Screening for sugarcane yellow leaf virus in sorghum in Florida revealed its occurrence in mixed infections with sugarcane mosaic virus and a new marafivirus

Authors: BOUKARI, WARDA - University Of Florida; Mollov, Dimitre; WEI, CHUNYAN - University Of Florida; TANG, LIHUA - University Of Florida; Grinstead, Sam; TAHIR, NOUMAN - Bahauddin Zakariya University; MULANDESA, EVA - University Of Florida; HINCAPPIE, MARTHA - University Of Florida; BEIRIGER, ROBERT - University Of Florida; ROTT, PHILIPPE - University Of Florida

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2020
Publication Date: 9/1/2020
Publication URL: https://handle.nal.usda.gov/10113/7094086
Citation: Boukari, W., Mollov, D.S., Wei, C., Tang, L., Grinstead, S.C., Tahir, N., Mulandesa, E., Hincappie, M., Beiriger, R., Rott, P. 2020. Screening for sugarcane yellow leaf virus in sorghum in Florida revealed its occurrence in mixed infections with sugarcane mosaic virus and a new marafivirus. Plant Pathology. https://doi.org/10.1016/j.cropro.2020.105373.
DOI: https://doi.org/10.1016/j.cropro.2020.105373

Interpretive Summary: Sugarcane is affected by many detrimental viruses including the aphid insect transmitted sugarcane yellow leaf virus (SCYLV). Most of the varieties currently used in sugarcane production in the U.S. are susceptible to SCYLV. We investigated whether sorghum, a related crop, may have viral resistance genes by planting numerous sorghum accessions adjacent to fields with endemic SCYLV infections. Screening for SCYLV infections in the sorghum was initially using an antibody assay, with additional testing using a nucleic acid assay. The results were highly discordant between the two tests so additional testing was conducted by high-throughput sequencing (HTS). Those results indicated the antibody assay was yielding many false positive results. The HTS data also led to the discovery of two additional viruses in the sorghum, including a new and not previously reported marifivirus. The complete genome sequence of this new virus, called Sorghum bicolor marifivirus, was determined. This research demonstrated that the SCYLV protein assay had a non-specific reaction and should not be used solely for testing and screening of germplasm, and additional methods should be implemented to increase the reliability of the tests. It also discovered a new virus of sorghum, on which additional research is needed to determine its host range and any damage it causes.

Technical Abstract: Sugarcane yellow leaf virus (SCYLV) is transmitted by aphids and Melanaphis sacchari is the main vector of this virus. Almost all sugarcane varieties grown in Florida are susceptible to SCYLV infection. Therefore, we investigated resistance to SCYLV in Sorghum bicolor which is also a natural host of this virus. Two field experiments, one in 2016 with 19 sorghum lines and the other in 2017 with 15 lines, were established at Belle Glade, FL. Stalks collected randomly in plant and ratoon crops were tested by tissue-blot immunoassay (TBIA) and reverse transcription-polymerase chain reaction (RT-PCR). Over the two-year period, 366 of 423 S. bicolor samples tested positive by TBIA but SCYLV was detected by RT-PCR in only 11 of 161 randomly selected subsamples. Full genome sequences of SCYLV, sugarcane mosaic virus (SCMV) and a new Marafivirus were obtained by high-throughput sequencing (HTS) from three TBIA positive sorghum samples. HTS data for all three viruses were confirmed by RT-PCR. The SCMV isolate from S. bicolor appeared to be a new strain of this virus species. Positive reaction of S. bicolor by TBIA using SCYLV antibodies could not be systematically associated with plant infection by SCYLV or another virus. This suggested the occurrence of a non-specific serological reaction with an unknown S. bicolor antigen. SCMV and the new Marafivirus were also detected in S. almum, suggesting that this weed is a reservoir for S. bicolor-infecting viruses in Florida.