scholarly journals Evaluation of Poinsettia Cultivars for Resistance to Pythium Root Rot Caused by Pythium aphanidermatum

2017 ◽  
Vol 27 (6) ◽  
pp. 805-812 ◽  
Author(s):  
Emma C. Lookabaugh ◽  
Brian Whipker ◽  
Barbara B. Shew
Keyword(s):  
North Carolina ◽  
Host Resistance ◽  
Root Rot ◽  
Partial Resistance ◽  
Integrated Management ◽  
Pythium Aphanidermatum ◽  
Euphorbia Pulcherrima ◽  
Predominant Species ◽  
Pythium Root Rot ◽  
Color Response

Pythium aphanidermatum is the predominant species causing pythium root rot of commercially grown poinsettia (Euphorbia pulcherrima) in North Carolina. Pythium root rot is primarily managed with strict sanitation practices and preventative fungicide applications. To determine if host resistance could play a role in the integrated management of pythium root rot, information on the susceptibility of commercial poinsettia cultivars is needed. Commercially available poinsettia cultivars were inoculated with P. aphanidermatum 3 weeks after transplant and evaluated for resistance to pythium root rot 2 months later. Thirty-four cultivars were evaluated for resistance in 2014 and 58 cultivars were evaluated in 2015, for a total of 62 cultivars evaluated. Twenty-nine cultivars were evaluated in both years. Most cultivars were susceptible to pythium root rot and none were completely resistant. However, several cultivars demonstrated partial resistance to pythium root rot. Interspecific hybrid cultivars, including Luv U Pink, had a higher level of partial resistance when compared with conventional cultivars. Partial resistance varied across bract color, response time, and plant vigor groupings. Overall, 6 of 13 partially resistant cultivars identified in 2015 had red bracts. These results indicate that growers should be able to choose among several red bract cultivars that have higher-level partial resistance to pythium root rot than others.

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.

scholarly journals Resistance of Nineteen Major Caladium Commercial Cultivars to Pythium Root Rot

EDIS ◽  
1969 ◽  
Vol 2005 (3) ◽  
Author(s):  
Zhanao Deng ◽  
Brent K. Harbaugh ◽  
Richard O. Kelly ◽  
Teresa Seijo ◽  
Robert J. McGovern
Keyword(s):  
Root Rot ◽  
Integrated Management ◽  
Ornamental Plants ◽  
Control Measures ◽  
Publication Date ◽  
Aesthetic Value ◽  
Resistance Level ◽  
University Of Florida ◽  
Pythium Root Rot ◽  
Commercial Cultivars

Caladiums (Caladium xhortulanum) are popular ornamental plants widely grown for their bright colorful leaves. Pythium root rot, caused by P. myriotylum, is one of the few soil-borne diseases in caladium that can dramatically reduce plant growth, aesthetic value, and tuber yield. Identification and use of disease-resistant cultivars has proven to be an important and economically viable strategy for integrated management of major diseases in crops and for reducing the use of pesticides. This strategy will be particularly useful for caladiums in the landscape and home gardens, because in such cases choices of root rot control measures are limited. However, information on the resistance level of commercial caladium cultivars has been lacking. This document is ENH996, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date December 2, 2004.  ENH996/EP251: Resistance of Nineteen Major Caladium Commercial Cultivars to Pythium Root Rot (ufl.edu)

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.

scholarly journals Screening for Resistance to Pythium Root Rot among Twenty-three Caladium Cultivars

EDIS ◽  
2019 ◽  
Vol 2005 (11) ◽  
Author(s):  
Zhanao Deng ◽  
Brent K. Harbaugh ◽  
Rick O. Kelly ◽  
Teresa Seijo ◽  
Robert J. McGovern
Keyword(s):  
Root Rot ◽  
Integrated Management ◽  
Cooperative Extension Service ◽  
Publication Date ◽  
University Of Florida ◽  
Resistant Cultivars ◽  
Evaluation Procedures ◽  
Pythium Root Rot ◽  
Commercial Cultivars ◽  
Screening For Resistance

Pythium root rot, caused by Pythium myriotylum (Ridings and Hartman, 1976), is a very damaging disease to caladium plants (Caladium x hortulanum). Use of disease-resistant cultivars has been an effective and economically viable strategy for integrated management of major diseases in numerous crops. This strategy could be used to control pythium root rot in caladium if resistant cultivars could be identified or developed. In an evaluation of 19 major commercial cultivars, 'Candidum', 'Candidum Jr.', 'Frieda Hemple', and 'White Christmas' were found to have a moderate level of resistance to Pythium. To find more resistant cultivars, twenty-three additional commercial cultivars were screened using the same Pythium isolates, inoculation and evaluation procedures as described earlier (Deng et al. 2004). This document is ENH1008, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date September 27, 2005. ENH1008/EP259: Screening for Resistance to Pythium Root Rot among Twenty-three Caladium Cultivars (ufl.edu)

scholarly journals Integrated Management Strategies for Phytophthora sojae Combining Host Resistance and Seed Treatments

Plant Disease ◽  
2009 ◽  
Vol 93 (9) ◽  
pp. 875-882 ◽  
Author(s):  
A. E. Dorrance ◽  
A. E. Robertson ◽  
S. Cianzo ◽  
L. J. Giesler ◽  
C. R. Grau ◽  
...  
Keyword(s):  
South Dakota ◽  
Host Resistance ◽  
Partial Resistance ◽  
Integrated Management ◽  
Management Strategies ◽  
Heavy Precipitation ◽  
Phytophthora Sojae ◽  
Growth Stages ◽  
Seed Treatments ◽  
The Past

Phytophthora sojae has re-emerged as a serious soybean pathogen in the past decade. This may be due in part to changes in resistance levels in current cultivars, adoption of P. sojae populations to deployed Rps genes, and highly favorable environments in the past decade. This multilocation study evaluated the effect of seed treatments on the incidence and severity of Phytophthora root and stem rot on soybeans with different combinations of Rps genes and levels of partial resistance. The efficacy of the seed treatments was highly variable across locations. Seed treatments (metalaxyl and mefenoxam) provided protection and increased yields across cultivars in locations where rain or irrigation occurred shortly after planting (Ohio, South Dakota, and Ontario). However, there were no significant differences in stand or yield consistently across cultivars in Iowa, Nebraska, Wisconsin, or Ohio, where heavy precipitation did not occur until later growth stages. The environment, levels of inoculum, and pathogen complex may have played a role in the different responses to the seed treatments and to the different combinations of Rps genes and levels of partial resistance to P. sojae in the cultivars. Fields that are poorly drained and have P. sojae populations with complex pathotypes may benefit the most from seed treatments. Individual fields where producers may see the greatest benefit to utilizing these integrated management strategies will need to be identified.

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 Pythium Root Rot of Sugarcane in Puerto Rico. I. Pathogenicity and Identification

1969 ◽  
Vol 64 (1) ◽  
pp. 54-62
Author(s):  
Lii-Jang Liu
Keyword(s):  
Puerto Rico ◽  
Root Growth ◽  
Root Rot ◽  
Pythium Aphanidermatum ◽  
Sugarcane Variety ◽  
Pythium Species ◽  
Southern Coast ◽  
Ratoon Stunting Disease ◽  
Pythium Root Rot ◽  
Greenhouse Tests

Pythium aphanidermatum, a previously unreported species for Puerto Rico, and P. deliense were frequently isolated from sugarcane fields in the southern coast of Puerto Rico where symptoms of ratoon stunting disease were also observed. P. acanthicum, P. butleri, P. echinocarpum, P. graminicola, P. oligandrum and P. periplocum were also isolated. The pathogenicity of these Pythium species to sugarcane variety PR 1152 was demonstrated in replicated laboratory and greenhouse tests. P. aphanidermatum alone significantly reduced dry weights of top and root growth of sugarcane variety PR 1085. Reductions in dry weights of top and root growth incited by the combination of P. deliense and P. aphanidermatum were the same as those caused by P. aphanidermatum alone. However, the reductions in dry weights of top by inoculation of sugarcane with both P. aphanidermatum and the ratoon stunting disease causal agent were greater than those caused by inoculation with either one alone.

scholarly journals Integrated Management of Downy Mildew on Slicing Cucumber With Fungicides and Host Resistance But Not Trellising

Plant Disease ◽  
2019 ◽  
Vol 103 (10) ◽  
pp. 2592-2598
Author(s):  
Anthony P. Keinath
Keyword(s):  
Downy Mildew ◽  
Host Resistance ◽  
Management Practices ◽  
Integrated Management ◽  
Cultivar Resistance ◽  
Fall Season ◽  
Fungicide Treatment ◽  
Progress Curve ◽  
Management Techniques ◽  
The Mean

The objective of this study was to evaluate fungicide applications, host resistance, and trellising, alone and in combination, as management practices for downy mildew on slicing cucumber. A split-split plot experimental design was used with three and four replications in spring and fall 2017, respectively. The whole-plot treatment was fungicide, four applications of chlorothalonil (Bravo Weather Stik 6SC) alternated with three applications of cyazofamid (Ranman 400SC), or water. Split plots were nontrellised or trellised with four strings supported by stakes. Split-split plots were cultivar Bristol, which is intermediately resistant to downy mildew, or cultivar Speedway, which is susceptible to downy mildew with similar parentage as Bristol. In both seasons, area under the disease progress curve (AUDPC) values were lower with fungicides than water for both cultivars. In the spring, AUDPC for Bristol was lower than for Speedway regardless of fungicide treatment. In the fall, Bristol had a lower AUDPC than Speedway with fungicides, but the AUDPC did not differ between the two cultivars with water. The mean AUDPC for trellised plants (376.2) was lower than for nontrellised plants (434.0; P = 0.007). Fungicide applications increased marketable and total fruit weights in both seasons (P ≤ 0.0002). Marketable weight with fungicides was almost double (93% greater) the marketable weight with water. Marketable weight was 55% greater for Bristol than for Speedway in spring, but yields did not differ between cultivars in fall (season-by-cultivar interaction, P ≤ 0.0003). Because trellising had no effect on marketable yields (P = 0.11), trellising is not recommended for managing downy mildew on slicing cucumber. Of the three management techniques examined, fungicides had the largest effects on disease and yields, followed by cultivar resistance.

Comparison of North Carolina, Georgia, and Florida Isolates of Cylindrocladium parasiticum

1999 ◽  
Vol 26 (2) ◽  
pp. 80-84
Author(s):  
J. E. Hollowell ◽  
B. B. Shew ◽  
M. K. Beute
Keyword(s):  
North Carolina ◽  
Root Rot ◽  
Regional Differences ◽  
Black Rot ◽  
Temperature Growth ◽  
Seedling Disease ◽  
Cylindrocladium Parasiticum ◽  
Temperature Controlled ◽  
Gradient Plate ◽  
Temperature Optima

Abstract Thirteen isolates of Cylindrocladium parasiticum Crous, Wingfield & Alfenas from North Carolina and 11 from Georgia were grown on plates of PDA at 20,25, and 30 C on a temperature-gradient plate. Culture diameters were measured daily for 6 d. Significant differences were not observed among isolates grown at 20 C and cultures was smaller as compared with those grown at 25 and 30 C. At 25 and 30 C, isolates varied consistently in growth. On average, Georgia isolates grew slightly less than North Carolina isolates, and all isolates grew better at the warmer temperature. Growth of three North Carolina isolates was compared to four Florida isolates in a second experiment. Florida isolates grew significantly faster than North Carolina isolates at all temperatures. Isolates from the three states were compared for their ability to cause root rotting on peanut at 25 and 30 C. Plants were grown in soil infested at a standardized inoculum density in temperature-controlled water bath tanks for 7 wk at which time roots were rated for Cylindrocladium black rot development. Georgia isolates caused more root rot than either North Carolina or Florida isolates at both temperatures and also caused more seedling disease. State effects were significant; Florida isolates caused less root rot than Georgia isolates. Temperature by state interactions were not significant which means that high temperature-tolerant isolates of C. parasiticum have not evolved from regional differences in soil temperature. Further, North Carolina field isolates do not appear to have changed in temperature optima since the 1970s.

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