Agriculture Reference
In-Depth Information
Source of infection and spread
Chalara paradoxa
is common in pineapple plantations.
The fungus will only invade wounds and is most active in
warm, wet weather.
Importance
White leaf spot occurs commonly between March and May
in Queensland during periods of overcast, rainy weather.
The disease is of no economic significance.
Management
Management measures are not warranted.
Fig 16.26 Internal symptoms of yeasty rot.
can result in the pineapple skin cracking between
fruitlets. Fruit affected by even minor frost damage
are prone to cracking as they ripen in spring. Yeasts
immediately invade the juice weeping from those
wounds, and these fruit are severely damaged or
destroyed as they ripen. The disease may occur before
or after harvest.
YEASTY ROT
■
Cause
The yeasts
Saccharomyces
spp.
Symptoms
Yeasts ferment sugar solution, producing alcohol and
releasing carbon dioxide. The first symptom is a bubbling
exudation of gas and juice through the crack or injury
where infection occurred. The shell then turns brown and
leathery and, as the juice escapes, the fruit becomes spongy.
Internally, the decaying f flesh turns bright yellow and
develops large gas cavities. Finally, all that remains of the
fruit is the shell and spongy tissue.
Importance
Yeasts are among the most common organisms found in
nature. Yeasty rot is widespread but occurs mainly during
spring in overripe or damaged fruit.
Management
•
Protect fruit that will ripen in spring in frost-prone areas
by covering young developing fruit with paper bags.
Source of infection and spread
In spring, rapid changes in fruit growth, resulting from
the shift from cold and dry to warm and wet weather,
Fruit showing even minor interfruitlet cracking should
not be consigned to the fresh-fruit market.
•
Any fruit showing fractures between fruitlets should be
picked at the earliest stages of fruit maturity to minimise
losses.
•
NEMATODES
■
Cause
Root-knot nematode (
Meloidogyne javanica
), the root-
lesion nematode (
Pratylenchus brachyurus
) and the
reniform nematode (
Rotylenchulus reniformis
).
Symptoms
Root-knot nematodes produce distinct terminal swellings
on the roots, stopping further root development. The root-
lesion nematode invades the outer root tissues, causing
black areas (lesions) of dead or injured plant cells on the
Fig 16.25 Yeasty rot symptoms on the outside of a pineapple. Note
the gas bubbles and juice exuding through the skin.
