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

Abstract

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.

Frequencies of Seed Infection and Transmission to Seedlings by Potato Spindle Tuber Viroid (A Pospiviroid) in Tomato

“…In fact we observed viroid titers as low as 0.006 ng/μl in one of the infected seeds; these levels may be too low to successfully initiate seedling infection. This is similar to results previously determined with an RNA virus, Zucchini yellow mosaic virus, where the reported viral titers were lower in the seed (11.3-60 ng/μl) than in the leaf (2000-3400 ng/μl) samples [26]. In addition it is also possible that the lower infection incidence in the seedlings may be due to the lower level of germination for infected versus the healthy seeds.…”

Incidence of viruses and virus-like diseases of watermelons and pumpkins in Uganda, a hitherto none-investigated pathosystem

“…Geographical prevalence and distribution of plant viruses often have a strong bearing to virus-vector relations (Power and Flecker, 2003;Power, 2008) implying that availability vectors transmitting the viruses is a key determinant in high virus incidence (Ng and Falk, 2006;Bragard et al, 2013;Whitfield et al, 2015). All the viruses under the current study are known to be transmitted by aphids (Dodds et al, 1984;Kishaba et al, 1992;Lecoq and Desbiez, 2012), but CMV (Zitter and Murphy, 2009;Jacquemond 2012;Sevik and Balkaya 2015) and ZYMV (Simmons et al, 2011(Simmons et al, , 2013 can also be seed-transmitted in different hosts. A relatively higher number of different aphid species were observed in central than eastern districts (Our unpublished data), and this may partly explain the observed low and high incidences in east and central respectively.…”

“…Aphids of different species transmit CMV, WMV and ZYMV non-persistently, or CABYV persistently (Dodds et al, 1984;Kishaba et al, 1992;Lecoq and Desbiez, 2012), but seed-transmission of ZYMV (Simmons et al, 2011(Simmons et al, , 2013 and CMV (Zitter and Murphy, 2009;Jacquemond, 2012) are also known. The geographical and host range of plant viruses is delimited more by virus-vector than virus-host relations (Power andFlecker, 2003, Power, 2008), which in accordance with its broad vector range makes CMV cosmopolitan infecting over 1200 species in over 100 families of plants worldwide (Zitter and Murphy, 2009;Jacquemond, 2012;Lecoq and Desbiez, 2012).…”

Detection and molecular characterization of Slovak tomato isolates belonging to two recombinant strains of potato virus Y

“…Environmental conditions, genetic factors or plant of the molecular variability of virus may play a role in symptom development (Simmons et al, 2013). As ascertained by experimental mechanical inoculation of tomato plants (Monalbo and Mobaci), despite the positive DAS-ELISA, the absence of symptoms was observed also on these genotypes, although a pronounced symptoms (chlorotic mottling, leaf puckering and deformations) were noted in inoculated N. benthamiana plants.…”