Preferred Abstract (Original):
Water samples were collected from effluent holding ponds
at one northern and two southern California nurseries that practice the
capture and recirculation of irrigation runoff water. Nursery effluent
samples were collected approximately monthly over a 12-mo period and
aliquots filtered through 0.45-µm Millipore filters. Filter residues
were resuspended and dispersed onto selective agar media in petri dishes
to estimate the numbers of viable propagules of
Phytophthora spp. or total pythiacious fungi. Propagule numbers varied greatly from month to month at each nursery location.
Pythium propagules were consistently the most numerous, ranging from 500 lo 1,500 per liter, whereas the number of
Phytophthora spp.
propagules ranged from 0 to 400 per liter. At the northern California
nursery, propagule numbers were lowest during winter months and highest
during warm seasons. Seasonal fluctuations in inoculum load were not
apparent in the southern California nurseries.
P. ciirophthora was the most commonly detected
Phytophthora sp. Other species frequently recovered included
P. citricola, P. cinnamomi, and
P.
cryptogea. Isolates of
P.
parasitica, P. megasperma, and
P.
syringae were recovered less frequently. Water samples also were tested for
Phytophthora spp.
using commercially available ELIS A tests. The ELIS A reaction
intensity of filter pad extracts was correlated with the numbers of
propagules estimated to be on the filters, but the correlation was
stronger at some times than at others. This is believed to reflect
temporal differences in water sample quality or species mixtures