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Nie X.,Agriculture and Agri Food Canada | Singh M.,Agricultural Certification Services
Canadian Journal of Plant Pathology | Year: 2013

Post-harvest screening of potato 'Kennebec' revealed a Potato virus Y (PVY) incidence of 15.8%, a rate that is unusually high for a cultivar possessing a high level of field resistance to the virus. Randomly selected tubers were planted in a field plot and the resulting plants were monitored. Approximately 16% of plants developed symptoms ranging from mild mosaic symptoms to severe necrosis/rugosity/stunting. ELISA and RT-PCR analysis revealed that infections with Potato virus S (PVS), Potato virus X (PVX) and PVY, mostly in mixed-infections, occurred commonly in 14 sampled plants. Two strains, namely the common strain (PVY°) and the recombinant tuber necrotic strain (PVY NTN) were identified in the PVY-positive plants. In general, mild mosaic was associated with infections with PVX and PVS; intermediated mosaic was associated with PVS and PVYNTN infections; whereas severe leaf deformation/necrosis/drop symptoms were associated with PVYNTN and PVX co-infections, or with PVY° and either PVS or PVX co-infections. Virus-free plantlets of potato 'Kennebec' were mechanically inoculated with PVX, PVY°, and PVYNTN alone or with PVX+PVY° or PVX+PVY NTN combinations in the greenhouse. Single infections with PVY° or mixed-infections with PVX+PVY° or PVX+PVYNTN incited severe mosaic symptoms and systemic necrosis soon after inoculation; whereas single infections with PVX and PVYNTN induced mild to intermediate mosaic symptoms only. The most severe symptoms occurred in the mixed-inoculation with PVX+PVYNTN, demonstrating dramatic synergism between these strains. Similarly, profound PVX and PVYNTN synergism was also found in tobacco and Physalis floridana plants, suggesting that the strain of PVY plays an important role in the level of synergistic reactions between PVX and PVY on host plants. © 2013 The contribution of Xianzhou Nie.

Nie X.,Agriculture and Agri Food Canada | Singh M.,Agricultural Certification Services | Pelletier Y.,Agriculture and Agri Food Canada | McLaren D.,Agriculture and Agri Food Canada
American Journal of Potato Research | Year: 2013

Significant progress has been made in recent years in understanding pathological, serological and molecular properties of various strains of PVY and the aphid-mediated transmission. PVYO and PVYN appear to be the basic strain groups. Through genome recombination between these two groups, progeny groups whose genome possess one (e. g., PVYN:O or PVYN-Wi) to three (e. g., recombinant PVYNTN or European-PVYNTN) recombinant joints of PVYO and PVYN emerged. PVYN:O causes PVYN-like veinal necrosis in tobacco, but reacts to PVYO-specific antibody. PVYNTN causes potato tuber necrotic ringspot diseases in sensitive potato cultivars, and PVYN-like necrosis in tobacco plants, and reacts to PVYN-specific antibody. Through single nucleotide mutation(s), non-recombinant PVYNTN (or North American PVYNTN) also emerged from PVYN. It is also noteworthy that PVYN isolates originated from North America and Europe may have evolved separately; and to date most recombinant strains appear to be progenies of Eu-PVYN and PVYO. Several RT-PCR-based methodologies have been developed to characterize and detect various strains of PVY. A field survey revealed that PVYN:O has become a predominant strain in Manitoba and neighbouring states in USA. Moreover, three distinct variant groups inciting severe, intermediate and mild veinal/petiole/stem necrosis, respectively, on tobacco plants were observed within the PVYN:O isolates collected in Manitoba. Pathological and molecular diversity within PVYO strain group were revealed in New Brunswick, represented by PVYO-FL as a severe variant and by PVYO-RB as a mild variant. Studies on the transmission of PVY by various species of aphids revealed that aphid behavior plays an important role in the vector-mediated transmission. Application of mineral oil on the growing crop, especially in combination with use of crop borders, reduces aphid-mediated PVY transmission. Based on recent PVY research studies, Bartlett Superior 70 Oil was approved in 2011 for application to potato crops in Canada. © 2012 Potato Association of America.

Li X.-Q.,Agriculture and Agri Food Canada | Sveshnikov D.,BioAtlantech | Zebarth B.J.,Agriculture and Agri Food Canada | Tai H.,Agriculture and Agri Food Canada | And 4 more authors.
American Journal of Potato Research | Year: 2010

In-season chemical or optical measures of crop N status can be effective tools in optimizing potato fertilizer N management. The feasibility of using a gene expression as an alternative approach for early detection of potato nitrate deficiency was examined using three potato cultivars (Shepody, Russet Norkotah, and Red Pontiac) with abundant (7.5 mM NO 3), limited (0.75 mM NO 3) or deficient (0 mM NO 3) nitrate supply in nutrient culture over a 7 d period. RNA was extracted from the last fully expanded leaf and quantified using realtime RT-qPCR. Reduced nitrate supply had no measurable effect on shoot dry weight or leaf chlorophyll concentration, but decreased petiole nitrate concentration. Under deficit nitrate supply, down-regulation of nitrate reductase and nitrite reductase was measured within 3 days for all cultivars, and down-regulation of asparagine synthetase was measured in two cultivars. Nitrate supply had no effect on expression of ammonium transporter. In this experimental system, plant gene expression markers detected a reduction of nitrate supply prior to measureable reductions in plant growth or in N status measured using common chemical or optical methods. © Potato Association of America 2009.

Liang Z.,Agriculture and Agri Food Canada | Liang Z.,Hunan Agricultural University | Dickison V.,Agriculture and Agri Food Canada | Singh M.,Agricultural Certification Services | And 2 more authors.
European Journal of Plant Pathology | Year: 2015

Potato virus Y (PVY) undergoes continuous nucleotide mutation and genome recombination, leading to novel strains with varying pathogenicity on host plants. Little is known about how tomato plants respond to infections with different PVY strains, especially the emerging strains such as PVYNTN and PVYN:O, and in combination with other viral species such as Potato virus X (PVX). In this study, the response of tomato (cultivar Rutgers) plants to single and mixed infections with PVY and PVX was investigated. Plants infected singly with PVYO, PVYN:O, PVYN or PVYNTN developed mosaic symptoms and leaf deformation; whereas plants infected with PVX developed mild local lesion and varying degrees of mosaic and leaf deformation symptoms. Mixed PVX+PVY infections induced more severe symptoms, which include severe local and systemic leaf necrosis, leaf drop and severe leaf deformation, compared to single infections with PVX or PVY, indicating PVX-PVY synergism. The level of PVX-PVY synergism was affected significantly by PVY strains, with PVYNTN being the greatest effector. Quantitative analysis of viral titre indicated that mixed PVX+PVY infections elevated PVX level and reduced PVY level. A comparative transcriptional analysis of 46 key genes involved in signal molecule synthesis and signal transduction using NanoString technology revealed diverse gene expression profiles in both single and mixed infections. Two hierarchical expression clusters, one up-regulated and the other down-regulated, were observed during the infections. In general, mixed infections led to more genes being differentially regulated than single infections. The expression alteration of genes involved in oxidative stress and salicylic acid (SA)-pathways is particularly noteworthy, as the mixed infections, especially PVX+PVYNTN infections, led to a further elevation of reactive oxygen species (ROS) and SA producing abilities and a reduction of ROS scavenging ability over single infections. © 2015 UK Crown

Nanayakkara U.N.,Agriculture and Agri Food Canada | Singh M.,Agricultural Certification Services | Pelletier Y.,Agriculture and Agri Food Canada | Nie X.,Agriculture and Agri Food Canada
American Journal of Potato Research | Year: 2012

The strain diversity and variant population of Potato virus Y (PVY) was investigated in potato lots with high PVY incidence in 2009 in New Brunswick, Canada, using reverse transcription (RT)-PCR, enzyme-linked immunosorbent assay (ELISA) and biological assays. Twenty lots with PVY infection rates < 3% were chosen following post-harvest testing for further investigation. Assays using multiplex RT-PCR revealed the existence of the common (PVY O), the recombinant N:O (PVY N:O) and the recombinant (European) potato tuber necrosis (Eu-PVY NTN) strains. PVY O was the predominant strain while PVY N:O and Eu-PVY NTN were widespread in these potato lots. PVY N:O and Eu-PVY NTN, either present alone or mixed with PVY O, were found in 19 and 13 of the 20 lots, respectively. Neither the tobacco veinal necrosis strain (PVY N) nor the non-recombinant (North American) PVY NTN was detected in the potatoes. Among the PVY O strain group, PVY O-Oz/-FL variant type was the predominant followed by the uncharacterized PVY O and the PVY O-139/-RB types. Biological assays of representative PVY positive-samples using tobacco and Yukon Gold were consistent with the findings of RT-PCR and serological assays. © 2012 Potato Association of America.

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