Potato virus Y (PVY O and PVY N:O) impact on potato cultivars and management through oil sprays

Project Code : BPI06-320

Project Lead

Debbie McLaren - Agriculture and Agri-Food Canada.

Objective

To determine the impact of potato virus Y (PVY O and PVY N:O) on potato yield and quality under Manitoba environmental conditions and to assess oil sprays for PVY management in commonly grown potato cultivars.

Summary of Results

Background

Potato virus Y (PVY) is of worldwide concern for potato producers. This important disease can reduce potato yields significantly, and even a low incidence of PVY can cause rejection of seed lots for certification. PVY is transmitted from infected to healthy plants by aphids. PVY virus particles reside on the mouthparts of aphids, a mode of transmission called non-persistent. As the virus is passed quickly from plant to plant, insecticides do not act rapidly enough to reduce transmission.

Several strains of PVY exist, and a recombinant (PVYN:O) was identified in Manitoba, North Dakota, Minnesota and Montana seed potato tubers. Little was known about the impact on yield of seedborne infection levels of PVYN:O compared with the common strain PVYO. In addition, a reduced risk product to control the spread of PVY and more information on the new strain were needed.

Approach

Research was undertaken from 2006 to 2008 to evaluate, under Manitoba environmental conditions, the potential of mineral oils, which are used in the United States and Europe, for reducing the incidence of this disease on potato cultivars. Mineral oils are an attractive option as they can reduce toxicity to both humans and the environment, can be applied with existing spray equipment and potentially reduce costs to the grower. The mineral oil, Superior 70 Oil, supplied by the Canadian company N.M. Bartlett Inc., was used in these studies. In addition, studies on PVYO and PVYN:O were carried out to compare the effects of these PVY strains on tuber quality and yield.

The project was originally planned as a two-year study but due to unforeseen circumstances, the project was extended for a third year. In year 1, virus-free plantlets of Russet Burbank and Shepody were mechanically inoculated with PVYO and a second group of plantlets with PVYN:O. This inoculation work was conducted at AAFC's Potato Research Centre in Fredericton, New Brunswick, Canada. The inoculated plantlets were planted in the field and tubers from the mature plants were collected in the fall of 2006 for the 2007 field study. A field experiment (Trial 1) was established in 2006 at the Canada-Manitoba Crop Diversification Centre (CMCDC), Carberry, MB to evaluate mineral oil sprays for PVY management in Russet Burbank. Eight plots were established, four of which sprayed with mineral oil.

The following year (2007) two trials were established in Manitoba. In Trial 2, the treatments were a factorial combination of +/- oil applications and five tuber infection levels (0, 10%, 25%, 50% and 75% infected tubers). PVY-infected tubers were obtained from the 2006 field trial. Forty plots were established with mineral oil sprays imposed on 20 plots. Trial 3 was established to increase PVY-infected tubers (PVYO and PVYN:O) in the field. Because of the limited number of tubers available, there were two plots of Russet Burbank with PVYN:O and one plot each of Shepody with PVYN:O and Shepody with PVYO.

Three trials were established in 2008. Trial 4 involved assessing five tuber infection levels (0, 10%, 25%, 50% and 75% infected tubers) for impact on PVY spread and yield. Trial 5, on management of PVY with oil sprays, included an untreated control, three rates of oil application and two treatments of different chemical applications (to reflect grower practices). Trial 6 was established at Brandon, MB to compare tuber yield and quality of potato plants (Russet Burbank and Shepody) grown from seed infected with PVY (PVYO or PVYN:O). Data collection for all field trials included disease assessment, tuber yield (excluding the 2006 trial), and tuber assessment for virus infection using RT-PCR.

Results

A reduction of PVY spread was evident with the application of Superior 70 Oil. In 2006, PVY spread was reduced in three of four replicates of the study. In 2007, spread of PVY was also reduced with the application of oil. The 2008 study included an assessment of three rates of Superior 70 Oil and the lowest incidences of PVY were observed with oil applied at the intermediate rate.

A concern with oil application is the possible development of phytotoxicity. A phytotoxic effect of oil application was observed in 2007, and developed after the application of oil at 2L/acre during very warm weather. However, there appeared to be little impact on Russet Burbank as yields in the control treatment were 15.3 and 15.0 metric tonnes/acre, with no oil and oil application, respectively.

Plot tuber yield decreased as PVY infection percentage of seed tubers increased. Yield was reduced by an average of 13% across all PVY infection levels in 2007. Yield losses were observed with both strains of PVY compared to plants grown from virus-free seed. The number of tubers per plant and average individual tuber weight were less from PVY-infected plants than from healthy plants. By reducing tuber size, PVY can reduce the total yield of a crop. Seedborne PVYO infections in Shepody had lower plant yield and smaller tubers than seedborne PVYN:O infections in Shepody (2008). Similar results were observed with Russet Burbank in 2008. However in the previous year, seedborne PVYN:O infections in Shepody had lower plant yield than seedborne PVYO infections in Shepody, but tuber size was similar. When this study was repeated in 2009, greater reductions in average yield per plant were observed with PVYO than with PVYN:O for both Russet Burbank and Shepody.

In October 2010, a regulatory data package including data generated during this project, which ended in 2009, was submitted to the Pest Management Regulatory Agency of Health Canada for the addition of management of aphid-borne viruses in potato production to the Superior 70 oil label. In April 2011, the label expansion for the use of Bartlett Superior 70 mineral oil to reduce the spread of PVY vectored by
aphids in potato was approved.

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