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Virus Diseases of Cucurbits

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Virus Diseases of Cucurbits http://hdl.handle.net/1813/43312 DISEASES OF CUCURBITS Virus Diseases Fact Sheet Page: 732.40 COOPERATIVE EXTENSION NEW YORK STATE CORNELL UNIVERSITY Date: 1 0-1984 mottling of fruit, making the product and squash in New York. The virus is Virus Diseases unmarketable. A complex of viruses is seedborne in muskmelon and is spread of Cucurbits able to infect cucurbits, a plant group in nature principally by the spotted and that includes cucumber, melon, squash, striped cucumber beetles. The virus is by T. A. Zitter and M. T. Banik pumpkins, and watermelon. The most carried within the seed and cannot be Dept. of Plant Pathology important viruses are cucumber mosaic eliminated by hot water or chemical (CMV), squash mosaic (SqMV), water­ treatment with trisodium phosphate. Cornell University melon mosaic I (WMV-1), watermelon Symptoms consist of pronounced and R. Provvidenti mosaic 2 (WMV-2), and zucchini yellow chlorotic mottle, green veinbanding, and Dept. of Plant Pathology mosaic (ZYMV). With the exception of distortion of leaves of young seedlings. New York State Agricultural SqMV, which is seedborne in melon On mature plants, leaves show intense Experiment Station, Geneva and transmitted by beetles, the other dark green mosaic, blistering, and har­ major viruses are transmitted by several dening, suggestive of a hormonal herbi­ aphid species in a nonpersistent manner. cide effect (fig. 1). Infected fruit coming Viruses are the most common causes from such plants show a strong mottled of diseases affecting cucurbits in New Major Cucurbit Viruses pattern with a lack of netting on melons York. These diseases result in losses (fig. 2). Control measures include selec­ through reduction in growth and yield Squash mosaic virus (SqMV) can tion of disease-free seed and cucumber and are responsible for distortion and cause an important disease of melons beetle control. Cucumber mosaic virus (CMV) is squash (fig. 4), and growers have seen a symptoms consist of a prominent yellow probably the most widely distributed lessening of foliar symptoms following mosaic, necrosis, distortion, and stunt- and important virus disease of cucurbits fertilization. Fruit distortion and color ing. Fruits remain small, greatly mal- in New York. The virus overwinters in breaking are still a problem on varieties formed, and green mottled, including many perennial weed sources especially like yellow straight-neck squash (fig. 5). fruit of the variety 'Multipik' (fig. 9). It attractive to aphids when weed growth Use of varieties such as 'Multipik' (fig. is too early to tell which weed hosts resumes in the spring. Early infection of 6) can prolong the harvest period may serve to overwinter this virus in squash and melons is particularly com- because the fruit are marketable in spite New York. mon. Aphids are the main and most effi- of foliar symptoms. The host range for cient method of virus spread. Summer WMV-2 is not limited to cucurbits, thus Minor Cucurbit Viruses or squash displays severe downward cup- opening the possible overwintering of Disease Agents ping along the midvein and leaf reduc- this virus in several leguminous species tion from which the plants fail to such as clover. Mixed infections of Tobacco ringspot virus (TRSV) is recover (fig. 3). Color breaking of cucurbits with CMV and WMV-2 are mainly transmitted by nematodes squash fruit is usually seen, but is not common by the end of the season. (Xiphinema americanumj. Melons and unique for this virus; other viruses caus- Watermelon mosaic virus 1 (WMV-I) cucumbers are most commonly affected ing this symptom include watermelon is aphid transmitted, and infection is by this virus. The virus has been known mosaic viruses I and 2, squash mosaic limited to cucurbits. Although more on rare occasions to be seed borne in virus, and zucchini yellow mosaic virus. common in the southern and western cucurbits. The newly infected leaves Early decline of muskmelon vines is regions of the United States, this virus show a very bright mosaic with plant usually attributed to CMV infection and has been recovered in New York several stunting (fig. 10), but subsequent leaves should not be confused with collapse or times since it first occurred in epidemic are reduced in size and develop a dark "sudden wilt," which is a more complex proportions in 1969. This virus is capa- green color. disease and a plant-stress-related syn- ble of infecting all commercial cucurbit Tomato ringspot virus (TmRSV) drome. CMV may be seedborne to a crops. The foliage of affected plants causes severe damage to summer and limited extent in some crops and weeds shows strong mosaic, distortion, and winter squash, but shows only mild such as common chickweed (Stellaria deep leaf serration (fig. 7). Fruits are symptoms in the other cultivated cucur- media). Good CMV-resistant (actually also malformed with knobby over- bits. Like TRSV, TmRSV is nematode tolerant since plants are infected by the growth (fig. 8). transmitted and can be overwintered on virus) cucumber varieties are commer- Zucchini yellow mosaic virus many weed species without expressing cially available and produce a high per- (ZYMV) is a recently described virus symptoms. centage of un mottled fruit. All other disease of cucurbits, first identified in Clover yellow vein virus (CYVV) is commercially grown cucurbits are sus- Europe in J981. It has since been an aphid-transmitted virus that can ceptible to CMV, although in yellow reported from most southern and infect summer squash and was pre- summer squash varieties that also carry southwestern states and was found in viously considered to be the severe a "precocious yellow gene," this gene New York State in J983. The virus has strain of bean yellow mosaic virus. The serves to mask the color breaking com- characteristics very similar to WM V-I virus produces a yellow specking on the mon with cucurbit viruses (see discus- and WMV-2 (nonpersistent aphid trans- foliage of infected plants. sion under WMV-2). mission, etc.), and like WMV-2, its host Aster yellow mycoplasma (A Y), for- Watermelon mosaic virus 2 (WMV-2) range is not limited to cucurbits. Cur- merly thought to be caused by a virus, is the second most important cucurbit rently, none of the genetic factors that has been recovered from infected squash virus in New York. This virus can infect confer resistance to WMV-J or WMV-2 in the state. This leafhopper-transmitted and produce symptoms on all commer- are able to control ZYMV, but other disease organism causes plants to cially grown cucurbits. This aphid-trans- resistance sources have been identified. become yellowed and stunted (fig. II). mitted virus causes milder symptoms on Muskmelon, watermelon, and squash the foliage of most infected plants like are severely affected by ZYMV. Foliar Quantity discount available. Cooperative Extension, New York State College of Agriculture and Life Sciences, New York State College of Human Ecology, and New York State College of Veterinary Medicine at Cornell University, and U.S. Department of Agriculture, cooperating. In furtherance of acts of Congress May 8 and June 30, 1914, and providing equal opportunities in employment and programs. Lucinda A. Noble, Director. 11/84 CRP 4M 9134b.
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