Inhibition of Pythium spp. and Suppression of Pythium Blight of Turfgrasses with Phosphonate Fungicides

Pythium aphanidermatum and other Pythium spp. cause Pythium blight of turfgrasses in the United States. Phosphonate fungicides suppress Pythium blight when applied preventatively, but efficacy may vary with product, rate and timing of application, and host species. The objectives of this study were to assess the inhibitory effects of phosphorous acid on Pythium spp. in vitro, and determine if active ingredient and formulation of phosphonate fungicides provide similar levels of Pythium blight suppression on perennial ryegrass and creeping bentgrass when applied at equivalent rates of phosphorous acid. Phosphorous acid EC50 values (effective concentration that reduces mycelial growth by 50%) for P. aphanidermatum isolates ranged from 35.6 to 171.8 μg/ml. EC50 values for isolates of six other Pythium spp. were between 38.7 and 220.8 μg/ml. In 2004 and 2005, all phosphonate treatments provided significant suppression of Pythium blight symptoms on creeping bentgrass and perennial ryegrass relative to the untreated control. No differences in percentage of blighted turf occurred among phosphonate treatments when applied at equivalent rates of phosphorous acid in either year of the study, regardless of active ingredient, formulation, or turfgrass species.

Download Full-text

Fungicide Sensitivity of Pythium spp. Associated with Cavity Spot of Carrot in California and Michigan

Plant Disease ◽

10.1094/pdis-07-11-0562 ◽

2012 ◽

Vol 96 (3) ◽

pp. 384-388 ◽

Cited By ~ 7

Author(s):

Xiao Hong Lu ◽

R. Michael Davis ◽

S. Livingston ◽

J. Nunez ◽

Jianjun J. Hao

Keyword(s):

United States ◽

Growth Inhibition ◽

Active Ingredient ◽

Mycelial Growth ◽

The United States ◽

Fungicide Sensitivity ◽

First Report ◽

Cavity Spot ◽

Pythium Violae

The identity of 172 isolates of Pythium spp. from cavity spot lesions on carrot produced in California and Michigan was determined, and their sensitivity to three fungicides was examined. Pythium violae accounted for 85% of California isolates, with P. irregulare, P. dissotocum (the first report as a carrot pathogen in the United States), P. ultimum, and P. sulcatum making the balance. P. sulcatum, P. sylvaticum, and P. intermedium were the most commonly recovered (85%) species in Michigan; others from Michigan included P. intermedium, P. irregulare, and an unclassified strain, M2-05. On fungicide-amended media, 93% of isolates were sensitive to mefenoxam (inhibition of mycelial growth was >60% at 10 μg active ingredient [a.i.]/ml); however, two of five isolates of P. irregulare from California were highly resistant (≤60% inhibition at 100 μg a.i./ml); about half of the isolates of P. intermedium and P. sylvaticum and a single isolate of P. violae were highly or intermediately resistant to mefenoxam (>60% inhibition at 100 μg a.i./ml, or ≤60% inhibition at 10 μg a.i./ml). P. dissotocum, P. irregulare, P. sulcatum, M2-05, and three of seven isolates of P. intermedium were insensitive to fluopicolide (effective concentrations for 50% growth inhibition [EC50] were >50 μg a.i./ml), while P. sylvaticum, P. ultimum, P. violae, and some isolates in P. intermedium were sensitive (EC50 < 1 μg a.i./ml). All isolates were sensitive to zoxamide (EC50 < 1 μg a.i./ml). Sensitivity baselines of P. violae to zoxamide and fluopicolide were established.

Download Full-text

Fungicide Sensitivity of U.S. Genotypes of Phytophthora infestans to Six Oomycete-Targeted Compounds

Plant Disease ◽

10.1094/pdis-05-14-0452-re ◽

2015 ◽

Vol 99 (5) ◽

pp. 659-666 ◽

Cited By ~ 35

Author(s):

Amanda Saville ◽

Kim Graham ◽

Niklaus J. Grünwald ◽

Kevin Myers ◽

William E. Fry ◽

...

Keyword(s):

United States ◽

Phytophthora Infestans ◽

The United States ◽

Effective Concentration ◽

Response Curves ◽

Baseline Sensitivity ◽

Fungicide Sensitivity ◽

The Past ◽

The Us

Phytophthora infestans causes potato late blight, an important and costly disease of potato and tomato crops. Seven clonal lineages of P. infestans identified recently in the United States were tested for baseline sensitivity to six oomycete-targeted fungicides. A subset of the dominant lineages (n = 45) collected between 2004 and 2012 was tested in vitro on media amended with a range of concentrations of either azoxystrobin, cyazofamid, cymoxanil, fluopicolide, mandipropamid, or mefenoxam. Dose-response curves and values for the effective concentration at which 50% of growth was suppressed were calculated for each isolate. The US-8 and US-11 clonal lineages were insensitive to mefenoxam while the US-20, US-21, US-22, US-23, and US-24 clonal lineages were sensitive to mefenoxam. Insensitivity to azoxystrobin, cyazofamid, cymoxanil, fluopicolide, or mandipropamid was not detected within any lineage. Thus, current U.S. populations of P. infestans remained sensitive to mefenoxam during the displacement of the US-22 lineage by US-23 over the past 5 years.

Download Full-text

Screening of Existing and New Boxwood Cultivars for Disease Resistance and In Vitro Fungicide Screening to Manage Boxwood Dieback Caused by Colletotrichum theobromicola

Plant Health Progress ◽

10.1094/php-03-21-0070-rs ◽

2021 ◽

Author(s):

Harleen Kaur ◽

Monique DeSouza ◽

Raghuwinder "Raj" Singh

Keyword(s):

Active Ingredient ◽

Spore Germination ◽

Mycelial Growth ◽

Management Practices ◽

Management Strategies ◽

Host Susceptibility ◽

Germination Inhibition ◽

Industry Professionals ◽

The U.S

Boxwood is one of the most common and widely planted perennial ornamentals in both home gardens and commercial landscapes. Recently reported boxwood dieback, a fungal disease caused by Colletotrichum theobromicola, has been spreading at an alarming rate within the U.S. Boxwood breeders, nursery growers, and landscape professionals have shown great concerns regarding the lack of effective management practices. Therefore, the primary objectives of this study were to devise effective disease management strategies including screening cultivars to determine their susceptibility to boxwood dieback and screening various fungicides to determine their effectiveness in managing the disease. Host range studies were conducted by screening a wide variety of boxwood cultivars under greenhouse conditions. Although, boxwood cultivar ‘Little Missy’ showed much delayed symptom expression as compared to rest of the cultivars but none of the 11 cultivars were found to be resistance to boxwood dieback. In vitro screening of nine fungicides was conducted to determine mycelial growth as well as spore germination inhibition of eight isolates of C. theobromicola collected from eight states in the U.S. Of the nine fungicides, difenoconazole+pydiflumetofen showed maximum mycelial growth and spore germination inhibition at 1 ppm active ingredient followed by fluxapyroxad+pyraclostrobin, and pyraclostrobin+boscalid at 5 ppm active ingredient. Azoxystrobin+benzovindiflupyr significantly inhibited mycelial growth at 1 ppm but reduced spore germination at 10 ppm active ingredient. This study provides the boxwood industry professionals with critical and applied information pertaining to host susceptibility and fungicide efficacy to effectively mitigate boxwood dieback and to reduce its further spread.

Download Full-text

Baseline Sensitivity of Penicillium spp. to Difenoconazole

Plant Disease ◽

10.1094/pdis-05-18-0860-re ◽

2019 ◽

Vol 103 (2) ◽

pp. 331-337 ◽

Cited By ~ 4

Author(s):

Wayne M. Jurick ◽

Otilia Macarisin ◽

Verneta L. Gaskins ◽

Wojciech J. Janisiewicz ◽

Kari A. Peter ◽

...

Keyword(s):

United States ◽

Mycelial Growth ◽

The United States ◽

Blue Mold ◽

Pome Fruit ◽

Baseline Sensitivity ◽

Single Spore ◽

Commercial Use ◽

Penicillium Spp

Penicillium spp. cause blue mold of stored pome fruit. These fungi reduce fruit quality and produce mycotoxins that are regulated for processed fruit products. Control of blue mold is achieved by fungicide application, and in 2015 Academy (active ingredients fludioxonil and difenoconazole) was released for use on pome fruit to manage postharvest blue mold. Baseline sensitivity for fludioxonil but not difenoconazole has been determined for P. expansum. To establish the distribution of sensitivity to difenoconazole before commercial use of Academy, 97 unexposed single-spore isolates from the United States and abroad were tested in vitro. Baseline EC50 values ranged from 0.038 to 0.827 µg/ml of difenoconazole with an average of 0.16 µg/ml. Complete inhibition of mycelial growth for all but three isolates occurred at 5 µg/ml of difenoconazole, whereas 10 µg/ml did not support growth for any of the isolates examined. Hence, 5 µg/ml of difenoconazole is recommended for phenotyping Penicillium spp. isolates with reduced sensitivity. Isolates with resistance to pyrimethanil and to both thiabendazole and pyrimethanil were observed among the isolates from the baseline collection. Academy applied at the labeled rate had both curative and protectant activities and controlled four representative Penicillium spp. from the baseline population. This information can be used to monitor future shifts in sensitivity to this new postharvest fungicide in Penicillium spp. populations.

Download Full-text

Assessment of quinone outside inhibitor sensitivity and frogeye leaf spot race of Cercospora sojina in Georgia soybean

Plant Disease ◽

10.1094/pdis-02-21-0236-re ◽

2021 ◽

Author(s):

Bennett Harrelson ◽

Bikash Ghimire ◽

Robert Kemerait ◽

Albert Culbreath ◽

Zenglu Li ◽

...

Keyword(s):

Leaf Spot ◽

Fungicide Resistance ◽

Mycelial Growth ◽

The United States ◽

In Vitro Assays ◽

Cercospora Sojina ◽

Quinone Outside Inhibitor ◽

Frogeye Leaf Spot ◽

Differential Cultivars

Frogeye leaf spot (FLS), caused by the fungal pathogen Cercospora sojina K. Hara, is a foliar disease of soybean (Glycine max L. (Merr.)) responsible for yield reductions throughout the major soybean producing regions in the world. In the United States, management of FLS relies heavily on the use of resistant cultivars and in-season fungicide applications, specifically within the class of quinone outside inhibitors (QoIs), which has resulted in the development of fungicide resistance in many states. In 2018 and 2019, 80 isolates of C. sojina were collected from six counties in Georgia and screened for QoI fungicide resistance using molecular and in vitro assays, with resistant isolates being confirmed from three counties. Additionally, 50 isolates, including a “baseline isolate” with no prior fungicide exposure, were used to determine the percent reduction of mycelial growth to two fungicides, azoxystrobin and pyraclostrobin, at six concentrations: 0.0001, 0.001, 0.01, 0.1, 1, and 10 g ml-1. Mycelial growth observed for resistant isolates varied significantly from both the sensitive isolates and the baseline isolate for azoxystrobin concentrations of 10, 1, 0.1, and 0.01 g ml-1 and for pyraclostrobin concentrations of 10, 1, 0.1, 0.01 and 0.001 g ml-1. Moreover, 40 isolates were used to evaluate pathogen race on six soybean differential cultivars by assessing susceptible or resistant reactions. Isolate reactions suggested 12 races of C. sojina present in Georgia, four of which have not been previously described. Species richness indicators (rarefaction and abundance-based coverage estimator - ACE) indicated that within-county C. sojina race numbers were undersampled in the present study, suggesting the potential for the presence of either additional undescribed races or known but unaccounted for races in Georgia. However, no isolates were pathogenic on differential cultivar ‘Davis’, carrying the Rcs3 resistance allele, suggesting the gene is still an effective source of resistance in Georgia.

Download Full-text

Resistance to QoI (Strobilurin-like) Fungicides in Isolates of Pyricularia grisea from Perennial Ryegrass

Plant Disease ◽

10.1094/pdis.2002.86.3.235 ◽

2002 ◽

Vol 86 (3) ◽

pp. 235-240 ◽

Cited By ~ 93

Author(s):

P. Vincelli ◽

E. Dixon

Keyword(s):

Perennial Ryegrass ◽

Fungal Pathogens ◽

The United States ◽

Gray Leaf Spot ◽

Pyricularia Grisea ◽

Lower Sensitivity ◽

Complete Control ◽

The Mean

In August 2000, azoxystrobin was ineffective in controlling gray leaf spot of perennial ryegrass at a golf course in Lexington, KY and at two golf courses in Illinois. Isolates suspected of being fungicide-resistant (“suspect isolates”) were compared to “baseline” isolates obtained from sites with no known use of quinol-oxidizing inhibitor (QoI) fungicides. Conidial germination of Pyricularia grisea was tested in vitro with 100 μg of salicylhydroxamic acid per ml. For baseline isolates, 50% effective concentration (EC50) values for azoxystrobin and trifloxystrobin were 0.015 to 0.064 and 0.013 to 0.078 μg/ml, respectively; EC50 values for suspect isolates were 2.39 to 44.8 and 0.31 to 111, respectively. All suspect isolates exhibited significantly (P = 0.05) lower sensitivity to QoI fungicides than all baseline isolates. The mean EC50 values for suspect isolates for azoxystrobin and trifloxystrobin were 690 and 827 times higher, respectively, than the means for baseline isolates. In the laboratory, azoxystrobin and trifloxystrobin provided essentially complete control of disease induced by nine baseline isolates in vivo. Azoxystrobin and trifloxystrobin provided poor to no control of disease induced by six of eight suspect isolates; control of disease induced by the remaining two isolates was partial for azoxystrobin and complete for trifloxystrobin. We conclude that one or more biotypes of perennial ryegrass-infecting strains of P. grisea with resistance to QoI fungicides have emerged. This is the first report of resistance to QoI fungicides in P. grisea. Furthermore, this is one of two QoIresistant fungal pathogens collected in the United States during the 2000 growing season, the first instances reported for North America.

Download Full-text

Impact of Azoxystrobin, Dimethomorph, Fluazinam, Fosetyl-Al, and Metalaxyl on Growth, Sporulation, and Zoospore Cyst Germination of Three Phytophthora spp.

Plant Disease ◽

10.1094/pdis.2000.84.4.454 ◽

2000 ◽

Vol 84 (4) ◽

pp. 454-458 ◽

Cited By ~ 77

Author(s):

M. E. Matheron ◽

M. Porchas

Keyword(s):

Life Cycle ◽

Disease Control ◽

Mycelial Growth ◽

Phytophthora Capsici ◽

Effective Concentration ◽

The Other ◽

In Vitro Activity ◽

Phytophthora Spp ◽

Cyst Germination

In vitro activity of azoxystrobin, dimethomorph, and fluazinam on growth, sporulation, and zoospore cyst germination of Phytophthora capsici, P. citrophthora, and P. parasitica was compared to that of fosetyl-Al and metalaxyl. The 50% effective concentration (EC50) values for)inhibition of mycelial growth of the three pathogens usually were lowest for dimethomorph and (metalaxyl, ranging from <0.1 to 0.38 μg/ml. However, the 90% effective concentration (EC90) levels for dimethomorph always were lower than the other four tested compounds, with values ranging from 0.32 to 1.6 μg/ml. Mycelial growth of P. capsici, P. citrophthora, and P. parasitica was least affected by azoxystrobin and fluazinam, with estimated (EC90) values >3,000 μg/ml. Reduction of sporangium formation by P. capsici, P. citrophthora, and P. parasitica in the presence of dimethomorph at 1 μg/ml was significantly greater than that recorded for the same concentration of azoxystrobin, fluazinam, and fosetyl-Al. For the three species of Phytophthora, zoospore motility was most sensitive to fluazinam (EC50 and EC90 values of <0.001 μg/ml) and (least sensitive to fosetyl-Al, with (EC50 and EC90 values ranging from 299 to 334 and 518 to 680 μg/ml, respectively). Germination of encysted zoospores of P. capsici, P. citrophthora, and P. parasitica was most sensitive to dimethomorph (EC50 and EC90 values ranging from 3.3 to 7.2 and 5.6 to 21 μg/ml, respectively), intermediate in sensitivity to fluazinam (EC50 and EC90 from 18 to 108 and 67 to >1,000 μg/ml, respectively) and metalaxyl (EC50 and EC90 from 32 to 280 and 49 to 529 μg/ml, respectively), and lowest in sensitivity to azoxystrobin and fosetyl-Al (EC50 and EC90 from 256 to >1,000 μg/ml). The activity of azoxystrobin, dimethomorph, and fluazinam on one or more stages of the life cycle of P. capsici, P. citrophthora, and P. parasitica suggests that these compounds potentially could provide Phytophthora spp. disease control comparable to that of the established fungicides fosetyl-Al and metalaxyl.

Download Full-text

Variability of Three Isolates of Botrytis cinerea Affects the Inhibitory Effects of Calcium on this Fungus

Phytopathology ◽

10.1094/phyto.2000.90.7.769 ◽

2000 ◽

Vol 90 (7) ◽

pp. 769-774 ◽

Cited By ~ 31

Author(s):

Catherine O. Chardonnet ◽

Carl E. Sams ◽

Robert N. Trigiano ◽

William S. Conway

Keyword(s):

Botrytis Cinerea ◽

Mycelial Growth ◽

Dna Analysis ◽

Epidemiological Studies ◽

Inhibitory Effects ◽

Apple Cultivars ◽

Sporulation Rate ◽

Polygalacturonase Activity

Botrytis cinerea is an economically important pathogen. Epidemiological studies are difficult because of the genetic variability within this species. The objectives of this work were to study the variability and to compare the inhibitory effects of Ca on three isolates of B. cinerea from decayed apple (B) and grape (C and C77:4). Among these isolates, B had the least radial growth but had a sporulation rate 40% higher than that of both C77:4 and C. In situ, isolate C incited the largest decay area in the fruit of two of four apple cultivars examined and had the highest polygalacturonase activity in vitro. Maximum mycelial growth was reached with CaCl2 at 1 g liter-1 for isolates B and C77:4 and at 4 g liter-1 for isolate C. Calcium (CaCl2) inhibited polygalacturonase activity at 1 g liter-1 for C and C77:4 and at 16 g liter-1 for B. Calcium infiltration reduced decay caused by all three isolates by three to five times. Mycelial DNA analysis showed that 42% of the character loci scored were polymorphic and the greatest similarities were found between B and C77:4. These results support the evidence that the biological and statistical variability in research can be affected by the B. cinerea isolate selected. Despite this variation, Ca treatment of apples reduced decay caused by all three Botrytis cinerea isolates.

Download Full-text

In vitro anti-motility and antispasmodic effects of Garcinia mangostana extracts in isolated chicken ileum preparation

International Journal of Research in Pharmaceutical Sciences ◽

10.26452/ijrps.v10i2.714 ◽

2019 ◽

Vol 10 (2) ◽

pp. 1444-1447

Author(s):

Michelle Ooi Yi Ching ◽

Sasikala Chinnappan ◽

Mogana Sundari Rajagopal

Keyword(s):

Effective Concentration ◽

Aqueous Extracts ◽

Inhibitory Effects ◽

Garcinia Mangostana ◽

Response Curves ◽

Half Maximal Effective Concentration ◽

Set Up ◽

Smooth Muscle Contractions ◽

Significant Concentration

Garcinia mangostana pericarps have been traditionally used in Southeast Asia for a variety of medicinal conditions. The present study was carried out to determine the anti-motility and antispasmodic effects of methanolic and aqueous G. mangostana extracts (MEM and AEM) on isolated chicken ileum. Extracts were prepared from the pericarp of G. mangostana using maceration technique with methanol and distilled water. Isolated ileum preparations were set up for recording in Tyrode’s solution at 37°C. Dose-response curves were plotted using various doses of agonist as control such as acetylcholine (ACh) and histamine. Atropine, mepyramine and extracts were used as an antagonist. The results showed that methanolic and aqueous extracts possess significant concentration-dependent inhibitory effects (p<0.05) on agonist-induced contractions. The half maximal effective concentration (EC50) of extracts and standard antagonists were higher than the agonist alone. Both methanolic and aqueous extract of G. mangostana exerts anti-motility and antispasmodic effects on smooth muscle contractions. The study provides findings that support G. mangostana can be the potential treatment for diarrhoea and spasm.

Download Full-text

Inhibitory Effects of Essential Oils for Controlling Phytophthora capsici

Plant Disease ◽

10.1094/pdis-11-11-0933 ◽

2012 ◽

Vol 96 (6) ◽

pp. 797-803 ◽

Cited By ~ 10

Author(s):

Yang Bi ◽

He Jiang ◽

Mary K. Hausbeck ◽

Jianjun J. Hao

Keyword(s):

Essential Oils ◽

Mycelial Growth ◽

Cucurbita Pepo ◽

Integrated Management ◽

Phytophthora Capsici ◽

Seedling Emergence ◽

Infested Soil ◽

Inhibitory Effects

Essential oils (EOs) were studied in vitro and in vivo for inhibiting Phytophthora capsici. Mycelial growth of P. capsici was examined on EO-amended media or after exposing it to EO volatiles. The efficacy of EOs was determined by estimating the effective concentration for 50% inhibition of P. capsici mycelial growth (EC50). Among 14 tested commercial products, oregano, palmarosa, and red thyme EOs had the lowest EC50 values (<0.15 μg/ml) for inhibiting the production and germination of sporangia and zoospores, and mycelial growth of P. capsici. The EOs had the same range of effect on inhibiting some mutant P. capsici isolates resistant to fluopicolide and zoxamide. P. capsici population in soil was reduced by the three EOs. Zucchini (Cucurbita pepo) fruit were protected against P. capsici infection when they were sprayed with red thyme (0.1 μg/ml) or oregano and palmarosa (0.2 μg/ml) EOs. Zucchini seedling emergence was affected by oregano, but not by red thyme. Zucchini seedlings survived in P. capsici–infested soil treated with red thyme at 0.1 μg/ml, while all of the nontreated seedlings died. These results taken together suggest that oregano, red thyme, and palmarosa EOs may be potential components for integrated management of P. capsici.

Download Full-text