Principles of Plant Pathology Exam 3 Study Guide

Vocabulary flashcards covering mycotoxins, plant parasitic nematodes, structural and chemical plant defenses, agricultural biotechnology, disease epidemiology, and plant disease control strategies from the Plant Pathology Exam 3 review key.

Aflatoxin

Affects maize and peanuts; causes liver damage and liver cancer.

Fumonisins

Affects maize; causes equine leukoencephalomalacia (ELEM / horse brain liquefaction), porcine pulmonary edema (PPE / pig lung fluid), esophageal cancer, and neural tube birth defects.

Ochratoxins

Affects cereal grains, coffee, and grapes; causes kidney damage (nephrotoxicity) and liver damage.

Trichothecenes (Deoxynivalenol - DON)

Affects wheat, oat, and barley; causes gastrointestinal distress, feed refusal, vomiting, and weight loss in livestock.

Zearalenone

Affects maize and small grains; causes reproductive abnormalities (hyperestrogenism, swelling of reproductive organs, infertility, and abortion in livestock).

Plant Parasitic Nematode

An unsegmented, microscopic roundworm enclosed by a protective outer cuticle that lacks respiratory and circulatory systems, moves via longitudinal muscles in a wave-like pattern, and uses a hollow needle-like stylet to infect plants.

Second-Stage Juvenile (J2)

The specific infective developmental stage in the nematode lifecycle that hatches in the soil and initiates plant parasitism by migrating to host roots via chemotaxis.

Nematode Stylet

A specialized, hollow, needle-like mouthpart used by plant-parasitic nematodes to puncture plant cell walls, secrete esophageal gland effectors or digestive enzymes, and withdraw cell cytoplasm.

Ectoparasitic Nematodes

Nematodes that remain entirely outside host plant roots and feed by inserting their long stylet into outer root cells (e.g., Xiphinema, the dagger nematode).

Endoparasitic Nematodes

Nematodes that completely enter and reside within host plant tissues to feed (e.g., Meloidogyne spp. and Heterodera glycines).

Migratory Nematodes

Nematodes that retain mobility throughout their entire lifecycle, tunneling through plant tissues while feeding and causing dark necrotic lesions (e.g., Pratylenchus).

Sedentary Nematodes

Nematodes that enter roots as mobile J2s, establish permanent feeding sites, lose mobility, and swell into spherical or pear-shaped adult females (e.g., Meloidogyne and Heterodera).

Giant Cell

An enlarged, multinucleate permanent feeding structure formed when host cell nuclei divide repeatedly in the absence of cytokinesis (cell division); induced by Root-Knot Nematodes (Meloidogyne spp.).

Syncytium

A multinucleate feeding site formed by the enzymatic dissolution of adjacent host cell walls and subsequent fusion of neighboring cell cytoplasm; induced by Cyst Nematodes (Heterodera spp. and Globodera spp.).

Foliar Nematodes

Nematodes such as Aphelenchoides besseyi and Aphelenchoides ritzemabosi that travel up stems in water films, enter leaf stomata, and produce angular V-shaped leaf lesions bounded by veins.

Pine Wilt Nematode (Bursaphelenchus xylophilus)

A tree-infecting nematode vectored by Pine Sawyer Beetles (Monochamus) that colonizes xylem and resin canals, resulting in rapid vascular wilt and tree mortality.

Fusarium-Nematode Wilt Complex

A disease complex where initial stylet wounding by nematodes (such as Meloidogyne) provides entry pathways for secondary fungal pathogens like Fusarium oxysporum in cotton and tomato.

Cyst Nematode (Heterodera spp. & Globodera spp.)

Sedentary endoparasites whose dead female body walls harden into brown, leathery cysts that protect enclosed viable eggs in the soil for $8$ to $20+$ years.

Root-Lesion Nematodes (Pratylenchus spp.)

Migratory endoparasitic nematodes that remain vermiform (worm-shaped) and mobile as adults, causing dark necrotic cortex lesions without inducing giant cells or syncytia.

Anhydrobiosis (Cryptobiosis)

A physiological dormant survival state enabling nematodes to withstand severe desiccation and extreme environmental drying.

Incubation Period

The time interval elapsed between initial host infection and the first appearance of visible disease symptoms.

Latent Period

The time interval from initial infection to pathogen reproduction or sporulation; critical for epidemic modeling as it controls the rate of secondary inoculum generation.

Lignin

An amorphous aromatic polymer that impregnates spaces between plant cell wall components, providing mechanical rigidity, waterproofing, and defense against enzymatic breakdown.

Hemicellulose

Complex branched matrix polysaccharides (such as xylans and glucans) that structurally cross-link cellulose microfibrils in plant cell walls.

Cellulose

Linear chains of $\beta\text{-(1,4)-linked}$ D-glucose microfibrils that provide the main structural scaffolding of plant cell walls.

Phytoanticipins

Pre-formed, constitutive antimicrobial secondary metabolites present in plant tissues before pathogen contact (e.g., terpenoids, phenolics, alkaloids, and avenacin in oats).

Tyloses

Balloon-like active parenchymal outgrowths that protrude into xylem vessels to physically block the upward vascular translocation of vascular wilt pathogens.

Papillae

Active structural deposits of callose and lignin laid down between the host cell wall and plasma membrane directly underneath fungal penetration attempts.

Phytoalexins

Low-molecular-weight antimicrobial chemicals synthesized de novo by host plant cells around infection sites following pathogen detection (e.g., camalexin, pisatin, resveratrol).

Oxidative Burst

The rapid, active generation and release of Reactive Oxygen Species (ROS, such as $H_2O_2$ and $O_2^-$) that directly kill invading microbes and cross-link host cell walls.

Microbe-Associated Molecular Patterns (MAMPs)

Evolutionarily conserved molecular signatures present across entire microbial groups (e.g., fungal chitin, bacterial flagellin flg22, LPS, nematode ascarosides) that trigger basal host immunity.

Pattern-Triggered Immunity (PTI)

The baseline plant immune response triggered when host surface Pattern Recognition Receptors (PRRs) identify conserved PAMPs or MAMPs.

Effector-Triggered Susceptibility (ETS)

The phase in the zig-zag plant defense model where specialized pathogens inject effector proteins to disable host PTI and establish infection.

Effector-Triggered Immunity (ETI)

An amplified defense response initiated when intracellular plant Resistance (R) proteins detect specific pathogen Avirulence (Avr) effectors, often triggering the Hypersensitive Response.

Hypersensitive Response (HR)

Rapid, localized programmed cell death occurring within $24\,\text{hours}$ at the pathogen infection site to restrict and starve biotrophic pathogens.

Systemic Acquired Resistance (SAR)

A whole-plant induced systemic defense response launched after localized infection and HR, mediated by Salicylic Acid (SA) signaling and accumulation of Pathogenesis-Related (PR) proteins.

Induced Systemic Resistance (ISR)

A whole-plant defense priming state stimulated by root colonization of non-pathogenic PGPR, regulated via Jasmonic Acid (JA) and Ethylene (ET) pathways without PR protein accumulation.

General Resistance (Horizontal / Quantitative)

Polygenic plant resistance controlled by multiple genes, offering durable, broad-spectrum, but incomplete (partial) protection against all pathogen races.

Specific Resistance (Vertical / Qualitative)

Monogenic resistance governed by individual major R-genes that offers complete ('all-or-nothing') race-specific protection but is prone to pathogen breakdown.

Boom-and-Bust Cycle

The recurrent cycle where widespread planting of a single R-gene cultivar delivers high yields ('Boom') until pathogen mutation overcomes the R-gene, causing epidemic failure ('Bust').

Agrobacterium tumefaciens Crown Gall Mechanism

A biological process wherein bacterial Vir proteins excise and transfer single-stranded T-DNA from the Ti plasmid into the host plant genome; T-DNA oncogenes direct auxin (hypertrophy) and cytokinin (hyperplasia) overproduction to form tumors.

Biolistics (Gene Gun Transformation)

A transformation procedure where microscopic gold or tungsten heavy-metal particles coated with DNA are propelled into plant tissues using high-pressure helium gas.

Golden Rice

Genetically modified rice producing $\beta\text{-carotene}$ in edible endosperm via transferred phytoene synthase (psy) from daffodil/corn and carotene desaturase (crtI) from Erwinia uredovora.

Rainbow Papaya

Papaya genetically modified with the Papaya Ringspot Virus (PRSV) coat protein (CP) gene, triggering native host RNA interference (RNAi) to degrade incoming viral RNA.

Disease Incidence

The proportion or percentage of plant units exhibiting visible symptoms within a sampled population.

Disease Severity

The proportion or percentage of plant tissue area damaged or destroyed by disease symptoms on affected plants.

AUDPC (Area Under the Progressive Disease Curve)

A quantitative epidemiological metric summarizing cumulative disease intensity by integrating the total area underneath the disease progress curve across successive evaluation dates.

Monocyclic Disease Progress Curve

A slow, linear epidemiological progression modeled by simple interest ($Q_1 = Q_0 + KQ_0$), where the pathogen undergoes only one infection cycle per season without secondary spread.

Polycyclic Disease Progress Curve

An exponential epidemiological curve modeled by compound interest ($q = q_0 \times e^{kt}$), driven by the apparent infection rate ($k$) through repeated cycles of secondary airborne inoculum.

Polyetic Disease

An epidemic system wherein pathogen inoculum builds up continuously over multiple successive calendar years or growing seasons (e.g., apple powdery mildew).

Seed Degeneration

The progressive viral, bacterial, or fungal pathogen build-up in vegetatively propagated seed stocks (such as potato tubers) across generations, elevating initial inoculum ($Q_0$).

Infection Period

The required duration of favorable environmental conditions (temperature and leaf wetness/relative humidity) necessary for an inoculated pathogen to successfully penetrate host tissue.

Severity Values

Numerical risk ratings calculated from temperature and relative humidity data (e.g., in Blitecast) used to forecast late blight risk and optimize fungicide application timing.

Protectant Pesticide

A chemical application made prior to pathogen contact that forms an external chemical barrier on plant surfaces to prevent spore germination and penetration.

Eradicant (Curative) Pesticide

A chemical applied following infection that penetrates plant tissue to suppress early internal mycelial colonization or inhibit pathogen sporulation.

FRAC Codes

Standardized classification numbers established by the Fungicide Resistance Action Committee grouping active ingredients by biochemical mode of action to manage fungicide resistance.

Gene Pyramiding

The breeding strategy of stacking multiple distinct resistance genes into a single cultivar to broaden resistance durability against shifting pathogen races.

Disease Suppressive Soils

Soils containing high communities of antagonistic native microflora that prevent soilborne pathogens from establishing or producing disease despite susceptible hosts and favorable weather.

Integrated Pest Management (IPM)

An ecological pest management framework comprising four core components: monitoring and identifying pests, establishing economic thresholds, prevention, and targeted control intervention.