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Influence of Ph and Etridiazole on Pythium Species

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Influence of Ph and Etridiazole on Pythium Species Influence of pH and Etridiazole on Pythium time of retail sale (Hausbeck et al., 1987; Moorman, 1986). Numerous Species Pythium species cause disease on or- namental crops; however, P. ulti- mum, P. aphanidermatum,and 1 2,3 Charles S. Krasnow and Mary K. Hausbeck P. irregulare are isolated frequently from symptomatic plants in commer- cial production (Del Castillo Munera ADDITIONAL INDEX WORDS. poinsettia, geranium, Phytophthora, oomycete and Hausbeck, 2016; Moorman SUMMARY. Pythium root rot (Pythium sp.) is ubiquitous in Michigan greenhouses et al., 2002). Pythium species are that produce herbaceous ornamentals, an industry worth $393 million in the state. ubiquitous in natural environments, Disease symptoms include stunting, flowering delay, root rot, and death. Fungi- and maintaining production facilities cides that are highly effective against pythium root rot are limited, and pathogen free of the pathogen is difficult. Path- resistance has been documented. The objectives of this study were to determine the ogenic Pythium species were found in sensitivity of Pythium irregulare, Pythium ultimum, and Pythium aphanidermatum isolates from symptomatic herbaceous greenhouse ornamentals to the fungicide irrigation water (Bush et al., 2003; etridiazole and to determine the influence of pH and etridiazole on Pythium Shokes and McCarter, 1979) and mycelial growth and asexual reproduction. Isolates were tested in vitro for dust from greenhouse walk alleys sensitivity to etridiazole by growing the pathogen on amended V8-agar plates sealed (Stephens et al., 1983). Soilless pot- in plastic containers to minimize fungicide loss from the vapor phase. The majority ting medium can be conducive of isolates of all three species were sensitive to the fungicide with EC50 (effective to pythium root rot because of lim- concentration resulting in 50% inhibition of linear growth) values ranging from ited microbial activity (Bolton, 1977; m Á L1 0.10 to 5.03 g mL . Two isolates of P. irregulare had an EC90 (effective Stephens and Stebbins, 1985). How- > m Á L1 concentration resulting in 90% inhibition of linear growth) value 80 g mL . ever, reductions in seedling diseases The acidity of the medium influenced the ability of etridiazole to inhibit Pythium L and root rot after amending potting mycelial growth and asexual reproduction. Agar plates amended with 1 mgÁmL 1 etridiazole and adjusted to pH 4.5 limited the mycelial growth of two P. medium with biological controls have aphanidermatum isolates and two P. irregulare isolates by 90% and 56%, re- heightened the use of such manage- spectively, compared with amended agar at pH 6.5. Sporangial formation by P. ment tools in ornamental crop pro- aphanidermatum was less frequent on mycelial disks incubated in etridiazole- duction (Lewis and Lumsden, 2001; amended sterile distilled water (SDW) at pH 4.5 than pH 6.5 (P < 0.05). P. Thrane et al., 2000). Sanitation and aphanidermatum zoospore cyst germination was less sensitive to etridiazole than preventive measures remain impor- sporangia or mycelial growth; however, the influence of pH and fungicide on cyst tant to reduce inoculum levels in the < m Á L1 germination was significant (P 0.01). At 250 g mL etridiazole and solution greenhouse (Stephens et al., 1983). pH 4.5, zoospore cyst germination was inhibited 99.9% compared with 94.2% at pH Additionally, greenhouses may in- 6.5. In a greenhouse experiment, disease symptoms were observed on ‘Pinto White’ advertently purchase plantlets or geranium (Pelargonium ·hortorum) in a potting medium infested with P. aphani- dermatum and adjusted to pH 4.5 or 6.5; however, plant health and fresh weight cuttings that are infected but asymp- were greater in low pH potting medium. Etridiazole, applied as a drench at tomatic from propagation green- transplant, did not improve control of root rot for plants grown at low pH (P > houses (Moorman and Kim, 2004; 0.05). Fresh weight of plants grown in infested potting medium adjusted to pH 4.5 van der Gaag et al., 2001). Infected and amended with a single drench of etridiazole (100 mgÁmLL1) was reduced 20%, roots or root mucilage support the statistically similar to the untreated control. Adjusting the acidity of irrigation production of oospores that may water at the time of etridiazole application in ebb and flow and flood floor become lodged in greenhouse fix- production systems could be beneficial in pythium root rot management of certain tures and piping (Zheng et al., ornamental crops if plants have tolerance to low pH. 2000) and are a source of primary inoculum. Survival of mycelium is ythium root rot causes signifi- plants, causing wilting, stunting, also possible in the controlled green- cant losses in ornamental green- delayed flowering, and plant death. house environment (Stanghellini, Phouse production in Michigan, Catastrophic losses can occur if 1974), making Pythium an intracta- an industry worth an estimated $393 plants develop symptoms near the ble problem. Greenhouse operations million (U.S. Department of Agricul- ture, 2014). Pythium species infect roots and root hairs of ornamental Units To convert U.S. to SI, To convert SI to U.S., multiply by U.S. unit SI unit multiply by Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI 48824 29,574 fl oz mL 3.3814 · 10–5 The authors thank Samantha Borowski for technical 29.5735 fl oz mL 0.0338 assistance. This research was partially funded through 25.4 inch(es) mm 0.0394 a Cooperative Agreement between the USDA-ARS 645.1600 inch2 mm2 0.0016 Plant Protection Research Unit, Ithaca, NY and the 1 micron(s) mm1 Michigan State University Department of Plant, Soil 28.3495 oz g 0.0353 and Microbial Sciences (#58-8062-5-036). 28,350 oz mg 3.5274 · 10–5 1Former Graduate Research Assistant 0.001 ppm gÁL–1 1,000 Á –1 2Professor 1 ppm mg L 1 1 ppm mgÁmL–1 1 3 Corresponding author. E-mail: [email protected]. 0.001 ppm mLÁL–1 1,000 doi: 10.21273/HORTTECH03633-16 (°F – 32) O 1.8 °F °C(°C · 1.8) + 32 • June 2017 27(3) 367 RESEARCH REPORTS that use flood floor or ebb and flow mitochondrial membrane between Pythium root rot continues to cause bench systems that recycle irrigation cytochromes b and c (Halos and losses in commercial greenhouses de- water are at increased risk of spread- Huisman, 1976b). The mode of ac- spite routine fungicide use (Hausbeck ing Pythium speciesasmultiple tion of etridiazole is considered mul- and Harlan, 2013; Moorman and ranges may be irrigated in the same tisite as cellular proteins may also be Kim, 2004), planting resistant culti- day and effectively disperse pathogen disrupted (Lyr, 1995). Resistance to vars (Chagnon and Belanger, 1991), propagules (Hoitink, 1991). etridiazole has not been observed in and preventive measures (Stephens The fungicides, mefenoxam [ac- Pythium species (Hausbeck and Harlan, and Stebbins, 1985), heightening tive enantiomer of metalaxyl (Subdue 2013; Jamart et al., 1988; Price and the importance of integrated disease Maxx; Syngenta Crop Protection, Fox, 1986; Raabe et al., 1981; management. Our objectives were Greensborough, NC)] and etridia- Stephens and Stebbins, 1985), al- to a) determine the sensitivity of P. zole (Terrazole; OHP, Mainland, though mechanisms for tolerance to ultimum, P. aphanidermatum, and P. PA), have been used for 40 years the fungicide are recognized (Halos irregulare isolates from Michigan to manage pythium root rot of orna- and Huisman, 1976a). Rotation of greenhouses to etridiazole; and mental crops (McCain and Byrne, fungicides with different modes of b) determine the influence of pH 1966; Moorman and Kim, 2004; action has been recommended to de- and etridiazole on P. aphaniderma- Raabe et al., 1981). Historically, lay the development of fungicide re- tum and P. irregulare growth and these fungicides have provided effec- sistance in Pythium and Phytophthora asexual reproduction. tive control of pythiaceous organ- populations (Ferrin and Rohde, isms when applied as soil drenches 1992; Hausbeck and Harlan, 2013); Materials and methods (Benson, 1979; Hausbeck and Harlan, however, there are limited numbers P. aphanidermatum (n = 9), P. 2013; Raabe et al., 1981; Stephens of additional fungicide options that irregulare (n = 14), and P. ultimum and Stebbins, 1985) or mixed into effectively control pythium root rot. (n = 14) isolates originally recovered the potting medium (McCain and Recently, labeled fungicides with ac- from symptomatic floriculture crops Byrne, 1966). Resistance to mefe- tivity toward phytophthora root rot in Michigan were selected from the noxam has developed in greenhouse (Phytophthora sp.), such as fenamidone culture collection of M.K. Hausbeck populations of Pythium and Phytoph- (Hausbeck and Harlan, 2013), have at Michigan State University (Table thora because of the site-specific been determined to be ineffective 1). The isolates were maintained on mode of action of the fungicide and against pythium root rot in green- cornmeal agar [CMA (17 gÁL–1 corn- selection pressure from the repeated house trials (Enzenbacher et al., meal)]. Molten V8 agar [163 mLÁL–1 use of this active ingredient (Del 2011; Santamaria and Uribe, 2013). V8 juice, 3 gÁL–1 calcium carbonate –1 Castillo Munera and Hausbeck, Cultural practices that reduce (CaCO3), 16 gÁL agar] was cooled 2016; Lamour et al., 2003; Moorman growth and dissemination of Pythium to 50 °C and amended with etridia- et al., 2002). In Michigan, greater species are important in disease- zole (Terrazole 35 WP dissolved in than 35% of Pythium species isolates management programs (Hausbeck and SDW) at concentrations of 0, 0.1, collected from greenhouses were re- Harlan, 2013; Price and Fox, 1986; 1.0, 2.5, and 6.2 mgÁmL–1 a.i. For six sistant to mefenoxam (Del Castillo Stephens and Stebbins, 1985). Lim- isolates of P. irregulare, preliminary Munera and Hausbeck, 2016). Con- iting the duration of irrigation in ebb EC50 values were outside of this range trol failures have been reported in and flow systems reduced pythium of concentrations.
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