Identification of Potato virus Y Strains Associated with Tuber Damage During a Recent Virus Outbreak in Potato in Idaho

Abstract

Potato virus Y (PVY) causes substantial losses in potato production by decreasing yields and affecting the quality of potato tubers. Management of PVY in potato is dependent primarily on potato seed certification programs to prevent or limit initial levels of virus inoculum. Prior to 1990, the ordinary strain of PVY (PVYO) was the predominant virus in North America. PVYO induces clear foliar symptoms in many potato cultivars, allowing successful management in seed potato through a combination of visual inspections and limited laboratory testing. In recent years, necrotic strains of PVY (PVYN, PVYNTN, and PVYN:O) have begun to spread in the United States, many of which induce mild symptoms in potato, making them more difficult to manage through visual inspections. In addition to reducing yield, necrotic isolates may also cause external and internal damage in tubers of susceptible cultivars, which is known as potato tuber necrotic ringspot disease (PTNRD). Tuber necrotic strains of PVY have been reported across the northern United States (1,2,4), although limited information is available on their incidence and spread in commercial potato production. During June and July of 2007, 38 random samples were collected from three different commercial fields displaying disease problems (cvs. Russet Ranger, Alturas, and Russet Burbank) in the vicinity of Idaho Falls, ID. Plants collected showed various degrees of mosaic and leaf yellowing. By using double-antibody sandwich (DAS)-ELISA and reverse transcription (RT)-PCR, 25 of these plants were identified as PVY positive. The mutiplex RT-PCR assay (3) confirmed that nine plants were infected with PVYNTN and 11 with PVYN:O. No RT-PCR products were amplified from five samples. During September and October of 2007, 25 tuber samples (cv. Russet Burbank) showing various degrees of unusual internal symptoms (e.g., brown spots) were collected near Idaho Falls, ID. Twenty-two tubers were found PVY positive by DAS-ELISA, and multiplex RT-PCR determined 13 of those were PVYNTN, three were PVYO, one was a PVYNTN/N:O mixture, and one was a PVYO/N:O mixture. No RT-PCR products were amplified from four samples. In October 2007, six tubers showing distinct external tuber damage characteristic of PTNRD (cv. Highland Russet) were collected near Twin Falls, ID. All six tubers were determined to be PVY positive by DAS-ELISA, and RT-PCR identified five as infected with PVYNTN and one with PVYN:O. All the mixtures were easily separated by inoculating tobacco plants followed by subsequent testing of individual plants. Asymptomatic tubers from the same lot not showing PTNRD damage were found PVY negative by DAS-ELISA and RT-PCR. All PVYNTN isolates collected during 2007 were inoculated into tobacco plants (Nicotiana tabacum L. cv. Xanthi) and confirmed to induce systemic vein necrosis. Limited sequencing of four of the PVYNTN isolates determined that they contained recombinant junctions 2 and 3, identifying them as being related to the European strain of PVYNTN (3). The data suggest an increase in distribution and incidence of necrotic strains of PVY in commercial, potato-production areas in Idaho during an outbreak in 2007 and the potential for an increase in PTNRD. References: (1) P. M. Baldauf et al. Plant Dis. 90:559, 2006. (2) J. M. Crosslin et al. Plant Dis. 90:1102, 2006. (3) J. H. Lorenzen et al. Plant Dis. 90:935, 2006. (4) L. M. Piche et al. Phytopathology 94:1368, 2004.

Genetic Diversity of the Ordinary Strain of Potato virus Y (PVY) and Origin of Recombinant PVY Strains

“…In Europe, the non-recombinant PVY strains PVY O and PVY N have all but disappeared, replaced by recombinant strains PVY NTN and PVY N-Wi (3,17). However, in the United States and Canada, PVY O remains the predominant strain infecting potato, and PVY N is rare, although recombinant strains are increasing in incidence and distribution (1,10,14,24). In New Zealand, contrary to the situation in Europe and even in North America, recombinant PVY strains have not been identified and only the PVY O and PVY N strains were found in potato (8).…”

Comparative analysis of virus-specific small RNA profiles of three biologically distinct strains of Potato virus Y in infected potato (Solanum tuberosum) cv. Russet Burbank

“…Isolates from the PVY-N strain group induce systemic veinal necrosis in tobacco, whereas potato cultivars carrying Nc or Ny genes do not show systemic veinal necrosis due to PVY-N infection. Production of different kinds of disease symptoms indicates that different PVY strains interact differently in different potato cultivars (Karasev et al, 2008;Singh et al, 2008).…”

Serological Properties of Ordinary and Necrotic Isolates of Potato virus Y: A Case Study of PVYN Misidentification

“…The necrotic strains were until recently on the list of quarantine pests for the North American Plant Protection Organization (NAPPO) countries (Canada, Mexico, and U.S.) (Anonymous 2003) and detection often resulted in regulatory actions and suspension of cross-border trade. Numerous reports of necrotic strains present in field grown potatoes (Baldauf et al 2006;Crosslin et al 2006;Crosslin et al 2005;Karasev et al 2008;Lorenzen et al 2006a;Nie and Singh 2003;Nie et al 2004;Piche et al 2004;Xu 2008;Xu et al 2005) and the adoption of a US-Canada Binational Tuber Necrotic Virus Management Plan in 2006 has resulted in the removal of necrotic strains of PVY from the quarantine list. Currently the entire PVY complex is managed primarily by seed certification standards.…”