PLANT IMMUNOLOGY lecture 2.pptxlllllllllllllllllllllllllllllllllllllllllllllllllllll

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1. PLANT IMMUNOLOGY (PBT-805) 1

2. What are plant diseases, why are they there and what do they do? Recommended book: Plant Pathology by Agrios (5 th Ed.) 2005 2

3. Plant disease Like humans plants also get sick! Sick plants grow poorly and produce less. Often, a part of the plant or the whole plant eventually dies. Disease is a compromised ability of a plant or its part to carry out one or more essential functions due to a pathogenic organism . The activities of the cells are disrupted, altered, or inhibited - the cells malfunction or die, and the plant is called diseased. The agents that cause diseases in humans are similar to those causing diseases in plants. They mainly include pathogenic microorganisms: Viruses Fungi Bacteria Nematodes Protozoa 3

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5. Why plant diseases are there? There are diseases because there are pathogens that cause diseases. A pathogen can be regarded as a kind of ‘parasite’ which invades a host because host is an excellent substrate for its growth and reproduction. Plant - a potential source of nutrients … natural selection of microbes should favour ‘ parasitism ’ to exploit this resource. The role of microorganisms as decomposers (recycling) is very well known. Hence the existence of microbes (pathogenic or non-pathogenic) is rational and fundamental. 5

6. The Disease Triangle For a plant disease to occur at least two components Host plant and pathogen must come in contact and interact. Despite the interacting host and microbe, the disease may not occur due to the unfavourable environment (e.g. too hot/cold/dry/wet/sunny weather) Hence, the interaction of three components is essential and can be visualized as a “Disease Triangle” Agrios (2005). Chp. 2, Pg. 79 6

7. Estimates suggests that there are about 100,000 diseases affecting various plants. One crop may be infected by several different pathogens: For example, tomato crop if infected by more than 200 diseases… ~ 80 species of fungi, ~11 species of bacteria, ~16 types of viruses, and several nematodes. Likewise, one pathogenic species usually have several different isolates/strains which render variable disease response, and so are different varieties against a particular isolate. 7

8. The disease process Pathogens Pathogens are transmissible biotic agents that can cause disease by disrupting the normal functioning and extracting nutrients from the host cells. Infection A process by which a pathogen establishes contact with the host tissues/cells and extract nutrients. Colonization Following infection, pathogens grow and multiply within the plant tissues – the process called ‘colonization’ Symptoms Successful infection and colonization results in the development of symptoms which may appear a few days to a few years after colonization. 8

9. Smut of wheat (and other grains) was recorded as early as 1900 BCE in ancient Babylon (southwest of current Baghdad, Iraq). Stinking Smut (Common Bunt) of Wheat R. Johnston R. Johnston, University of Montana, Copyright free J. Riesselman , University of Montana, Copyright free

10. In 715 BCE, the Romans created the gods “ Robigo ” and “ Robigus ” to protect wheat from the wheat leaf rust fungus, which has reddish-colored spores. The Robigalia festival was held in April to protect the fields from this disease. USDA Cereal Lab

11. Today, another type of rust on wheat is threatening the world: wheat stem rust, specifically strain Ug99, which was first detected in Uganda, Africa. USDA Cereal Lab

12. Plant Pathology: Past to Present White vs. Dark Bread In ancient times, poor people ate bread made from rye, which produced a dark bread.

13. But, during cool, wet weather, the developing rye grain often became infected with a fungus and produced purplish-black grain-like structures called “ergots”. These were ground with the grain and used to make bread. By Burgkirsch at german wikipedia , CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3665162 By Rasbak - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=295119 14

14. Ergot contains the chemical ergotamine. Consuming ergotamine in the bread caused gangrene. “St. Anthony’s Fire” was the name of a condition in the Dark Ages. Many victims hallucinated and died in horrible pain.

15. Ergotamine causes severe constrictions in blood vessels (vasoconstrictor). Today, ergotamine is safely used as a vasoconstrictor for migraines (usually with caffeine) or post-partum bleeding. Majority of ergot alkaloids derived via fermentation But, some are obtained by growing of triticale (hybrid of wheat and rye)

16. Potato (from Peru) was introduced into Europe about 1750. It eventually became a food staple in Europe among the poor. In Ireland, tenant farmers paid the landlord in wheat but survived on potatoes. But, in the 1840s, a series of wet, cool summers led to an epidemic of a potato disease called “late blight”.

17. Thousands of Irish starved to death, and 1.5 million emigrated to escape starvation.

18. Late blight is still a serious disease worldwide on potato and tomato. D. Inglis , Washington State University, Copyright free

19. Why do the British drink tea? Coffee has been a popular beverage in Europe since 1600s. But, in the 1800s, the fungal disease “coffee rust” devastated the British coffee plantations in Ceylon (now Sri Lanka). British switched to growing and drinking tea .

20. Tulip Mania Plant diseases affect ornamental plants too! In the 1630s in the Netherlands (current name), tulips with a particular multi-color trait became highly prized – lots of speculative buying, future contracts, short selling, buying on margin, market bubble, etc. Most highly prized were tulips with streaks on solid color background.

21. Tulip Mania Now know the streaking was due to the tulip-breaking virus, actually two viruses. Viruses are spread by an insect called an aphid. Viruses are still present today, especially in southern Europe. Today, tulips with streaks are due to breeding .

22. Chestnut Blight and Dutch Elm Disease A chestnut tree or an American elm tree Both native trees were essentially wiped out by fungal pathogens which were accidently introduced into the U.S. http://www.washington.edu/news/2010/08/05/campus-losing-another-tree-to-dutch-elm-disease/

23. Laurel Wilt The latest invader is a fungus that is killing trees in the Lauraceae (laurel) family, which includes redbay , sassafrass and avocado .

24. Laurel Wilt Fungus initially spread by an exotic ambrosia beetle that was introduced into Georgia in 2002 by infested packing materials, such as wooden crates and pallets. Still unclear if the fungus was introduced or was already present (and just needed the right vector!) Based on greenhouse studies, native ambrosia beetles appear capable of transmitting the fungus.

25. Citrus Greening or Huanglongbing

26. Citrus Greening or Huanglongbing The pathogen is a fastidious bacterium that is vectored by the Asian citrus psyllid. Both the pathogen and the insect were introduced into Florida.

27. Some devastating crop diseases - Fungal Rusts Wheat leaf rust (Brown rust) - P. triticina Wheat stem rust (Black rust) - P. graminis Wheat stripe rust (Yellow rust) - P. striiformis Moreover, the rusts of legumes, fruit plants, coffee and trees are also very common 28

28. Some devastating crop diseases - Fungal Smuts Corn Smut Barley infected with loose smut Bunt (or covered smut) Rice Blast Botrytis cinerea 29

29. Some devastating crop diseases - Bacterial Bacterial wilt of tomato Cotton blight Bacterial spot on tomato leaves and fruit Corn leaf blight 30

30. Some devastating crop diseases - Viral Tobacco mosaic virus (TMV) infection on tobacco plant Cotton leaf curl disease (CLCV) Barley yellow dwarf disease caused by BYDV 31

31. Some plant pathogens are useful: Free-branching poinsettia is due to a phytoplasma (special type of bacterium). Mike Klopmeyer of Ball FloraPlant Mike Klopmeyer of Ball FloraPlant Mike Klopmeyer of Ball FloraPlant

32. Some plant pathogens are edible: Corn smut is a delicacy in Mexico, where it is called huitlacoche . To get more people to eat it in the U.S., they renamed it the “Mexican truffle”.

33. Some plant pathogens are medicinal: Ganoderma lucidum complex ( lingzhi mushroom or reishi mushroom) contains compounds used for medicinal purposes in Asia for thousands of years. By Eric Steinert - photo taken by Eric Steinert at Paussac , France, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=452328

34. Botrytis is a fungus you often see on fresh strawberries. It also causes a disease of wine grapes, but under certain conditions it is called Noble Rot, as it will result in a grape that is used to make sweet dessert wines, such as Sauternes. Some plant pathogens are useful

35. Some plant pathogens are useful: Sometimes we deliberately use plant pathogens to control exotic, invasive weeds. Tobacco Mild Green Mosaic Virus controlling Tropical Soda Apple in Florida Patented by Drs. R. Charudattan and E. Hiebert , formerly UF/IFAS Pathology Department; now BioProdex , Inc. https://plants.ifas.ufl.edu/plant-directory/solanum-viarum/#VII-F

36. Some plant pathogens are useful 37