Virus Diseases of Cucurbits
M. Babadoost
Many viruses affect cucurbits and cause mosaic diseases. The most important of these viruses are
cucumber mosaic virus (CMV), squash mosaic virus (SqMV), watermelon mosaic
virus (WMV), zucchini yellow mosaic virus (ZYMV), and papaya ring spot virus
(PRSV). The viruses differ in the range
of host plants they infect, how they survive between crops, and the ways in
which they are transmitted. Since
control programs are based on this information, it is important that the virus
or viruses involved be identified. This
virus complex has caused growers in certain areas to stop growing these crops.
The
symptoms caused by different cucurbit viruses are commonly very similar. It is impossible to identify these viruses
with certainty based on symptoms alone.
Usually special laboratory tests are required to correctly identify a
cucurbit virus.
Leaves of virus-infected plants often appear mottled and distorted.
Pumpkin plants infected early in their development (near or before the time of
flowering) are severely affected and produce few fruit, and most of the
pumpkins that are produced are likely to be misshapen or off-color. However,
plants infected after fruit reach full size may not show any effect on yield or
quality. Late-season pumpkins are especially prone to losses associated with
virus disease.
Viruses
survive in infected weed hosts. SqMV is seed-borne. These pathogens are spread
by insect vectors (especially aphids) and mechanical operations that disturb
plants and bruise leaves and vines.
Virus diseases of cucurbits
can be controlled by planting resistant varieties (wherever available), using
virus-free seed, cultural practices, and insect control. Early planted field
tend to have less damage than those that are planted later. Weed control within
and around field is important. Avoiding mechanical transmission of viruses is
important. Insect control for reducing incidence of virus diseases is
effective. However, Attempts to control insects for virus disease control may
be futile, because insects may transmit the virus before insecticides are
effective.