First Report of Potato Virus H on Solanum muricatum in China

Solanum muricatum, commonly known as pepino, pepino dulce, or tree melon, is a perennial shrub well known for its attractive, sweet, flavorful fruits and is frequently cultivated as an annual. It has gained increasing popularity in China and is grown as a cash crop in many provinces. S. muricatum belongs to the family Solanaceae and is closely related to tomato, eggplant, and potato. In 2012, during a study of serological relationships between PVH and PVM on potatoes, potato virus H (PVH) was detected serendipitously in symptomless pepino plantlets in Beijing, grown from tissue culture stocks. PVH is a recently discovered carlavirus reported from potato plants from Huhhot, Inner Mongolia Autonomous Region. Since then, it was found on potatoes in Yunnan, Hebei, Liaoning, Heilongjiang, and Xinjiang provinces. PVH induces mild symptoms with a slight leaf curl in systemic leaves, but most often it is almost symptomless or latent on potatoes (2). To confirm the presence of PVH on S. muricatum, surveys were conducted in 2012 and 2013 in Gansu, Yunnan, and Guangxi provinces and Beijing. Fruits and leaves were collected randomly from pepino plants displaying no obvious symptoms. For PVH detection, a combination of RT-PCR, genome sequencing and serological assays were used. RNAs extracted from fruits and leaves were amplified using RT-PCR with primer pairs PVHCPF and PVHCPR (2), and extracted samples were probed by Western blotting with the specific polyclonal antiserum against PVH (2). Among the 50 plants randomly collected, fruits and leaves of nine plants tested positive for PVH. Subsequently, an RT-PCR product of the expected size (2.6 kb) encompassing the triple-gene block, the capsid protein gene, and the cysteine-rich protein gene, was amplified with a specific primer pair (PVHB1F 5′-TGATGGAATTTACAAAAAC-3′ and PVHUR 5′-CTTATGCGCATCTATCAATC-3′), and then cloned into pMD19-T (TaKaRa, Dalian, China) and sequenced (PVH-Pepino with GenBank Accession No. KF546312). Further sequence comparison showed that PVH-Pepino shared 91 to 98% nucleotide sequence identity in the genes mentioned above with those of the reported potato isolates PVH-Ho and PVH-YN (HM584819 and JQ904630, respectively). PVH-Pepino shared deduced amino acid identity of 98 to 99% in CP gene with PVH-Ho and PVH-YN, respectively, but only shared 57 to 67% amino acid identities with other reported carlaviruses (1,2). Thus, latent infection of PVH on S. muricatum was confirmed. To our knowledge, this is the first report of S. muricatum as a natural host of PVH. Our results suggest that PVH, as a new member of the genus Carlavirus, has a wider host range than originally expected. Potatoes and pepinos are crops widely grown in China. The fact that no symptoms were expressed by PVH in pepino plants (symptomless carrier) and only mild symptoms expressed by PVH in diseased potatoes makes detection and remediation of this disease more difficult. Although this finding does not show that PVH is economically important to pepino, this cannot be excluded in the presence of other viruses (2). References: (1) A. King et al. Page 881 in: Virus Taxonomy, Ninth Report of the International Committee on Taxonomy of Viruses. Elsevier Academic Press, London, 2011. (2) Y. Y. Li et al. PLOS ONE 8(6):e69255, 2013.