R. D. Peters

Variation in aggressiveness of Canadian isolates of Phytophthora infestans as indicated by their relative abilities to cause potato tuber rot

Studies were conducted in 1995, 1996, and 1997 to determine the ability of Canadian isolates of Phytophthora infestans to cause tuber disease in a variety of potato cultivars. Most isolates of recently introduced multilocus genotypes (US-7, US-8, g11, g26, g29, and g40) were more aggressive on tuber tissue than isolates of the traditional US-1 genotype, based on surface necrosis (SN), lesion depth (LD), and compound aggressiveness index (CAI = SN × LD) components. Other multilocus genotypes (g30, g41, g42, and UN-3) were similar in aggressiveness to US-1. The g11 (US-11) genotype consistently displayed aggressiveness that was intermediate to that of the US-8 and US-1 genotypes. Variation also occurred within a multilocus genotype, and an isolate of the US-8 genotype from New Brunswick was consistently less aggressive than other US-8 isolates. Cvs. Dorita and Island Sunshine were consistently the most resistant to infection, regardless of isolate, relative to the more susceptible responses of Green Mountain, Russet Bur-bank, Kennebec, Superior, Shepody, Red Pontiac, Sebago, and Bintje. Even so, isolates of the newly introduced US-8 genotype were able to cause significantly more disease on these resistant cultivars than isolates of the US-1 genotype. The predominant genotypes currently found in potato production areas in Canada (US-8 and g11) have higher fitness on tuber tissue than displaced, preexisting strains (US-1).

Characterization of changes in populations of Phytophthora infestans in Canada using mating type and metalaxyl sensitivity markers

Isolates of Phytophthora infestans were obtained from individual fields of potato and tomato and from potato storages across Canada in 1994 (142 samples yielding 555 isolates), 1995 (185 samples yielding 914 isolates), and 1996 (300 samples yielding 1013 isolates). Characterization of these isolates according to mating type and sensitivity to metalaxyl revealed the changing nature of P. infestans populations in Canada. In 1994, isolates of the traditional Al, metalaxyl-sensitive (MS) phenotype were common, but by 1996, they were no longer recovered from any tissue samples. Isolates of the A2 mating type, which were predominantly insensitive to metalaxyl (MI), were prevalent in 1996, except in British Columbia (B.C.). In B.C., Al isolates highly insensitive to metalaxyl predominated. Isolates of the Al, MI phenotype were also found in a sample of tomatoes from Ontario in 1996. New populations composed of the A2 mating type were predominantly insensitive to metalaxyl, but they showed an intermediate respons...

Proteomics analysis suggests broad functional changes in potato leaves triggered by phosphites and a complex indirect mode of action against Phytophthora infestans

UNLABELLED Phosphite (salts of phosphorous acid; Phi)-based fungicides are increasingly used in controlling oomycete pathogens, such as the late blight agent Phytophthora infestans. In plants, low amounts of Phi induce pathogen resistance through an indirect mode of action. We used iTRAQ-based quantitative proteomics to investigate the effects of phosphite on potato plants before and after infection with P. infestans. Ninety-three (62 up-regulated and 31 down-regulated) differentially regulated proteins, from a total of 1172 reproducibly identified proteins, were identified in the leaf proteome of Phi-treated potato plants. Four days post-inoculation with P. infestans, 16 of the 31 down-regulated proteins remained down-regulated and 42 of the 62 up-regulated proteins remained up-regulated, including 90% of the defense proteins. This group includes pathogenesis-related, stress-responsive, and detoxification-related proteins. Callose deposition and ultrastructural analyses of leaf tissues after infection were used to complement the proteomics approach. This study represents the first comprehensive proteomics analysis of the indirect mode of action of Phi, demonstrating broad effects on plant defense and plant metabolism. The proteomics data and the microscopy study suggest that Phi triggers a hypersensitive response that is responsible for induced resistance of potato leaves against P. infestans. BIOLOGICAL SIGNIFICANCE Phosphie triggers complex functional changes in potato leaves that are responsible for the induced resistance against Phytophthora infestans. This article is part of a Special Issue entitled: Translational Plant Proteomics.

Changes in mating types, resistance to metalaxyl, and Gpi-allozyme genotypes of Phytophthora infestans in Canadian provinces from 1996 to 1998.

Variations within Phytophthora infestans populations in Canada, in terms of mating type, metalaxyl resistance, and glucose-6-phosphate isomerase allozyme genotypes, are presented for the period 1996-1998. During 1996, only the A2 mating type was found in most Canadian provinces. However, both Al and A2 mating types were found in Ontario and British Columbia (BC). In 1997, samples of late blight-infected plants were received from five provinces only. The A2 mating type was isolated from samples from Prince Edward Island, New Brunswick, and Quebec (QC), while both Al and A2 mating type isolates were found in BC and Manitoba. In 1998, late blight was confirmed in all provinces, and all samples were of the A2 mating type, except those from BC and QC, which had both mating types. Changes in levels of metalaxyl-sensitive (MS), metalaxyl-intermediate (MI), and metalaxyl-resistant (MR) strains of P. infestans in Canada were also observed. Within the A2 mating type, the frequency of MS isolates increased in most provinces, except in BC, where this rate is decreasing. For the Al mating type, there is an increase in MR individuals that have been displacing the MI strains from 1996 to 1998. A high variability was recorded either among Canadian provinces or from year to year inside each province in terms of mating types, Gpi-allozyme genotypes, and especially metalaxyl response. In general, during 1996-1998, samples from four Canadian provinces have included both Al and A2 mating types. In addition, beside US-8 and US-11, isolates with characteristics of US-7. US-10, and US-14 were found during 1998, with different levels of resistance to metalaxyl.

Genetic Composition of Phytophthora infestans in Canada Reveals Migration and Increased Diversity

A dramatic increase in the incidence of late blight and changes within populations of Phytophthora infestans have been observed in various regions of Canada. In this study, the occurrence of several new genotypes of the pathogen was documented with associated phenotypes that dominated pathogen populations. Genotype US-23, previously detected only among isolates from the United States, dominated in the western Canadian provinces of British Columbia, Alberta (AB), Saskatchewan, and Manitoba (MB). Although isolates of US-23 infect both potato and tomato, these isolates were the only genotype recovered from commercial garden centers in Canada. Isolates of genotype US-8, previously dominant throughout Canada, represented the only genotype detected from the eastern Canadian provinces of New Brunswick and Prince Edward Island. Isolates of other genotypes detected in Canada included US-11 in AB, US-24 in MB, and US-22 in Ontario (ON). An additional genotype was detected in ON which appears to be a derivative of US-22 that may have arisen through sexual reproduction. However, evidence of clonal reproduction dominated among the isolates collected, and opportunities for sexual reproduction were probably limited because of a surprising geographic separation of the A1 and A2 mating types in Canada. Sensitivity of the US-22, US-23, and US-24 isolates to the fungicide metalaxyl, movement of potato seed and transplants, and weather conditions may have contributed to reduced opportunities for contact between the mating types in fields in Canada. All P. infestans isolates were readily distinguished from other related oomycetes with RG57 restriction fragment length polymorphism analysis. Long-distance movement in seed tubers and garden center transplants may have contributed to the rapid spread of the P. infestans genotypes across Canada. Tracking pathogen movement and population composition should improve the ability to predict the genotypes expected each year in different regions of Canada.

Use of allozyme markers to determine genotypes of Phytophthora infestansin Canada

A comparison of allozyme banding patterns at two loci, for glucose-6-phosphate isomerase (Gpi) and peptidase (Pep), with markers for mating type, metalaxyl sensitivity, and cultural morphology revealed eight distinct genotypes among 726 isolates of Phytophthora infestans collected in Canada between 1994 and 1996. Banding patterns for allozymes of the Gpi locus alone proved to be adequate for distinguishing seven of the genotypes. Five of these genotypes (US-l, US-6, US-7, US-8, and gll (or US-ll)) were comparable to genotypes described in the United States. The US-l genotype (Al mating type, metalaxyl-sensitive) was recovered commonly (41% frequency) throughout Canada (outside the province of British Columbia) during 1994. By 1996, the US-l genotype was no longer recovered from any samples of potato or tomato tissue taken from across Canada. The US-8 genotype (A2 mating type, metalaxyl-insensitive) dominated populations of the pathogen in Ontario, Quebec, and New Brunswick during 1994 and by 1996, the US-...

Relationships between pathotypes and RAPDs, Gpi-allozyme patterns, mating types, and resistance to metalaxyl ofPhytophthora infestans in Canada in 1997

Relationships between pathotypes and other markers such as mating types, metalaxyl resistance, Gpi-allozyme and random amplified polymorphic DNA (RAPD) patterns, were investigated among 33 isolates ofPhytophthora infestans obtained from both potato and tomato across Canada in 1997. Pathogenicity testings, based on virulence against potato differentials carrying single-resistance genes and the size of lesions on leaves, revealed higher pathogenic diversity in 1997 than in the few past years, with more pathotypes and more race-complex isolates. A higher pathogenic diversity was observed within A2 (US-8) than within A1 (US-11) isolates. There was no correlation between the level of resistance to metalaxyl of an isolate and its pathogenicity. Nevertheless, when grouped into metalaxyl-sensitive (MS), -intermediate (MI), and -resistant (MR) classes, both average pathotype complexity and average lesion size were lowest for MS group. RAPD data revealed a good distinction between A1 (US-11) and A2 (US-8) mating type groups, and between isolates from British Columbia and those from other provinces. The detection in the last few years of both A1 and A2 mating types in Canada and the occurrence in 1997 of some isolates sharing different characteristics of both of these two groups suggest that sexual reproduction may have occurred locally.ResumenSe investigaron las relaciones entre patotipos y otros mart-adores, como tipos de apareamiento, resistencia al metalaxil, alozima Gpi y patrones de polimorfismo en el ADN amplificado aleatoriamente (RAPD), entre 33 cultivos aislados dePhytophthora infestans obtenidos de cruces de papa y tomate en Canada en 1997. Las pruebas de patogenicidad, basadas en la virulencia contra diferenciales de papa portadoras de genes simples de resistencia y el tamaño de la lesión en las hojas, revelaron una mayor diversidad patógena en 1997 que en los años previos recientes, con aislamiento de mayor cantidad de patotipos y cepas complejas. En A2 (US-8) se observó una mayor diversidad patógena que en Al (US-11). No hubo correlación entre el nivel de resistencia a metalaxil de un cultivo aislado y su patogenicidad. No obstante, cuando se agrupó por clases, de acuerdo a sensibilidad al metalaxil (SM), -intermedia (MI) y -resistente (MR), tanto el promedio de complejidad del patotipo como el tamaño promedio de la lesión fueron menores para el grupo SM. Los datos del RAPD revelaron una gran diferencia entre los grupos de apareamiento A1 (US-11) y A2 (US-8) y entre los cultivos aislados en British Columbia con los de otras provincias. La detección en años recientes de los tipos de apareamiento A1 y A2 en Canadá y la ocurrencia en 1997 de algunos aislados que comparten características diferentes de ambos grupos, sugieren que la reproducción sexual podría haber ocurrido localmente.

Impact of seed potatoes infected withPhytophthora infestans (US-1 or US-8 genotypes) on crop growth and disease risk

As the surface area with late blight symptoms of seed tubers increased, the incidence of plant emergence decreased. This relationship was more dramatic with the US-8 genotype than the US-1 genotype ofhytophthora infestans, causal agent of late blight. However, when seed tubers were inoculated with both US-1 and US-8 isolates, the plant growth responses were generally intermediate to those obtained with the two genotypes alone. More resistant cultivars (eg. Dorita, Island Sunshine, and Sebago) had greater plant emergence and less seed rot than more susceptible cultivars (eg. Green Mountain and Shepody) but the response differences between resistant and susceptible cultivars was less clear with US-8 as most cultivars had 100% seed rot. Seed handling treatments affected crop growth and disease risk; as the inoculum levels and in some cases, the pre-planting storage period increased, plant emergence decreased generally due to greater seed rot incidences. Of the one registered seed treatment fungicide and several non-registered and/or experimental fungicides tested, only two significantly improved plant emergence.During three years of study, “diseased” seed treatments generally led to seed rot except in 1996 when one plant in one experimental plot of infected seed had subsequent spread of the disease to the foliage. Furthermore, within one week, a field epidemic developed outwardly from the single infected plant due to the occurrence of favourable weather conditions. Further research opportunities are discussed relative to the impact of infected seed on crop growth and disease risk

Characterization of Phytophthora infestans population diversity in Canada reveals increased migration and genotype recombination

Abstract Late blight, caused by Phytophthora infestans, is a devastating disease of potatoes and tomatoes that causes significant crop losses worldwide. Late blight diversity has been increasing since 2009 in many areas of Canada on both potatoes and tomatoes. Although the US-8 genotype of P. infestans has dominated pathogen populations in much of Canada for the past 15 years, novel genotypes have emerged in recent years. A comprehensive survey of late blight samples collected across Canada in 2011 indicated that although the US-8 genotype of P. infestans still dominated pathogen populations in Prince Edward Island, new US-23 and US-24 genotypes had become established in other parts of Canada. The US-11 and US-22 genotypes dominated populations of the pathogen from specific areas of Alberta and Ontario, respectively. Clonal propagation and migration contributed to long-distance transport of P. infestans genotypes and in some situations, both A1 and A2 mating types of the pathogen were found in the same production region. This finding is of concern because it increases the potential for sexual recombination within pathogen populations, leading to the production of oospores that can survive in the absence of host tissue and create new strains of P. infestans. Evidence for recombination in the P. infestans population was detected in Ontario on tomato. Segregation of Gpi allozymes and mating type appeared to occur independently of the RG57 loci, producing several new P. infestans genotypes. Prediction and management of late blight will need to be evaluated and modified to accommodate these new potentially aggressive P. infestans genotypes.

Protein profiling in potato (Solanum tuberosum L.) leaf tissues by differential centrifugation.

Foliar diseases, such as late blight, result in serious threats to potato production. As such, potato leaf tissue becomes an important substrate to study biological processes, such as plant defense responses to infection. Nonetheless, the potato leaf proteome remains poorly characterized. Here, we report protein profiling of potato leaf tissues using a modified differential centrifugation approach to separate the leaf tissues into cell wall and cytoplasmic fractions. This method helps to increase the number of identified proteins, including targeted putative cell wall proteins. The method allowed for the identification of 1484 nonredundant potato leaf proteins, of which 364 and 447 were reproducibly identified proteins in the cell wall and cytoplasmic fractions, respectively. Reproducibly identified proteins corresponded to over 70% of proteins identified in each replicate. A diverse range of proteins was identified based on their theoretical pI values, molecular masses, functional classification, and biological processes. Such a protein extraction method is effective for the establishment of a highly qualified proteome profile.