II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES) – 123
Papaya ringspot virus Type W (PRSV)
This Potyvirus is distributed worldwide. PRSV is transmitted in a non-persistent
manner by various aphids such as the peach aphid Myzus persicae (Brunt et al., 1996).
It can also be transmitted mechanically by humans. It is not seed transmitted (Brunt et al.,
1996). This virus was originally called water melon mosaic virus 1 (WMV1) but today
is considered to be the W strain of PRSV. PRSV-W should not be confused with what
had been called watermelon mosaic virus 2 (WMV2) but is now simply WMV (Lecoq
and Desblez, 2009). PSRV has a different host range, different serological properties and
no sequence homology with WMV. As with other mosaic viruses, leaves of infected
plants become mottled and vines are stunted (Brunt et al., 1996).
Squash mosaic virus (SqMV)
SqMV is a Comovirus and was first reported in California in 1956 (Brunt et al.,
1996). SqMV is probably distributed worldwide. This virus can infect and produce
symptoms on several commercially grown cucurbits, including C. maxima, C. moschata
and C. pepo. It can also infect some plants in the Leguminosae and the Chenopodiaceae.
The virus is insect-transmitted in a non-persistent fashion by several insects (Acalymma
vitatta, Acalymma thiemei, Diabrotica undecimpunctata, Diabrotica bivittula, Epilachna
chrysomalina, Epilachna paenulata) (Brunt et al., 1996). In nature it is spread principally
by the spotted cucumber beetle (Diabrotica undecipunctata) and striped cucumber beetle
(Acalymma vittata). The virus can also be transmitted by seed and by mechanical
inoculation.
Watermelon mosaic virus (WMV)
In the 1990s, this Potyvirus was referred to as WMV2 to distinguish it from WMV1.
Today, WMV1 is considered to be the W strain of papaya ringspot virus (PRSV), while
WMV2 is referred to as WMV (Lecoq and Desblez, 2009). WMV has worldwide
distribution and is a major viral pathogen of cucurbit crops (Adlerz et al., 1983;
Provvidenti, Gonsalves and Humaydan, 1984; Davis and Mizuki, 1987; Chala, Harrison
and Halliwell, 1987). This virus can infect and produce symptoms on all commercially
grown cucurbits. It can also infect several leguminous and malvaceous species. The virus
is aphid-transmitted in a non-persistent fashion. As the host range for WMV is not limited
to cucurbits, overwintering of this virus in several leguminous species such as clover can
occur. Mixed infections of cucurbits with CMV and WMV are common. WMV causes
mosaic and mottle diseases of cantaloupe, cucumber, pumpkin, squash and watermelon
and reduces fruit production and quality in squash and other cucurbits (Thomas, 1971;
Greber, 1978). Leaves of infected plants become mottled and vines are stunted.
Zucchini yellow mosaic virus (ZYMV)
This Potyvirus is a recently described virus disease of cucurbits, first identified
in Europe in 1981. The virus is serologically related to, and has characteristics very
similar to, WMV (Brunt et al., 1996). ZYMV is also serologically related to bean yellow
mosaic virus (Brunt et al., 1996). Like WMV, the ZYMV host range is not limited to
cucurbits. The known host range of ZYMV includes Cucurbita pepo, Cucumis melo,
Cucumis sativus and Citrullus lanatus (ANU, 2005). ZYMV is transmitted in a non-
persistent manner by aphid transmission (Lecoq, Pitrat and Clement, 1981; Lisa et al.,
1981; Adlerz et al., 1983; Purcifull et al., 1984; Dodds et al., 1984; Adlerz, 1987).
It can also be transmitted vertically through seed. Its effects are severe leaf mosaic,