Pythium spp. associated with root rot and stunting of winter wheat in North Carolina

Plant Disease ◽  
2020 ◽  
Author(s):  
Ella Reeves ◽  
James Patrick Kerns ◽  
Christina Cowger ◽  
Barbara Shew
Keyword(s):  
North Carolina ◽  
Winter Wheat ◽  
Root Rot ◽  
In Vitro Growth ◽  
Pythium Species ◽  
Nitrogen Application ◽  
Pythium Irregulare ◽  
Severe Stunting ◽  
Eastern North Carolina

In eastern North Carolina, mild to severe stunting and root rot have reduced yields of winter wheat, especially during years with abundant rainfall. Causal agents of root rot of wheat in this region were previously identified as Pythium irregulare, P. vanterpoolii, and P. spinosum. To investigate species prevalence, 114 isolates of Pythium were obtained from symptomatic wheat plants collected in 8 counties. Twelve species were recovered, with P. irregulare (32%), P. vanterpoolii (17%), and P. spinosum (16%) the most common. Pathogenicity screens were performed with selected isolates of each species, and slight to severe necrosis of young roots was observed. The aggressiveness of five isolates each of P. irregulare, P. vanterpoolii, and P. spinosum was compared on a single cultivar of wheat at 14°C, and very aggressive isolates were found within all species. In vitro growth of these isolates was measured at 14°C and 20°C, and all isolates grew faster at the warmer temperature. The effects of varying temperatures and rates of nitrogen on root rot caused by Pythium species alone or in combination were investigated. All inoculation treatments caused severe root rot under all conditions tested, and disease was more severe at 12/14°C compared to 18/20°C, but there was no effect of nitrogen application.

scholarly journals Mefenoxam Sensitivity, Aggressiveness, and Identification of Pythium Species Causing Root Rot on Floriculture Crops in North Carolina

Plant Disease ◽  
2015 ◽  
Vol 99 (11) ◽  
pp. 1550-1558 ◽  
Author(s):  
E. C. Lookabaugh ◽  
K. L. Ivors ◽  
B. B. Shew
Keyword(s):  
North Carolina ◽  
Host Species ◽  
Root Rot ◽  
Internal Transcribed Spacer ◽  
Ornamental Plants ◽  
Pythium Species ◽  
Selective Media ◽  
Microtiter Plates ◽  
Pythium Root Rot

Herbaceous ornamental plants exhibiting symptoms of Pythium root rot were collected from 26 greenhouses in 21 counties in North Carolina (NC) from 2010 to 2012. Plant symptoms ranged from mild stunting to severe wilting, root rot, and death. Roots were plated on selective media, and 356 isolates of Pythium were recovered from 34 host species. Selected isolates were identified by sequencing of the internal transcribed spacer (ITS) rDNA gene region. Seventeen Pythium species were identified, with P. aphanidermatum, P. irregulare, and P. myriotylum comprising 75% of the 320 isolates sequenced. Twelve of the 26 greenhouses had more than one species present. Mefenoxam sensitivity was tested in vitro by growing isolates in wells of microtiter plates containing clarified V8 agar amended with 100 µg a.i./ml mefenoxam. Colonization was scored after 24 to 48 h using a scale of 0 (no growth) to 5 (entire well colonized). Fifty-two percent of the isolates were resistant to mefenoxam (mean score ≥4). All 32 isolates of P. myriotylum were sensitive, whereas sensitivity varied among isolates of P. aphanidermatum and P. irregulare. Resistant and sensitive isolates of the same species were found within the same greenhouses. The aggressiveness of P. aphanidermatum and P. irregulare isolates was evaluated on poinsettia, Gerbera daisy, and petunia. P. aphanidermatum was more aggressive than P. irregulare on poinsettia and petunia; symptoms were mild and no differences in aggressiveness were observed on Gerbera daisy. Sensitivity to mefenoxam was not related to aggressiveness.

Pythium spp. associated with root rot and stunting of winter crops in North Carolina

Plant Disease ◽  
2021 ◽  
Author(s):  
Ella Reeves ◽  
James Patrick Kerns ◽  
Barbara Shew
Keyword(s):  
North Carolina ◽  
Winter Wheat ◽  
Cover Crops ◽  
Root Rot ◽  
Growing Seasons ◽  
Salvia Sclarea ◽  
Root Necrosis ◽  
Winter Crops ◽  
Eastern North Carolina ◽  
Isolated Species

Annual double-crop rotation systems that incorporate winter wheat, clary sage, or a cover crop are common in eastern North Carolina. Stunting and root rot of clary sage (Salvia sclarea L.) reduce yields of this crop, especially in wet soils. Stunting and reduced stand establishment also afflict winter cover crops, including rye, rapeseed, and winter pea. Pythium spp. are causal agents of root rot of winter wheat in this region, but their role in root rot and stunting of other winter crops is not understood. During the growing seasons of 2018-2019 and 2019-2020 samples of clary sage, rye, rapeseed, and winter pea displaying symptoms of stunting were collected across eastern NC, resulting in the recovery of 420 isolates of Pythium from the roots of all hosts. P. irregulare, P. spinosum, and the complex Pythium sp. cluster B2A were the most frequently isolated species from clary sage. P. irregulare and P. spinosum were aggressive pathogens of clary sage at 18°C, and caused moderate root rot at 28°C. Koch’s postulates confirmed that isolates belonging to Pythium sp. cluster B2A, P. sylvaticum, P. pachycaule, P aphanidermatum, P. myriotylum, and P. oopapillum are pathogens of clary sage. P. irregulare (37% of all isolates) and members of the species complex Pythium sp. cluster B2A (28% of all isolates) comprised the majority of isolates collected from all hosts and were the most frequently isolated species from rye, rapeseed, and winter pea. In pathogenicity assays, isolates representing P. irregulare and P. spinosum caused slight to moderate root necrosis on rye, rapeseed, and winter pea. Isolates representing Pythium sp. cluster B2A caused slight to moderate root necrosis on rapeseed and clary sage, but no symptoms on rye or winter pea.

scholarly journals Three Pythium Species Isolated From Severely Stunted Wheat During an Outbreak in North Carolina

2017 ◽  
Vol 18 (3) ◽  
pp. 169-173
Author(s):  
Emma Lookabaugh ◽  
Barbara Shew ◽  
Christina Cowger
Keyword(s):  
United States ◽  
North Carolina ◽  
Root Rot ◽  
Yield Loss ◽  
The United States ◽  
Pythium Species ◽  
Wheat Roots ◽  
Soil Waterlogging ◽  
Pythium Root Rot ◽  
Eastern North Carolina

Large portions of eastern North Carolina experienced prolonged soil waterlogging in 2016. Severely stunted wheat plants from saturated fields were examined and Pythium spp. consistently were associated with the symptoms observed. Three species of Pythium were identified among 15 isolates derived from wheat roots and crowns: P. irregulare, P. spinosum, and P. vanterpoolii. Each species was isolated from samples that came from between two and five counties. Pythium vanterpoolii and P. spinosum have not previously been reported as pathogens in wheat in the United States. All three species caused root rot when reinoculated on wheat plants. These species are not opportunistic or mainly saprophytic on other hosts; therefore, it is likely that they contributed to the extreme stunting and yield loss observed in North Carolina wheat in 2016. The 15 isolates were tested for sensitivity to mefenoxam at 100 μg/ml a.i. and none was insensitive. Prolonged hypoxia likely predisposed North Carolina wheat to unusual levels of Pythium root rot in 2016.

scholarly journals Variation Among Isolates of Fusarium graminearum Associated with Fusarium Head Blight in North Carolina

Plant Disease ◽  
2001 ◽  
Vol 85 (4) ◽  
pp. 404-410 ◽  
Author(s):  
Scott L. Walker ◽  
Steven Leath ◽  
Winston M. Hagler ◽  
J. Paul Murphy
Keyword(s):  
North Carolina ◽  
Fusarium Head Blight ◽  
Fusarium Graminearum ◽  
Phenotypic Diversity ◽  
In Vitro Growth ◽  
Head Blight ◽  
Potential Threat ◽  
Previous Crop

Fusarium head blight (FHB) can reduce yield of wheat and decrease the value of harvested grain by accumulation of detrimental toxins. Understanding the variability of the fungal population associated with infection could improve disease control strategies. Sixty-six isolates of Fusarium graminearum associated with FHB were collected in North Carolina and tested for in vitro growth rate, in vitro production of deoxynivalenol (DON) and zearalenone, and pathogenicity on three cultivars of soft red winter wheat. Significant differences among isolates were found for all three traits. Randomly Amplified Polymorphic DNA (RAPD) analysis revealed high levels of genotypic diversity among isolates. Isolates of F. graminearum, F. culmorum, and F. avenaceum acquired from the Pennsylvania State University Fusarium Center were included for comparison in all tests. In vivo levels of DON were measured for the five isolates associated with the highest levels of disease and the five isolates associated with the lowest levels of disease, and no significant differences were found. However, all ten isolates produced detectable levels of DON in vivo. Mean disease ratings ranged from 3.4 to 96.4%, in vitro (DON) levels ranged from 0 to 7176.2 ppm, and zearalenone ranged from 0 to 354.7 ppm, among isolates. A multiple regression model using in vitro growth, in vitro DON, and zearalenone production, collection location, wheat cultivar of isolate origin, plot, tillage conditions, and previous crop as independent variables and percent blighted tissue as the dependent variable was developed. The cumulative R2 value for the model equaled 0.27 with in vitro rate of growth making the largest contribution. Analysis of phenotype and genotype among isolates demonstrated diversity in a single plot, in a single location, and in North Carolina. Genotypic and phenotypic diversity were significant under both conventional and reduced tillage conditions, and diversity was high regardless of whether the previous crop had been a host or non-host for F. graminearum. These data indicate a variable pathogen population of F. graminearum exists in North Carolina, and members of this population can be both highly pathogenic on wheat and produce high levels of detrimental toxins, indicating a potential threat for problems with FHB within the state.

Root rot caused by Pythium irregulare Buisman, an important factor in the decline of established subterranean clover pastures

1974 ◽  
Vol 25 (4) ◽  
pp. 537 ◽  
Author(s):  
GE Stovold
Keyword(s):  
Root Rot ◽  
Subterranean Clover ◽  
Common Disease ◽  
Crop Species ◽  
Pythium Irregulare ◽  
Factors Affecting ◽  
South Wales ◽  
Matter Production ◽  
Pathogenicity Tests

The problem of poor re-establishment and poor seasonal production in long-term subterranean clover pastures has been recognized for some time, particularly on the Southern Tableland and Slopes regions of New South Wales. Field and laboratory investigations showed that rotting of the lateral feeder roots was a common disease of subterranean clover during the cool part of the growing season. Isolations made from diseased roots yielded a predominance of Pythium spp. of which Pythiurn irregulare was the most common. Pathogenicity tests demonstrated that P. irregulare consistently caused damping-off of germinating subterranean clover. This fungus also infected established plants and at low temperatures caused severe reduction of dry matter production. Symptoms produced on artificially inoculated plants were identical with those observed on plants infected in the field. Soil moisture and the level of fungal inoculum added did not have a critical effect on the severity of root disease. A range of other important pasture and crop species were also artificially infected with P. irregulare, with resulting necrosis of feeder roots. In vitro studies of factors affecting the growth of P. irregulare showed that this pathogen was well adapted to survive and cause disease in cold wet soils, the conditions most favourable for root rot in the field. The importance of P. irregulare as a pathogen of established plants and possible means of reducing its effect on the growth of subterranean clover are discussed.

scholarly journals Pathogenicity and Mefenoxam Sensitivity of Pythium, Globisporangium, and Fusarium Isolates From Coconut Coir and Rockwool in Marijuana (Cannabis sativa L.) Production

2021 ◽  
Vol 3 ◽  
Author(s):  
Cora S. McGehee ◽  
Rosa E. Raudales
Keyword(s):  
Root Rot ◽  
Cannabis Sativa ◽  
Disease Incidence ◽  
Elongation Factor ◽  
Pythium Myriotylum ◽  
Internal Transcribed Spacer Region ◽  
Pythium Irregulare ◽  
Coconut Coir

Oomycetes and fungi were recovered from coconut coir and rockwool substrates where marijuana (Cannabis sativa L. cv. Silver and Citron) plants with root rot and wilt symptoms were grown in a commercial growing facility in Connecticut. The objectives of this study were to identify the isolates collected from these substrates, determine the pathogenicity of the isolates on hemp seedlings in vitro and in vivo, and evaluate the pathogens' sensitivity to mefenoxam. Pythium and Globisporangium isolates were identified by sequencing the mitochondrially-encoded cytochrome oxidase genes (COI and COII) and Fusarium sp. with the translation elongation factor (EF-1α) region and internal transcribed spacer region (ITS4 and ITS5) genes. Three isolates were identified as Globisporangium irregulare (formerly Pythium irregulare), 21 isolates were Pythium myriotylum, and one was Fusarium oxysporum. All the isolates tested were pathogenic to hemp plants in vitro and in vivo, with disease incidence between 6.7 and 100%. Inoculated plants were smaller by 32% or more compared with the non-inoculated control. On average, hemp plants infected with Pythium myriotylum produced the lowest biomass and relative greenness values. None of the Pythium and Globisporangium isolates were resistant to mefenoxam—all were sensitive to ≥5 μg·mL−1 mefenoxam. This is the first report of G. irregulare causing root rot on marijuana and hemp plants. The results of this study provide information about the characteristics of pathogens that can be found potentially in soilless substrates in controlled environment agriculture.

Effects of Some Benzoxazinoids on in Vitro Growth ofCephalosporium gramineumand Other Fungi Pathogenic to Cereals and onCephalosporiumStripe of Winter Wheat

2006 ◽  
Vol 54 (4) ◽  
pp. 1036-1039 ◽  
Author(s):  
Stefan Martyniuk ◽  
Anna Stochmal ◽  
Francisco A. Macías ◽  
David Marín ◽  
Wieslaw Oleszek
Keyword(s):  
Winter Wheat ◽  
In Vitro Growth

Pathogenicity of root and stolon-colonising fungi to white clover

2001 ◽  
Vol 41 (6) ◽  
pp. 763 ◽  
Author(s):  
M. I. Zahid ◽  
G. M. Gurr ◽  
A. Nikandrow ◽  
W. J. Fulkerson ◽  
H. I. Nicol
Keyword(s):  
Plant Growth ◽  
White Clover ◽  
Root Rot ◽  
New South ◽  
Field Soil ◽  
Pythium Irregulare ◽  
Phytophthora Megasperma ◽  
South Wales ◽  
Roots In Vitro

Fungi isolated from white clover plants growing in dairy pastures in northern New South Wales and south-eastern Queensland were tested for their pathogenicity to seedlings, excised stolons and mature white clover plants. Thirty out of 65 isolates tested, including species of Fusarium, Phytophthora, Pythium, Rhizoctonia, Phoma, Codinaea, Gliocladium, Microsphaeropsis, Trichoderma, Nectria and Macrophomina, were pathogenic to white clover roots in vitro. Ten of the fungi, including the genera Alternaria, Colletotrichum, Drechslera, Fusarium, Phoma, Macrophomina, Phomopsis and Rhizoctonia, caused stolon rot symptoms. Of the 23 fungi tested on seedlings and mature white clover plants Phytophthora megasperma, Phoma nebulosa and Pythium irregulare were the most pathogenic to both seedlings and mature plants. Root rot and plant growth suppression was more severe in pot tests using field soil compared with pasteurised potting mix. Novel methods are described for testing pathogenicity to excised stolons.

Evaluating fungicide selections to manage Pythium root rot on poinsettia cultivars with varying levels of partial resistance

Plant Disease ◽  
2020 ◽  
Author(s):  
Emma Christine Lookabaugh ◽  
James Patrick Kerns ◽  
Barbara Shew
Keyword(s):  
North Carolina ◽  
Root Rot ◽  
Partial Resistance ◽  
Euphorbia Pulcherrima ◽  
Trichoderma Spp ◽  
Pythium Root Rot ◽  
In Vitro Sensitivity ◽  
Potassium Phosphite ◽  
Sensitive Isolate

Pythium aphanidermatum is the predominant species causing Pythium root rot of commercially grown poinsettia (Euphorbia pulcherrima Willd. ex Kotzch) in North Carolina. Pythium root rot is managed primarily through a combination of sanitation practices and preventative fungicide applications of mefenoxam or etridiazole. Insensitivity to mefenoxam is common but growers continue to rely on it due to lack of inexpensive and efficacious alternatives. This research was conducted to identify alternative fungicides for Pythium root rot control and evaluate their efficacy on poinsettia cultivars with varying levels of partial resistance. Greenhouse studies were conducted to assess efficacy of fungicide treatments in seven poinsettia cultivars inoculated with a mefenoxam-sensitive isolate of P. aphanidermatum. One study examined control with a single fungicide drench made at transplant and a second study examined repeat fungicide applications made throughout the experiment. Treatments containing etridiazole, mefenoxam, fenamidone, and cyazofamid provided control of Pythium root rot across all cultivars in both experiments whereas Fosetyl-al, potassium phosphite, and Trichoderma spp. failed to offer satisfactory control. Azoxystrobin, pyraclostrobin, and propamocarb reduced disease on some cultivars but failed to control Pythium root rot on highly susceptible cultivars. Four isolates of P. aphanidermatum cultured from plants growing in commercial greenhouses were evaluated for in vitro sensitivity to fungicides labeled for Pythium root rot control at four rates. Etridiazole, fosetyl-al, and potassium phosphite completely inhibited mycelial growth, whereas isolates varied in response to mefenoxam, cyazofamid, propamocarb, fenamidone, azoxystrobin, and pyraclostrobin in vitro. Twenty-one additional isolates then were evaluated at label rates of these fungicides. Seven isolates were insensitive to label rates of all three quinone outside inhibitors (QoIs) and one isolate was insensitive to the QoIs and mefenoxam. These results provide guidelines for selecting fungicides to maximize control of Pythium root rot on poinsettia cultivars.

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