DISEASES AND TREES

1. DISEASES AND TREES • What exactly is a disease? It is the outcome of an interaction between a plant and the environment, resulting in an altered physiology of the host • Sustained interaction=biotic • Single event= abiotic

4. What is a pathogen? • Strictly speaking a pathogen is the causal agent of disease • Bacteria • Viruses • Nematodes • Stramenopiles • Algae • Phytoplasmas • Higher plants

5. And of course… fungi • Fungi: saprophytic, symbionts, and pathogens • Polyphyletic group in evolutionary terms • Basidiomycetes Ascomycetes Zygomycets Animals Plants Red algae Brown algae Myxomycetes

6. Fungi… again! • Filamentous somatic (vegetative body) • High surface, good for extrogenous digestion • Good infection structures, infection peg, appressoria, rhizomorphs Chitin in cell wall Nuclear ploidy very unique Reproduction by spores: asexual mode very well represented Small nuclei, but with a lot of plasticity

7. Hyphae, sporangia, and zoospores of P. ramorum

8. Fungi do not photosynthesize • Biotrophic: mycorrhyzae, rusts • Endophites: clavicipetaceae, • Necrotrophic; most pathogens • Saprobes: primary (involved in litter decomposition)

9. Some pathogen roles in natural plant communities • Selection of individuals best suited for the site • Maintenance of genetic diversity and stability in host plant populations • Establishment or maintenance of host geographic ranges • Natural succession • Regulation of stand density, structure, and composition

10. DISEASE!! • Symptoms vs. signs; e.g. chlorosis vs. fruit-body • The disease triangle

11. host-pathogen-environment • Susceptibility of individuals or of portions of individuals • Genetic variability • Basic compatibility (susceptibility) between host and pathogen • Ability to withstand physiological alterations

12. Genetic resistance in host

13. host-pathogen-environment • Basic compatibility with host (virulence) • Ability to maintain diversity: sex vs. no sex • Size of genetic pool • Agressiveness (pathogenicity) towards hosts • Ability to survive without host

14. Chlamydospores of P. ramorum

15. Pr75 Qa Monterey Pr87 Am Marin Pr86b Am Marin Pr86a Am Marin Pr84 Soil Marin Pr82 Vo Marin Pr80 Vo Marin Pr72 Rh Alameda Pr65 Qp Santa Cruz Pr58 Vo Marin Pr50 Qa Sonoma Pr201b Rh Santa Cruz Pr201a Rh Santa Cruz Pr47b Qa Sonoma Pr47a Qa Sonoma Pr35 Qa Sonoma Pr28 Ld Sonoma Pr24 Qa Sonoma Pr22 Qa Sonoma Pr20 Qa Sonoma Pr19 Qa Napa Pr16 Qa Santa Cruz Clone group Pr13 Qa Santa Cruz Pr11b Qa Monterey Pr11a Qa Monterey Pr10 Ld Monterey Pr08 Qa Napa Pr06 Qa Marin Pr05 Ld Marin Pr04 Qk Marin Pr03 Ld Marin Pr88 Uc Sonoma Pr89 Uc Sonoma Pr90 Qa Marin Pr91 Uc Sonoma Pr97 Qa Napa Pr102 Qa Marin Pr103 Ld Marin Pr104 Ld Marin Pr107 Uc Sonoma Pr110 Uc Marin Pr112 Uc Marin Pr113 Uc Marin Pr114 Uc Marin Pr115 Uc Marin Pr116 Uc Marin Pr136 Uc Marin Pr156 Ld Oregon Pr157 Ld Oregon Pr158 Ld Oregon PrJL3.1 Ss Sonoma PrSDC21.6 Ss Sonoma Pr36 Qa Sonoma Pr27 Qa Marin Pr57 Ld Santa Clara Pr70 Vo Marin Pr159 Ld Oregon 67 Pr52a Rh Santa Cruz Pr52b Rh Santa Cruz 89 PrCoen Rh Santa Cruz PrJL3.5.3 Ss Sonoma 96 Pr106 Uc Sonoma 93 Pr71 Qa Sonoma Pr01 Qa Marin PrE9/95 Rh Germany PrE16/99 Vb Germany 100 European group PrE12/98 Rh Germany PrE104 Water Germany PrE69082 Rh Germany PrE9/3 Water Germany PrE14/98-a Rh Germany Pl33 Cl Del Norte P. lateralis (outgroup) Pl16 Soil Josephine 0.1 Pl27 Tb Del Norte

16. West Coast Europe P. lateralis

17. host-pathogen-environment • Temperatures • Shading • Relative humidity • Free standing water • pH and any potentially predisposing factors • Nutrient status

18. Colony diameter (mm) at 13 days

19. Presence of free water Between 6 and 12 hours required for infection of bay leaves

20. Human activities affecting disease incidence in forests • Introduction of exotic pathogens • Planting trees in inappropriate sites • Changing stand density, age structure, composition, fire frequency • Wound creation • Pollution, etc.

22. Effects of fire exclusion

23. DISEASE: plant microbe interaction • Basic compatibility need to be present • Chemotaxis, thighmotropy • Avirulence in pathogen matched by resistance in host according to the gene for gene model • Pathogenicity factors such as toxins and enzymes important in the infection process

24. Effects of diseases on host mortality, growth and reproduction • Young plants killed before reaching reproductive age • Affect reproductive output • Directly affect flowers and fruits

25. Complexity of forest diseases • At the individual tree level: 3 dimensional • At the landscape level” host diversity, microclimates, etc. • At the temporal level

26. Complexity of forest diseases • Primary vs. secondary • Introduced vs. native • Air-dispersed vs. splash-dispersed, vs. animal vectored • Root disease vs. stem. vs. wilt, foliar • Systemic or localized

27. Progression of cankers Hypoxylon, a secondary sapwood decayer will appear Older canker with dry seep

28. Stem canker on coast live oak

29. Cankers by P. ramorum at 3 months from time of inoculation on two coast live oaks

30. Root disease center in true fir caused by H. annosum

33. Categories of wild plant diseases • Seed decay • Seedling diseases • Foliage diseases • Systemic infections • Parasitic plants • Cankers, wilts , and diebacks • Root and butt rots • Floral diseases

34. Seed diseases • Up to 88% mortality in tropical Uganda • More significant when seed production is episodic

35. Seedling diseases • Specific diseases, but also diseases of adult trees can affect seedlings • Pythium, Phytophthora, Rhizoctonia, Fusarium are the three most important ones • Pre- vs. post-emergence • Impact: up to 65% mortality in black cherry. These diseases build up in litter • Shady and moist environment is very conducive to these diseases

36. Foliar diseases • In general they reduce photosynthetic ability by reducing leaf area. At times this reduction is actually beneficial • Problem is accentuated in the case of small plants and in the case other health issues are superimposed • Often, e.g. with anthracnose,needle cast and rust diseases leaves are point of entry for twig and branch infection with permanent damage inflicted

39. Systemic infections • Viral? • Phytoplasmas • Peronospora and smuts can lead to over 50% mortality • Endophytism: usually considered beneficial

40. Grass endophytes • Clavicipetaceae and grasses, e.g. tall fescue • Mutualism: antiherbivory, protection from drought, increased productivity • Classic example of coevolutionary development: Epichloe infects “flowers” of sexually reproducing fescue, Neotyphodium is vertically transmitted in species whose sexual reproductive ability has been aborted

41. Parasitic plants • True (Phoradendron) and dwarf mistletoe (Arceuthobium) • Effects: • Up to 65% reduction in growth (Douglas-fir) • 3-4 fold mortality rate increase • Reduced seed and cone production Problem accentuated in multistoried uneven aged forests

45. Cankers, wilts, and die-backs • Includes extremely aggressive, often easy to import tree diseases: pine pitch canker, Dutch elm disease, Chestnut blight, White pine blister rust • Lethal in most cases, generally narrow host range with the exception of Sudden Oak Death

46. Root diseases • Extremely common, probably represent the most economically damaging type of diseases • Effects: tree mortality (direct and indirect), cull, effect on forest structure, effect on composition, stand density, growth rate • Heterobasidion, Armillaria, Phellinus weirii, Phytophthora cinnamomi

48. Floral diseases • Pollinator vectored smut on silene offers an example of well known dynamic interaction in which pathogen drives genetic variability of hosts and is affected by environmental condition • Puccinia monoica produces pseudoflowers that mimic real flowers. Effects: reduction in seed production, reduction in pollinators visits

49. POPULATION DYNAMICS Species interactions and diversity

50. Density-dependence • Most diseases show positive density dependence • Negative dependence likely to be linked to limited inoculum: e.g. vectors limited • If pathogen is host-specific overall density may not be best parameter, but density of susceptible host/race • In some cases opposite may be true especially if alternate hosts are taken into account