Large scale seedling grow-out experiments do not support seed transmission of sweet potato leaf curl virus in sweet potato

Authors: ANDREASON, SHARON - Oak Ridge Institute For Science And Education (ORISE); OLANIYI, OMOTOLA - Oak Ridge Institute For Science And Education (ORISE); Gilliard, Andrea; Wadl, Phillip; Williams, Livy; JACKSON, MICHAEL - Retired ARS Employee; Simmons, Alvin; Ling, Kai-Shu

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2021
Publication Date: 1/12/2021
Citation: Andreason, S.J., Olaniyi, O.G., Gilliard, A.C., Wadl, P.A., Williams Iii, L.H., Jackson, M.D., Simmons, A.M., Ling, K. 2021. Large scale seedling grow-out experiments do not support seed transmission of sweet potato leaf curl virus in sweetpotato. Plants. 10(1):139. https://doi.org/10.3390/plants10010139.
DOI: https://doi.org/10.3390/plants10010139

Interpretive Summary: Sweetpotato is the sixth most important food crop worldwide. One of the most economically important sweetpotato viruses is sweet potato leaf curl virus (SPLCV), which is a predominant begomovirus infecting sweetpotato in the United States. SPLCV is typically transmitted via infected vegetative propagating materials or by whitefly (Bemisia tabaci) vector. However, a recent publication claimed that SPLCV is seed transmitted. To assess the validity of seed transmission of SPLCV, ARS scientists conducted large-scale seedling grow-out experiments over 4 years using over 23,000 sweetpotato seedlings of 118 genotype entries from breeder’s seeds derived from SPLCV-infected maternal plants. All those grow-out seedlings under strict insect-proof conditions in a greenhouse or growth chamber showed no evidence of seed transmission. A very small number of seedlings growing on open benches in a greenhouse (without insect exclusion) was positive for SPLCV, but we also observed the presence of some incidental whiteflies. Vector transmission tests using viruliferous whiteflies demonstrated the transmission of SPLCV to sweetpotato seedlings. We concluded that there is no seed transmission of SPLCV in sweetpotato. This result is in agreement with another report on no evidence of seed transmission of another begomovirus, tomato yellow leaf curl virus on tomato. Incorrect reports on seed transmission of SPLCV and other begomoviruses could have a negative impact on strategies in disease management, which might also impose unnecessary burden to the seed companies as well as to governmental regulatory agencies.

Technical Abstract: Sweet potato leaf curl virus (SPLCV) threatens global sweetpotato production. SPLCV is transmitted by Bemisia tabaci or via infected vegetative planting materials; however, SPLCV was suggested to be seed transmissible, a characteristic that is disputed for geminiviruses. The objective of this study was to revisit the validity of seed transmission of SPLCV in sweetpotato. Using large scale grow-out of sweetpotato seedlings from SPLCV-contaminated seeds over 4 consecutive years, approximately 23,034 sweetpotato seedlings of 118 genotype entries were evaluated. All seedlings germinating in a greenhouse under insect-proof conditions or in a growth chamber were free of SPLCV; however, a few seedlings grown in an open bench greenhouse lacking insect exclusion tested positive for SPLCV. Inspection of these seedlings revealed that B. tabaci had infiltrated the greenhouse. Therefore, transmission experiments were conducted using B. tabaci MEAM1, demonstrating successful vector transmission of SPLCV to sweetpotato. Additionally, tests on contaminated seed coats and germinating cotyledons demonstrated that SPLCV contaminated a high percentage of seed coats collected from infected maternal plants, but SPLCV was never detected in emerging cotyledons. Based on the results of grow-out experiments, seed coat and cotyledon tests, and vector transmission experiments, we conclude that SPLCV is not seed transmitted in sweetpotato.