124 – II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES)
yellowing and eventually shoestring symptoms in the leaves. The fruits are stunted,
twisted and deformed by raised protuberances. In cultivated crops, plants cease producing
marketable fruits within a week or two of infection. On a given cucurbit host, ZYMV
usually causes more severe symptoms than WMV, and there is some indication that
WMV may make the plant more susceptible to ZYMV (Xu et al., 2004). Leaves of
infected plants become mottled and vines are stunted.
Tobacco ringspot virus (TRSV)
TRSV is a Nepovirus and considered a minor cucurbit virus. It is primarily nematode
transmitted (Xiphinema americanun) but can also be transmitted nonspecifically by
insects such as aphids (Aphis gossypii) and mites (Tetranychus ssp). Melons and
cucumbers are the cucurbits most commonly affected by this virus, but it has been found
in the Cucurbita (Jossey and Badadoost, 2006). It has been reported to spread in
North America and China, and has been reported in Australia, Germany, New Zealand
and the United Kingdom (Brunt et al., 1996).
Tomato ringspot virus (ToRSV)
ToRSV is a Nepovirus and is considered a minor cucurbit virus. It causes severe
damage to summer and winter squash, but shows only mild symptoms in the other
cultivated cucurbits. Like TRSV, ToRSV is nematode transmitted (Xiphinema
americanun) and can overwinter on many weed species without expressing symptoms
(Brunt et al., 1996). It has been reported in Australia, Bulgaria, Chile, China, Germany,
Italy, Japan, Korea, New Zealand, North America, Peru, Puerto Rico, Turkey and the
former Soviet Union (Brunt et al., 1996).
Clover yellow vein virus (CYVV)
CYVV is a Potyvirus and considered a minor cucurbit virus. It is aphid-transmitted
in a non-persistent manner and can infect summer squash. Infected plants mostly show
chlorotic or necrotic local lesions. It is probably distributed worldwide (wherever white
clover occurs). It was previously considered to be the severe strain of bean yellow mosaic
virus (Brunt et al, 1996).
Fungi
The most economically important fungal diseases of the Cucurbita are the powdery
mildews (OMAFRA, 2011).
Cladosporium cucumerinum
C. cucumerinum causes a disease known as scab or gummosis. The fungus can attack
any aboveground portion of the plant, including the leaves, petioles, stems and fruits.
Scab produces its greatest damage when infection occurs on the fruit. Infected fruit
appears to have small spots or sunken areas similar to insect stings. A sticky substance
may ooze from the infected area, especially on fleshy fruit. Soft-rotting bacteria may
invade these lesions resulting in foul-smelling decay (Strider and Konsler, 1965; Agrios,
1997; American Phytopathological Society, 2011; OMAFRA, 2011).
