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PHP21303 Summary of learning objectives in lectures
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This documents elaborates on the learning objectives mentioned in the lectures of the course PHP21303
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Lecture 1: Explain a brief history of how plant diseases affected mankind
370 BC first disease symptoms of trees and crops described: leaf scorch, rots, scab and rust.
In biblical times, roman times and middle age, diseases and plagues are important and tried
to be explained by god.
Explain what disease is and when it occurs
Disease is the abnormal functioning of an organism by internal dysfunction or external
factors (biotic agents or other causes).
Infectious disease is the abnormal functioning of an organism caused by disease-causing
agents, their multiplication, and the reaction of host tissues to these organisms or the toxins
they produce.
Discriminate and describe disease-causing agents
Insects, bacteria, fungi, viruses, nematodes, oomycetes, viroids, phytoplasmas, parasitic
plants.
Explain how plant diseases can be diagnosed
Diagnosis is required to reveal the cause of a disease. Disease symptoms describe
malfunction of plant tissues that are affected but… disease symptoms are not sufficient for
accurate diagnosis of many plant diseases.
Various symptoms on various tissues:
Leaves: discoloration (mosaic, mottle, streak, stripe, yellowing)
Leaves: 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: find and identify pathogen (signs for pathogen are spores,
fruiting bodies, eggs). An abiotic agent will show symptoms on more plants with a similar age
of development.
Koch’s postulates: 1. The suspected pathogen must be consistently associated with diseased
host, 2. The suspected pathogen must be isolated in pure culture, 3. The disease should be
reproduced healthy host inoculated with the isolated organism, 4. The same pathogen
isolated in step 2 must be isolated again from the diseased host.
Different feeding styles: Biotroph (require living host tissue, attack healthy tissue only, narrow
host range, keeps host cells alive, direct penetration or via natural openings) or necrotrophy
(feed on dead host tissue, attack young weak or senescing host tissue, broad host range, host
cell killing through toxins and/or enzymes, penetration through wounds or natural openings).
An obligate biotroph lives and multiplies on another living organism and cannot be cultured
on synthetic media.
Saprotrophs feed on dead organic matter and are not parasitic.
Two different feeding structures: piercing/sucking (insects and nematodes) and haustoria
(fungi and oomycetes).
Explain disease and life cycles, and their differences
A disease cycle is 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.
Monocyclic: one disease and life cycle per growing season.
Polycyclic: multiple life cycles per growing season (asexual reproduction).
, Infection: invasion of host tissues by a disease-causing agent, leading to disease.
Colonization: infection of the host by the pathogen followed by multiplication and growth
Inoculation: treatment of a host with a parasite in order to establish infection.
Pathogenesis: establishment and development of disease.
Pathogenicity: the ability to cause disease.
Virulence: degree or measure of pathogenicity; relative capacity to cause disease.
Disease triangle: Susceptible host plant, pathogen, right environment are required for disease
to occur.
Lecture 2:
Explain the basic cellular biology of fungi
Eukaryotic, heterotrophic, uptake of nutrients through absorption, structure with hyphae
(mycelium).
Diverse life styles: Saprophytic or symbiotic (parasitic, commensalistic or mutualistic).
Fungal cell: nucleus, organelles, vacuole and cell wall
Hyphae (filamentous structure) form together mycelium -> septae separate cells, have
openings for cytoplasmic contact
Cell wall main components: chitin and Beta-glucans, furthermore proteins, chitosan, melanin
and lipids
Understand asexual and sexual reproduction modes and the link to fungal taxonomy
Asexual reproduction: spores that are passively dispersed (wind/water), spores are formed
outside (exogenous) or in special organ (endogenous). Spore forming structures standing
singular or together in fruiting bodies.
Sexual reproduction: actively discharged
Many fungi can both reproduce sexually as asexually
Asexual stage: anamorph, sexual stage: telomorph
Know the various asexual fruiting bodies
Pycnidium: Globose or flask-shaped, often black (melanin)
Acervulus: Saucer-shaped, braid of mycelium covered by epidermis of the host
Sporodochium: pillow-shaped spore-forming tissue
Synnema (coremium): Bundle of parallel spore-forming hyphae (conidiophores) that fuse to a
stem
Explain and illustrate the life cycle of Zygomycota
No septae in hyphae, saprophytes
Mycorrhizae and soft rot of fruits
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