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Papers by Tyler MacKenzie

Cyanobacteria acclimate to environmental inorganic carbon (Ci) concentrations through re-organisa... more Cyanobacteria acclimate to environmental inorganic carbon (Ci) concentrations through re-organisations of photosynthetic function and the induction of carbon concentrating mechanisms (CCMs), which alter and constrain their subsequent acclimation to changing light. We grew cells acclimated to high Ci (4 mM) or low Ci (0.02 mM), shifted them from 50 μmol m−2 s−1 to 500 μmol m−2 s−1, and quantified their photosynthetic performance in parallel with quantitation of allocations to key indicator macromolecules. Pigments cell−1 declined, PsbA (PS II), AtpB (ATP Synthase), RbcL (Rubisco) and GlnA (Glutamine Synthetase) increased, and PsaC (PS I) remained stable through the light shift. The increase in these protein pools was slower and smaller in low Ci cells, but acted in both cell types to re-normalise the electron fluxes through the catalytic complexes back toward values before the light shift (for PsbA and GlnA) or even below the initial flux per complex (for RbcL). In contrast, an incre...

Plant Disease

In-field management of potato virus Y (PVY) faces challenges by changing availability and environ... more In-field management of potato virus Y (PVY) faces challenges by changing availability and environmental acceptability of chemical agents to control aphid vectors of the virus, and by proliferation of PVY strains with different symptomology and rates of spread. Over 2018-2020, foliar spray treatments were compared in field experiments in New Brunswick, Canada, to measure effectiveness at reducing spread of PVYO, PVYN:O and PVYNTN strains. Mineral oil, insecticide, combined oil and insecticide spray and a biopesticide (i.e., LifeGard® WG) were compared. Insecticide-only and mineral oil-only were not effective, though several combined oil and insecticide, and biopesticide treatments significantly reduced PVY spread. The biopesticide was proportionately more effective with recombinant PVYN:O and PVYNTN strains, possibly from exciting the plant’s hypersensitive resistance response only caused naturally in cv. Goldrush by PVYO. Pesticide residue analysis showed that mineral oil enhanced t...

Emerging Trends in Plant Pathology

Journal of Economic Entomology

Plant Disease

Potato virus Y (PVY) exists as several strains with distinct symptomology and tuber yield effects... more Potato virus Y (PVY) exists as several strains with distinct symptomology and tuber yield effects in different potato varieties. Recently, new recombinant strains have proliferated and dominated local populations around the world. In this study, PVYO, PVYN:O, PVYN-Wi, and PVYNTN strains were tracked across Canada from 2014 to 2017, showing rapid evolution of populations away from the traditionally dominant PVYO to recombinants PVYN-Wi (western Canada) and PVYNTN (eastern Canada). Simultaneously, 30 potato varieties were inoculated with PVYO, PVYN:O, and PVYNTN in controlled greenhouse experiments. Foliar symptoms of primary (mechanical inoculation mimicking aphid infection) and secondary (tuber seedborne) infection were cataloged, and tuber yield measured. On average, and generally similar in primary and secondary infection, symptom expression and yield reduction were most severe with PVYO, followed by PVYN:O and PVYNTN. Strong mosaic symptoms were most commonly expressed with PVYO ...

American Journal of Potato Research

Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recent... more Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recently, populations of PVY strains have shifted dramatically toward recombinant strains such as PVYNTN and PVYN:O. A 2010 to 2016 survey of PVY strains in commercial fields of New Brunswick (NB), Canada, and five field trials tracking PVY spread in NB and Manitoba, were conducted to study the current status of PVY strains and their relative rates of spread. In NB, PVYO dropped from 82% of infections in 2010 to 14% in 2016, replaced mostly by PVYNTN (64%) and PVYN:O (22%).In field trials with Russet Burbank and Gold rush varieties, PVYNTN spread most effectively compared to PVYN:O and PVYO. Strain-specific PVY spread varied with the potato variety, possibly due to selective PVYO resistance in Goldrush, mostly expressed at the plant-to-plant transmission level with little difference in transduction to tubers in infected plants. Relevance of in-field differences in spread of strains to changes in regional PVY populations, and potential mechanisms responsible, are discussed.ResumenEl virus Y de la papa (PVY) es una causa importante de pérdida de rendimiento y calidad en los cultivos de papa en el mundo. Recientemente, las poblaciones de las variantes de PVY han girado dramáticamente hacia recombinantes, tales como el PVYNTN y PVYN:O. Se condujo un estudio de 2010 a 2016 de las variantes de PVY en campos comerciales de New Brunswick (NB), Canada, y cinco ensayos de campo, siguiendo la huella de la dispersión en NB y Manitoba, para estudiar el estatus actual de las variantes del PVY y sus niveles relativos de dispersión. En NB, PVYO bajó de 82% de infecciones en 2010 a 14% en 2016, reemplazado mayormente por PVYNTN (64%) y PVYN:O (22%). En ensayos de campo con las variedades Russet Burbank y Goldrush, el PVYNTN se dispersó más efectivamente comparado con PVYN:O y PVYO. La dispersión específica por variante varío con la variedad de papa, posiblemente debido a la resistencia selectiva al PVYO en Goldrush, mayormente expresada en el nivel de la transmisión de planta a planta, con poca diferencia en la transducción a tubérculos en plantas infectadas. Se discuten la relevancia de las diferencias en el campo en la dispersión de las variantes a cambios en las poblaciones regionales de PVY, y mecanismos potenciales responsables.

American Journal of Potato Research

American Journal of Potato Research

Archives of virology, 2017

The complete sequence of a strawberry vein banding virus (SVBV) isolate collected in Nova Scotia,... more The complete sequence of a strawberry vein banding virus (SVBV) isolate collected in Nova Scotia, Canada, and designated NS8, was determined. The 7,856-nucleotide circular double-stranded DNA genome contains seven open-reading frames (ORFs), which is consistent with other SVBV isolates and other members of the genus Caulimovirus. Comparison of NS8 with other whole-genome sequences retrieved from databases revealed that NS8 shares the highest sequence similarity (96.5% identity) with isolate China (accession number HE681085) and the lowest (88.3% identity) with clone pSVBV-E3 (accession number X97304). Despite the overall high sequence similarity between NS8 and China, the coat protein encoding ORF IV of NS8 shares only 90.9% sequence identity with the China isolate. Phylogenetic analysis at the complete-genome level placed NS8 and all Chinese isolates in one clade and clone pSVBV-E3 in a separate clade. Interestingly, phylogenetic analysis of all available ORF IV sequences, includin...

American Journal of Potato Research, 2016

In this study, on-farm within-season spread of Potato virus Y (PVY) was measured in 56 seed, proc... more In this study, on-farm within-season spread of Potato virus Y (PVY) was measured in 56 seed, processing and tablestock potato fields in New Brunswick, Canada between 2010 and 2014. These represented 13 potato varieties, managed by 16 growers employing a wide range of PVY control techniques. Many aspects of management techniques were quantified, as well local aphid abundances and climatological data. PVY spread, measured in leaves and tubers (by ELISA and RT-PCR), was tracked through the season in individually marked plants. Over the five seasons under study, on-farm PVY spread overall has declined substantially. Across all 56 fields, however, it has varied widely, from 10 fields not showing any spread during the crop season, up to as high as 76 % spread in one 2012 field. Factors correlated with increased PVY spread included seed-borne PVY inoculum planted in the field, aphid abundance early in the season, and to a lesser degree temperatures in July and over the preceding winter. Factors correlated with decreased spread included numbers of foliar mineral oil and insecticide sprays (especially of the lambda-cyhalothrin and flonicamid types), later crop planting and earlier first spraying dates. A mid-season leaf test for PVY was shown to be strongly indicative of ultimate PVY spread at harvest, and may prove a useful test in advising growers. A set of locally-relevant best management practices based on these results is discussed.ResumenEn este estudio, se midió la dispersión del virus Y de la papa (PVY) en el campo en el ciclo de cultivo, en 56 campos de semilla, de proceso y de mercado fresco, en New Brunswick, Canadá, entre el 2010 y el 2014. Esto representó 13 variedades de papa, manejadas por 16 productores, empleando una gran amplitud de técnicas de control del PVY. Se cuantificaron muchos aspectos de técnicas de manejo, así como la abundancia local de áfidos y datos climatológicos. La dispersión del PVY, medida en hojas y tubérculos (por ELISA y RT-PCR) se siguió a lo largo del ciclo en plantas marcadas individualmente. A lo largo de los cinco ciclos bajo estudio, la dispersión en general del PVY en el campo ha declinado substancialmente. No obstante, a través de los 56 campos, ha variado ampliamente, de 10 campos que no mostraron ninguna dispersión durante el ciclo de cultivo, hasta 76 % de dispersión en un campo en 2012. Los factores correlacionados con el incremento en la dispersión del PVY incluyeron el inóculo del PVY en la semilla sembrada en el campo, la abundancia de áfidos temprano en el ciclo, y a una menor temperatura en julio y durante el invierno anterior. Los factores correlacionados con una disminución en la dispersión incluyeron al número de aspersiones foliares de aceite mineral e insecticidas (especialmente del tipo lambda-cyhalothrina y flonicamida), plantaciones tardías, y fechas tempranas de la primera aspersión. Una prueba foliar a mitad del ciclo para PVY mostró ser fuertemente indicativa de dispersión ultima del PVY a la cosecha, y pudiera probar ser una prueba útil en advertir a los productores. Se discute un conjunto de las mejores prácticas locales relevantes de manejo basadas en estos resultados.

Canadian Journal of Plant Pathology, 2016

Plant Physiol, 2008

The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton p... more The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton photosynthesis. However, the marine environment imposes serious restraints to carbon fixation. First, the equilibrium between CO 2 and bicarbonate (HCO 3 2) is pH dependent, and, in normal, slightly alkaline seawater, [CO 2 ] is typically low (approximately 10 mM). Second, the rate of CO 2 diffusion in seawater is slow, so, for any cells unable to take up bicarbonate efficiently, photosynthesis could become carbon limited due to depletion of CO 2 from their immediate vicinity. This may be especially problematic for those dinoflagellates using a form II Rubisco because this form is less oxygen tolerant than the usually found form I enzyme. We have identified a carbonic anhydrase (CA) from the free-living marine dinoflagellate Lingulodinium polyedrum that appears to play a role in carbon acquisition. This CA shares 60% sequence identity with d-class CAs, isoforms so far found only in marine algae. Immunoelectron microscopy indicates that this enzyme is associated exclusively with the plasma membrane. Furthermore, this enzyme appears to be exposed to the external medium as determined by whole-cell CA assays and vectorial labeling of cell surface proteins with 125 I. The fixation of 14 CO 2 is strongly pH dependent, suggesting preferential uptake of CO 2 rather than HCO 3 2 , and photosynthetic rates decrease in the presence of 1 mM acetazolamide, a non-membranepermeable CA inhibitor. This constitutes the first CA identified in the dinoflagellates, and, taken together, our results suggest that this enzyme may help to increase CO 2 availability at the cell surface.

Methods in Molecular Biology

Potato virus Y (PVY) is a major threat to potato crops around the world. It is an RNA virus of th... more Potato virus Y (PVY) is a major threat to potato crops around the world. It is an RNA virus of the family Potyviridae, exhibiting many different strains that cause a range of symptoms in potato. ELISA detection of viral proteins has traditionally been used to quantify virus incidence in a crop or seed lot. ELISA, however, cannot reliably detect the virus directly in dormant tubers, requiring several weeks of sprouting tubers to produce detectable levels of virus. Nor can ELISA fully discriminate between the wide range of strains of the virus. Several techniques for directly detecting the viral RNA have been developed which allow rapid detection of PVY in leaf or tuber tissue, and that can be used to easily distinguish between different strains of the virus. Described in this chapter are several protocols for the extraction of RNA from leaf and tuber tissues, and three detection methods based upon reverse-transcription-PCR (RT-PCR). First described is a traditional two-step protocol ...

Plant Disease, 2014

The current-season spread of Potato virus Y (PVY) was monitored in 19 fields under various manage... more The current-season spread of Potato virus Y (PVY) was monitored in 19 fields under various management practices in New Brunswick, Canada, through the 2011 and 2012 growing seasons. The focus of this study was to evaluate the role of seedborne PVY inoculum, aphid vector abundance, and the numbers, timing, and types of insecticide and mineral oil sprays, and to confirm the reliability and forecasting capacity of midseason PVY testing. In each field, 100 to 110 virus-free plants were identified shortly after emergence and were assessed four times from early July to early September (after top-kill) with enzymelinked immunosorbent assay (ELISA) and reverse-transcription polymerase chain reaction (RT-PCR) to track PVY spread. In addition, tubers harvested during development in August and after top-kill were grown-out in the greenhouse for ELISA testing. PVY spread to selected virus-free plants varied widely, ranging from 0 to 76.2% across all studied fields. Of the 19 fields over two seasons, 10 fields were planted with no detectable seedborne PVY, and they showed 0 to 8.7% (mean 2.9%) PVY spread by harvest. The remaining nine study fields with 0.9 to 5.8% seedborne PVY showed 1 to 76.2% (mean 15.2%) PVY spread by harvest. PVY spread was detected in most fields during midseason testing with ELISA and RT-PCR; all tests correlated well with final PVY rates after top-kill, though RT-PCR detection in developing tubers was most sensitive and correlated. Logistic regression modeling was used to identify major factors in PVY spread, including seedborne PVY, early-season aphid abundance, and the numbers of insecticide and mineral oil sprays. The best-fitting model, constructed using these factors as well as a measurement of July PVY incidence (ELISA July), strongly explained PVY spread by harvest, with the most significant management factor being the number of mineral oil sprays supplemented with insecticide used during the growing season. A similar model fitted without the ELISA July did not adequately predict ultimate PVY spread. The analysis suggests that mineral oil alone was effective at lowering PVY spread, and more effective when combined with insecticide, particularly when used early in the season. No evidence was found for differences in PVY spread across the eight cultivars used or across the range of mineral oil application rates, whereas some evidence was found for differences in the effectiveness of different insecticide types. Materials and Methods Selection of fields, cultivar, and sample collection. Ten potato fields managed by different growers and separated widely across the potato-growing region of New Brunswick, Canada were selected for the study in the 2011 crop season. The fields consisted

Marine Biotechnology, 2005

Peridinin-containing dinoflagellates are a group of generally marine and photosynthetic protists ... more Peridinin-containing dinoflagellates are a group of generally marine and photosynthetic protists whose plastids display a number of unusual features. In particular, the plastid genome may be reduced to as few as a dozen genes, and it is not clear if all ...

Plant physiology, 2008

The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton p... more The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton photosynthesis. However, the marine environment imposes serious restraints to carbon fixation. First, the equilibrium between CO 2 and bicarbonate (HCO 3–) is pH ...

Plant, Cell & Environment, 2011

Circadian rhythms are the observed outputs of endogenous daily clocks and are thought to provide ... more Circadian rhythms are the observed outputs of endogenous daily clocks and are thought to provide a selective advantage to cells adapted to daily light/dark cycles. However, the biochemical links between the clock and the overt rhythms in cell physiology are generally not known. Here, we examine the circadian rhythm in O2 evolution by cultures of the dinoflagellate Lingulodinium, a rhythm previously ascribed to rhythmic electron flow through photosystem II. We find that O2 evolution rates increase when CO2 concentrations are increased, either following addition of DIC or a rapid decrease in culture pH. In medium containing only nitrate as an electron acceptor, O2 evolution rates mirror the circadian rhythm of nitrate reductase activity in the cells. Furthermore, competition between photosynthetic electron flow to carbon and to nitrate varies in its relative efficiency through the day-night cycle. We also find, using simultaneous and continuous monitoring of pH and O2 evolution rates over several days, that while culture pH is normally rhythmic, circadian changes in rates of O2 evolution depend not on the external pH but on levels of internal electron acceptors. We propose that the photosynthetic electron transport rhythm in Lingulodinium is driven by the availability of a reductant sink.

Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered dependi... more Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered depending on inorganic carbon (C i) availability. Under steady light of 50 lmol photons. m À 2. s À 1 , the growth rate of Synechococcus elongatus PCC7942 was similar in cells grown in high C i (4 mM) and low C i (0.02 mM), with induced carbon concentrating mechanisms compensating for low C i. Growth under fluctuating light of a 1-s period averaging 50 lmol photons. m À 2. s À 1 caused a drop in growth rate of 28% AE 6% in high C i cells and 38% AE 8% in low C i cells. In high C i cells under fluctuating light, the PSI/PSII ratio increased, the PSII absorption crosssection decreased, and the PSII turnover rate increased in a pattern similar to highlight acclimation. In low C i cells under fluctuating light, the PSI/ PSII ratio decreased, the PSII absorption cross-section decreased, and the PSII turnover remained slow. Electron transport rate was similar in high and low C i cells but in both was lower under fluctuating than under steady light. After acclimation to a 1-s period fluctuating light, electron transport rate decreased under steady or long-period fluctuating light. We hypothesize that high C i cells acclimated to exploit the bright phases of the fluctuating light, whereas low C i cells enlarged their PSII pool to integrate the fluctuating light and dampen the variation of the electron flux into a rate-restricted C i pool. Light response curves measured under steady light, widely used to predict photosynthetic rates, do not properly predict photosynthetic rates achieved under fluctuating light, and exploitation of fluctuating light is altered by C i status.

Cyanobacteria acclimate to environmental inorganic carbon (Ci) concentrations through re-organisa... more Cyanobacteria acclimate to environmental inorganic carbon (Ci) concentrations through re-organisations of photosynthetic function and the induction of carbon concentrating mechanisms (CCMs), which alter and constrain their subsequent acclimation to changing light. We grew cells acclimated to high Ci (4 mM) or low Ci (0.02 mM), shifted them from 50 μmol m−2 s−1 to 500 μmol m−2 s−1, and quantified their photosynthetic performance in parallel with quantitation of allocations to key indicator macromolecules. Pigments cell−1 declined, PsbA (PS II), AtpB (ATP Synthase), RbcL (Rubisco) and GlnA (Glutamine Synthetase) increased, and PsaC (PS I) remained stable through the light shift. The increase in these protein pools was slower and smaller in low Ci cells, but acted in both cell types to re-normalise the electron fluxes through the catalytic complexes back toward values before the light shift (for PsbA and GlnA) or even below the initial flux per complex (for RbcL). In contrast, an incre...

Plant Disease

In-field management of potato virus Y (PVY) faces challenges by changing availability and environ... more In-field management of potato virus Y (PVY) faces challenges by changing availability and environmental acceptability of chemical agents to control aphid vectors of the virus, and by proliferation of PVY strains with different symptomology and rates of spread. Over 2018-2020, foliar spray treatments were compared in field experiments in New Brunswick, Canada, to measure effectiveness at reducing spread of PVYO, PVYN:O and PVYNTN strains. Mineral oil, insecticide, combined oil and insecticide spray and a biopesticide (i.e., LifeGard® WG) were compared. Insecticide-only and mineral oil-only were not effective, though several combined oil and insecticide, and biopesticide treatments significantly reduced PVY spread. The biopesticide was proportionately more effective with recombinant PVYN:O and PVYNTN strains, possibly from exciting the plant’s hypersensitive resistance response only caused naturally in cv. Goldrush by PVYO. Pesticide residue analysis showed that mineral oil enhanced t...

Emerging Trends in Plant Pathology

Journal of Economic Entomology

Plant Disease

Potato virus Y (PVY) exists as several strains with distinct symptomology and tuber yield effects... more Potato virus Y (PVY) exists as several strains with distinct symptomology and tuber yield effects in different potato varieties. Recently, new recombinant strains have proliferated and dominated local populations around the world. In this study, PVYO, PVYN:O, PVYN-Wi, and PVYNTN strains were tracked across Canada from 2014 to 2017, showing rapid evolution of populations away from the traditionally dominant PVYO to recombinants PVYN-Wi (western Canada) and PVYNTN (eastern Canada). Simultaneously, 30 potato varieties were inoculated with PVYO, PVYN:O, and PVYNTN in controlled greenhouse experiments. Foliar symptoms of primary (mechanical inoculation mimicking aphid infection) and secondary (tuber seedborne) infection were cataloged, and tuber yield measured. On average, and generally similar in primary and secondary infection, symptom expression and yield reduction were most severe with PVYO, followed by PVYN:O and PVYNTN. Strong mosaic symptoms were most commonly expressed with PVYO ...

American Journal of Potato Research

Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recent... more Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recently, populations of PVY strains have shifted dramatically toward recombinant strains such as PVYNTN and PVYN:O. A 2010 to 2016 survey of PVY strains in commercial fields of New Brunswick (NB), Canada, and five field trials tracking PVY spread in NB and Manitoba, were conducted to study the current status of PVY strains and their relative rates of spread. In NB, PVYO dropped from 82% of infections in 2010 to 14% in 2016, replaced mostly by PVYNTN (64%) and PVYN:O (22%).In field trials with Russet Burbank and Gold rush varieties, PVYNTN spread most effectively compared to PVYN:O and PVYO. Strain-specific PVY spread varied with the potato variety, possibly due to selective PVYO resistance in Goldrush, mostly expressed at the plant-to-plant transmission level with little difference in transduction to tubers in infected plants. Relevance of in-field differences in spread of strains to changes in regional PVY populations, and potential mechanisms responsible, are discussed.ResumenEl virus Y de la papa (PVY) es una causa importante de pérdida de rendimiento y calidad en los cultivos de papa en el mundo. Recientemente, las poblaciones de las variantes de PVY han girado dramáticamente hacia recombinantes, tales como el PVYNTN y PVYN:O. Se condujo un estudio de 2010 a 2016 de las variantes de PVY en campos comerciales de New Brunswick (NB), Canada, y cinco ensayos de campo, siguiendo la huella de la dispersión en NB y Manitoba, para estudiar el estatus actual de las variantes del PVY y sus niveles relativos de dispersión. En NB, PVYO bajó de 82% de infecciones en 2010 a 14% en 2016, reemplazado mayormente por PVYNTN (64%) y PVYN:O (22%). En ensayos de campo con las variedades Russet Burbank y Goldrush, el PVYNTN se dispersó más efectivamente comparado con PVYN:O y PVYO. La dispersión específica por variante varío con la variedad de papa, posiblemente debido a la resistencia selectiva al PVYO en Goldrush, mayormente expresada en el nivel de la transmisión de planta a planta, con poca diferencia en la transducción a tubérculos en plantas infectadas. Se discuten la relevancia de las diferencias en el campo en la dispersión de las variantes a cambios en las poblaciones regionales de PVY, y mecanismos potenciales responsables.

American Journal of Potato Research

American Journal of Potato Research

Archives of virology, 2017

The complete sequence of a strawberry vein banding virus (SVBV) isolate collected in Nova Scotia,... more The complete sequence of a strawberry vein banding virus (SVBV) isolate collected in Nova Scotia, Canada, and designated NS8, was determined. The 7,856-nucleotide circular double-stranded DNA genome contains seven open-reading frames (ORFs), which is consistent with other SVBV isolates and other members of the genus Caulimovirus. Comparison of NS8 with other whole-genome sequences retrieved from databases revealed that NS8 shares the highest sequence similarity (96.5% identity) with isolate China (accession number HE681085) and the lowest (88.3% identity) with clone pSVBV-E3 (accession number X97304). Despite the overall high sequence similarity between NS8 and China, the coat protein encoding ORF IV of NS8 shares only 90.9% sequence identity with the China isolate. Phylogenetic analysis at the complete-genome level placed NS8 and all Chinese isolates in one clade and clone pSVBV-E3 in a separate clade. Interestingly, phylogenetic analysis of all available ORF IV sequences, includin...

American Journal of Potato Research, 2016

In this study, on-farm within-season spread of Potato virus Y (PVY) was measured in 56 seed, proc... more In this study, on-farm within-season spread of Potato virus Y (PVY) was measured in 56 seed, processing and tablestock potato fields in New Brunswick, Canada between 2010 and 2014. These represented 13 potato varieties, managed by 16 growers employing a wide range of PVY control techniques. Many aspects of management techniques were quantified, as well local aphid abundances and climatological data. PVY spread, measured in leaves and tubers (by ELISA and RT-PCR), was tracked through the season in individually marked plants. Over the five seasons under study, on-farm PVY spread overall has declined substantially. Across all 56 fields, however, it has varied widely, from 10 fields not showing any spread during the crop season, up to as high as 76 % spread in one 2012 field. Factors correlated with increased PVY spread included seed-borne PVY inoculum planted in the field, aphid abundance early in the season, and to a lesser degree temperatures in July and over the preceding winter. Factors correlated with decreased spread included numbers of foliar mineral oil and insecticide sprays (especially of the lambda-cyhalothrin and flonicamid types), later crop planting and earlier first spraying dates. A mid-season leaf test for PVY was shown to be strongly indicative of ultimate PVY spread at harvest, and may prove a useful test in advising growers. A set of locally-relevant best management practices based on these results is discussed.ResumenEn este estudio, se midió la dispersión del virus Y de la papa (PVY) en el campo en el ciclo de cultivo, en 56 campos de semilla, de proceso y de mercado fresco, en New Brunswick, Canadá, entre el 2010 y el 2014. Esto representó 13 variedades de papa, manejadas por 16 productores, empleando una gran amplitud de técnicas de control del PVY. Se cuantificaron muchos aspectos de técnicas de manejo, así como la abundancia local de áfidos y datos climatológicos. La dispersión del PVY, medida en hojas y tubérculos (por ELISA y RT-PCR) se siguió a lo largo del ciclo en plantas marcadas individualmente. A lo largo de los cinco ciclos bajo estudio, la dispersión en general del PVY en el campo ha declinado substancialmente. No obstante, a través de los 56 campos, ha variado ampliamente, de 10 campos que no mostraron ninguna dispersión durante el ciclo de cultivo, hasta 76 % de dispersión en un campo en 2012. Los factores correlacionados con el incremento en la dispersión del PVY incluyeron el inóculo del PVY en la semilla sembrada en el campo, la abundancia de áfidos temprano en el ciclo, y a una menor temperatura en julio y durante el invierno anterior. Los factores correlacionados con una disminución en la dispersión incluyeron al número de aspersiones foliares de aceite mineral e insecticidas (especialmente del tipo lambda-cyhalothrina y flonicamida), plantaciones tardías, y fechas tempranas de la primera aspersión. Una prueba foliar a mitad del ciclo para PVY mostró ser fuertemente indicativa de dispersión ultima del PVY a la cosecha, y pudiera probar ser una prueba útil en advertir a los productores. Se discute un conjunto de las mejores prácticas locales relevantes de manejo basadas en estos resultados.

Canadian Journal of Plant Pathology, 2016

Plant Physiol, 2008

The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton p... more The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton photosynthesis. However, the marine environment imposes serious restraints to carbon fixation. First, the equilibrium between CO 2 and bicarbonate (HCO 3 2) is pH dependent, and, in normal, slightly alkaline seawater, [CO 2 ] is typically low (approximately 10 mM). Second, the rate of CO 2 diffusion in seawater is slow, so, for any cells unable to take up bicarbonate efficiently, photosynthesis could become carbon limited due to depletion of CO 2 from their immediate vicinity. This may be especially problematic for those dinoflagellates using a form II Rubisco because this form is less oxygen tolerant than the usually found form I enzyme. We have identified a carbonic anhydrase (CA) from the free-living marine dinoflagellate Lingulodinium polyedrum that appears to play a role in carbon acquisition. This CA shares 60% sequence identity with d-class CAs, isoforms so far found only in marine algae. Immunoelectron microscopy indicates that this enzyme is associated exclusively with the plasma membrane. Furthermore, this enzyme appears to be exposed to the external medium as determined by whole-cell CA assays and vectorial labeling of cell surface proteins with 125 I. The fixation of 14 CO 2 is strongly pH dependent, suggesting preferential uptake of CO 2 rather than HCO 3 2 , and photosynthetic rates decrease in the presence of 1 mM acetazolamide, a non-membranepermeable CA inhibitor. This constitutes the first CA identified in the dinoflagellates, and, taken together, our results suggest that this enzyme may help to increase CO 2 availability at the cell surface.

Methods in Molecular Biology

Potato virus Y (PVY) is a major threat to potato crops around the world. It is an RNA virus of th... more Potato virus Y (PVY) is a major threat to potato crops around the world. It is an RNA virus of the family Potyviridae, exhibiting many different strains that cause a range of symptoms in potato. ELISA detection of viral proteins has traditionally been used to quantify virus incidence in a crop or seed lot. ELISA, however, cannot reliably detect the virus directly in dormant tubers, requiring several weeks of sprouting tubers to produce detectable levels of virus. Nor can ELISA fully discriminate between the wide range of strains of the virus. Several techniques for directly detecting the viral RNA have been developed which allow rapid detection of PVY in leaf or tuber tissue, and that can be used to easily distinguish between different strains of the virus. Described in this chapter are several protocols for the extraction of RNA from leaf and tuber tissues, and three detection methods based upon reverse-transcription-PCR (RT-PCR). First described is a traditional two-step protocol ...

Plant Disease, 2014

The current-season spread of Potato virus Y (PVY) was monitored in 19 fields under various manage... more The current-season spread of Potato virus Y (PVY) was monitored in 19 fields under various management practices in New Brunswick, Canada, through the 2011 and 2012 growing seasons. The focus of this study was to evaluate the role of seedborne PVY inoculum, aphid vector abundance, and the numbers, timing, and types of insecticide and mineral oil sprays, and to confirm the reliability and forecasting capacity of midseason PVY testing. In each field, 100 to 110 virus-free plants were identified shortly after emergence and were assessed four times from early July to early September (after top-kill) with enzymelinked immunosorbent assay (ELISA) and reverse-transcription polymerase chain reaction (RT-PCR) to track PVY spread. In addition, tubers harvested during development in August and after top-kill were grown-out in the greenhouse for ELISA testing. PVY spread to selected virus-free plants varied widely, ranging from 0 to 76.2% across all studied fields. Of the 19 fields over two seasons, 10 fields were planted with no detectable seedborne PVY, and they showed 0 to 8.7% (mean 2.9%) PVY spread by harvest. The remaining nine study fields with 0.9 to 5.8% seedborne PVY showed 1 to 76.2% (mean 15.2%) PVY spread by harvest. PVY spread was detected in most fields during midseason testing with ELISA and RT-PCR; all tests correlated well with final PVY rates after top-kill, though RT-PCR detection in developing tubers was most sensitive and correlated. Logistic regression modeling was used to identify major factors in PVY spread, including seedborne PVY, early-season aphid abundance, and the numbers of insecticide and mineral oil sprays. The best-fitting model, constructed using these factors as well as a measurement of July PVY incidence (ELISA July), strongly explained PVY spread by harvest, with the most significant management factor being the number of mineral oil sprays supplemented with insecticide used during the growing season. A similar model fitted without the ELISA July did not adequately predict ultimate PVY spread. The analysis suggests that mineral oil alone was effective at lowering PVY spread, and more effective when combined with insecticide, particularly when used early in the season. No evidence was found for differences in PVY spread across the eight cultivars used or across the range of mineral oil application rates, whereas some evidence was found for differences in the effectiveness of different insecticide types. Materials and Methods Selection of fields, cultivar, and sample collection. Ten potato fields managed by different growers and separated widely across the potato-growing region of New Brunswick, Canada were selected for the study in the 2011 crop season. The fields consisted

Marine Biotechnology, 2005

Peridinin-containing dinoflagellates are a group of generally marine and photosynthetic protists ... more Peridinin-containing dinoflagellates are a group of generally marine and photosynthetic protists whose plastids display a number of unusual features. In particular, the plastid genome may be reduced to as few as a dozen genes, and it is not clear if all ...

Plant physiology, 2008

The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton p... more The oceans globally constitute an important sink for carbon dioxide (CO 2) due to phytoplankton photosynthesis. However, the marine environment imposes serious restraints to carbon fixation. First, the equilibrium between CO 2 and bicarbonate (HCO 3–) is pH ...

Plant, Cell & Environment, 2011

Circadian rhythms are the observed outputs of endogenous daily clocks and are thought to provide ... more Circadian rhythms are the observed outputs of endogenous daily clocks and are thought to provide a selective advantage to cells adapted to daily light/dark cycles. However, the biochemical links between the clock and the overt rhythms in cell physiology are generally not known. Here, we examine the circadian rhythm in O2 evolution by cultures of the dinoflagellate Lingulodinium, a rhythm previously ascribed to rhythmic electron flow through photosystem II. We find that O2 evolution rates increase when CO2 concentrations are increased, either following addition of DIC or a rapid decrease in culture pH. In medium containing only nitrate as an electron acceptor, O2 evolution rates mirror the circadian rhythm of nitrate reductase activity in the cells. Furthermore, competition between photosynthetic electron flow to carbon and to nitrate varies in its relative efficiency through the day-night cycle. We also find, using simultaneous and continuous monitoring of pH and O2 evolution rates over several days, that while culture pH is normally rhythmic, circadian changes in rates of O2 evolution depend not on the external pH but on levels of internal electron acceptors. We propose that the photosynthetic electron transport rhythm in Lingulodinium is driven by the availability of a reductant sink.

Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered dependi... more Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered depending on inorganic carbon (C i) availability. Under steady light of 50 lmol photons. m À 2. s À 1 , the growth rate of Synechococcus elongatus PCC7942 was similar in cells grown in high C i (4 mM) and low C i (0.02 mM), with induced carbon concentrating mechanisms compensating for low C i. Growth under fluctuating light of a 1-s period averaging 50 lmol photons. m À 2. s À 1 caused a drop in growth rate of 28% AE 6% in high C i cells and 38% AE 8% in low C i cells. In high C i cells under fluctuating light, the PSI/PSII ratio increased, the PSII absorption crosssection decreased, and the PSII turnover rate increased in a pattern similar to highlight acclimation. In low C i cells under fluctuating light, the PSI/ PSII ratio decreased, the PSII absorption cross-section decreased, and the PSII turnover remained slow. Electron transport rate was similar in high and low C i cells but in both was lower under fluctuating than under steady light. After acclimation to a 1-s period fluctuating light, electron transport rate decreased under steady or long-period fluctuating light. We hypothesize that high C i cells acclimated to exploit the bright phases of the fluctuating light, whereas low C i cells enlarged their PSII pool to integrate the fluctuating light and dampen the variation of the electron flux into a rate-restricted C i pool. Light response curves measured under steady light, widely used to predict photosynthetic rates, do not properly predict photosynthetic rates achieved under fluctuating light, and exploitation of fluctuating light is altered by C i status.