Potato Science Lecture 7 Potato diseases – foliar, soilborne , viruses, and tuber rots.

1. Potato Science Lecture 7 Potato diseases – foliar, soilborne, viruses, and tuber rots.

2. What is plant disease? • Anything that causes disfunction • Many (most?) are caused by “infectious biological agents” that are parasitic • Others are physiological or “abiotic” (Lecture 15) • We will discuss several important infectious diseases of potato

3. Causal agents of disease • Viruses • Viroids • Prions? • Bacteria • Actinomycetes • phytoplasmas • fastidious bacteria • Fungi • Nematodes

4. Disease Triangle Host Pathogen Disease! Environment

5. Disease Triangle • Plant Pathology is about interactions • Host can be altered by choice of variety • Use of certified seed reduces pathogen • Alter irrigation or drainage changes environment • Usually these factors can’t be controlled very well • Disease is the result

6. Epidemic • Susceptible host • Large population of virulent pathogen • Very favorable environment • Over a large area • Usually wind-borne • Can be very expensive • Even deadly

7. Important Terms • Primary inoculum • Secondary inoculum • Symptom • Sign • Incubation period • Latent period

8. Sign Symptom

9. Infection • Many pathogens require a wound • Some use “natural openings” • Stomates • Lenticels • Some penetrate directly • Mechanical • Enzymatic • Combination

10. Infection • Some require a “vector” • Provides mobility • Provides wound • Insects (aphid, thrip, leafhopper) • Fungi (powdery scab vectors PMTV) • Nematode (Stubby root vectors TRV)

11. Causal agents of disease • Viruses • Viroids • Prions? • Bacteria • Actinomycetes • phytoplasmas • fastidious bacteria • Fungi • Nematodes

12. Plant Pathology G. Agrios

13. Bacterial Diseases

14. Bacteria: Characteristics • Very small • Require microscopic techniques to see • Biochemical techniques also needed • Rapid generation times (20 minutes!?) • Prokaryotic • Rigid cell walls • Phytoplasmas = no cell wall = ameoboid

15. Bacteria: Characteristics • Damage often due to enzymatic activity • Some may clog vascular system

16. Specific Bacterial Diseases

17. Disease: Soft rot / Blackleg Organism: Pectobacteriumcarotovorum (=Erwiniacarotovora) Symptoms: Foliar blackleg appears as a black stem rot starting at the seed that kills the stem. Soft rotted tissues appear creamy and very soft, can become discolored and odiferous Source and Spread: Inoculum originates from multiple sources and spreads during handling, field spread is in water

19. Key Features Soft rot bacteria • Are everywhere • Very opportunistic secondary invader • Thrives with or without O2 • Facultative anerobe • Storage rot – major player • Seed piece decay – major player • Aerial stem rot

21. Disease: Bacterial Ringrot (BRR) Organism: Clavibactermichiganensissubsp. sepedonicus Symptoms: Plants can show wilting and leaf rolling, tubers show a slimy yellow exudate in the vascular ring Source and Spread: Seed tubers provide inoculum which spreads during seed cutting and handling

22. Bacterial Ring Rot “BRR”

23. Key Features Bacterial Ring Rot • Almost exclusively seed borne • Zero tolerance in seed • Confined to vascular tissues • Can spread during seed cutting • Survives on equipment and in storages

24. Disease: Common scab Organism: Streptomyces scabies Symptoms: Corklike scabby areas or pitted depressions on the tuber surface Source and Spread: Endemic to many soils or introduced on seed, infects upon contact with tuber skin

26. Key Features Common Scab • Superficial only • Only develops while tuber is growing • Progress stops in storage • “Cosmetic” disease

27. Fungal Diseases

28. Plant Pathology G. Agrios

29. Fungi: Characteristics • Most plant diseases caused by fungi • Larger, some can be seen with naked eye • Also require microscopic techniques • Biochemical techniques also needed • Complex life cycles in some

30. Fungi: Characteristics • Eukaryotic • Multicellular • Main body is thread-like “hypha” • Many “hyphae” = “mycelium” • Many form spores and other structures • Spores sexual or asexual • Overwintering and dispersal structures

31. Fungi: Characteristics • Wind, soil, water, seed, equipment • Single or multicycle • Many ways of entering plant • Foliar, tuber or both affected

32. Fungi: Characteristics • Wind, soil, water, seed, equipment • Single or multicycle • Many ways of entering plant • Foliar, tuber or both affected

33. Specific Fungal Diseases

34. Disease: Late Blight Organism: Phytophthorainfestans Symptoms: Leaf and stems lesions, foliage destruction, tuber rot Source and Spread: Seed, cull piles and volunteer potatoes provide inoculum, sporangia move with wind and water

37. Key Features Late Blight • Most important disease of potatoes • Responsible for Irish famine • Very rapid disease development • Spores windborne • Must have wet conditions • Effects foliage and tubers • Recent changes in capabilities

38. Disease: Early blight Organism: Alternariasolani Symptoms: Brown to black leaf lesions (bullseye) appear first on the older leaves, leaf death and defoliation, sunken surface tuber lesions Source and Spread: Inoculum in soil overwinters on debris, moves onto the plants is from splashing water, additional spore movement in air and water , tubers infected during harvest

39. Early blight

40. Early blight

41. Late blight Early blight

42. Key Features Early Blight • Attacks senescing tissues • May show up on lower leaves first • Favored by alternating wet and dry • Mostly foliage but tubers can be affected

43. Disease: Verticillium wilt Organism: Verticilliumdahliaeor albo-atrum Symptoms: Wilt of stems and leaves, early death of foliage, necrotic stem vascular streaking Source and Spread: Inoculum occurs naturally in the field and overwinters on refuse, disease moves with seed and soil, only plants in infested fields are infected

44. Verticillium wilt

45. Verticillium wilt

46. Key Features Verticillium wilt • Soil borne disease • One major reason for fumigation • Some varieties worse than others • Mostly wilt but some SED is possible

47. Disease: Rhizoctonia Canker Organism: Rhizoctoniasolani Symptoms: Reddish brown lesions on underground stems and stolons that occasionally result in girdling or “damping off”, black “scurf” on the surface of mature tubers Source and Spread: Overwinters in soil or on seed tubers as sclerotia which invade developing sprouts or stolons in the spring.

48. Rhizoctonia

49. Rhizoctonia

50. Key Features Rhizoctonia • Seed and soil borne • Cankers girdle new shoots • More susceptible before emergence • Yield unchanged, quality affected • Cosmetic = “dirt that won’t wash off”