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Summary Fundamentals of plant pathology and entomology
- Instelling
- Wageningen University (WUR)
Summary of all lectures in the course Fundamentals of plant pathology and entomology notes given during lectures
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Summary Fundamentals of plant pathology and entomologyLecture 1: introduction
History of plant pathology
- Romans sacrificed red animals on 25th of april against yield losses through cereal rust
(robigalia)
- Witches were burned at the stake, because they were acting weird because hallucinating
compounds in mouldy rye (holy fire/st. anthony’s fire)
- There are many irish descendants in the USA because of the irish potato famine (causes by
Phytophthora infestans)
- English drink many tea because of destruction of coffee cultivation by coffee rust
Botanist Theophrastus was the first to describe disease symptoms of trees, cereals and legumes
Plant attackers: Insects, bacteria, funguses, viruses, nematodes but also:
Oomycetes: fungal-like non-photosynthetic brown algae
Viroids: small (~ hundred BP) complementary, circular, single-stranded RNA
Phytoplasmas: small ‘bacteria’ without cell wall
Parasitic plants: e.g. mistletoe on oak tree
Multiple attackers may co-operate. E.G. Tomato spotted wilt virus (TSMV) is transmitted by thrips (=
vector).
Dutch elm disease: causal agent identified in the Netherlands, caused by fungus Ophiostoma (novo-
)ulmi. Carried with bark beetles. Larvae of elm bark beetle (scolytus ssp.) dig tunnels in dying trees.
They move out as new beetles and carry spores that were picked up in the tunnels
Control:
- Break up potential root contact, removal of dead elms, remove barkor burnthe wood
immediately
- Insecticide treatment against beetles
- Fungicide treatment of infected plants (expensive)
- Dutch trig → biological control. Injection of conidiospores of verticillium ssp. in the xylem
activate natural defense
- Plant new elms minimum 15 meter apart
What is a disease?
- The abnormal functioning of an organism → internal dysfunction or external factors (biotic
agents or other causes)
- Infectious disease is the abnormal functioning of an organisms caused by disease-causing
agents, their multiplication, and the reaction of host tissue to these organisms or the toxins
they produce
Diagnosis:
- Required to reveal the cause of a disease
- Various symptoms on various tissues:
Leaves -Discoloration (mosaic, mottle, streak, stripe, yellowing)
-Necrosis (spots, blotches, blights, scorches)
Fruits Soft rots, dry rots
Wood Bleeding, gummosis, canker
Whole plant Stunting, Wilting (xylem)
Seedlings Damping off
How to diagnose a disease:
,Disease symptoms describe malfunction of the plant tissues that are affected but are not always
sufficient for accurate diagnosis of many plant diseases.
- Is the causal agent a biotic agent?
- Find and identify the pathogen -> signs of biotic pathogens or its parts or products on a host
- Signs of abiotic agents -> more plants show them, similar age of development
- Primary vs secondary infection
, Koch’s postulates:
Four criteria to establish a causal relationship between causative microbe and disease
1. The MO must be found in abundance in all organisms suffering from the disease, but should not be
found in healthy organisms
2. the MO must be isolated form a diseased organism and grown in pure culture
3. the cultured MO should cause disease when introduced into a healthy organisms
4. the MO must be reisolated form the inoculated, diseased experimental host and identified as
being identical to the original specific agent
→ ca not be used for obligate biotrophic pathogens, nematodes and viruses
Biotroph: parasite that lives and multiplies on another living organism, but can also be cultured on
synthetic media. → obligate biotroph lives and multiplies only on another living organism, and
cannot be cultured on synthetic media.
Necrotroph: parasite that kills host cells and obtains nutrients form dead cells
Saprotroph: organism that feeds on dead organic matter; not parasitic
Ectoparasite: on the outside of the plant. E.g. powdery mildew
Nematode symptoms show a typical patchy symptoms in the field because the ploughing direction of
the farmer
Biotrophs Necrotrophs
Require living host tissue Feed on dead host tissue
No growth as saprophyte Can grow as saprophyte
Attack healthy tissue only Attack young, weak, senescing host tissue
Narrow host range Broad host range
Keep host cells alive; host cell decay slowly Host cell killing through toxins/enzymes
Direct penetration, or through natural openings Penetration through wounds or natural openings
Feeding structures of a parasite
- Piercing/sucking organisms (e.g. insects and nematodes use a stylet)
- Haustorium, used by fungi and oomycetes
The disease cycle;
The succession of all events and interactions among the host, parasite and environment that occur in
a disease, from initial infection of the plant by a causal agent, through pathogenesis, to over-
seasoning, until another infection occurs in the next season.
• Primary inoculum, dispersal of inoculum, infection court, infection and colonization,
secondary inoculum, survival of parasite
Monocyclic disease: one disease and life cycle per growing seasing
Polycyclic disease: multiple life cycles per growing season
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