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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #312652
Title: First report of an ipomovirus infecting cucurbits in the Imperial Valley of California

Author
item BATUMAN, OZGUR - University Of California
item NATWICK, ERIC - University Of California - Cooperative Extension Service
item Wintermantel, William - Bill
item TIAN, TONGYAN - California Department Of Agriculture
item McCreight, James - Jim
item Hladky, Laura
item GILBERTSON, ROBERT - University Of California

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2015
Publication Date: 6/10/2015
Citation: Batuman, O., Natwick, E.T., Wintermantel, W.M., Tian, T., Mccreight, J.D., Hladky, L.L., Gilbertson, R.L. 2015. First report of an ipomovirus infecting cucurbits in the Imperial Valley of California. Plant Disease. doi: 10.1094/PDIS-12-14-1248-PDN.

Interpretive Summary: In the fall of 2014, pumpkin plants grown at the University of California Desert Research Extension Center (DREC) in Holtville, CA showed severe stunting, leaf yellowing, crumpling, and epinasty. These plants were also infested with high whitefly populations. Molecular tests performed on leaf samples from 21 of these plants revealed infection with the crinivirus Cucurbit yellow stunting disorder virus (CYSDV) and the begomovirus Squash leaf curl virus (SLCV) in all plants. Additional molecular tests (RT-PCR) confirmed the presence of the potyvirus CI gene but not another gene from the virus, suggesting the presence of a member of the family Potyviridae, but perhaps not closely related to most viruses in the genus Potyvirus. Sequencing of portions of the CI gene from nine plants revealed the closest identity (82%) with the CI gene of Squash vein yellowing virus (SqVYV), a whitefly-transmitted ipomovirus (family Potyviridae). Amplification with primers for the SqVYV coat protein (CP) gene confirmed infection in all 17 plants from which the CI fragment was amplified, and not from healthy pumpkin plants or the plants from which the CI fragment was not amplified. Sequence analysis of these fragments revealed 98% identity with the SqVYV CP gene. Pumpkin and squash plants inoculated with sap prepared from leaves of three pumpkin plants in which the ipomovirus CI fragment was amplified by RT-PCR, developed mild mottling, vein clearing and yellowing symptoms. These plants tested positive for ipomovirus infection and negative for infection by CYSDV and SLCV. Transmission electron microscope examination of infected sap-inoculated squash and pumpkin plants revealed ipomovirus-like virus particles. Serological tests using an antiserum raised against a Florida isolate of SqVYV was positive for leaves of all pumpkin and squash plants previously confirmed to be infected after sap-inoculation. Molecular and serological tests performed on leaves of nine melon plants collected from the DREC station with interveinal yellowing, mottle and flecking symptoms, revealed infection with both the ipomovirus and CYSDV. In contrast, tests with melons showing interveinal yellowing symptoms from commercial fields in Imperial County revealed infection only with CYSDV. Together, these results indicate that an ipomovirus, most closely related to SqVYV from Florida, was infecting cucurbits in the Imperial Valley. This is the first report of an ipomovirus in California. It is not clear from where the California ipomovirus originated, or whether it is a strain of SqVYV or a distinct species; however, it represents a potential threat to cucurbit production in the state, especially watermelons, which can develop the devastating vine decline disease.

Technical Abstract: In the fall of 2014, pumpkin plants grown at the University of California Desert Research Extension Center (DREC) in Holtville, CA showed severe stunting, leaf yellowing, crumpling, and epinasty. These plants were also infested with high populations of B. tabaci. RT-PCR and PCR tests performed on leaf samples from 21 of these plants revealed infection with the crinivirus Cucurbit yellow stunting disorder virus (CYSDV) and the begomovirus Squash leaf curl virus (SLCV) in all plants; whereas RT-PCR with degenerate potyvirus CI and HC-Pro primers revealed only the expected ~700 bp fragment with the CI primer pair for 17 plants, but no fragment with the HC-Pro primers. Sequence analysis of the CI fragments from nine plants revealed the closest identity (82%) with the CI gene of Squash vein yellowing virus (SqVYV), a B. tabaci-transmitted ipomovirus (family Potyviridae). RT-PCR analysis with primers specific for the SqVYV capsid protein (CP) gene directed the amplification of the expected size ~1,100 bp fragment from all 17 plants from which the CI fragment was amplified, and not from healthy pumpkin plants or the plants from which the CI fragment was not amplified. Sequence analysis of these fragments revealed 98% identity with the SqVYV CP gene. Pumpkin and squash plants inoculated with sap prepared from leaves of three pumpkin plants in which the ipomovirus CI fragment was amplified by RT-PCR, developed mild mottling, vein clearing and yellowing symptoms. These plants tested positive for ipomovirus infection by RT-PCR with the CP primers and negative for infection by CYSDV and SLCV. Transmission electron microscope examination of leaf-dip and mini-purification preparations from infected sap-inoculated squash and pumpkin plants revealed potyvirus-like virus particles. Serology (ELISA) with an antiserum raised against a Florida isolate of SqVYV was positive for leaves of all pumpkin and squash plants infected with the ipomovirus after sap-inoculation. RT-PCR tests performed on leaves of nine melon plants collected from the DREC station with interveinal yellowing, mottle and flecking symptoms, revealed infection with both the ipomovirus and CYSDV. Ipomovirus infection of melon was also confirmed using the SqVYV antiserum. In contrast, RT-PCR tests with melons showing interveinal yellowing symptoms from commercial fields in Imperial County revealed infection only with CYSDV. Together, these results indicate that an ipomovirus, most closely related to SqVYV from Florida, was infecting cucurbits in the Imperial Valley. This is the first report of an ipomovirus in California. It is not clear from where the California ipomovirus originated, or if it is a strain of SqVYV or a distinct species; however, it represents a potential threat to cucurbit production in the state, especially watermelons, which can develop the devastating vine decline disease.