2.VL Lipka Basics

relationship between individuals of diffrent species where both individuals derive a benefit “mutualism”.

It can be either :

• “obligate” necessary for the survial of at least one of the organisms involved

  • rhiziobia, lichens (fungi obligate, algae not)

• “ facultative” where the relation is beneficial but not essential of the oraganism

  • Mycorrhizal fungi: absorb nutrients receive carbohydrates

one benefits and the other is not signifiantly harmed or helped

• commensal derive nutrition from host without affecting host fitness (asymptomatic)

• inhabiting plants surface: epiphytes

• inhabiting plant interior: endophytes

Parasites derive nutrition from host and reduce the host fitness and can cause diseases

-> removes too many nutrients from the host

• all plant pathogens are considered as parasites

Disease in general: abnormal functioning of organism, leads to malfunctioning of host’s cells and tissues, leads to symptoms

Biotic

• caused by a living organism (I.e. pathogen)

• Infectious

• transmissible

Abiotic

• injurious physical, chemical, enviromental factors

• Non-infectious

• Non-transmissible

• The pathogen must be able to overcome plant defenses.

• The host plant must be susceptible to the pathogen.

• The environment must tip the balance in favor of the pathogen.

(It takes all three)

-> humans have an impact on diseases

Organism, usually a microorganism (microbe), capable of inciting a disease, while obtaining nutrition from the host plant. Each pathogen has particular “host range”.

Pathogenicity

qualitative basal capability to cause disease: – “YES” (pathogenic) or “NO” (nonpathogenic)

Virulence

quantitative degree of pathogenicity of a particular pathogen (how severe are the symptoms?)

GENERAL RULE – “Most pathogens are nonpathogenic on most host plants”

1. Replicative particles

   • Virus- nucleic acid + proteins

   • viroids- circular RNA

2. Prokaryotes- no nuclei

   • Mollicutes (Phytoplasms) - wall less

   • Bacteria- walled

3. Eukaryotes -nuclei

   • Oomycets

   • Fungi

   • Nematodes

   • Parasitic plants

f.sp.: forma specialis,

pv.: pathovar

as in the subgroup of pathogen that infects a certain host

Can be used mostly interchangeable

Susceptible – lacking ability to resist infection by a given pathogen, resulting in disease

Resistant – capable of impeding infection by a given pathogen, thereby reducing disease development

– quantitative: infected to some degree

Immune: non-host. Cannot be infected by given pathogen and does not develop disease symptoms

obligate biotrophs are unable to grow in absence of a host i.e. on synthetic media

- produce few, or no, toxins and cytolytic enzymes - keep their host cells alive

-usually have a rather narrow host range

Examples: TMV, powdery mildew, rust disease

- can grow as saprobes (i.e. obtain nutrition from nonliving organic carbon and nitrogen sources) in absence of a living host

- produce toxins and cytolytic enzymes

- rapidly kill their host cells

- generally have a broad host range

Examples: White mold (s.sclerotiorum)

- infect host cells biotrophically but eventually kill their host cells

- initial infection with few symptoms followed by necrotic symptoms

- usually culturable in vitro

example: Anthracnose caused by Colletotrichum spec.

Common: have mycelllar network, sporulate

Differences: cell wall composition

• ascomycetes with asexual reproduction

• obligate biotrohpic ectoparasites

• invades the upper epidermis and build hausoria in the cells

• Actively suppresses cell death and keeps photosynthetic activity high

Upper leaf side: adaxial

Lower leaf side: abaxial

Extrahaustorial membrane is built by plant cell

Haustorial plasma membranes are equipped with proton symporters and ATPases. A proton gradient drives nutrient uptake through aminoacid and hexose symporters

A solitary haustorium is sufficient to allow completion of the powdery mildew life cycle

The Mlo seven-transmembrane protein (G-coupled receptor protein). When deleted, a variety of plants are resistant