute                                            Packer Newsletter No.88, page 1
                                                 Continued from page 1

In general, fruit should be promptly dispatched to the                   throughout storage, the highest incidence is usually
packing facility where high humidity (>90% RH) can                       within the first 2 weeks after packing (Petracek et.
be maintained before and after packing. Where high                       al. 1998a).
humidity cannot be maintained, storing ‘Valencia’                        Postharvest pitting is a good example of the
oranges at cool temperatures (40C) is preferable to                      difficulty in accurate diagnosis of many postharvest
ambient (210c or higher), and can substantially delay                    disorders. Pitting damage in white grapefruit was
the expression of SERB (Dou et. al. 2001)                                originally misdiagnosed as chilling injury as both
                                                                         result in collapse and discolouration of the rind
                                                                         (Petracek et. al. 1995). However, pitting is primarily
                                                                         caused by the collapse of oil glands, rather than
                                                                         damage to epidermal cells. Pitting in Fallglo
                                                                         tangerines was misdiagnosed as stem end rind
                                                                         breakdown (SERB) because pitting is primarily
                                                                         around the stem end (Petracek et. al 1998a).
                                                                         However, postharvest pitting occurs in clusters
                                                                         associated with oil glands, and although primarily at
                                                                         the stem end, pitting spreads into the midsection
                                                                         and stylar end. In addition, SERB has a
                Typical age-related rind collapse
                                                                         characteristic narrow band of unaffected rind
                  around orange calyx around
                                                                         surrounding the stem-end of fruit, which is absent
                                                                         in postharvest pitting. Navel oranges are prone to
Postharvest pitting                                                      postharvest pitting, and also express SERB-like
                                                                         symptoms that are apparently morphologically
Postharvest pitting' of citrus is a specific term to
                                                                         indistinguishable from postharvest pitting (Petracek
describe a rind disorder that affects waxed fruit stored
                                                                         et. al. 2006).
at non-chilling temperatures. The disorder is
                                                                         Wax formulation studies showed that shellac-based
characterised by clusters of collapsed oil glands
                                                                         waxes caused more pitting than and polyethylene-
scattered over the fruit surface and has been studied
                                                                         and carnauba-based waxes. Pitting is not a
in white grapefruit, ‘Fallglo’ tangerines and ‘Temple’
                                                                         phytotoxic response to the wax constituents, but is
oranges (Petracek et. al. 1995; Petracek et. al. 1997;
                                                                         more likely related to the relative gas permeability
Petracek et. al. 1998a; Petracek and Davis 2000). It has
                                                                         of the waxes. Low levels of oxygen within the fruit
also been observed in other citrus, including red
                                                                         are associated with pitting (Petracek et al. 1998b).
grapefruit, ‘Sunburst’ tangerine, ‘Hamlin’, ‘Valencia’
                                                                         This can result from high respiration rates during
and navel oranges. Pitting occurs only intermittently
                                                                         high temperature storage and low gas exchange
depending on environmental and cultural practices. It
                                                                         caused by high shine waxes.
also appears to be more severe on larger fruit sizes.
                                                                         Control of pitting is achieved through prompt cold
An initial symptom of pitting is the collapse of small,
                                                                         temperature storage. Waxing with coatings that
circular regions of the rind corresponding to damaged
                                                                         have higher gas permeability has been shown to
oil glands. Damage to cells surrounding the collapsed
                                                                         reduce pitting (Petracek et. al. 2006).
oil gland is highly localised, and epidermal cells
between the oil glands are often not damaged. The
region above the damaged oil cells becomes
bronze/brown to brown/black over time. Oil glands
collapse in clusters of up to 100, but usually <12, to
form areas of roughly circular damage. The damage
does not progress outwards from the initial damaged
cells, but spreads over the fruit by forming new
clusters. Initial signs of cell collapse can be visible
from four days after waxing (Petracek and Davis
                                                                                     Example of localised pitting
2000). Although pitting can continue to occur                                            in navel orange
                                                                                                                     Continued on page 3

  South Australian Research and Development Institute                                                        Packer Newsletter No.88, page 2
                                                      Continued from page 2

   Rind staining in navel oranges                                               production and water potential. Postharvest Biol. Technol.
                                                                                28: 143-152.
   Rind staining is a condition that can occur while the
                                                                                Coggins C. W. and Eaks I. L. (1967) gibberellin research
   fruit are still on the tree, but symptoms are more
                                                                                on navel oranges. Calif. Citrograph 52. 475-491.
   commonly expressed after harvest. The Spanish
                                                                                Dou H., Zhang J, Ismail M. A and Ritenour M. A.
   have serious rindstaining problems with ‘Navelate’
                                                                                (2001) Postharvest factors influencing stem-end rind
   fruit during maturation on the tree and during post-
                                                                                breakdown (SERB) of ‘Valencia’ oranges. Proc. Fla. Stat.
   harvest storage, but ‘Navelina’, ‘Washington navel’
                                                                                Hort. Soc. 114, 164-169.
   and ‘Lane late’ fruit only develop this disorder
                                                                                McCormack A.A. and Grierson W. (1965) Practical
   during postharvest storage (Agusti et. al. 2001).
                                                                                measures for the control of stem-end rind breakdown of
   These symptoms are also seen on fruit harvested
                                                                                oranges. Fla. Agr. Ext. Circ. 286.
   where climatic conditions similar to the
                                                                                Petricek P.D. Kelsey D.F. and Grierson W. (2006)
   Mediterranean-type conditions in Spain, such as
                                                                                Physiological peel disorders. pp. 374-419. In Fresh Citrus
   California and southern Australia.
                                                                                Fruits. Wardowski W. F., Miller W. M., Hall D. J. and
   Rind stained fruit are characterised by irregular
                                                                                Grierson W. (Editors) Florida Science Source, Florida,
   collapsed areas in the rind, which become reddish-
                                                                                USA. 397-419.
   brown over time. The symptoms begin in the
                                                                                Petracek P. D. and Davis C. (2000) Ultrastructure
   transitional zone between the albedo and flavedo,
                                                                                comparison of postharvest pitting, chilling injury, and
   and advances into the albedo to the epidermis.
                                                                                preharvest physical damage of white grapefruit. Proc. Intl.
   Affected cells have twisted and squashed cells, with
                                                                                Soc. Citricult. Congr. 2, 1079-1083.
   reduced amounts of cytoplasm (Agusti 2001).
                                                                                Petracek P. D., Dou H. and Pao S. (1998b) The influence
   The symptoms appear on fruit at non-chilling
                                                                                of applied waxes on postharvest physiological behaviour and
   temperatures, and fruit blemish increases with
                                                                                pitting of grapefruit. Postharvest Biol. Technol. 14, 99-106.
   maturity. Water stress is thought to play an
                                                                                Petracek P.D., Montalvo L., Huating D., and Davis C.
   important role in its development when followed
                                                                                (1998a) Postharvest pitting of Fallglo tangerine. J. Amer.
   by sudden changes in relative humidity. Harvesting
                                                                                Soc. Hort. Sci. 123, 130-135.
   water stressed fruit, and allowing high water loss
                                                                                Petracek P. D., Wardowksi W. F., and Brown G. E.
   prior to packing, followed by storage at high
                                                                                (1995) Pitting of grapefruit that resembles chilling injury.
   relative humidity increases the incidence of rind
                                                                                HortScience 30: 1422-1426.
   staining (Alferez et. al. 2003). As such, the delivery
   of loaded bins to packing sheds should be prompt,
   In Spain, storing fruit at low temperatures (20C),
   and degreening with ethylene are recommended to
   delay expression in ‘Navelina’ oranges. (Lafuente
   and Sala 2002). In California, rind staining in navel                                        Recommended Reading
   oranges is associated with over maturity, and                              A very valuable resource on citrus postharvest
   gibberellic acid sprays are used reduce its incidence                      handling, which includes significant contributions by
   (Coggins and Eaks 1967).                                                   a number of the authors referenced in the above
                                                                              article, is the recently revised book
   Agusti M. Almela V. Jaun M. Tadeo F.R and Zacarias                                 ‘Fresh Citrus Fruit, 2nd Edition’.
   L. (2001) Histological and physiological characterization of                  Wardowski W. F., Miller W. M., Hall D. J. and
   rind breakdown of “Navalate’ sweet orange. Ann. Bot. 88:                                Grierson W. (Editors)
   Albrego L. G. (1972) Ultrastructure of cuticular surfaces                  For more information and purchase this book use the
   and stomata of developing leaves and fruit of the Valencia                 following link;
   orange. J. Amer. Soc. Hort. Sci. 97, 761-766.                    
   Alferez F. Agusti M. and Zacarias L. (2003) postharvest
   rind staining in navel oranges is aggravated by changes in
   storage relative humidity: effect on respiration, ethylene

South Australian Research and Development Institute                                                                   Packer Newsletter No.88, page 3
   Market Access using                                                    them. After oil treatment, the fruit can be washed using a
                                                                          high pressure wash. Normally, high pressure washes will
   complementary methods                                                  not remove FRW eggs, but it was hoped that this may
                                                                          change after treatment with oil. In fact, we have evaluated
   – combining postharvest                                                a number of chemicals used in fruit processing, such as

   oil with high pressure                                                 sanitizers, prior to washing to assess any change in the
                                                                          removal of FRW eggs. The results will be published in due
   washing                                                                course, but a reliable source informs me that FRW eggs
                                                                          have the tenacity of a limpet.
   Peter Taverner
                                                                          Deliberately combining the effects of two or more
                                                                          treatments to control pests in not new, and is referred to
   This season, market access issues have preoccupied the                 as a ‘systems approach’. This usually involves treatments
   minds of many packers and exporters. Quarantine                        and contributions along the whole supply chain from
   problems in existing markets such as USA and Japan,                    orchard management, packing treatments to storage
   coupled with difficulties in emerging markets, such as                 temperatures. It requires a coordinated and shared
   Korea and China, have clearly focused the spotlight on                 responsibility to incrementally achieve the desired end
   a number of insect pests.                                              result. I feel that this is an important concept that the
   The importance of these issues was eloquently stated in                industry needs to embrace to overcome certain market
   late 2006 by John Tesoriero, Chief Executive, Murray                   access issues. For instance, Riverland growers are under
   Valley Citrus Board in letter written on behalf of                     increasing pressure to control citrophilus mealybug, but
   Australian Citrus Growers Inc., Murray Valley Citrus                   they can’t achieve control to quarantine levels by
   Board, Riverina Citrus and the South Australian Citrus                 themselves. A realistic threshold for field control must be
   Industry Development Board.                                            determined, and then the remaining mealybug should be
                                                                          dealt with in the packingshed. Postharvest oil should be
   “……… the expanding production base of the Australian citrus            able to remove a large proportion of mealybug. However,
   industry, coupled with the fluctuating prices paid for processing      the proportion removed may not high enough when the
   fruit, makes it imperative for our industry to increase fresh fruit    orchard supplies fruit with a consistently high level of
   production in order to maintain sustainability. In order to divert     mealybug. It is very much a numbers game, with each
   fruit to fresh fruit markets we need to expand access to potentially   party contributing to the end result.
   lucrative export markets. The presence of Fuller’s Rose Weevil in
                                                                          Our approach with the removal of FRW eggs aims to be
   Australian citrus orchards seriously threatens the development of
                                                                          complimentary, which is subtly different from a typical
   the lucrative Chinese market…… “
                                                                          ‘systems approach’. We are re- examining processes that
                                                                          already have legitimate roles in the packing process, and
   At the time, Fuller’s Rose Weevil (FRW) was the centre
                                                                          seeing if we can add a market access function. For
   of attention, and the above groups were championing
                                                                          instance, high pressures washes are becoming more widely
   the need for further work to be done in this area.
                                                                          adopted in citrus packinglines. In Australia, they are
   However, through events this season, it has become
                                                                          primarily used to clean the fruit of sooty mould, and,
   apparent that there is actually a ‘hit list’ of several
                                                                          thereby, increase the sooty mould. However, they also
   insects that need to be addressed in concert. By ‘in
                                                                          ‘blast out’ soft rot tissue to allow better sorting. They
   concert’, I mean dealing with at least some of these
                                                                          remove many of the surface microbes associated with
   insects together, rather than picking them off one at a
                                                                          health and decay, and cleaner fruit goes through you
                                                                          fungicides keeping solution cleaner for longer and
   One pathway to solutions requires looking at ‘systems                  reducing the dumping of fungicides. And, if you still
   approaches’ and also treatments that are complimentary.                haven’t worked out that you should have a high pressure
   Let me give you an example of what I mean: Our group                   wash; they can remove a lot of your surface pests too.
   has been looking at ways of physically removing FRW
                                                                          For many years, high pressure washes were primarily used
   eggs from fruit. One approach that we have used is to
                                                                          to remove red scale, and in many respects, this is where
   treat the fruit with postharvest oil. In this instance, we
                                                                          received a bad name. Generally, pressures were set very
   are looking at the oil to loosen the eggs rather than kill
                                                                                                                        Continued on page 5

South Australian Research and Development Institute                                                        Packer Newsletter No.88, page 4
                                                      Continued from page 4

high to remove live scale, and as a result, they also                         the calyx quite effectively. This is the advantage of using
damaged fruit. In recent times, lower pressures and                           complimentary methods and looking at a range of pests
longer dwell times have helped to significantly reduce                        in concert.
the risk of physical damage and still retain the majority
                                                                              However, there are still some interesting questions to
of benefits.
                                                                              answer. In a variation of the chicken or egg conundrum;
If high pressure washes are already a useful process in                       which should come first the oil treatment or the high
the packingline, our aim is to further ‘value add’ by                         pressure wash?
using them to contribute to overcoming some of our
                                                                              On the one hand, applying the oil first, particularly
pest issues. However, we certainly don’t want to return
                                                                              when carbonates salts are included, will penetrate,
to the bad old days when the smell of rind oil filled the
                                                                              soften and aid in cleaning under the calyx. There is also
air after high pressure washing. Our studies in
                                                                              a benefit in removing the surplus oil residues with the
commercial packinglines suggest that the current
                                                                              high pressure wash before other processes, such as
settings for high pressure washes can remove significant
numbers of pests, even from under the calyx. However,
it is not likely to be sufficient on its own to allow fruit to                On the other hand, applying the high pressure first
regularly pass quarantine inspection, especially for FRW                      cleans out a lot of the debris under the calyx and
eggs.      Is there something that can be done to                             exposes the remaining insects to oil treatment. Oil
complement the process?                                                       treating cleaner fruit also keeps the solution cleaner,
                                                                              which should allow the solution to be dumped less
As mentioned in the start of this article, we have looked
at postharvest oil to fill this role. The oil has direct
toxicity on lightbrown apple moth and is likely to have                       We are interested in determining the relative costs and
toxicity against a range of pests. It already has a                           benefits in each of these approaches as we continue to
legitimate role to control LBAM, but can we use it to                         develop postharvest oil.
complement high pressure washing. The oil has strong                          In addition, there has been an interest in developing in-
solvent properties and this study was conducted to                            line baths for the application of postharvest oil. The
determine whether it could reduce the adherence of the                        immersion of fruit will provide the best coverage
eggmass to the fruit. A short study in the last few                           possible and will minimize emulsion stability issues
months has yielded partial success; oil treatment prior to                    associated the shearing motion of pumping, but will
high pressure washing can remove a greater proportion                         provide its own set of application questions to answer.
of eggs, but the rate of removal is still too low to
constitute a good quarantine treatment. The oil may also                      As you can see, there is still much work to be done to
require a significant period on the fruit prior to washing                    resolve these market issues. In regard to packingline
to sufficiently release eggs, which would limit its                           treatments, it will be important to recognise the
usefulness when applied inline and immediately prior to                       influence these treatments have on other packing
washing.                                                                      processes, and to maximize the benefits (complimentary
                                                                              methods). This may be achieved by controlling more
The results are based on limited work, and the search                         than one pest and/or by improving the efficacy of
should continue to find a treatment to release the FRW                        another process.
eggs from the fruit prior to high pressure washing.
Regardless, the combination of oil and high pressure                          We acknowledge the contribution by the Murray Valley Citrus
washing may be useful for other pests. Preliminary                            Board, Riverina Citrus and the South Australian Citrus
results suggest that combining high pressure washing                          Industry Development Board to fund work on the removal of
with oil treatments can remove and kill mealybug under                        FRW eggs through Horticulture Australia.

         Note: Articles are the results of research and the best information available to the author at
       publication. Mention of a pesticide or a commercial or propriety product does not constitute an
        endorsement or recommendation of its use. The South Australian Research and Development
        Institute (SARDI) makes no warranty of any kind expressed or implied concerning the use of
                                    technology mentioned in this document.

South Australian Research and Development Institute                                                               Packer Newsletter No.88, page 5

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