Agriculture Reference
In-Depth Information
only from production, but also harvesting, packing and
distribution. It is further difficult to determine actual end
point losses due to the fact that at a retail level, hospitality
sector, the informal market and kitchens, fresh produce
losses in nutritional value and quality are generally over-
looked (Wilson & Wisniewski 1989).
In developing countries, where protection and proper
handling of fresh fruit is often inadequate, losses during
transit and storage are even greater and primarily due to
post-harvest decays. Losses can represent in excess of 50%
of the harvested crop (Eckert & Ogawa 1985; Wisniewski
& Wilson 1992). In countries such as Spain, the percentage
of fruit rotting after harvest in a typical season is between
3% and 6% (Tuset 1987). However, under favourable
disease conditions, losses up to 50% can occur during
marketing (Eckert 1993, Abd-El-Aziz & Mansour 2006).
In north-eastern Brazil, a survey of post-harvest diseases in
citrus indicated a 21.9% incidence of fungal rots (Dantas
et al
. 2003). Post-harvest losses therefore remain an impor-
tant challenge in sustainable food production.
The importance of different post-harvest diseases is
characteristic of the climate of the production area,
species and cultivar, time of harvest, infection during fruit
growth and harvesting and handling practices. Post-harvest
losses and decay of citrus fruits can be traced to infections
that occur either between flowering and fruit maturity or
during harvesting and subsequent handling and storage
activities (Naqvi 2004). Post-harvest diseases where inocu-
lation and infection are initiated during fruit growth are
stem-end rot, alternaria rot, anthracnose, brown rot and
grey mould. The wound pathogens (
Penicillium digitatum,
P. italicum, Geotrichum candidum
and
Trichoderma
viride
) on the other hand typically infect through wounds
that form during harvesting and handling, as well as insect
damage in the orchards (Eckert & Eaks 1989; Timmer
et al
. 2000). The following section deals with the epidemi-
ology of the major citrus post-harvest diseases, control
methods and the most important aspects of the various
post-harvest diseases have been summarised in Table 4.4.
of production losses during post-harvest handling
(Macarisin
et al
. 2007), particularly in production areas
characterized by low summer rainfall (Eckert & Eaks
1989) and is seen as one of the most important post-harvest
diseases in citrus fruit (Lanza
et al
. 2000). Artificial inocu-
lation done by Ortuno
et al
. (2009) indicated that the degree
of fungal development is dependent on the citrus species. It
was found that the mature fruit of
C. paradise
are more
susceptible to
P. digitatum
than
C. limon
and
C. sinensis
.
Morphology
Penicillium digitatum
grows restricted and thinly on
Czapek and other similar media. On malt agar, rapid
growth appears velvety and changes to dull yellow green to
greyish olive with age, with a strong decaying citrus odour.
These colonies on artificial media are similar in appear-
ance to the mould that develops on infected fruit.
Penicillium digitatum
produce conidia (4-7 × 6-8
m
m) in
chains, often with only one branch (Onions & Brady 1987;
Timmer
et al
. 2000) that is at first cylindrical, becoming
elliptical, smooth and thick walled (Carlos 1982).
Disease cycle and epidemiology
Green mould survives in the orchard from season to season
primarily as conidia and is produced in massive quantities
on infected fruit (Olsen
et al
. 2000). Infection occurs as a
result from these airborne spores that enter the peel of the
fruit where there are small injuries or blemishes (Kuramoto
1979; FFTC 2003). Green mould is a necrotroph, requiring
nutrients only for germination around the wound site.
A minor injury to the oil glands during harvesting and
transportation promotes infection (Brown 1973). The fun-
gus can also invade fruit which have been damaged on the
tree by chilling injury (FFTC 2003) and stem-end rind
breakdown (Brown 2003a). Therefore, the disease can
occur at any stage in the supply chain where the fruit is
wounded (i.e. on the tree, in the packinghouse, in transit, in
storage or in the marketplace). In packed containers, the
fungus usually does not spread from decayed fruit to adja-
cent intact healthy fruit, although the abundant green
spores that are produced can soil the skin of adjacent fruit
(FFTC 2003). The infection and sporulation cycle can be
repeated several times throughout the season in pack
houses. Inoculum pressure increases as the picking season
advances, therefore it is critical that precautions are taken
(Janisiewicz & Korsten 2002). Contamination spreads
when spores detach from diseased fruit during the opening
of packing cartons. Green mould grows optimally at tem-
peratures near 25°C but more slowly at temperatures above
30°C and below 10°C (FFTC 2003, Zhang & Swingle
Green mould
Green mould is caused by the fungus
Penicillium digitatum
(Pers.) Sacc., (1883) which is ubiquitous to all citrus grow-
ing regions and commonly causes post-harvest decay
(Carlos 1982). It usually occurs in countries with a cooler
climate or under cold storage conditions of citrus fruit
(Food and Fertilizer Technology Centre [FFTC] 2003).
Green mould is a common post-harvest disease of citrus in
many Asian Mediterranean climate countries (Eckert &
Eaks 1989). Green mould can be responsible for up to 90%
