Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/10/2012
Publication Date: 10/15/2012
Citation: Wintermantel, W.M., McCreight, J.D. 2012. Emergence and management of whitefly-transmitted viruses affecting melon production in southern California. Epidemiology and Management of Whitefly-Transmitted Viruses Workshop. p. 21.
Technical Abstract: Melon production in the southwestern United States has been impacted by several whitefly-transmitted viruses over the past few decades. This has led to increased research for both vector management and identification and control of whitefly-transmitted viruses. During the 1980s Lettuce infectious yellow virus (LIYV; family Closteroviridae; genus Crinivirus) was a significant threat to production of melon as well as lettuce, sugarbeet, and other crops. Populations of Bemisia tabaci biotype A increased over the summer months annually, and resulted in early infection and severe losses for fall melon production in California and Arizona. During the early 1990s, a sudden shift in the whitefly population from biotype A to biotype B virtually eliminated LIYV from the region due to the extremely poor rate of transmission of LIYV by B. tabaci biotype B. Consequently, fall melon production was renewed in the region over the next decade with effective usage on new insecticides to control the high populations of B. tabaci biotype B. The emergence of Cucurbit yellow stunting disorder virus (CYSDV) in 2006, resulted in universal infection of the entire melon crop in the region, reducing sugar content in fruit and rendering melons unmarketable, again drastically reducing Fall melon production from the American Southwest as well as northern Mexico. CYSDV incidence was low in Spring melons and limited to a small number of fields. The severity and speed with which CYSDV affected melon production led to an intensive effort to characterize the epidemiology of this virus in its new range and aggressive efforts toward control. Early studies indicated the host range of CYSDV was limited to members of the Cucurbitaceae, but survival through a severe freeze that eliminated virtually all cucurbit hosts suggested the possibility of alternative hosts for CYSDV. Weed and crop hosts were collected from throughout California’s Imperial Valley over a period of 26 months, and were tested for the presence of CYSDV by RT-PCR using CYSDV HSP70h- and coat protein gene-specific primers to identify potential reservoir hosts and elucidate virus epidemiology. Many non-cucurbits collected from infected melon fields and nearby areas were asymptomatic and virus-free; however, CYSDV was detected in plants from eight different families. Transmission tests demonstrated that lettuce, snap bean, alkali mallow, Wright’s ground cherry and buffalo gourd (Cucurbita foetidissima) are potential reservoir hosts from which the virus could be transmitted to melon. These results greatly expanded the previously known host range of CYSDV. Several reservoir hosts are being evaluated for virus titer and efficiency of virus transmission to cucurbits in efforts to identify the more significant alternate hosts during periods in which cucurbits are not present in the field. Melon PI 313970 exhibited high-level resistance to CYSDV in replicated field tests in Yuma, Arizona and Imperial Valley, California. Mean plant condition ratings of PI 313970 were significantly (P0.05) better than those of the susceptible control, ‘Top Mark .’. Data from a cross with the CYSDV-resistant melon TGR-1551 indicated potential for significantly higher resistance than that exhibited by either resistance source alone. Although resistance to CYSDV may be increased with these sources combined, they must be used in combination with an active insecticide treatment program due to excessively high whitefly feeding pressure. Breeding to transfer resistance form PI 313970 and TGR-1551 to horticulturally acceptable germplasm, and research to optimize vector and alternate host management are anticipated to eventually restore the potential for fall melon production within the region.