Baiting Phytophthora spp. from Water: A Southeastern Perspective

Phytophthora spp. in Water:
A Southeastern Perspective
Steve Jeffers & Jaesoon Hwang
Clemson University
Clemson, SC

Things to Cover…
• Isolation of Phytophthora spp. from water
• our philosophy after years of “playing”
• Why bait??
• Understanding the baiting process
• Our experience in the southeastern USA
• isolation of Phytophthora spp. from water
• isolation of P. ramorum from water

Isolation from Water:
Our Perspective
• Isolating Phytophthora spp. from water is a
2-step process: Recovery & Detection
• Step 1: Recovery of propagules from water
• using baits or filters
• Step 2: Detection of propagules on filters
or developing colonies in baits
• using selective medium, PCR, ELISA

Baiting to Recover Phytophthora
spp. from Water
• Advantages of baiting vs. filtering
• sample larger volume of water
• sample a given waterway over time: 1-3 weeks
• easy, simple, longer self-life
• Disadvantages of baiting vs. filtering
• requires a minimum & constant volume of water
• requires 2 trips to site – added cost & time
• potential to lose samples – theft, intense flow
• not quantitative

Why is Baiting Effective?
• Relies on the biology of Phytophthora spp.
• Zoospores are released & present in water
• Some unique features of zoospores
• negatively geotropic = rise to surface
• chemotactic = attracted to chemicals released
by host plants
• Typical or standard baits
• fruits, leaves (wounded & non-wounded), leaf
pieces, seedlings, cotyledons
• selected to be susceptible to target species

Recovery of Phytophthora spp.
from Water by Baiting
• Allows for the selective isolation of
Phytophthora spp. from water
• Used primarily for static bodies of water
• irrigation ponds, runoff water, lakes
• subsample of moving water: 1 to several liters
• flooded soil and plant parts
• Allows zoospores to seek out baits, encyst,
and infect – all of which takes time!

Baiting an irrigation pond

Baiting an irrigation pond

Recovery of Phytophthora spp.
from Streams
• In theory, baiting should not be effective!
• negative geotropism & chemotaxis should not
be factors in moving water
• zoospores do not have time to seek out baits,
encyst, and infect
• In reality, though, baiting streams does
work!
• Why??

Baiting a stream

Baiting a stream

Baiting Streams to Recover
Phytophthora spp.: Some Thoughts
• For infection to occur, zoospores need to
get “stuck” on baits
• like a bug on the windshield – but less lethal!
• What is the “glue”? biofilms, other??
• If this is true…
• recovery of propagules relies mostly on chance
• recovery cannot occur until the “glue” is
present, so propagules present early in the
baiting period will not be recovered
• Food for thought…

Isolating Phytophthora spp. from
Streams in the Southeast
• Based on 6 years of experience
• Evaluated recovery methods
• compared baiting & filtration
• compared types of baits
• wounded & non-wounded leaves
• currently evaluating in vitro baiting
• using a subsample of water
• Evaluating detection methods
• comparing culturing & PCR
• comparing types of PCR: real-time vs. nested

Species/Method
(based on 8 months & 5 locations)
Species
Recovery Method
Filter Bait: Wounded Leaf Bait: Non-wounded Leaf
P. cambivora +
P. cinnamomi +
P. citricola + + +
P. citrophthora + + +
P. gonapodyides + + +
P. heveae + +
P. seudosyringae + + +
Group A +
Group B +
Group C + + +
Group F + + +
Group I +
Group J +
Group L +

P. ramorum in Water in the
Southeast
• Filtration has been used most often
• baiting is not an option at most retail nurseries
• survey efforts still use baiting and P. ramorum is
being found
• All P. ramorum finds are associated with
nurseries where the pathogen is/was present
• primarily retail nurseries that have received
infected or infested plants

P. ramorum in SE Nurseries
• Since 2006 we have collected samples at
retail and production nurseries in six
Southeastern states where P. ramorum has
been found on diseased plants:
• AL, FL, GA, MS, NC, SC
• P. ramorum has been recovered from field
soil or water at one or more nurseries in
each state
• In most cases, P. ramorum has been
recovered in multiple years
• even after recommended mitigation treatments

P. ramorum in SE Nurseries
• P. ramorum is present in runoff
water leaving infested nurseries
• So far, P. ramorum has not become
established in natural ecosystems

Run-off water leaving a nursery…

Conclusions
• We need to re-think the baiting process
• can we refine the procedure to be more
effective for streams?
• P. ramorum is present in waterways in the
Southeast and is escaping from nurseries
• Infested water at nurseries needs to be
captured and treated before being released