Epidemiology Research in Simulated Rhododendron Nursery Conditions

Transcription

1 Epidemiology Research in Simulated Rhododendron Nursery Conditions How does P. ramorum move and cause disease in a commercial nursery? Irrigation Water Inoculum from streams Aerial Inoculum from infected plant foliage Soil Inoculum from leaf litter/soil surface Experimental site, Felton California, in the vicinity of the First North American detection of P. ramorum in a commercial nursery Three experimental periods: Nov , Nov , Nov 2005-present

2 Seasonal Symptom Expression, Detection, and Infectivity on Rhododendron and Camellia Symptom Development in Field 1. Characterize leaf abscission: when and how frequently 2. Canker formation: when and how frequently 3. Lesion-size development rate Seasonal Inoculation Summer, fall, winter, spring Rhododendron and Camellia Detection Success with Analytical Methods 1. ELISA 2. Culture 3. PCR (Nested and Real Time) Lesion Viability and Infectivity Two experimental periods: July and July Sporulation Potential in vitro

3 Inoculum from Stream Water Inoculum could be spread on to new nursery and landscape hosts Could disease occur?

4 Inoculum from stream water Experimental factors tested Rhododendron Inoculum present (local stream water) Inoculum absent (city water) Sprinkler irrigation (overhead micro sprinkler) Drip irrigation Experimental layout Drip Sprinkler

5 P. ramorum presence in stream irrigation water / 18 2/ 11 2/ 18 2/ 25 3/ 18 3/ 4 4/ 1 4/ 15 4/ 22 4/ 26 5/ 14 5/ 20 5/ 4 6/ 19 6/ 29 6/ 3 7/ 15 7/ 22 7/ 29 7/ 8 Mean # active lesions detected per pear 2005 Detection and quantification by pear baiting

6 Infection Observed with Stream Water and Sprinkler Irrigation Experimental factors tested 1. City Water/ Drip 2. City Water/ Sprinkler 3. Stream Water/ Drip 4. Stream Water / Sprinkler Experimental Layout: (NORTH) 4/22/2005 only BLOCK Treatment # of necrotic lesions on multiple plants

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8 Infected Plants Observed within Plant Block Season 1/24/ Central Inoculated plant 10 inoculated leaves # Number of infected leaves in all 5 replicated blocks

9 4 m 2 Aerial dispersal 2004/2005 Rainfall collections during storms 1 4 m 2 1 =infected plant m Counts: CFU / liter = raintrap, trap # # = plant trap distance from center 4 m Traps 6-20, CFU/liter = 0.0 hours rainfall trap 1 trap 2 trap 3 trap 4 trap 5 mean SE 12/26/ /31/ /2/ /6/ /11/

10 2003, Marin County California Bay is a host surrounding some nurseries

11 Grand fir Infection Only Under or Near California Bay Los Gatos, 2005

12 Potential soil inoculum and undetected movement Leaf Drop

13 Viability of Infested Leaf Inoculum 100 infected leaf disks in sachet, per pot Viability of Soil Inoculum Weeks T = 0 T = 3 T = 6 % Viability T = 13 T = 18 T = 28 T = Field sachets 0 NA Greenhouse sachets T = Experiment

14 Could inoculum from soil eventually cause disease on new plants?

15 Dispersal from soil to plant Irrigation regimes tested, city water only Rainfall + Sprinkler Rainfall + Drip Experimental plot Central container inoculated with 100 infected 6mm rhododendron leaf disks, mixed in top 1 cm of soil Experimental layout

16 Dispersal from soil to plant Treatments 1. Drip / Soil inoculated 2. Sprinkler / Soil inoculated 3. Drip 4. Sprinkler Experimental Layout: (NORTH) BLOCK Treatment

17 Leaves touching soil become infected Season

18 Dispersal from soil to plant 4/22/2005 Treatments 1. Drip / Soil inoculated 2. Sprinkler / Soil inoculated 3. Drip 4. Sprinkler Experimental layout (before irrigation systems installed) BLOCK Leaf infection found on lower leaves and only above inoculated soil, not adjacent plants Experimental Layout: (NORTH) Treatment leaf leaf leaf

19 Sporulation of Infested Leaf Disks, Removed, and Flooded with Water Experiment Field 6 mm rhododendron leaf disk at 50 weeks Greenhouse

20 Seasonal Symptom Expression, Detection, and Infectivity on Rhododendron and Camellia Camellia Rhododendron Photo : C. Blomquist

21 Experimental Layout Potted plant with 10 infected leaf lesions Camellia consists of 6 blocks with 7 potted plants per block. Total of 70 infected leaves per block Rhododendron: consists of 6 blocks with 7 potted plants per block. Total of 70 infected leaves per block

22 1 week 2 week 4 week 8 week 12 week 16 week Fall 2005 Season

23 Rhododendron leaf lesion growth rate affected by season Summer inoculation: 8/18/05 Fall inoculation: 10/26/05 Winter inoculation: 2/1/06 Weeks after inoculation

24 Camellia leaf lesion growth rate affected by season Summer inoculation: 8/18/05 Fall inoculation: 10/26/05 Winter inoculation: 2/1/06 Leaf drop Weeks after inoculation

25 Leaf drop is a common result of foliar infection Leaf Drop Leaf Drop

26 Dropped leaves

27 Camellia Leaf Abscission Rate versus seasonal inoculation

28 Sporulation of Leaf Lesion Flooded Leaf Disks in vitro

29 Rhododendron Sporangia Production in Vitro NA Rhododendron Chlamydospore Production in Vitro NA Weeks after inoculation

30 Camellia Sporangia and Chlamydospore Production in vitro Leaf drop Weeks after inoculation

31 Is irrigation or rainfall sufficient to cause sporulation and movement within a nursery or landscape?

32 Laboratory Detection with PARP Selective Media

33 Camellia Flower Bud Blight

34 Camellia stem canker

35 Internal development

36 Rhododendron Flower Bud Blight

37 Secondary Leaf Infection 20,000 CFU / liter DI Water Wash

38 Flower bud drop

39 Acknowledgement USDA Forest Service California Association of Nurseries and Garden Centers David Chamber Research Associate, UCCE, Santa Cruz Co. Steve Koike Plant Pathology Cheryl Blomquist Diagnostician, CDFA, Sacramento Jennifer Davidson Research Affiliate, U of Hawaii Plant Pathology Farm Advisor, UCCE Monterey Co. Elizabeth Fitchner Sylvia Mori Statistician, USDA FS, Albany Post Doctoral Researcher, UCD

40 Steve Tjosvold University of California Cooperative Extension Santa Cruz and Monterey Counties