Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2008
Publication Date: 12/1/2008
Citation: Ling, K. 2008. Pepino Mosaic Virus on Tomato Seed: Virus Location and Mechanical Transmission. Plant Disease. 92:1701-1705.
Interpretive Summary: Pepino mosaic virus (PepMV) is an emerging disease for greenhouse tomato. It poses a great threat to the $400 million greenhouse tomato industry in the United States. Although commercial tomato seed is suspected to spread the disease, its importance as an initial virus inoculum for PepMV has not been established. This study was conducted using an imported commercial tomato seed produced in Chile for a large scale seedling grow-out test under greenhouse conditions. Although tomato seed was shown to be heavily contaminated with PepMV in serological tests, none of 10,000 grow-out seedlings were infected. However with the aid of mechanical transmission, PepMV was transmitted from the contaminated seed to tomato and Nicotiana benthamiana seedlings. The mechanism for the seed borne but not seed transmission of PepMV in tomato seed was likely due to the localization of PepMV in tomato seed coats and not in embryos. Because PepMV is seed-borne in tomato, the efficient mechanical transmission of PepMV from virus-contaminated tomato seed to seedlings may help to initiate the disease epidemic in a new tomato growing area. Therefore, it is important to plant a certified commercial seed that is tested free of PepMV.
Technical Abstract: Pepino mosaic virus (PepMV) is an emerging disease of tomato which poses a great threat to greenhouse tomato productions in Europe, North America and South America. Although commercial tomato seed is suspected to spread the disease, its importance as an initial virus inoculum for PepMV has not been established. To determine the potential seed transmission, an imported tomato seed lot highly contaminated with PepMV was used for large scale seedling grow-out test. None of 10,000 grow-out seedlings was infected as determined by symptom expression, enzyme-linked immunosorbent assay (ELISA), and infectivity assay on Nicotiana benthamiana plants. Even though PepMV was not seed transmitted in tomato, the virus was effectively transmitted to tomato and N. benthamiana seedlings through mechanical transmission. Efficiency of virus transmission however increased dramatically from 5% infection rate with a single inoculation to 100% infection after the second inoculation with seed extract. To examine the virus location on tomato seed, seed coats and embryos were carefully isolated and tested separately by ELISA and bioassay on N. benthamina. PepMV was found in the seed coat but not in the embryo. This localization of PepMV in seed coat was also found using freshly extracted immature tomato seed. This seed-borne nature of PepMV in tomato seed may due to the hairy structure in tomato seed coat. In N. benthamiana with a smooth seed coat, PepMV was neither seed-borne nor seed-transmitted. Because PepMV is seed-borne in tomato, the efficient mechanical transmission of PepMV from virus-contaminated tomato seed to tomato seedlings may help to initiate the disease epidemic in a new tomato growing area. Therefore, it is important to plant a certified commercial seed that is tested free of PepMV.