Other common diseases of apples and pears include the black spot or
scab, caused by the ascomyceteVenturia inaequalis(anamorphSpilocaea
pomi¼Fusicladium dendriticum), and a brown rot caused by another
ascomycete, Monilinia fructigena (¼Sclerotinia fructigena, anamorph
Monilia fructigena). Apple scab spoils the appearance of fruit, and would
certainly reduce its commercial value, but does not cause extensive
rotting of the tissue. The brown rot, however, can lead to extensive
damage of fruit both on the tree and in storage. The typical brown rot is
usually associated with rings of brown powdery pustules of the imper-
fect, or anamorph, stage, however fruit which is infected, but apparently
healthy when it goes into store, can be reduced to a shiny black mum-
mified structure in which much of the fruit tissue has been replaced by
fungal material and the whole apple has become a functional sclerotium,
or overwintering resting body, of the fungus. Although rarely seen in the
United Kingdom, it is this structure which may germinate in the spring
to produce the stalked apothecia of the perfect, or teleomorph, stage.
An especially widespread mould on both fruits and vegetables is the
grey mould Botrytis cinerea, which is the imperfect stage of another
ascomycete,Botryotinia fuckeliana(¼Sclerotinia fuckeliana). Its role in
the spoilage of strawberries was described in Section 2.5. Infection of
grapes on the vine by this same mould can lead to drying out of the grape
and an increase in sugar concentration and wines made from such
contaminated fruit are considered to be very special. Under these
circumstances the fungus has been referred to asLa Pourriture Noble–
the noble rot!
To avoid excessive mould spoilage of harvested fruit during storage
and transport it is necessary to harvest at the right stage of maturity and
avoid damage and bruising. Mouldy fruit should be removed and
destroyed and good hygiene of containers and packaging equipment is
essential to prevent a build-up of mould propagules. The development of
international trade in many fruit species has led to the use of some
biocides (Figure 5.9) to prevent mould spoilage. Benomyl has proved
useful where it can be applied to the surface of fruits, such as citrus and
bananas, in which the skins would normally be discarded (this, of course,
is not the case for citrus used for marmalade and other preserves). In
some parts of the world moulds likePenicillium digitatumhave devel-
oped increased resistance to benomyl. Biphenyl is quite an effective
protectant when incorporated into the wrapping tissues of fruit such as
oranges when they are individually wrapped. Captan has been used as a
spray for strawberries in the field to controlBotrytisbut its use must be
stopped well before harvest.
Reduced temperature and increased carbon dioxide concentration
may also be useful in controlling mould spoilage during storage and
transport but many fruits are themselves sensitive to low temperatures
152 Microbiology of Primary Food Commodities