Zucchini yellow mosaic virus (ZYMV, Potyvirus): Vertical transmission, seed infection and cryptic infections

• Published in: Virus research 2013-09, Vol.176 (1-2), p.259-264
• Main Authors: Simmons, H.E., Dunham, J.P., Zinn, K.E., Munkvold, G.P., Holmes, E.C., Stephenson, A.G.
• Format: Article
• Language: English
• Subjects: 5' Untranslated Regions; Cucurbita - virology; Cucurbita pepo; Disease Transmission, Infectious; Genetic Variation; haplotypes; Illumina sequencing; infection; Infectious Disease Transmission, Vertical; Molecular Sequence Data; mutation; pathogens; Plant Diseases - virology; population dynamics; Potyvirus; Potyvirus - isolation & purification; RNA, Viral - genetics; seed germination; Seed transmission; seedling growth; Seeds - virology; Sequence Analysis, DNA; Symptomless infection; transmissions; vertical transmission; virulence; Virus Diseases - transmission; Virus Diseases - virology; Zucchini yellow mosaic virus
• ISSN: 0168-1702; 1872-7492
• DOI: 10.1016/j.virusres.2013.06.016

•We obtained deep sequence data from nine vertically transmitted ZYMV populations.•The 5′UTR region is variable, with 26 major haplotypes observed in this region.•Vertically infected plants are symptomless unlike those infected horizontally.•Seed infection higher than seed transmission rate, possible population bottleneck. The role played by seed transmission in the evolution and epidemiology of viral crop pathogens remains unclear. We determined the seed infection and vertical transmission rates of zucchini yellow mosaic virus (ZYMV), in addition to undertaking Illumina sequencing of nine vertically transmitted ZYMV populations. We previously determined the seed-to-seedling transmission rate of ZYMV in Cucurbita pepo ssp. texana (a wild gourd) to be 1.6%, and herein observed a similar rate (1.8%) in the subsequent generation. We also observed that the seed infection rate is substantially higher (21.9%) than the seed-to-seedling transmission rate, suggesting that a major population bottleneck occurs during seed germination and seedling growth. In contrast, that two thirds of the variants present in the horizontally transmitted inoculant population were also present in the vertically transmitted populations implies that the bottleneck at vertical transmission may not be particularly severe. Strikingly, all of the vertically infected plants were symptomless in contrast to those infected horizontally, suggesting that vertical infection may be cryptic. Although no known virulence determining mutations were observed in the vertically infected samples, the 5′ untranslated region was highly variable, with at least 26 different major haplotypes in this region compared to the two major haplotypes observed in the horizontally transmitted population. That the regions necessary for vector transmission are retained in the vertically infected populations, combined with the cryptic nature of vertical infection, suggests that seed transmission may be a significant contributor to the spread of ZYMV.