Agriculture Reference
In-Depth Information
Source of infection and spread
Papaya ringspot virus
is spread from plant to plant by
aphids - small sap-sucking insects that are very common
in subtropical and tropical areas. Aphids can spread the
virus between plants while feeding for less than a minute.
Many aphid species are able to spread the virus, although
their efficiency in doing so varies between species.
Papaya is not a preferred host for aphids and almost all the
spread of the virus is by transitory feeding by aphids as
they brief ly probe plants while moving through an area.
This feeding pattern can result in very rapid spread of the
virus through a plantation.
The hosts of PRSV-P is restricted to papaya, some related
Va sc onc e ll e a
species and several cucurbits, for example
squash, pumpkin, zucchini.
The W or watermelon strain of PRSV does not infect papaya.
Fig 14.28 Leaf symptoms of powdery mildew. Inset: white, powdery
fungal growth along leafstalk and veins.
Importance
Papaya ringspot is a major disease in most countries where
papaya is grown. PRSV-P was first found in Queensland
in 1991 and has remained restricted to south-east
TRANSIT ROT
See the chapter on Common diseases of perennial fruit
crops for information about transit rot.
■
Importance
Transit rot, although sporadic, can be extremely destructive.
VIRUSES
PAPAYA RINGSPOT
■
Cause
Papaya ringspot virus
-type P (PRSV-P).
Symptoms
Plants of all ages are susceptible and symptoms are
generally more severe during cooler weather. The disease
derives its name from the characteristic dark green
sunken rings that develop on fruit of affected plants.
These rings often remain as dark orange to brown
markings as the fruit mature. Dark green, water-soaked
streaks develop on petioles and stems. Mottle and mosaic
patterns of varying severity develop on leaves that often
have a ruff led appearance. Leaf lobes may become
severely distorted and reduced in size, giving a shoestring
appearance. Infected plants become stunted and fruit set
is markedly reduced or absent. Fruit from infected plants
have a poor f lavour, a leathery appearance, and are
predisposed to fungal fruit rots.
Fig 14.29 Papaya ringspot showing symptoms on green and ripe fruit.