Preferred Abstract (Original):
Commercially available ELISA tests for detecting
Phytophthora and
Pythium species were used to detect propagules of these genera in water samples. Samples were filtered through 0.45-
?m
filters to concentrate propagules before extraction. Heating filter
residues to 100 C for 5 min yielded extracts that were equal or superior
in reactivity to those obtained by liquid nitrogen disruption. As few
as 30–40 zoospore cysts were detected in filter pad extracts. Detection
sensitivity (propagules per liter) depends on the volume of water that
can be passed through the filters. A water sample collected in late
winter from a recycling pond in a northern California nursery did not
contain any viable propagules of pythiaceous fungi or detectable
antigen. A similar water sample collected in early spring from a
southern California nursery contained 442 viable propagules per liter of
water. The species recovered on agar media were
Phytophthora parasitica, P. citrophthora, P. cryptogea, and an unidentified
Phytophthora species, in addition to
Pythium coloratum, P. rostratum, P. middletonii, P. ultimum var.
sporangiferum,
and Pythium ‘L’ group. Reactivity of filter extracts in Phytophthora
ELISA tests was proportional to the quantity of filter residue
extracted. All of the
Phytophthora species recovered reacted positively with Phytophthora kits and negatively with Pythium kits. All of the
Pythium
species recovered also reacted positively with Phytophthora and
negatively with Pythium kits. With a relatively simple filter-extraction
procedure, the ELISA kits effectively detected
Phytophthora and
Pythium
in water samples. Although the tests are fallible at the genus level,
they still could be used in commercial nurseries, where there is no
known acceptable tolerance for these genera in irrigation water.