Maritimes Regional Meeting, 2011/Réunion régionale des Maritimes, 2011

Efficacy of selected fungicides, plant by-products, and soil amendments against powdery scab of potatoes. K. I. AL-MUGHRABI, K. JAYASURIYA AND R. POIRIER. Potato Development Centre, New Brunswick Department of Agriculture, Aquaculture and Fisheries, 39 Barker Lane, Wicklow, NB E7L 3S4, Canada

Powdery scab, caused by Spongospora subterranea (Wallr.) Lagerh. f. sp. subterranea Tominson, is a challenge in almost all potato growing regions in the world which leads to significant reduction in marketable yield. Powdery scab lesions on tubers downgrade quality of seed, fresh or processing potatoes. Two field trials were conducted in 2010 and 2011 in a powdery scab infested potato field in New Denmark, New Brunswick, Canada to assess the efficacy of various products. Disease-free ‘CalWhite’ seed potatoes were used in 2010 and treatments included: [1] Control; [2] fluazinam (25 g/100 kg seed); [3] fluazinam (50 g/100 kg seed); [4] fludioxonil (2.5 g/100 kg seed); [5] mancozeb (40 g/100 kg seed); [6] fluazinam (2 kg ha⁻¹; in-furrow); [7] fluazinam (4 kg ha⁻¹; in-furrow); [8] mancozeb (7.5 kg ha⁻¹; in-furrow); [9] mancozeb (15 kg ha⁻¹; in-furrow); [10] cyazofamid (1.86 kg ha⁻¹; in-furrow); [11] sulfur (168 kg ha⁻¹; soil); [12] boron (2.8 kg ha⁻¹; soil); [13] ammonium nitrate (168 kg ha⁻¹; soil); and [14] mustard meal (1064 kg ha⁻¹; soil). Treatments had no significant effect on plant emergence or vigor. Fluazinam (1× and 2×), mancozeb (1×) or cyazofamid applied in-furrow significantly reduced disease incidence and severity and increased marketable yield by 22.1%, 26.5%, 41.6% and 30.5%, respectively. Boron soil amendment significantly reduced the disease incidence by 66.9% and increased marketable yield by 23.9%. The trial was repeated in the same field in 2011 using disease-free seed of two potato cultivars (‘CalWhite’ and ‘Red Lasoda’) and the following treatments: [1] Control; [2] fluazinam (25 g/100 kg seed); [3] mancozeb (40 g/100 kg seed); [4] fluazinam (2 kg ha⁻¹; in-furrow); [5] mancozeb (7.5 kg ha⁻¹; in-furrow); [6] cyazofamid (1.86 kg ha⁻¹; in-furrow); [7] sulfur (168 kg ha⁻¹; soil); [8] boron (2.8 kg ha⁻¹; soil); and [9] mustard meal (1064 kg ha⁻¹; soil). For ‘CalWhite’, fluazinam applied at 2 kg ha⁻¹, mancozeb at 7.5 kg ha⁻¹, and cyazofamid at 1.86 kg ha⁻¹ significantly reduced powdery scab incidence and increased marketable yield by 75.5%, 57.0%, and 65.9%, respectively. For ‘Red Lasoda’, in-furrow treatment with fluazinam or mancozeb significantly reduced disease incidence and increased marketable yield by 109% and 150%, respectively. In-furrow application of cyazofamid significantly increased marketable yield by 86.5% due to significant reduction in disease severity. Addition of boron significantly suppressed the disease in both cultivars and increased marketable yield. The results of this 2-year study suggest that in-furrow application of fluazinam, mancozeb or cyazofamid in S. subterranean-infested fields can significantly suppress powdery scab incidence and increase marketable yield. Soil amendment with boron can be a potential alternative for fungicides.

Late blight fungicide Confine^TM triggers broad changes in gene expression in potatoes. T. BORZA, G. SIMPSON, R. PETERS, Z. GANGA AND G. WANG-PRUSKI. Department of Plant and Animal Sciences, Nova Scotia Agricultural College, 50 Pictou Road, Truro, NS B2N 5E3, Canada; (R.P.) Crops and Livestock Research Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada; and (Z.G.) Cavendish Farms, New Annan, PE C1N 4J9, Canada

Phosphites represent a class of reduced-risk fungicides that are effective in suppressing the development of late blight [Phytophthora infestans (Mont.) de Bary], a major disease of cultivated potato (Solanum tuberosum). The toxic effect of phosphites to P. infestans is well-documented; however, it is not clear if phosphites suppress P. infestans development directly or indirectly, by activating specific plant defence mechanisms. In order to further investigate the molecular mechanisms by which phosphites enhance the resistance of potatoes to P. infestans infection, the expression pattern of 15 potato genes involved in carbohydrate metabolism, energy production and plant defence mechanisms was analysed using quantitative RT-PCR. The experiment employed Confine^TM, a mono- and di-potassium salt formulation of phosphorous acid (Winfield Solutions, LLC, St. Paul, MN). Leaf samples of Confine-treated (sprayed with 1% Confine) and untreated (control) potato plants were collected 30 min, 2 h, 6 h, 24 h and 48 h and 10 days after the treatment. Quantitative RT-PCR analyses indicated that most of the genes analysed were up-regulated upon Confine treatment and the strongest induction was generally evident at 24 h after treatment. Ten days after Confine treatment, the expression level of almost all genes analysed regressed to the pre-treatment levels. Ten days after the Confine treatment, untreated and treated plants were inoculated with P. infestans at the rate of 10⁵ sporangia/plant and the severity of disease was monitored during a 4-week period. Four weeks after the inoculation, the percentage of foliar infection in untreated plants was >95% while in Confine-treated plants it was <20%.

Prediction of Potato virus Y incidence in post-harvest tubers based on pre-harvest tuber tests using real-time RT-PCR. M. S. FAGERIA, M. SINGH, U. NANAYAKKARA, Y. PELLETIER AND X. NIE. Agricultural Certification Services, 245 Hilton Road, Unit 25, Fredericton, NB E3B 5N6, Canada; and (U.N., Y.P., X.N.) Potato Research Centre, Agriculture and Agri-Food Canada, 850 Lincoln Road, P.O. Box 20280, Fredericton, NB E3B 4Z7, Canada

Potato virus Y (PVY) incidence was compared in pre- and post-harvest tuber testing in 11 potato fields in New Brunswick with cultivars ‘Adirondack Red’, ‘Calwhite’, ‘Goldrush’, ‘Innovator’, ‘Russet Burbank’ and ‘Shepody’ during 2009 and 2010. One hundred randomly selected plants from each field were tested for PVY using real-time RT-PCR. Pre-harvest tubers were tested for PVY in week of August 17^th and post-harvest tubers at the end of the growing season (week of September 6^th). In all the fields, the PVY incidence was higher in post-harvest tubers than pre-harvest tubers. The PVY incidence in pre-harvest tubers ranged from 1% (‘Innovator’ field no. 1) to 21% (‘Shepody’ field no. 2) in 2009 and 2% (‘Adirondack Red’) to 30% (‘Goldrush’ field no. 2) in 2010. However, in post-harvest tubers conducted the week of September 6^th PVY incidence ranged from 2% (‘Adirondack Red’) to 37% (‘Shepody’ field no. 1) in 2009 and 5% (‘Calwhite’ field no. 1) to 39% (‘Goldrush’ field no. 2) in 2010. In all the fields, the post-harvest tuber tests showed higher PVY incidence than pre-harvest tuber tests. However, there was a high correlation (r) between pre- and post-harvest tuber tests, i.e., 0.839, and 0.802 in 2009 and 2010, respectively. This data suggests that on the basis of pre-harvest tuber testing, decisions can be made about whether to use top-kill where the virus threshold is required for post-harvest testing. For instance, if a field shows 3% PVY incidence at the time of pre-harvest tuber testing means this field may not show PVY incidence < 3% at the time of post-harvest testing. The pre-harvest test can be conducted 20–30 days before the final harvesting of tubers.

Detection of Ralstonia solanacearum race 3 biovar 2 in potato. X. LI, J. NIE AND S. H. DE BOER. Canadian Food Inspection Agency, Charlottetown Laboratory, 93 Mount Edward Road, Charlottetown, PE C1A 5T1, Canada

Introduction of the potato brown rot pathogen, Ralstonia solanacearum (Smith) Yabuuchi et al. biovar 2 (race 3), is considered to be a major threat to the potato industries in temperate regions like Canada and the USA. Numerous methods have been developed for detection of this pathogen, some of which have been used in combination as routine methods in post-entry quarantine testing programs. However, the detection limit for each of the methods is largely unknown but is required information to design the most economic and effective methods and protocols for detection of the bacterium. In this study, we evaluated the sensitivity and specificity of nine protocols for assaying the presence of R. solanacearum biovar 2 (race 3) strains. The Bio-Taqman assay with internal control had several advantages over other protocols, and detected three R. solanacearum biovar 2 (race 3) strains pre-inoculated into potato sap samples at a sensitivity of 10² CFU/mL. The assay did not cross-react with other biovar strains tested. The negative effect of PCR inhibitors was eliminated in this assay. The serological assays tested, ELISA and immuno-lateral flow devices (immuno-LFD), were highly efficient for confirming the identity of R. solanacearum strains to species level, but could not be used to differentiate R. solanacearum biovar 2 (race 3) from biovars 1 and 3. The detection sensitivity of serological assays, determined using five R. solanacearum strains spiked potato sap samples, was 10⁴-10⁶ CFU/mL. The best strategy for monitoring the presence of R. solanacearum biovar 2 (race 3) was a combination of molecular and serological tests.

White mold, caused by Sclerotinia sclerotiorum - an emerging disease in potato production in Prince Edward Island. R. D. PETERS, K. A. DRAKE, A. MACPHAIL AND C. J. BANKS. Crops and Livestock Research Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada

The fungus Sclerotinia sclerotiorum (Lib.) de Bary is a pathogen of over 400 different plant species. In potato (Solanum tuberosum L.), the pathogen infects senescing leaves or blossoms via ascospores dispersed by wind and rain. Infected blossoms lodge in the canopy and initiate stem lesions which can girdle the stem leading to plant wilting and premature senescence. In some parts of North America, particularly potato production regions using high fertility and irrigation, white mold can cause significant yield losses. However, in Canada, the incidence of white mold in potato is sporadic and the disease is rarely targeted for management by growers. In 2011, a very wet summer contributed to a high incidence of white mold in potatoes grown for tablestock in eastern Prince Edward Island. In some cultivars, up to 90% of the stems in certain fields were infected and harboured the black sclerotia of the fungus observed when stems were cracked open to reveal the pith. Affected fields senesced earlier than healthy fields resulting in reduced tuber yields. Two applications of fluazinam, one at 90% crop flowering and a second 1–2 weeks later, significantly reduced stem infection by 50–60%. More research is needed on the impact of white mold on potato production in Canada and potential disease control alternatives.

Late blight suppression in Confine^TM treated potatoes achieved by fungicide's translocation to leaves and tubers - growth chamber and field experiments. G. WANG-PRUSKI, T. BORZA, A. SCHOFIELD, M. HICKEY, J. RAND, Z. GANGA, R. PETERS, J. COFFIN AND R. COFFIN. Department of Plant and Animal Sciences, Nova Scotia Agricultural College, 50 Pictou Road, Truro, NS B2N 5E3, Canada; (J.R.) Ivan Curry School of Engineering, Acadia University, Wolfville, NS B4P 2R2, Canada; (Z.G.) Cavendish Farms, New Annan, PE C1N 4J9, Canada; (R.P.) Crops and Livestock Research Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada; and (J.C., R.C.) Privar Farms, 909 Eliot River Road North Wiltshire, PE C0A 1Y0, Canada

The suppressing effects of phosphite-based fungicides on a variety of pathogens, including the oomycetes Phytophthora infestans (Mont.) de Bary (late blight causing agent) and Phytophthora erythroseptica Pethybr. (pink rot causing agent), are well documented. However, less is known about essential aspects such as the rate of phosphite translocation, the optimum concentration in plants necessary to obtain maximum protection against pathogens, and the timing of applications. In order to address some of these questions, we investigated the suppressing effects of the phosphite-based fungicide Confine^TM on potato late blight disease. Field and growth chamber experiments followed by phosphite analysis by ion chromatography demonstrated that Confine^TM is readily translocated when applied as a foliar spray; and detectable amounts of phosphite accumulated in both leaves and tubers. Whole plant infection and detached leaf experiments indicated a strong positive correlation between the build-up of phosphite by plants and increased resistance to late blight infection. The amount of phosphite translocated into tubers during the growth season had no negative influence on seed germination and overall plant growth. Tubers originating from plants treated with Confine^TM showed less susceptibility to late blight infection; however, the additional postharvest treatment on tubers when being placed into storage may still be necessary to maximize the resistance to late blight.

Interception of potato pests in imported microplants at the Canadian Food Inspection Agency Potato Post Entry Quarantine program during the past 10 years. H. XU. Canadian Food Inspection Agency, Charlottetown Laboratory, 93 Mount Edward Road, Charlottetown, PE C1A 5T1, Canada

Small quantities of Solanum germplasm can be introduced into Canada, as tissue culture microplants and tubers for vegetative propagation. Potato germplasm approved for entry under an import permit must be subjected to a process of quarantine testing in the Potato Post Entry Quarantine (PPEQ) program at the Charlottetown Laboratory of the Canadian Food Inspection Agency. Over the past 10 years (2000–2010), 328 accessions of potato germplasm were imported and tested under the PPEQ program. Approximately 80% of the accessions were imported from only five countries, the Netherlands (51.22%), United Kindom (15.24%), Chile (6.7%), France (4.88%) and South Korea (3.05%) and the other 20% of the accessions were from 10 other countries. Over 85% of the imported potato germplasm accessions were from eight European countries. The entire quarantine testing scheme for this program consists of three testing streams, pre-greenhouse testing of microplants, testing mother plants grown out in the greenhouse, and pre-release testing of microplants. The complete process of quarantine testing takes over 6 months. In the past 10 years, 33 of the 328 applications (10.1%) were rejected due to the detection of potato pests during quarantine testing. Of the 33 rejected import applications, 60% and 30% were due to the detection of bacteria and viruses, respectively. Fungi and Potato spindle tuber viroid were also detected in some accessions. Most of the viruses detected were characterized and identified and many of them are regulated or quarantine pests listed in Canada. The interception of these harmful or destructive pathogens of potatoes by the PPEQ program prevented the introduction of foreign potato pests into Canada.