title: Use of Dehydrated Agar to Estimate Microbial Water Quality for Horticulture Irrigation.
abstract: Petrifilms are dehydrated agar culture plates that have been used to quantify colony forming units (CFU) mL of either aerobic bacteria (Petrifilm-AC) or fungus (Petrifilm-YM), depending on substrate composition. Microbes in irrigation systems can indicate biofilm risk and potential clogging of irrigation emitters. The research objective was to compare counts on Petrifilms versus traditional, hydrated-agar plates using samples collected from recirculated irrigation waters and cultures of isolated known species. The estimated count (in CFU mL) from a recirculated irrigation sample after 7 d of incubation on Petrifilm-YM was only 5.5% of the count quantified using sabouraud dextrose agar (SDA) with chloramphenicol after 14 d. In a separate experiment with a known species, Petrifilm-YM did not successfully culture zoospores of . Isolates of viable zoospores were cultured successfully on potato-dextrose agar (PDA), with comparable counts with a vegetable juice medium supplemented with the antibiotics pimaricin, ampicillin, rifamycin, pentochloronitrobenzene and hymexazol (PARP-H). The quantification of pv. Begoniaceae on Petrifilm-AC was not significantly different ( < 0.05) than on PDA, but was lower than on Reasoner and Goldrich agar (R2A) or with a hemocytometer. The current formulation of Petrifilm-YM is unlikely to be a useful monitoring method for plant pathogens in irrigation water because of the inability to successfully culture oomycetes. However, Petrifilm-AC was an effective method to quantify bacteria and can provide an easy-to-use on-farm tool to monitor biofilm risk and microbial density.
authors.forename: Dustin P
authors.initials: DP
authors.lastname: Meador
authors.forename: Paul R
authors.initials: PR
authors.lastname: Fisher
authors.forename: Charles L
authors.initials: CL
authors.lastname: Guy
authors.forename: Philip F
authors.initials: PF
authors.lastname: Harmon
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Peres
authors.forename: Max
authors.initials: M
authors.lastname: Teplitski
mesh_terms: D000362:Agar; D001419:Bacteria; D015169:Colony Count, Microbial; D003470:Culture Media; D060753:Water Quality
chemical_list: D003470:Culture Media; D000362:Agar