lecture 2

lecture 2 - 8/17/10 Introductory Plant Pathology BTNY...

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Unformatted text preview: 8/17/10 Introductory Plant Pathology BTNY 301 R. D. Martyn Fall, 2010 Lecture #2 How do we recognize and diagnosis diseases? RD Martyn, Purdue University 1 What types of organisms cause plant diseases? •  _____________________________________________ –  ___________  ­_______________  ­ _______  ­ ___________ –  ____________ ______________  ­_________  ­___________ RD Martyn, Purdue Univ 2 1 8/17/10 How do we recognize disease? _________________  ­_________________  ­ ___________________  ­ _____________ RD Martyn, Purdue University 3 How do we recognize disease? __________________ _________ _______ ________ _________ _____________ RD Martyn, Purdue University 4 2 8/17/10 How do we recognize disease? __________________ A. Take ­all patch of bentgrass B. Vine decline of melon C. Soybean cyst nematode RD Martyn, Purdue University D. Lesion nematode on carrots 5 How do we recognize diseases? ______________________  ­ ___________  ­ _________________ A. Powdery mildew B. Brown rot of peach (Monilina frui+cola)  ­ _____________________  ­ ___________________ C. Vine decline (Monosporascus cannonballus) D. Bacterial wilt (Ralstonia solanacearum) RD Martyn, Purdue University 6 3 8/17/10 Pathogen Signs – _______________ A. Corn smut (Us+lago maydis) B. Wood decay (Fomes sp. RD Martyn, Purdue University 7 Pathogen __________ A. Bacterial ooze (Ralstonia solanacearum) B. Root nematodes RD Martyn, Purdue University 8 4 8/17/10 Brown patch of turf  ­ ? ???? RD Martyn, Purdue University 9 How do we diagnosis plant diseases? •  _______________ and ____________ –  Macroscopic and microscopic (hand lens, pocket knife) RD Martyn, Purdue University 10 5 8/17/10 _________________ Uredinia of Phakospora pachyrhizi (Soybean rust) ___________________ Vascular browning caused by Fusarium oxysporum f. sp. niveum (Fusarium wilt of watermelon) RD Martyn, Purdue University 11 How do we diagnosis plant diseases? •  Symptoms and signs –  Macroscopic (hand lens, pocket knife) •  _________________________ –  ____________________________________ RD Martyn, Purdue University 12 6 8/17/10 Microscopic examina_on of _ssue Symptom or sign? __________________________ Spermagonium of Puccinia graminis (stem rust of wheat) Oospores of Pythium sp. RD Martyn, Purdue University 13 How do we diagnosis plant diseases? •  Symptoms and signs –  Macroscopic (hand lens, pocket knife) •  Laboratory examina_on –  Microscopic sec_ons (dissec_ng / compound) –  ______________________________________ RD Martyn, Purdue University 14 7 8/17/10 Isola_on / culturing plant pathogens RD Martyn, Purdue University 15 Microscopic Examina_on of Cultures Fusarium oxysporum f. sp. niveum Teliospores and basidium of P. graminis tri+ci RD Martyn, Purdue University 16 8 8/17/10 How do we diagnosis plant diseases? •  Symptoms and signs –  Macroscopic (hand lens, pocket knife) •  Laboratory examina_on –  Microscopic sec_ons (dissec_ng / compound) –  Pathogen isola_on (culturing on growth medium) –  _______________________________________ _________________________________________ RD Martyn, Purdue University 17 How do we diagnosis plant diseases? RD Martyn, Purdue University 18 9 8/17/10 Can you isolate and grow all plant pathogens on culture medium? •  ________ •  Why? __________________ ________________________ RD Martyn, Purdue University 19 It’s all about food! •  Obligate Saprophytes – _______________________________ ___________________________________________________ –  Most fungi and bacteria (decomposers, molds) –  No plant pathogens •  Obligate Parasites (Biotrophs) – _________________________ ____________________________________________________ –  Some plant pathogens –  All _________, some fungi (rusts, powdery mildews, downy mildews), some bacteria (Xylella, phytoplasmas); __________ _____________________________________ RD Martyn, Purdue University 20 10 8/17/10 It’s all about food! •  Faculta8ve saprophytes (Necrotrophs) – ______________________________________ ______________________________________ –  Some plant pathogens (smuts, bunts) •  Faculta8ve parasites (Necrotrophs) – ______________________________________ ______________________________________ –  Many plant pathogens (fungi and bacteria) RD Martyn, Purdue University 21 How do we iden_fy an ‘unknown’ disease? _______________ (1864) – Disproved theory of spontaneous genera_on  ­Fermenta_on ____________________ (1873) Germ theory of disease – Koch’s postulates  ­Sheep anthrax (Bacillus anthracis) 22 RD Martyn, Purdue University 11 8/17/10 Germ theory of disease first proven with plant pathogens! •  1755 – ____________. “Black bunt dust”. First to show s_nking smut of wheat was ‘contagious’ •  1807 – _______________ Proved s_nking smut of wheat was caused by a fungus (studied life cycle / ‘bunt dust’ was spores) •  1861 – _______________ Detailed experiments showing P. infestans was the cause of late blight of potato. Heinrich Anton de Bary (1831 ­1888) ‘Father of Plant Pathology’ RD Martyn, Purdue University 23 Koch’s Postulates (Rules for proof of pathogenicity) 1.  The suspected pathogen must be ________________ ___________________________________________ 2.  The suspected pathogen must be ________________ ___________________________________________ 3. The disease must be __________________________ ___________________________________________ 4.  The same pathogen must be ____________________ ___________________________________________ (This step was actually added by E.F. Smith in 1880s) RD Martyn, Purdue University 24 12 8/17/10 Pathogen ≠ Disease _________________ Xanthomonas axonopodis pv citri ________________ Citrus canker • ________________ are not isolated from plants – ________________ are • ________________ are not cultured on a Petri dish –______________ are • Plants are not inoculated with ____________– they are inoculated with __________ • ___________________ are not vectored – _______________ are RD Martyn, Purdue University 25 13 ...
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