scholarly journals Sensitivity of North American Isolates of Phytophthora erythroseptica and Pythium ultimum to Mefenoxam (Metalaxyl)

Plant Disease ◽  
2002 ◽  
Vol 86 (7) ◽  
pp. 797-802 ◽  
Author(s):  
R. J. Taylor ◽  
B. Salas ◽  
G. A. Secor ◽  
V. Rivera ◽  
N. C. Gudmestad
Keyword(s):  
Pythium Ultimum ◽  
Effective Management ◽  
Potato Tubers ◽  
Pink Rot ◽  
Phytophthora Erythroseptica ◽  
Disease Management Strategy ◽  
Potato Tuber Rot ◽  
Canadian Provinces ◽  
Production Areas ◽  
First Time

A 4-year study (1997 to 2000) was conducted to determine the sensitivities of the potato tuber rot pathogens, Phytophthora erythroseptica and Pythium ultimum, to mefenoxam (metalaxyl). A total of 2,277 tubers showing symptoms of “water rot” were collected from 16 states and 2 Canadian provinces. From these, 849 isolates of P. erythroseptica and 213 isolates of P. ultimum were obtained, and 805 and 190 isolates, respectively, were tested for their ability to grow on V8 medium amended at 0.01 to 100 μg/ml with fungicide. Isolates ranged widely in their responses to mefenoxam. The presence of resistant isolates (EC50 > 100 μg ml-1) of P. erythroseptica in the potato producing areas of Maine was confirmed. The presence of P. erythroseptica isolates in Idaho and Minnesota resistant to mefenoxam is reported for the first time. The proportion of P. erythroseptica isolates resistant to mefenoxam varied from 2.9 to 36.2% between 1997 and 2000. The proportion of resistant P. ultimum isolates represented only a small proportion of the isolates tested (3.7%). A single resistant P. ultimum isolate was recovered from Washington, whereas most of the resistant isolates obtained (5 of 7) were collected in Minnesota during the final year of the study. This is the first report of resistance in P. ultimum pathogenic to potato tubers. These observations suggest that pink rot and leak could become significant problems in the future, particularly in those areas where resistance has been detected. Our results have implications for the effective management of water rot. Monitoring the sensitivity of the pathogen population to mefenoxam in all production areas should be considered and integrated as a part of the overall disease management strategy.

scholarly journals Differences in Etiology Affect Mefenoxam Efficacy and the Control of Pink Rot and Leak Tuber Diseases of Potato

Plant Disease ◽  
2004 ◽  
Vol 88 (3) ◽  
pp. 301-307 ◽  
Author(s):  
Raymond J. Taylor ◽  
Bacilio Salas ◽  
Neil C. Gudmestad
Keyword(s):  
Foliar Application ◽  
Potato Production ◽  
Pythium Ultimum ◽  
Potato Tubers ◽  
Disease Etiology ◽  
Factors Affecting ◽  
Pink Rot ◽  
Application Rates ◽  
Phytophthora Erythroseptica ◽  
Production Areas

Data supplementing a previously published survey of North American isolates of Phytophthora erythroseptica and Pythium ultimum demonstrated that the proportion of the populations sensitive to mefenoxam remains high, 79.6 and 96.9% with EC50 sensitivities ranging from <0.01 to 0.9 µg ml-1 and <0.01 to 0.8 µg ml-1, respectively. Mefenoxam should provide control of these pathogens in most potato production areas. Factors affecting the development of pink rot and leak in potato tubers and the efficacy of mefenoxam to control these diseases with different etiologies were examined. Results confirmed that P. erythroseptica is capable of directly infecting potato tubers causing pink rot, whereas Pythium ultimum requires a wound to infect and cause leak. Mefenoxam was applied to replicated field plots as a single in-furrow application at planting, as an in-furrow application at planting followed by an additional sidedress application 3 weeks after planting, as a single foliar application when tubers were 7 to 8 mm in diameter, and as two foliar applications when the tubers were 7 to 8 mm in diameter and 14 days later. The recommended label rate plus two additional lower application rates were used with each method. For tubers challenge-inoculated after harvest, mefenoxam was found to be more effective in controlling pink rot relative to leak over all application methods. The greatest level of pink rot control (89%) was attained with the in-furrow at planting and sidedress application. All rates tested provided similar levels of control with this application method, but this method provided only a modest level of leak control (35%), and leak was not controlled by foliar applications of mefenoxam at any rate tested. In contrast, the foliar applications of mefenoxam resulted in 10 to 50% control of pink rot. Since the isolates of both pathogens were highly sensitive to me-fenoxam, disease-specific control was attributed to differences in disease etiology. Therefore, the use of mefenoxam to control pink rot in the field and storage appears to be well founded.

scholarly journals Evaluation of the Risk of Development of Fluopicolide Resistance in Phytophthora erythroseptica

Plant Disease ◽  
2019 ◽  
Vol 103 (2) ◽  
pp. 284-288 ◽  
Author(s):  
Xuemei Zhang ◽  
He Jiang ◽  
Jianjun Hao
Keyword(s):  
Agar Medium ◽  
Effective Concentration ◽  
Potato Tubers ◽  
Wild Type ◽  
Moderate Risk ◽  
Baseline Sensitivity ◽  
Pink Rot ◽  
Phytophthora Erythroseptica ◽  
Resistant Mutants ◽  
Resistance Stability

Fluopicolide has shown effective pink rot (Phytophthora erythroseptica) control in potato disease management. To efficiently utilize this chemical, the risk of fluopicolide resistance in P. erythroseptica needs to be assessed. In this study, 34 isolates of P. erythroseptica were obtained from symptomatic potato tubers with pink rot in Maine. The sensitivity of these wild-type isolates to fluopicolide was assessed by culturing them on agar medium amended with fluopicolide at various concentrations. The 50% effective concentration (EC50) of fluopicolide for the inhibition of mycelial growth was determined and used to establish a baseline sensitivity of these P. erythroseptica isolates to fluopicolide. The wild-type isolates were sensitive to fluopicolide, with EC50 values ranging from 0.08 to 0.35 μg/ml. By exposing P. erythroseptica zoospores to agar medium containing 100 μg/ml fluopicolide, 6 out of the 34 wild-type isolates produced fluopicolide-resistant mutants. The mutants were transferred to fungicide-free V8 medium consecutively for 10 times, and the 10th transfer of mutants was examined for resistance stability and biological fitness. In general, the mutants had similar or slower growth rates compared with their wild-type parents, and the virulence of some mutants was significantly reduced. The results indicated a low to moderate risk of P. erythroseptica developing resistance to fluopicolide, and suggested a trade-off between fluopicolide resistance and biological fitness in P. erythroseptica.

scholarly journals Formation of Phytophthora infestans Oospores in Nature on Tubers in Central Mexico

Plant Disease ◽  
2002 ◽  
Vol 86 (1) ◽  
pp. 73-73 ◽  
Author(s):  
S. P. Fernández-Pavía ◽  
N. J. Grünwald ◽  
W. E. Fry
Keyword(s):  
Late Blight ◽  
Phytophthora Infestans ◽  
Field Conditions ◽  
Central Mexico ◽  
Potato Tubers ◽  
Dry Rot ◽  
Pink Rot ◽  
Phytophthora Erythroseptica ◽  
Oospore Formation ◽  
Toluca Valley

Oospore formation by Phytophthora infestans in nature has been detected on potato leaflets in central Mexico (1), but there are no reports of oospore formation on tubers. A severe late blight epidemic occurred in Calimaya, Mexico, in fields where potato cv. Alpha was planted during the summer of 2000. Yield was reduced despite numerous applications of fungicide. Four hundred potato tubers left in the field were collected from the upper 10 cm of soil and examined for late blight symptoms. Tubers with soft and dry rot symptoms were observed, but symptoms of pink rot (Phytophthora erythroseptica) were not found. Four percent of the tubers showed late blight symptoms. Sections of 10 tubers with late blight symptoms were air-dried for 2 weeks in the laboratory and homogenized with a mortar and pestle. Glycerol was added to the homogenized tissue and observed microscopically. Aplerotic oospores (10 to 15 oospores per tuber) with amphyginous antheridia typical of P. infestans were observed. P. mirabilis morphologically similar to P. infestans is present in the area but it does not infect potato tubers. The number of oospores observed in our tuber sample was much lower than the number reported on leaflets (>1,000 oospores per leaflet) in the Toluca Valley. Low numbers of oospores have been reported on tubers artificially inoculated with P. infestans under field conditions (2). Infected tubers left in the field may act as a source of primary inoculum. To our knowledge, this is the first report of oospores of P. infestans found on tubers in Mexico under natural field conditions. References: (1) M. E. Gallegly and J. Galindo. Phytopathology 48:274, 1958. (2) A. Levin et al. Phytopathology 91:579, 2001.

scholarly journals In-Furrow Applications of Metalaxyl and Phosphite for Control of Pink Rot (Phytophthora erythroseptica) of Potato in New Brunswick, Canada

Plant Disease ◽  
2007 ◽  
Vol 91 (10) ◽  
pp. 1305-1309 ◽  
Author(s):  
Khalil I. Al-Mughrabi ◽  
Rick D. Peters ◽  
H. W. (Bud) Platt ◽  
Gilles Moreau ◽  
Appanna Vikram ◽  
...  
Keyword(s):  
New Brunswick ◽  
Disease Incidence ◽  
Field Trials ◽  
Russet Burbank ◽  
Viable Option ◽  
Potato Plants ◽  
Pink Rot ◽  
Phytophthora Erythroseptica ◽  
Sensitive Isolate ◽  
The Mean

The efficacy of metalaxyl-m (Ridomil Gold 480EC) and phosphite (Phostrol) applied at planting in-furrow against pink rot (Phytophthora erythroseptica) of potato (Solanum tuberosum) ‘Shepody’ and ‘Russet Burbank’ was evaluated in field trials conducted in 2005 and 2006 in Florenceville, New Brunswick, Canada. Inoculum made from a metalaxyl-m-sensitive isolate of P. erythroseptica from New Brunswick was applied either in-furrow as a vermiculite slurry at planting or as a zoospore drench in soils adjacent to potato plants in late August. After harvest, the number and weight of tubers showing pink rot symptoms were assessed and expressed as percentages of the total tuber number and total weight of tubers. Metalaxyl-m applied in-furrow was significantly more effective against pink rot than phosphite. The mean percentage of diseased tubers as a percentage of total tuber weight was 1.5% (2005) and 1.2% (2006) for metalaxyl-m-treated plots and 9.6% (2005) and 2.8% (2006) for phosphite-treated plots, a percentage similar to that obtained in inoculated control plots with no fungicide treatment. The mean percentage of diseased tubers expressed as a percentage of the total number of tubers was 1.7% (2005) and 1.3% (2006) for metalaxyl-m-treated plots and 10.1% (2005) and 3.1% (2006) for phosphite-treated plots. Disease incidence was significantly higher using the late-season inoculation technique (respective means in 2005 and 2006 were 9.9 and 3.8% diseased tubers, by weight, and 10.6 and 3.9%, by number) than with the in-furrow inoculation method (respective means in 2005 and 2006 were 3.3 and 0.7% by weight, and 3.7 and 1.3%, by number). The potato cv. Shepody was significantly more susceptible to pink rot (9.9 and 3.3% diseased tubers, by weight, in 2005 and 2006, respectively, and 10.6 and 3.9%, by number) than Russet Burbank (respective means in 2005 and 2006 were 3.4,% and 1.2%, by weight, and 3.7,% and 1.2%, by number). Our findings indicate that metalaxyl applied in-furrow at planting is a viable option for control of pink rot caused by metalaxyl-sensitive strains of P. erythroseptica, whereas phosphite was ineffective.

scholarly journals APPLYING OF ACTIVITIES MANAGEMENT BASED ON SELF-LEARNING

2018 ◽  
Vol 1 ◽  
pp. 29-38 ◽  
Author(s):  
Valerii Samsonkin ◽  
Valerii Druz’ ◽  
Albert Feldman
Keyword(s):  
Quality Management ◽  
Technological Process ◽  
Human Activities ◽  
System Approach ◽  
Human Operator ◽  
Statistical Regularity ◽  
Effective Management ◽  
The Individual ◽  
First Time ◽  
Self Learning

The article is devoted to a brief presentation and application in practice of an effective management way of human activities and human-technical communities one. This way was called Method of statistical regularity (Method of self-organizing processes). In fact, this is a system approach. For the first time, the application of this approach is shown on the example of quality management of the technological process. Practical management is shown using an algorithm. The effectiveness of the author's system approach is explained by the consideration of the final result of the activity as a goal and a system-forming factor of activity, taking into account the individual features of the management object, real statistics of activity. The system approach described in the article is a universal devise of management. It can be used and already used to manage individual functions of the enterprise, the process, the human operator, the community

scholarly journals Effect of 2,4-Diacetylphloroglucinol on Pythium: Cellular Responses and Variation in Sensitivity Among Propagules and Species

2003 ◽  
Vol 93 (8) ◽  
pp. 966-975 ◽  
Author(s):  
Jorge T. de Souza ◽  
Christine Arnould ◽  
Chrystel Deulvot ◽  
Philippe Lemanceau ◽  
Vivienne Gianinazzi-Pearson ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Plant Pathogens ◽  
Pythium Ultimum ◽  
Cellular Responses ◽  
Low Ph ◽  
Cell Content ◽  
Pseudomonas Spp ◽  
Transmission Electron ◽  
First Time ◽  
Resistant Structure

The antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) plays an important role in the suppression of plant pathogens by several strains of Pseudomonas spp. Based on the results of this study, there is variation within and among Pythium spp. to 2,4-DAPG. Also, various propagules of Pythium ultimum var. sporangiiferum, that are part of the asexual stage of the life cycle, differ considerably in their sensitivity to 2,4-DAPG. Mycelium was the most resistant structure, followed by zoosporangia, zoospore cysts, and zoospores. Additionally, we report for the first time that pH has a significant effect on the activity of 2,4-DAPG, with a higher activity at low pH. Furthermore, the level of acetylation of phloroglucinols is also a major determinant of their activity. Transmission electron microscopy studies revealed that 2,4-DAPG causes different stages of disorganization in hyphal tips of Pythium ultimum var. sporangiiferum, including alteration (proliferation, retraction, and disruption) of the plasma membrane, vacuolization, and cell content disintegration. The implications of these results for the efficacy and consistency of biological control of plant-pathogenic Pythium spp. by 2,4-DAPG-producing Pseudomonas spp. are discussed.

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