Plant Pathology Glossary

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.

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

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.

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

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

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.

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.

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

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

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.

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

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

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

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.

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.

Death of plant cells or tissue, often appearing as brown or black lesions. Necrosis can result from pathogen attack, toxins, or abiotic stress.

A pathogen that kills host cells, often through toxins and cell-wall-degrading enzymes, and feeds on the dead tissue. Examples include Botrytis cinerea (gray mold) and Sclerotinia sclerotiorum.

Microscopic roundworms that parasitize plant roots and other tissues. Plant-parasitic nematodes use a stylet to pierce cells and extract nutrients, causing root galls, lesions, and yield loss.

A group of filamentous organisms resembling fungi but classified in the kingdom Stramenopila. They have cellulose cell walls and diploid hyphae. Major genera include Phytophthora, Pythium, and Plasmopara.

A group of plant proteins induced upon pathogen infection that contribute to disease resistance. They include chitinases, glucanases, and other antimicrobial proteins.

An official document issued by a national plant protection organization certifying that a consignment of plants or plant products meets the quarantine requirements of the importing country.

A plant gene encoding a protein (often an NLR receptor) that directly or indirectly recognizes a specific pathogen effector, triggering a defense response. R genes typically confer race-specific resistance.

A compact, hardened mass of fungal mycelium that serves as a survival structure, allowing the pathogen to persist through unfavorable conditions. Common in Sclerotinia and Rhizoctonia species.

The production of spores by a pathogen. Spores serve as reproductive and dispersal units and are critical for the spread of many fungal and oomycete diseases.

Race-specific, qualitative resistance controlled by single major R genes. Provides complete protection against specific pathogen races but can be overcome when the pathogen evolves to avoid recognition.