Comparison of membrane filters as a tool for isolating pythiaceous species from irrigation water.

ABSTRACT Filter-based isolation is the primary approach for quantifying plant pathogens in irrigation water; however, the performance of various membranes is largely unknown. This study evaluated nine hydrophilic membranes for recovery of pythiaceous species, a group of very common and destructive pathogens on numerous ornamental plants and many agronomic crops. Three sources of water samples and three plating methods were used for the membrane comparison. Durapore5, Millipore5, and Osmonics5 filtered 100 ml of irrigation water or 50 ml of irrigation runoff in 10 s or less, whereas the other membranes required 34 s to 13.5 min or even a second membrane to filter the same water sample volume. Millipore5 and Durapore5 showed greater recovery rates than other membranes for all water sources when the membranes were directly inverted onto agar plates. Durapore5 was also one of the top two membranes for spore suspension and irrigation water samples when membrane washings were spread over the agar surface. Durapore5 was the only membrane that consistently performed well for both spore suspension and irrigation water samples. These data suggest that use of Durapore5 not only increases the sensitivity of filter-based isolation for quantifying pythiaceous species in irrigation water but also saves filtering time.