E.J. FICHTNER Department of Plant Pathology, UC Davis

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1 E.J. FICHTNER Department of Plant Pathology, UC Davis

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3 25 Soil Organic Matter Content b 2 % organic matter 15 1 a a 5 Bay Tanoak Redwood annual ph range:

4 Seasonal Distribution of Inoculum in Soil Bay Tanoak Redwood 3 Frequency of recovery 2 1 D J F M A M J J A S O N D J F M A M J J A S O N D F Winter 24 Winter 25 Winter 6

5 25 Seasonal Distribution of Inoculum in Leaf Litter Bay Tanoak Redwood 2 Frequency of recovery D J F M A M J J A S O N D J F M A M J J A S O N D F Winter 24 Winter 25 Winter 6

6 Objectives 1. Assess summer and winter survival of P. ramorum in infected leaf tissue in the upper portion of the soil profile and forest floor. 2. Investigate the influence of soil factors on pathogen survival. 3. Illustrate transmission of the pathogen from infected tissue to the bulk soil. 4. Investigate contribution of chlamydospores to pathogen survival. 5. Assess dormancy potential in life cycle.

7 Methods 4, Rhododendron leaf disks were inoculated with P. ramorum. The isolate was baited from soil at Jack London State Park in Glen Ellen, CA. Inoculated disks were placed in moist chambers and misted daily for 1 week. 1 leaf disks were placed in each of 36 nylon mesh sachets.

8 Site: Jack London State Park, Sonoma Co., CA 1 trees each of bay, tanoak, and redwood 4 points at 1.5 m radius from each tree 3 vertical locations: surface of leaf litter interface of leaf litter and soil 7 cm below soil surface Cylindrical barrier to lateral movement

9 Introduced: April 27, 24 Sampled: May 4, 24 May 11, 24 June 22, 24 October 2, 24 May 24, 25 May 31, 25 May 11, 25 July 19, 25 October 25, 25 Timepoints: 1 week 2 week 8 week 6 months

10 Sampling and data collection Leaf disk wet weight (bulked within sachet) Percent recovery of P. ramorum. Leaf disks submerged in PARP + hymexazol; stored at room temperature in dark for 2 wks. Gravimetric water content Soil ph soil sampled inside each pot; 5 subsamples per pot Soil baiting of P. ramorum Soils sampled inside and outside pots; Soil organic matter content Rhododendron leaf bait.

11 Recovery of P. ramorum from bulk soil 35 3 % positive recovery wk. 2 wk. 8 wk. 24 wk. 1 wk. 2 wk. 8 wk. 24 wk. Inside Pot Outside Pot

12 7 6 Soil moisture content tree P.1 time P.1 % water by weight Bay Tanoak Redwood /27/4 5/11/4 6/22/4 time (weeks) 1/2/4

13 Recovery of P. ramorum from infected leaf tissue 1 location*time P.1 8 % recovery 6 4 soil interface surface /27/4 5/11/4 6/22/4 Time (weeks) 1/2/4

14 Post-summer pathogen recovery 1 % recovery soil interface surface Field season

15 Precipitation at Jack London State Park Rainfall (mm) N D J F M A M J Data collection: K. Falk month

16 Soil Moisture in Subsequent Field Seasons 3 25 Bay Ψ= - 17 bars Bay Ψ= - 11 bars % gravimetric water week 24 week Ψ data: Swiecki, Fichtner, Dileo Field season

17 Significant Correlations (p <.5) Tree species-soil moisture Organic matter-soil moisture Soil moisture- water retention Soil moisture-water retention Water retention-recovery Water retention-recovery

18 Recovery after incubation in water 1 8 % Recovery 6 4 soil interface surface /27/4 6/22/4 1/2/4 Time (days)

19 Evidence of chlamydospore germination

20 Chlamydospore populations in leaf disks # spores/fov a b b Higher spore production in soil. Similar spore production in pre-hydration positive and negative disks. Suggests similar level of colonization soil interface surface P.r. (+) P.r. (-) More spores in posthydration positive disks. Suggests role of chlamydospores in recovery t=.2

21 Winter Survival: Soil Moisture 1 8 Bay Tanoak Redwood % water by weight Jan, 25 Feb, 25 March, 25 May, 25 time (weeks)

22 Two plant tissue types: Bay and rhododendron 4, leaf disks each of bay and rhododendron Deployed during rainstorm in January, 25 January, 26 Bay Rhododendron

23 1 8 Bay disks: Pre-hydration recovery P <.1 Soil Interface Surface % recovery Jan, 25 March, 25 May, 25 Feb, 25 Time (weeks) Evidence of chlamydospore germination? Break of dormancy?

24 1 Bay disks: Pre-hydration recovery Tree*time P < Bay Tanoak Sequoia % recovery Time (weeks) Recovery sig. lower in redwood-associated soils

25 1 Rhododendron disks: Pre-hydration recovery location*time p.1 % recovery Soil Interface Surface Chlamy germ? Dormancy? Jan, 25 March, 25 Feb, 25 May, 25 Time (weeks)

26 Chlamydospores: Rhododendron disks 1 a a species*location p.5 # chlamydospores/1x fov b ab ab ab ab b ab Bay Tanoak Redwood soil interface surface Vertical location

27 Conclusions Infected plant material may transmit the pathogen to bulk soil, creating hot spots of infestation. Evidence of long-term survival in leaf litter and soil. recovery from decomposing leaf fragments Culture methods not adequate to detect all viable inoculum. Dormancy of the pathogen? Chlamydospore germination? Winter: reduced survival in bay inoculum associated with redwoods. redwood soils suppressive to chlamydospore production in rhod. but Summer: Moisture retention in these organic soils may enhance survival.

28 Acknowledgements Funding: USDA Forest Service--Pacific Southwest Research Station Gordon and Betty Moore Foundation American Philosophical Society Jack London State Park, Glen Ellen,CA Technical assistance: Dave Rizzo, Jenny Davidson, Tricia Maloney, Cheryl Blomquist, Steve Tjosvold, Daniel Hüberli, Jennifer Parke, Ted Swiecki, Shannon Lynch