Factors affecting the success and spread of invasive species. Matteo Garbelotto Department of ESPM

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1 Factors affecting the success and spread of invasive species Matteo Garbelotto Department of ESPM

2 1000 canker disease of walnuts 2001 California invaded: 1849 A.D. Port Orford Cedar Root Disease 1950s Xylella scorch of maples 2000s Expansion of root pathogens Post 1880s Root canker of Pacific Madrone and Bay laurel (70s) Sudden Oak Death 1990s Cypress canker 20s Colored canker of sycamore 70s Pitch canker disease 1980s Manzanita die-back 2004 White pine blister rust 1930s Dutch Elm Disease 1960s Oak root canker 2000

3 Invasion success: 1)- History of introduction: introduction pathways, single vs. multiple introductions 2)- Diversity of Founder populations: is higher diversity necessary? 3)- Further spread: multiple pathways, single large-scale pathway, only natural spread 4)- Is Invasiveness correlated to transmission efficacy? 5)- Ecological and landscape-level constraints to spread of invasive species 6)- What can we do to mitigate introductions

4 Invasive species Rank as second in importance in the reduction of biodiversity after loss of habitat Invasive pathogens and pests are particularly insidious because of their direct impact on hosts Invasive pathogens/pests can be native and increasing their incidence due to changes in the ecology of sites or exotic because introduced from other world regions

5 Differences in outbreaks if species is native vs. exotic Emerging native species will lead to progressive increase in diseases incidence Exotic species normally leads to abrupt outbreaks Lag phase: is time necessary to identify an introduced pathogen or pest: it is directly proportional to the effective transmission rate

6 Number of invasive forest pathogens (on y axis) since the 1800s from Santini et al.

7 History of introduction: introduction pathways, single vs. multiple introductions

8 No evidence of introductions linked to travel, almost all cases linked to trade connections Very few cases of proven single introductions leading to a successful invasion. If invasion started by a single introduction, then normally multiple isolates facilitate establishment. Single introductions result in more restricted zones of infestations.

9 INTRODUCTION - The model system: Heterobasidion annosum s.l. (Fr.) Bref. H. irregulare (North american) H. annosum s.s. (European) (Garbelotto and Gonthier, 2013) The model system: Heterobasidion annosum s.l. (Fr.) Bref. Heterobasidion annosum s.l. is a species complex comprising five species: H. irregulare, H. occidentale, H. parviporum, H. abietinum and H. annosum sensu strictu. All species are necrotrophic pathogens regarded as the most destructive disease agents of conifers.

10 Single introduction of three isolates through infected wood by US Army in In 2014, ZOI was about 100 km long H. irregulare Invasion area

11 How was Heterobasidion introduced from Eastern North America? The Estate of Castelporziano has been closed to the public since 1562, and is comprised of an exclusively native Italian flora (Manes et al., 1997) June 5 th - July 10 th, 1944 training and resting camp 337 th Regiment Review Castelporziano

12 Some facts about Heterobasidion irregulare New trees are infected only by airborne basidiospores (sexually produced spores). Sex requires presence of multiple isolates Most effective infection courts are stumps: standing trees are infected by stump-to-tree root contagion. This expands the extent of the lag phase It can infect multiple hosts but has preference for Pinaceae and possibly oaks; so host range is somewhat limited Origin has been identified in Georgia- Alabama: movements at the same latitude most successful but climate is not Mediterranean

13 Suitable forests are extremely fragmented: main cause for slow expansion 20 km 20 km

14 Different outcome when invasive species is vectored by insect Oak wilt caused by Ceratocystis fagacearum is vectored by nitidulid beetles and some oak bark beetles

15 Spread is accelerated even more when: We have a mixed spread pathway Laurel wilt spread by exotic ambrosia beetle carrying exotic fungus Raffaelea lauricola 1000 canker disease of walnut caused by the emergent fungus Geosmithia pallida vectored by the invasive walnut twig beetles In both of these cases short distance spread is commonly effected by insects, insects can be carried by winds long distances leading to medium or long distance spread, and wood with insects can be moved very long distance across or between continents

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17 Distribution of TCD as of 2009

18 Distribution of TCD as of 2013

19 Walnut twig beetle

20 Close-up symptoms Mortality caused by coalescence of multiple cankers

21 The most insidious spread pathways are those mediated by humans Movement of plant parts, plant products and wood Movement of live plants: both ornamental and used for production, reforestation, restoration efforts Agriculture: movement of rootstock or of prized varieties of crop species

22 White Pine Blister rust: long distance dispersal but Eastern and Western Introductions through pine seedlings are still clearly distinct. Also there were multiple introduction in the East and Midwest

23 Introduction of Asian chestnuts resistant to Phytophthora spp. may have caused the Western outbreak of the Chestnut blight in France. Note there are two distinct populations suggesting at least two introductions

24 P Sudden Oak death: a destructive disease of wildlands Phytophthora ramorum Ramorum blight: a controllable disease of ornamental plants emerged in the mid 1980s

25 Molecular fingerprinting and populations genetics analyses have helped us reconstruct the history of SOD on the West Coast 1- Pathogen strains from ornamental nurseries are basal, i.e. nursery strains are the founder genotypes of the West Coast infestation 2- When the pathogen was still unknown, infected plants were being bought and carried throughout the State 3- We have been able to identify over a dozen introductions and/or escapes of the pathogen 4- Those introductions are responsible for most of the range of the pathogen (they approximately correspond to the darker circles) 5- Thus initial success of SOD pathogen due to its pervasive presence in the ornamental pant industry

26 Pine pitch canker (Fusarium circinatum) Spores can be found on infected plants and seeds. Connection between early spread in Ca and Christmas trees industry

27 Phylogram of P. cinnamomi based on SSR markers Some pathogens are pervasive in multiple commodities Sierra Different commodities may harbor different genotypes The presence of the same genotype in distant locations but in the same industry indicates that industry is responsible for long distance movement of the pathogen Sierra South Sierra Bay area Commodities are the most likely source for wildland infestations; in order to corroborate this point it is necessary to show that wildland-commodity genotypes are the same and in the same general area In California distribution of wildland genotypes is not random but linked to local commodity

28 Number of Invasive Forest pathogens on Y axis, by medium of introduction (left) and by type of disease (right)

29 Range expansion of invasive species Host specificity and host availability Competitors Climatic requirements Latent period Sporulation potential and spore size Ability to survive in absence of hosts Epidemiology Phenotypic plasticity

30 Host specificity and host availability The more host-specific, the tighter he relationship with presence and density of host. Where host is present with significant population sizes, invasive will move fast Generalists usually move slower, because of a phenomenon known as Inoculum Dilution. i.e. inoculum infects plants that may not support good sporulation Jury is still out on how host diversity affects invasive spread but there is some support for simple ecosystem being moderately resilient to spread, low diversity being less resilient, and high diversity being the most resilient

31 Competitors In general they slow down range expansion by pre-occupying the niche that the invasive species would have picked, but there are different scenarios: Synergy: co-infection may be beneficial Hybridization: this can lead to speciation with changes in virulence and host range, and it can lead to adaptation through gene introgression between species

32 SOD Bay/Oak association Bay Yearly Coast Live Oak (no sporulation) Canker margin in phloem Wave years Bleeding canker Sporangia Soil

33 Bay tips can be infected by other Phytopthoras that are only mildly pathogenic P. ramorum P. nemorosa EARLY 2009 PEAK 2009 LATE 2009 EARLY PEAK LATE Sampling Period/Year EARLY 2011 PEAK 2011 LATE 2011

34 Sporulation Key trait linked to transmission Both mito- and meiospores- can be beneficial Latent phase needs to be short if there is competition Large spores may have larger germination success but recent studies have shown smaller spores are in general a key trait aiding invasion. So in order to be successful either you produce smaller spores or you may produce large spores combined with a huge sporulation ability (e.g. ramorum) How strict are the parameters necessary to sporulate?

35 Fusarium circinatum can sporulate as long as temperature >0 C and there is humidity in the form of rain or fog Phytopthora ramorum has strict Requirements for sporulation in the wild It requires rainfall

36 Ability to survive in absence of hosts Cryptic hosts? Resting propagules such as chlamydospores, oospores, sclerotia Sporangia (infectious) Chlamydospores (resting)

37 Epidemiology Long distance airborne: not necessarily best strategy due to failure to contact host Medium distance airborne: very insidious and almost impossible to control because new outbreaks coalesce soon in large outbreak Short distance airborne: very sensitive to habitat structure Soilborne: water flow, gravity, root contacts, in theory spread rate is low, but in reality because undetected for long periods it can be inadvertently moved around Soil- and water-borne: can also use watercourses Insect vectored

38 Spread from roads/paths

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41 Invasion requires ability to adapt to new environments For this reason latitudinal introductions are more successful For this reason multiple introductions facilitate the invasive species (both multiple introductions of the same genotype or of multiple genotypes) But microbes sometimes puzzle us by being extremely good invasives with very limited genetic variability why or how?

42 Success without variability Pathogen has been selected to be extremely competitive, it may even have left behind sexual reproduction in order not to loose that gain Phenotypic plasticity may be key, so if a pathogen comes in many colors and sizes, that could be a sign of plasticity

43 Typical P. cinnamomi sporangia

44 What can we do Prevent introductions: this requires knowledge of spread pathways, means, and political leverage. How to deal with spread from production areas into wildlands? Minimize risky behavior and use appropriate best management practices if on the production side of things Eradication may be possible if caught really early, but unfortunately in most cases it fails because: a) we are too late, and b)- it requires knowledge on the organism which is normally not available Know the threat: when and how does it sporulate/transmit, how far can it move by itself Based on knowledge acquired formulate simple but effective recommendations to mitigate the threat Mitigation may be costly, but not only does it reduce disease or pest incidence it also prevents a site from becoming a stepping stone for a further outbreak Are biocontrol, host resistance or chemical treatments options? As scientists are we providing up to date info to stakeholders: two examples Thanqs and Calinvasives

45 Which species is going to be the next threat? We simply do not know, and 1- Symptoms may be absent 2-100% testing is not realistic 3- Need to understand the optimal sampling intensity combined with the management practices that is going to give confidence 4- Change consumer/industry behavior: no sales of potted plants? No intercontinental or interregional shipments

46 When does it sporulate and how far does it travel Minimize management or traffic during infectious periods Understanding the spread potential is essential to scale management and number 1 reason why eradication efforts fail

47 Mantel test among all individuals. [Moran s I vs ln (geographic distance)] Site ID Correlation coeff. (r) P-value (1000,000 perm) ALL <

48 Large SOD outbreaks are source of further outbreaks

49 Predicted survival of seedlings with and without selection based on resistance to P. ramorume Survival highest in families with at least average growth, and leaf or stem resistance.

50 One can use host disease tolerance and some stand manipulations to reach survival, even without true resistance Likewise do not plant what could become superspreaders: off site trees (for instance Monterey cypress inland becomes very susceptible to Cypress canker) or highly susceptible trees (Leyland cypress, a hybrid variety is 100% susceptible to Cypress canker) Do not move isolates within a Zone of Infestation or between zones of infestations

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52 Tree Health Answers & Questions Good or new questions are published and help create a database of important issues in CA

53 Pathogen database