Plant Pathology Cheat Sheet

The core ideas of Plant Pathology distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/plant-pathology/cheatsheet

Quick Reference

Koch's Postulates

A set of four criteria established by Robert Koch to prove that a specific microorganism causes a specific disease: the pathogen must be found in all diseased organisms, isolated from the host, cause disease when introduced to a healthy host, and be re-isolated from the newly diseased host.

Disease Triangle

A foundational concept in plant pathology stating that plant disease results from the interaction of three factors: a susceptible host, a virulent pathogen, and a favorable environment. All three must be present simultaneously for disease to occur.

Hypersensitive Response (HR)

A rapid, localized cell death reaction at the site of pathogen invasion that restricts pathogen growth. It is a key component of plant innate immunity, often triggered by the recognition of pathogen effector molecules by plant resistance (R) proteins.

Systemic Acquired Resistance (SAR)

A whole-plant immune response triggered after a localized pathogen attack that provides broad-spectrum, long-lasting protection against subsequent infections. SAR is mediated by the signaling molecule salicylic acid and the expression of pathogenesis-related (PR) proteins.

Gene-for-Gene Hypothesis

Proposed by Harold Flor in the 1940s based on studies of flax rust, this model states that for each resistance (R) gene in the host plant, there is a corresponding avirulence (Avr) gene in the pathogen. Disease occurs only when the pathogen lacks the recognized Avr gene or the host lacks the corresponding R gene.

Integrated Pest Management (IPM)

A holistic approach to disease and pest management that combines biological, cultural, physical, and chemical methods to minimize economic, health, and environmental risks. IPM emphasizes monitoring, threshold-based decision-making, and preventive strategies over routine chemical applications.

Pathogen Effectors

Molecules, typically proteins, secreted by pathogens into host cells to suppress plant immune responses, manipulate host cell processes, and promote colonization. Effectors are key determinants of pathogen virulence and host specificity.

Mycotoxins

Toxic secondary metabolites produced by certain fungi that contaminate food and feed crops, posing serious risks to human and animal health. Major mycotoxins include aflatoxins, fumonisins, deoxynivalenol, and ochratoxins.

Plant Quarantine

Regulatory measures designed to prevent the introduction and spread of plant pathogens, pests, and invasive species across geographic boundaries. Quarantine involves inspection, certification, treatment, and sometimes destruction of infected plant material.

Biological Control (Biocontrol)

The use of living organisms or their products to suppress plant diseases. Biocontrol agents include antagonistic fungi, bacteria, and viruses that compete with, parasitize, or induce resistance against pathogens.

Key Terms at a Glance

Avirulence Gene (Avr):A pathogen gene whose product is recognized by a corresponding plant resistance (R) protein, triggering an immune response. Loss or modification of the Avr gene allows the pathogen to evade detection.

Biotroph:A pathogen that requires living host tissue to grow and reproduce. Obligate biotrophs like rusts and powdery mildews cannot be cultured on artificial media.

Canker:A localized, sunken, necrotic lesion on a stem, branch, or trunk caused by pathogen infection. Cankers may girdle branches and disrupt water and nutrient flow.

Chlorosis:Yellowing of plant tissue due to loss or reduced production of chlorophyll, often caused by pathogen infection, nutrient deficiency, or environmental stress.

Disease Cycle:The complete sequence of events involved in disease development, including inoculation, penetration, infection, colonization, reproduction, dissemination, and survival of the pathogen.

Epidemiology:The study of how plant diseases develop and spread through populations over time and space. Includes analysis of disease progress curves, spatial patterns, and environmental factors.

Etiology:The study of the cause or origin of a disease. In plant pathology, etiology involves identifying the pathogen responsible and understanding how it initiates disease.

Gall:An abnormal swelling or outgrowth of plant tissue caused by pathogens (e.g., Agrobacterium tumefaciens), insects, or nematodes. Crown gall is a classic example.

Haustorium:A specialized feeding structure produced by biotrophic fungi and oomycetes that penetrates plant cell walls to absorb nutrients from living cells without killing them.

Hemibiotroph:A pathogen that initially colonizes living host tissue as a biotroph before switching to a necrotrophic lifestyle, killing and feeding on dead cells. Examples include Magnaporthe oryzae and Colletotrichum species.

Horizontal Resistance:Non-race-specific, quantitative resistance controlled by multiple genes. Provides partial but broad-spectrum and more durable protection against pathogens compared to vertical resistance.

Hyperparasitism:A form of biological control where one organism parasitizes a plant pathogen. Trichoderma species that parasitize soilborne fungi are a well-known example.

Inoculum:The pathogen material (spores, bacterial cells, viral particles, nematode eggs) that initiates infection. Primary inoculum starts the epidemic; secondary inoculum causes subsequent spread.

Latent Infection:An infection in which the pathogen is present in the host without causing visible symptoms. The pathogen may become active and produce symptoms under changed environmental conditions or host stress.

Mosaic:A viral disease symptom characterized by irregular patches of light green, yellow, and dark green tissue on leaves, caused by uneven chlorophyll distribution due to viral replication.

Get study tips in your inbox

We'll send you evidence-based study strategies and new cheat sheets as they're published.

We'll notify you about updates. No spam, unsubscribe anytime.