Effects of Border Crops and Intercrops on Control of Cucurbit Virus Diseases

Content Provider	Semantic Scholar
Author	Edelson, Jonathan V.
Copyright Year	2007
Abstract	Virus diseases are important constraints on the production of cucurbit vegetable crops in the United States and worldwide. The potyviruses Watermelon mosaic virus (WMV) (5,24), Papaya ringspot virus type-W (PRSV-W) (23), and Zucchini yellow mosaic virus (ZYMV) (18,19); and the cucumovirus Cucumber mosaic virus (CMV) (11) are found at varying levels wherever these crops are grown (7,22,25,34). The viruses cause mosaic, mottling, enation, and puckering of foliage; mosaic and distortion of fruit; and plant stunting (27). Effects on yield can be severe, particularly where early infections severely stunt plants and where symptoms render fruit unmarketable. In viral disease outbreaks in Oklahoma and Texas, each of these viruses has been identified alone or in mixed infections, with WMV being the most frequently detected (6,14,15,37). The viruses are spread by aphids in a nonpersistent (stylet-borne) manner, and many species are involved in virus spread. Of the 38 aphid species known to transmit WMV (22,24), only the melon/cotton aphid is considered a primary cucurbit pest. The other vectors are noncolonizing alates that move through crops searching for suitable feeding hosts. Aphid vectors acquire virus quickly while probing infected plants and remain infective for only short periods of time that vary from minutes to hours depending on temperature and feeding (21,30). Generally, viruliferous aphids transmit the virus to only one or a few plants before infectivity is lost (21). There are limited options for managing virus diseases of cucurbits. Insecticide sprays against the aphid vectors are not effective in reducing virus disease because aphids transmit virus before the insecticides act to kill them (16,20,28,36). Reflective film mulches of white or silver color have been effective in providing partial disease control by delaying the onset of virus epidemics (6,13). A limitation of reflective films in cucurbits has been that plant growth rapidly covers the mulch and thereby lessens reflectivity. The application of row covers to summer squash until flowering was not effective in reducing virus disease, and caused some yield reduction (6). Frequent applications of mineral oil, which interferes with nonpersistent viral transmission, have been evaluated for virus disease control (29). In watermelons, biweekly applications of mineral oil delayed the time at which 50% of plants were infected with WMV or PRSV-W by 5 to 7 days, but did not increase yield compared with the untreated control (36). In melons, biweekly sprays of mineral oil reduced the incidence of plants infected with WMV and CMV from 69% in the unsprayed control to 52% in one trial but not in another, where virus incidence exceeded 90% for both sprayed and unsprayed treatments (35). Adoption of these management practices by growers has been limited because the labor and expense involved often do not outweigh the resulting small and inconsistent benefits. The elimination of primary sources of virus inoculum by crop isolation in time and space, and by elimination of alternate hosts, are potential management strategies that have been successful for some virus diseases (30). In production areas of the southern United States, successive cucurbit crops grown during the spring, summer, and fall serve as sources of inoculum for subsequent crops. While important alternate hosts have been identified in Florida (1) and Texas (5), CMV and WMV have wide host ranges, making identification of important source species difficult. Furthermore, viruliferous alate aphids may immigrate into fields from a distance, making the elimination of alternate hosts impractical. The availability of genetic resistance to virus diseases in cucurbits is limited to cucumber and a few squash cultivars. Transgenic resistance achieved through the genetic transformation of plants with viral coat protein genes has led to the release of several squash cultivars with resistance to one or more viruses (12). In Oklahoma, the effectiveness of transgenic squash cultivars for virus disease control has been limited because PSRV-W resistance was lacking. Based on the behavior of alate aphids that transmit virus diseases, conventional cropping practices for cucurbit production favor virus disease outbreaks. Because none of the major virus diseases described above are seedborne in cucurbits (27), the viruses are introduced into fields from external sources. Under low wind conditions, low-flying alates searching for feeding hosts are attracted to long wavelength light reflected from contrasting edges of soil and plant interfaces, i.e., isolated patches of vegetation bordered by bare ground (17,20). As a result, occurrence of virus disease is increased in fields where plant density is low (17,31,32). Generally, cucurbit plants are widely spaced both within and between rows and are particularly attractive to alates searching for suitable hosts. Under windy conditions, wind direction and landscape influence the disABSTRACT Damicone, J. P., Edelson, J. V., Sherwood, J. L., Myers, L. D., and Motes, J. E. 2007. Effects of border crops and intercrops on control of cucurbit virus diseases. Plant Dis. 91:509-516.
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Language	English
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Subject Keyword	Aphids Aphis chenopodii glauci preparation Avian crop Coinfection Cucumber mosaic virus Cucumovirus Distortion Excretory function Growth Disorders Incidence matrix Infection Insecticides Limbo Mineral Oil Mosaic Organism Mosaic Viruses Onset (audio) Papaya ringspot virus Plague Plant Development Potyvirus Primary source Silver Sixty Nine Spray Dosage Form Stunt Island Stylet, device Transformation, Genetic Virus Diseases Watermelon mosaic virus Zucchini yellow mosaic virus benefit viral transmission wavelength
Content Type	Text
Resource Type	Article