|WANG, X - University Of Hawaii|
|LARREA-SARMIENTO, A - University Of Hawaii|
|BORTH, WAYNE - University Of Hawaii|
|BARONE, R - University Of Hawaii|
|OLMEDO-VELARDE, A - University Of Hawaii|
|MELZER, MICHAEL - University Of Hawaii|
|HU, JOHN - University Of Hawaii|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2020
Publication Date: 3/30/2020
Citation: Wang, X., Larrea-Sarmiento, A., Borth, W.B., Barone, R., Olmedo-Velarde, A., Melzer, M.J., Suzuki, J.Y., Wall, M.M., Hu, J.S. 2020. First report of Basella alba naturally infected with basella rugose mosaic virus in Hawai'i. Plant Disease. 104(8):2296. https://doi.org/10.1094/PDIS-06-19-1266-PDN.
Interpretive Summary: Malabar spinach or Basella alba, is a plant native to tropical Asia and Africa and is grown in Hawaii as a vegetable crop. In December 2018, plants with mottling symptoms akin to viral infection were found growing in a community garden on Oahu, Hawaii. Diagnostic methods were used to identify the presence of a plant virus belonging to the family known as potyviruses from five symptomatic plant samples. DNA sequence analyses further showed that this virus was highly related to a strain of basella rugose mosaic virus (BaRMV) that was reported infecting peace lily (Spathiphyllum patinii, family Araceae) in Vietnam in 2008. The report describing the original BaRMV was made in 2006 on a potyvirus that was discovered infecting Malabar spinach in Taiwan. However, this is the first known report of BaRMV infecting Malabar spinach in the United States. Molecular diagnostic methods were developed during this study to specifically identify and help track this virus from plants in the field and the results on a small sampling of 20 plants in Hawaii indicates that incidence of this virus in Malabar spinach is as high as 92%. Further studies are also necessary to obtain more information on the virus’s entire genetic makeup, the identity of insect vector(s) that transmit and spread the virus to new plants, and its geographic distribution in order to help control BaRMV infection in B. alba and other vegetables among Hawaii’s community and family gardens.
Technical Abstract: In December, 2018, samples of Basella alba, or Malabar spinach, a native of tropical Asia and Africa grown in Hawaii as a vegetable crop were found with mosaic and rugose symptoms growing in a community garden on Oahu, Hawaii (21°17'05' N, 157°49'40' W). Five leaf samples with severe symptoms from plants from different plots in the same garden tested positive by ELISA using potyvirus-specific antibodies. Reverse transcription (RT)-PCR was subsequently conducted on RNA from virus-positive samples using a universal primer pair designed to amplify a ~600 bp amplicon corresponding to the potyviral cylindrical inclusion protein (CI) gene. The PCR product sequence (MN075828) was found by BLASTn analysis to share 97% and 95% nucleotide and amino acid sequence identity, respectively, with the corresponding region of Peace lily mosaic virus (PeLMV) that was reported in 2008 on peace lily (Spathiphyllum patinii, family Araceae) in Vietnam (accession nos. DQ851494/ABI34613). The original isolate of PeLMV has since been reclassified in the literature as a strain of basella rugose mosaic virus or BaRMV, based on 83% and 92% shared nucleotide and amino acid sequence identity, respectively with that virus. BaRMV is potyvirus that was first reported in 2006 on B. alba in Taiwan (DQ821939/ABH10135). The sequence of the newly identified Hawaii isolate of BaRMV is similarly 83% and 94% identical at the nucleotide and amino acid levels, respectively to the original Taiwan isolate of BaRMV. New BaRMV CI gene-specific primers were designed from the Hawaii isolate sequence to further characterize this viral isolate in B. alba. The 389-bp sequence of the resulting CI fragment amplicon (accession no. MN075829) obtained from the Hawaii isolate of BaRMV indicated that it shared 98% and 96% identity with the nucleotide and amino acid sequences, respectively with the corresponding regions of the same Vietnam isolate (accession nos. DQ851494/ABI34613). The CI fragment amplicon also showed 83% and 95% nucleotide and amino acid sequence identities, respectively, to the corresponding regions of the Taiwan isolate of BaRMV (accession nos. DQ821939/ABH10135). Diagnostic tests using the BaRMV CI gene-specific primers on an additional 20 B. alba plants from the original field indicated that BaRMV was detected in all 18 symptomatic samples, but not in the asymptomatic samples. This result indicates that the incidence of BaRMV in B. alba was 23 out of 25 or 92%. To our knowledge, this is the first report of BaRMV infecting B. alba plants in the United States. Further studies to obtain information on the full length viral genome sequence, identity of insect vector(s), and geographic distribution are necessary in order to help control BaRMV infection in B. alba and other vegetables among Hawaii’s community and family gardens.