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113 Cards in this Set

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What are plasmids?
-circular, double stranded DNA
-useful vectors in biotechnology, can induce traits into the plasmid, therefor transfering to generations after
What are PASSIVE DEFENSES? 3 types.
-AKA Pre-existing Defenses

Three types:
1)Pre-existing structural defenses
-plant surface structures and cell walls such as wac, cutin, suberin, lignin, calcium, silicon
-may present a structural barrier to a physical penetration by the invading pathogen
-may contain components which directly inhibit pathogen growth
-may contain a signal compound to initiate the defense

2)Pre-existing Chemical Defenses
-inhibitors released by the plant in its environment
-antimicrobial compounds are present in the plant cells before infection

3)Defense through lack of essential factors
-lack of recognition between host and pathogen
-lack of host receptors and sensative sites for toxins, such as the T-toxin receptor
-lack of essential substances for the pathogen
What is Sapronin?
-an antimicrobial compound in plant cells
-a group of secondary metabolic founded in many major crops
-Sapronin deficient mutants are susceptable to fungal disease, provide good evidence that sapronins may protect oats againts pathogen attack
-sapronins coupled with sterols in fungal membranes to cause loss of membrane integrity
What are Pathogen induced structural defenses?
-AKA Histological Defense

Cork Layer (Periderm)
-an external, secondary tissue impermeable to water, viral gasses, often formed in response to evolving infections

Tylosis
-an overgrowth of the protoplast of a parenchyma cell into air adjacent xylem vessel or tracheid

Papilla
-a nipple like structure deposited beneath the cell wall on the inside of a cell being attacked by a fungus, apparantly serving as a defense mechanism against infection
What are the roles of papillae in disease resistance?
-as a physical barrier
-may contain antimicrobial components components (ROS, lignin precursors)
-the active oxygen species can be a primary defense signal
What are Pathogen Induced Biochemicals?
-exactly as the name says

Phytoalexins (phyton=plant, alexin=protecting substance)
-Pisatin, the first phytoalexin was isolated from pea infected with Monilla fructicola by Cruikshank and Perrin
-it i currently defined as low molecular weight antimicrobial compounds that are both synthesized by and accumlated in plants, which have been exposed to microorganisms

Classified mainly into 2 major groups:
1) Isoflavanoids: common in legume family
2) Terpenoids: characteristic phytoalexins of Solanoceae

**many pathogenic fungi and bacteria can degrade phytoalexins, apparently mediating the toxicity of those compounds**
What are the roles of Phytoalexins in defense response?
-antimicrobial ability
-accumulation at the right time, concentration, and location to be effective in the incompatible interaction
-studies on phytoalexin tolerance in pathogenic fungi have also shown a relationship betwen virulence and the ability of fungi to detoxify phytoalexins
-Aradopsis mutants deficient in phytoalexincamalexin synthesis are more susceptible to some pathogens
-however, the defense significance of these compounds is not clear for the majority of host parasite systems
What are Hypersensitive Reactions/Responses (HR)?
-excessive sensitivity of plant tissues to certain pathogens. Affected cells are killed quickly blocking the advance of obligate parasites
-a rapid local reaction of plant tissue to attck by a pathoen, resulting in the death of tissue around infection sites preventing further spread of infection

**different from necrosis because necrosis does not involve the active participation of the cell in its own demise**
What is Programmed Cell Death?
-activation of genetically regulated cell suicide machine

Apoptosis:
-term was originally used to dexcribe petals falling from flowers or leaves from trees
-form of cell death in which a suicide program is activated within the cell, leading to fragmentation of the DNA, shrinkage of the cytoplasm, membrane changes and cell death

Autophagy:
-a conserved process in eukaryotes in which double membrane vesicles engulf cytoplasm and sometimes organelles
How does Hypersensitive Reactions/Responses (HR) contribute to resistance?
-physically isolates the pathogen within the cells/lesions which are small defined areas of plant tissues that contain dead or dying cells
-fostering the release of antimicrobial enzymes and metabolites
-enhancing local and systemic signalling to activate defenses in non infected cells

-HR is considered to be one of the most important factor in impeding growth of obligate pathogens
-the dead tissues, however, facilitate the colonization by necrotophic pathogens
What are Pathogenesis Related Proteins (PR Proteins)?
-these proteins were initially detected from tobacco after infection with TMV
-groups of plant proteins induced specifically in pathological or related situations
-usually possess unique chemical properties (ie: extracellular location, extreme IEP and high stability)
-not only accumlate locally in the infected leaf, but are also induced systemically
-classically grouped into 5 families (PR1-PR5) and recently divided into 14 families
What are the functions of PR1->PR5?
PR1- inhibits the differentiation of rust infection hyphae in leaves of acquired resistence

PR2- inhibits B-1, 3-gluconase

PR3- inhibits chitinase

PR4- unknown

PR5- thaumatin; like protein

**extensively used as resistence targets in transgenic studies or as molecular markers in plant defense responses**
What are Free Radicals?
-involves 2 groups,

1)Active Oxygen Spp's (AOS) -OR- Reactive Oxygen Intermediates/Spp's (ROI's or ROS's)

2)Nitrogen Oxide Spp's

**discussed in another card**
What are Active Oxygen Spp's (AOS) -OR- Reactive Oxygen Intermediates/Spp's (ROI's or ROS's)
-a collective term for radicals and other non radical but reactive spp's derived from oxygen, including superoxide, hydrogen peroxide and hydroxyl radical

the oxidative burst is required for:
-cell wall x-linking
-directly killing the invading pathogen
-signalling for systemic acquired resistence (SAR)
-involvement in HR
What are the mechanisms for generating Active Oxygen Spp's (AOS) -OR- Reactive Oxygen Intermediates/Spp's (ROI's or ROS's)?
-use of pharmaceutical agents confirms the function of NADPH oxidase system in plant defense responses
-mammalian phagocyte NADPH oxidase homologues were identified in plant spp's
-Arabidopsis NADPH oxidase gp91 mutations eliminated the majority of total ROS production
What role do Nitric Oxide Spp play in plant resistance?
-functions as a signal in resistance response
-it was just recently hypothesized that NO functions together with AOS participating in signal of plant defense responses
-it is likely that this signal pathway exists in plant systems
-however, no mammalian NO synthase (NOS) was predicted from reported plant DNA sequences
-plants use different enzyme systems to generate NO (eg: nitrate reductase and some other shit)
What is Induced Resistence?
-AKA Acquired Resistence
-developes after a primary infection (or treatment with certain chemical) and it is effective against a secondary infection, this phenomenon resembles acquired immunity in animals
What are Local Acquired Resistance (LAR)/ Induced Local Resistance (IAR)?

What are Systemic Acquired Resistance (SAR)?
-IAR is confined to the site of infection
**********************************
-SAR, which can be induced by a local infection, provides the plants with long lasting resistence against a broad spectrum of pathogens in distant uninfected plant parts
-is a form of systemically induced disease resistence that is triggered upon infection by a necrotizing pathogen
-the state of SAR is characterized by an early increase in endogenously synthesized salicylic acid (SA) and the concomitant activation of genes encoding PR-proteins
-SAR has been demonstrated in many plant spp
-the SAR pathway is dependant on SA accumulation, which is induced upon pathogen infection
-SAR mostly found in dicots, not too sure about monocots
What is Induced Systemic Resistence (ISR)?
-Jasmonic acid dependant ISR pathway, which is triggered by a non pathogenic Pseudomonas fluorescens (rhizobacteria)
-ISR functions independantly of salicylic acid (SA) and PR gene activation
-ISR signal molecules include: jasmonic acid; ethylene; mutants; ISR marker proteins
What are the significances of Salicylic Acid and Jasmonic Acid as endogenous signals?
-both have been recognized as inducers of plant defense response for many years
-dramatically accumulated after infection
-induce a set of defense gene expressions
-exogenous application evokes the protection against pathogen attack
-deficient mutants exhibit reduced gene expression and enhances disease developement
Give 7 examples of where genetic info is encoded in DNA or RNA.
1-genomic
2-chromosome
3-nuclear
4-cytoplasmic
5-plasmid
6-mitochondrial
7-chloroplast
Define HOST SPECIFICITY
-a pathogen can only attack certain types of plant spp and cultivars
-a host plant suffers diseases only from certain pathogens and pathotypes
Define PATHOGEN ADAPTATION
-an evolutionary modifaction that improves a pathogens chances of survival and reproductive success
How do genetic modifications occur?
-can occur in both sexual and asexual stages
-general mechanisms include mutation and recombination
Define MUTATION
-a change in the nucleotide sequence of DNA; the ultimate source of genetic diversity
-substitution, addition and deletion of single or multiple base pairs
-insertion or deleiton of DNA fragments
-insertion or transposable elements: transposon (jumping around of DNA frag) or retro transposon (re-inserted genes that are inactive)
Define RECOMBINATION
-occurs during secual reproduction of plants, fungi and nematodes
-recombination of genetic materials occurs during the meitotic division of the zygote as a result of genetic x over in which parts of chromatids (and the gene they carry) of one chrome of a pair are exchanged with parts of chromatids of the other chromosome pair
Define HETEROKARYOSIS
-the condition of having 'different' nuclei
-a cell that contains genetically different nuclei or a thallus made up of such cell
Define PARASEXUALISM
-a sequence involving heterokaryon formation, diploidization, and haploidization, often resulting in the formation of recombinant nuclei
-unlike the sexual cycle, the parasexual cycle may occur at any point or continuously throughout the life cycle (shitty mitosis)
-like sexualism, but when it returns to the haploid state, genetic info is not distributed evenly
Define HETEROPLOIDY
-a condition in which a cell, tissue, or organism that contains more or few chromosomes per nucleus than the normal 1N, 2N for that organism (ie: 4n, 6n, etc.)
What are the 3 sexual like processes in bac involved in horizontal gene transfer?
1)Conjugation
2)Transformation
3)Transduction
Define CONJUGATION
-when 2 compatible bac come in contact with one another and a small portion of the chromosome or plasmid from one bacterium is transferred to the other through a conjugation bridge or pilus
Define TRANSFORMATION
-bacterial cells are transformed genetically by absorbing/incorporating in their own cells, genetic material secreted by, or released during rupture of other bacteria
Define TRANSDUCTION
-a bacterial virus (bacteriophage) transfers genetic material from the bacterium in which the phage was produced to the bacterium it infects next
What does f.sp. stand for (eg: Blumeria graminis f.sp. tritici
-f.sp. means formae speciales or form species

-some individuals of the spp's attack only certain spp's of host plants
Define PATHOVARS (PV)
-in bacteria, a subspecies on group of strains that can cause disease only on plants within a particular genus or spp's
Define STRAINS
-a general trm to denote a single isolate or a group of similar isolates
Define ISOLATES
-a single pure culture made by direct isolation from diseased material, or a sub culture of such a culture
Define RACES (PHYSIOLOGICAL RACES)
-within a special form, some individuals attack a set of the host variesties but not the others which make up a race such as Puccinia graminis f.sp. tritici race 1,2&3
Define VARIANT
-occasionally, one of the offspring of a race can suddenly attack a new variety that it can barely infect before
-this individual is called a variant
Define BIOTYPES
-the identical individuals produced asexually by a variant make up of a biotype (clone)
-each race consists of one or several biotypes
What are the 3 plant resistance phenotypes?
1) Non-Host Resistance
2) R-Gene Resistance
3) Apparent Resistance

**on other flashcards**
Define NON-HOST RESISTANCE
-a plant resistance phenotype
-non host resistance is an operational def that describes the resistence observed when ALL MEMBERS OF A PLANT SPP EXHIBIT RESISTANCE TO ALL MEMBERS OF A GIVEN PATHOGEN SPP
-is completely resistentto pathogens of other plants, usually even under the most favorable condition for disease development
-often occurs at early stage of the infection associated with a penetration deficiency and a rapid cell death
-due to lack of something in the plant that the pathogen needs or to the presence of substances incompatible with the pathogen
-however, the detail mechanisms are unknown
Define R-GENE RESISTANCE
-a plant resistance phenotype
-AKA cultivar specific, true resistence or gene for gene resistence
-plants possess genes for resistance against the pathogen with avirulence genes

Involves...
1)Horizontal Resistance:
-non specific, general, or multigene resistence
-partial resistance equally effective against all races of a pathogen
-resistence is controlled by many genes and quantitively inherited
-resistence mechanisms involved in many physiological steps providing nonspecific, general, quantitative, adult plant, field or durable resistence
-resistant phenotypes may not provide the distinguishing among different races
-resistance can be affected by environment factors
-resistance can be maintained for a long period

2)Vertical Resistance:
-specific, strong, or monogenic/oligogenic resistence
-complete resistance to some races of a pathogen but not to others
-resistence is always controlled by 1 or a few genes called R-genes
-resistance mechanism is determined at the major step of the physiological responses providing strong, major, specific, qualitative or differential resistance
-can be distinguished among varieties, which provide the host range to determine the pathogen races
-resistence can be easily broken down by variation of the pathogen virulence

3)Cytoplasmic Resistance:
-resistence is determined in cytoplasm
-such as corn cytoplasmic resistence against the southern corn leaf blight
Define APPARENT RESISTENCE.







Escape and Resistance
-a plant resistance phenotype
-for various reasons, the plants escape or tolerate infection by some pathogens

Disease Escape:
-the failure of a host to become diseased because of seperation, in space or time, of susceptible host tissues and the infective units of the pathogen
-such as unfavorable environmental conditions, plant developemental stages (adult resistance) and absence of pathogens, these are important factors for the practical management of plant diseases

Tolerance:
-the abilty of a plant to sustain the effects of a disease without dying or suffering serious injusry or crop loss
-the phenomena are often observed with some mild virus strain
-the mechanisms are unknown and in some cases, it may associate with horizontal resistence
What is the GENE FOR GENE CONCEPT?
-a single plant resistance gene reacts with the matching single avirulence gene of a pathogen
-for each gene that confers virulence to the pathogen, there is a corresponding gene in the host that confers resistence to the host, and vice versa
-the specificity (susceptibility and resistance) in each host/pathogen combo is predetermined by the gentic material of the host and the pathogen
-the incompatible interaction (resistance) is a specific recognition between an avirulence (avr) gene product encoded by a dominant gene in the pathogen and a product of the resistence (R) gene from the plant
-the absence of either the R-gene or the avr gene product results in a compatible interaction (susceptibility)
-a mutation in either the avr or the R-gene, which results in loss of function, will result in a change from an incompatible to a compatible interaction
What are Avirulence Genes?
-avr genes are believed to govern the production of elicitors (ligands) which can be recognized by receptors encoded by host R-genes and cause a plant pathogen or pest to elicit a resistance response in a host plant
-structures of avr gene products are quite different and the biological function of only a few avr genes have been determined
-a large number of avr genes have been cloned from pathogenic bacteria(in hrp clusters), fungi(in avr4 & 9 from C.fulvum and so on...) and viruses (in the coat proteins)
What are ELICITORS?
-compounds of the pathogen that the plant senses to initiate defense reactions
Why do pathogens possess avr genes producing elicitors negatively acting factors that limit the pathogens accessing to their host?
-studies have indicated that many avr genes have dual functions, having a role in virulence (effector) as well as avirulence (elicitor), & thus function as important mediators of the interaction between pathogen and plant
What was the first resistance gene cloned?
-Hm1 from maize by transposon taggine
-the gene encodes an HC-toxin reductase, which reduces and thereby detoxifies the HC toxin in resistant varieties
What doe LRR stand for?
Leucine
Rich
Repeat
What does TM stand for?
Trans
Membrane domain
What does NBS stand for?
Nucleotide
Binding
Site
Discuss Elicitor-Receptor Interactions.
-the direct phsical interaction between R-gene and avr gene products has been demonstrated in 2 systems includin PTOAvrPto and Pita-Avr-Pita by th eyeast 2-hybrid system and the immune precipitation
-therefor it is finally confirmed that the R-gene product functions as the receptor and the avr gene product functions as the elicitor
Discuss the specificity of R-Genes.
-several R gene locus sequences provide evolution or polymorphism information, which provides useful genetic background for predicting and evaluating the resistance specificity
-recent studes showed that the LRR and N-terminal sequence in certain resistance genes might determine the resistance specificity
Define EPIDEMIC
-a widespread temporary increase in the incidence of an infectious disease, particularily within a season
-it generally implies the developement and rapid spread of a pathogen on a particular kind of crop plant cultivated over a large area
Define EPIDEMIOLOGY
-the study of factores affecting the outbreak and spread of infectious disease
Give some examples of major epidemics.
-Irish potatoe famine (1845-46 in Europe)
-rice brown spot epidemic (Bengal famine, 1943 in S. Asia)
-Ort Victoria blight epidemic (1945 in USA)
-
What is a DISEASE TETRAHEDRON?
-AKA DISEASE PYRAMID
-the interaction of components of plant disease can be expanded to include time and human
-can be visualized as:
PATHOGEN, ENVIRONMENT, HOST, & TIME occupying the sides, while HUMAN occupies the top point **discussed in other FC's**
-the volume of the pyramid is indicative of the amount of disease
What are the 3 STRUCTURAL ELEMENTS OF AN EPIDEMIC?
1) Host Factors
2) Pathogen Factors
3) Environmental Factors
In the terms of STRUCTURAL ELEMENTS OF AN EPIDEMIC, what are the HOST FACTORS?
Resistance or susceptibility level:
-sysceptible host plant lacking genes for resistence against pathogens favor the disease epidemic

Degree of genetic uniformity:
-genetic uniformity in the host provides an important factor in disease epidemics of crop plants

Age:
-the age of the host plant affects the disease developement depending on the articular plant pathogen interaction
-dampin off and downey mildew diseases occur at the early stages during growth, and host plants become resistant during the adult period
-Botrytis and many leaf spot diseases attack the host at the adult peroid, when host plants become senescing
-stem rusts attack ceral crops at the blooming stage, but not before or after
-canola stem blight is most conspicuous in the fild when the crop is fully podded
In the terms of STRUCTURAL ELEMENTS OF AN EPIDEMIC, what are the PATHOGEN FACTORS?
Amount of primary inoculants/inoculums:
-seed borne (eg: loose smut), infects or contaminates
-soil borne
-plant residues
-vectors (must be available to spread)
-alternate/alternative hosts

Pathogen genetics:
-related to the level of virulence
-type of reproduction
I)Polycyclic: produces a shitload of shit in short time. eg: rusts, mildew and leaf spots
II)Reproduce inside the plant, reproduce in 1 or a few reproductive cycles
III)Monocyclic: only one point in life cycle where infection is possible. eg: smuts (infect during flowering stage) and bunts (infects the sedling stage

Ecology and mode of spread of the pathogen:
-air borne (eg: rusts)
-soil borne (eg: fusarium, nematodes)
-seed borne (eg:bunts)
-vector dependancy (eg: MLO's)
In the terms of STRUCTURAL ELEMENTS OF AN EPIDEMIC, what are the ENVIRONMENTAL FACTORS?
-moisture
-temperature

effect of human culture practice:
-monoculture
-amount of inoculums: seed quality, disease residues, rotation, alternative host, etc
-introduction of new pathogens
-chemical and biological control
What are DISEASE PROGRESS CURVES?
-the pattern of an epidemic in terms of the number of lesions, the amount of disease tissues or the numbers of diseased plants s given by a curave that shows the progress of the epidemic over time

-SATURATION CURVE (monocyclic disease; fast growth then levels out)
-SIGMOIDAL CURVE (polycyclic disease)
-BIMODAL CURVE (polycyclic disease affecting different organs or stages; 2 humps on the curve)
What are DISEASE GRADIENT/DISPERSAL CURVES?
the pattern of an epidemic in terms of the numbers of lesions, the amount of disease tissues or the numbers of diseased plants as it spreads over distances is given by a 'hockey stick' like curve
How do you model and forecast plant disease epidemics?
-observation, measurements, mathematical formulas and computations are needed to study the disease development and to predict the epidemics
-consider all components and subcomponents
-quantitative treatment by mathematical formula (model)
-computer simulation
-disease forecast allows us to determine whether, when and where to sue control measures
-however, growers must always weight the ristks, costs and benefits of each of numerous decisions
Define PLANT QUARANTINE
-control of import and export of plants oto prevent spread of diseases and pests
Define LEGISLATIVE/REGULATORY CONTROL
-an attempt to exclude pathogens from areas where they do not already exist
What are some ways of moving plant pathogens
Moved on:
-vectors
-infected/contaminated plants
-seed
-transplants
-planting materials
-equipment
-etc.
What conditions must be fulfilled in order for the plant quarantine to be effective?
-pathogen must be transported on diseased host material, or by some other vector, such as man himself
-must be controlled
-can't be under the influence of uncontrollable agents such as the wind
What is a QUARANTINE PROGRAM?
-a large scope project
-investigates disease distributions
-lists all dangerous pathogens wih their host plant
-introduce germplasms from disease free areas
-grow introduced plants in a restricted area
-apply seed treatment (to kill fungal, bac, etc. infection)
What is are QUARANTINE METHODS?
-direct to specific targets
-direct inspection
-blotting assay
-growing plants
-chemical, serological and molecular methods
What diseases are under quarantine regulations in SK?
Dwarf Bunt (Tilletia controversa)

Flag Smut (Urocystis agropyri)

Karnal Bunt (partial bunt) (Neovossia indica, Tilletia indica)
What diseases are under warning in SK?
-Fusarium head blight
-Dutch elm disease
-Bean halo blight
What are SEED HEALTH TESTING PROGAMS?
-test seeds for the presence of plant pathogens
-hasn't occurred until recently because of lack of established assay techniques and belief that chemical seed treatments could effectively control seed borne diseases
-chemical treatment of seed has been of relatively limited use with bacterial and viral pathogens
-seed health testing progams are still useful for detecting a number of seed borne bacteria
Define TOLERANCE LEVEL.
-the level of seed infection that can be accepted in a seed certification program
-established to each particular disease

**USA seed health certification program has established a zero tolerance to halo blight**
Define CROP SANITATION
-cultural control of disease
-to reduce the inoculum by removal or detruction of diseased materials
-it is more likely to be effective in the case of diseases spreading rather slowly, such as many cankers
-mainly employed in market garden, glasshouse, and orchard
Give 8 methods used to CULTURALLY CONTROL PLANT DISEASES.
1)Crop Sanitation

2)Eradication of alternate and alternative host

3)Crop rotation

4)Avoidance

5)Multilines and mixture of cultivars

6)Non chemical soil treatment

7)Special methods

8)Harvesting and storage
Define ERADICATION OF ALTERNATE AND ALTERNATIVE HOST
-cultural control of disease
-to reduce the inoculum
-to remove an important source of variation in the pathogen
Define CROP ROTATION
-to reduce inoculum
-many pathogns persist on or in the dead remains of the previous crops, or in soil in which a susceptible crop has been grown
-the period of persistence is very varied: where 1 or 2 years break is sufficien, rotation is practical, where 10 or more years are required, some other control method has to be used
-the 4 course rotation formerly practiced widely in various ceral diseases such as take all caused by Gaeumannomyces graminis
-rotation is also sometimes effective with many other plant diseases, such as Fusarium on banana, Fusarium and Verticillum on cotton by a 2-3 year break during which rice is grown
Define AVOIDANCE
-cultural control of disease
-if a crop is grown in an area where the conditions are such that the disease does not occur, susceptibility to that disease may be ignored
What are MULTILINES AND MIXTURE OF CULTIVARS?
-cultural control of disease
-to protect against devastating epidemics
-basic idea is to use a shitload of shit, so if one sucks, they don't all suck
-a multiline cultivar is a mechanical mixture of a number of lines of a cultivar each carryiga different gene for resistance to the pathogen to be controlled but otherwise more or less identical
-eg: the most fully developed multiline program are those involving oats against crown rust in Iowa
-the use of mixtures of different cultivars or varieties might provide an acceptable and much quicker and cheaper substitute of the multiline system, which has been demonstrated successfully on rice against rice blast, the major disease of rice in southern china
********************************
at least several mechanisms operate, or may operate, in reducing disease incidence:
-reduce the amount of susceptible tissues per unit area of crop, and hence the amount of infection and the amount of inoculum
-increase the average distance for the inoculum to reach a susceptible plant surface
-hinder the movement of inoculum from one susceptible plant to another
-cross protection may occur (ie: pre inoculation with a race to which the line is resistant may protect it from a race to which it is normally susceptible)
What are NON CHEMICAL SOIL TREATMENTS?
-in greenhouses, the partial sterilization of soil is carried out routinely in control soil borne pathogens such as species Pythium, Fusarium, Verticillium, Rhizoctonia and also nematodes
-in hot climates, covering the soil with polyethylene film raises the termperature enough to provide partial sterilization
What are SPECIAL METHODS OF PROPAGATION?
-planting materials free of pathogens (viruses, viroids, mollicutes, systemic fungal/bacterial pathogens) can be obtained through tissue culture
What are HARVESTING AND STORAGE?
-cultural control of disease
-many storage rots originate as latent infections present at harvest and epidemics can occur during transport and storage
-to avoid this, take care at harvesting and check humidity and temperature control at storage
What are 3 ways to CHEMICALLY CONTROL PLANT DISEASE?
1)Soil fumigants
2)Protectant fungicides
3)Systemic fungicides
What are SOIL FUMIGANTS?
-a chemical control
-toxic volatile substance that is used to manage various pests
-often volatile compounds
-can be non specific
-applied to the soil before the crop is sown
-not leave phytotoxic residues
-the most widely used fumigant is methyl bomide to control diseases caused by species of Fusarium ad Veticillum, always applied in a mixture with the volatile insecticide chloropicrin (nematocide)
What are PROTECTANT FUNGICIDES?
-a chemical control
-preventative, contact, surface fungicides
-protect an uninfected plant/seed by killing/inhibiting the development of fungus spores or mycelia on the surface, but are ineffective against established infections; they do not normally enter the plant to any extent
-most protectant fungicides are toxic if they enter the plant
-with a broad spectrum effective against a wide variety of pathogens
-act as a multi site inhibitor
-pathogen strains resistant to them are unlikely to develop
-are subject to weathering
-applied as high volume or low volume sprays, or occasionally as dusts
-the oldest and still the most extensively used protectant fungicides are inorganic sulphur and copper compounds
-sulpur is good against powdery mildew, copper was involved in the Bordeaux mixture

Ditiocarbamates:
-these compounds may react with sulfydryl groups in the cell of the pathogen
-excellent broad spectrum fungicides for control of foliage and fruit diseases of many vegetables

Aromatic protectants:
-inhibit production of compounds that have -NH2 and -SH groups

Heterocyclic compounds:
-the compound inhibits thio containing enzymes, and may also react with the sulfydryl groups in the cells of pathogens
What are SYSTEMIC FUNGICIDES?
-are absorbed and translocated in the plant

ERADICANT/CURATIVE FUNGICIDES:
-used to control disease after infection has occurred as rescue treatments of crops, it kills the fungus insde the host or may suppress the sporulation of the fungus without killing it

Unlike a protectant fungicide, a systemic must be:
-reasonably water soluble, must enter the plant and to be translocated
-highly selectie, being toxic to the pathogen but not to the host; inhibiting only one or perhaps a few steps in the metabolism of the pathogen
-as a result, the pathogen easily gains resistance through simple mutation
-most systemic fungicides are translocated in the apoplast, though some, aminly compounds related to the bezimidazoles, appear to move in the symplast also
-applied to the root for systemic effect
-applied to the shoot for local effect
-eg's given in another FC
Give 4 examples of SYSTEMIC FUNGICIDES.
Acylalanines
-metalaxyl
-sold as Ridomil; apron; Subdue
-one of the best systemic fungicides against oomycetes
-binds to RNA polymerase of sensitive strains

Benzimidazole
-Benomyl, carbendazim, thiabendazole and thiophanate
-effective against a large number of important fungal pathogens
-Benomyl sold as Benlate, which is rapidly hydrolysed in the plant to methylbenzimidazol-2-ylcarbamate (carbendazim)
-inhibits mitosis

Oxathiins:
-the first systemic fungicides to be discovered in 1966
-carboxin (carbathin) (sold as Vitavax) and oxycarboxin (sold as Plantvax)
-effective against damping off diseases, smuts and rusts
-interfere with certain polypeptides witin complex II of the mitochondrial succinic dehydrogenase complex

Steroid Inhibitors:
*including
-Imidazoles
-Pyrimidines
-Triazoles

-most effective broad spectrum
-inhibiting the biosynthesis of ergosterol in vrious ways; some of them also induce the phytoalexin production
What 5 factors are considered when applying fungicides?
-time of application
-deposition
-adhesion
-distribution
-persistence
What are the 5 main application methods of fungicides?
-foliage sprays and dust
-seed treatment
-soil treatment
-tree treatment
-treatments of fruits and vegetables
In regards to fungicides, hwat would you do to avoid the effects of the developent of resistant strains of pathogen?
Use less frequently
-integrate all IPM methods with appropriate fungicide application

Fungicide mixture or alternations
-avoid repeated uses of fungicides having identical biochemical modes of action
What is BIOLOGICAL CONTROL OF PLANT DISEASES?
-an alternative to synthetic chemical pesticide in an Integrated Pest Management (IPM) program
-involves the partial or total destruction of pathogen populations by other organisms
-the reduction of the amount of inoculum or disease producing activity of a pathogen accomplished by or through one or more organisms other than man
-the control of plant disease by modifying biological interactions in the ecosystem, especially by the use of natural enemies of the pathogen

**Anything other than chemical control of plant diseases could be classified as a biological control**
What are the most common ways to control plant diseases?
-Cultural
-Chemical
-Biological
-Resistance Breeding
-Integrated Pest Management (IPM)
What are some pros to BIOLOGICAL CONTROL OF PLANT DISEASES?
-effective control of plant diseases
-highly specific and selective in the pathogens
-ecologically safe
-environmentally friendly
-compatible with sustainable agriculture
Define ANTAGONISM
-a relationship between different organisms in which one (antagonist) partly or completely inhibits the growth of another or kill it; usually applied to the effects of toxic metabolites of one organism on another
Who is Guthrie B.Sanford
-studied the common scab disease of potatoes in SK and late transferred to alberta in 1928
-he sugested that the control of potato scab by green maure was a biological control and becmae the first scientist in NA suggesting that the disease might be inhibited by the activity of saprophytic bacteria developing in decomposing green manure
-Sanford and his colleagues expended the theory to control take all disease in the field
List the 4 MECHANISMS OF BIOLOGICAL CONTROL.
1) Antibiosis
2) Competition
3) Hyperparasitism
4) Induced Resistance
What is ANTIBIOSIS?
-a mechanism of biological control
-includes any chemical product(s) of one organism (antagonist) which directly inhibits or destroys another
-this includes antibiotic compounds and some extracellular enzymes
-penicillin was the first antibiotics discovered by Fleming in 1928
-among the most important antibiotics in plant disease control are streptomycin and tetracyclines. Both are produced by Streptomyces.
-Bacillus and other bacterial agents produce antibiotics against a broad spectrum of plant pathogens
-lytic enzymes like chitinase, B-1, 3-glucanase and oocellulase are most often implicated as major features of Trichoderma spp
What is COMPETITION?
-a mechanism of biological control
-deprives a pathogen of essential nutrients by encouraging the growth of nutrient consuming antagonists
-in a broad sense, competition refers to the interaction of 2 organisms striving for the same thing (eg: space, nutrients and molecules)

Suppressive Soil
-in which the pathogen may persist, but either causes little or no damage, or cause disease for a short time and then declins
-the suppression occurs as a result of the build up of saprophytic competitors or antagonsists in th esoil

Hypovirulent Strains
-the reduced virulence strain
-hypovirulence of a pathogen strain is often resulted of the presence of transmissible double stranded RNA

Cross Protection
-acquired immunity, acrquired tolerance, cross immunization, and premunity
-the phenomenon in which plant tissues infected with one strain of a virus are protected from nfection by other more severe strains of the same virus
Who is Mckinney?
-1929
-one of the first to report on the phenomenon of cross protection in describing the ability of a light green mosaic strain of TMV to prevent symptom expression of another strain which indeuced a yellow mosaic
What is HYPERPARASITISM?
-a mechanism of biological control
-parasitism on another parasite
-the mycelium and resting spores or sclerotia of several pathogenic soil fungi are invaded and parasitized (mycoparasitism) or lysed (mycolysis) by several non pathogenic fungi

-eg: Trichoderma spp on Rhizoctonia solani
What is INDUCED RESISTANCE?
-a mechanism of biological control
-induced resistance in the host by inoculation with non pathogenic or avirulent strains of a pathogen has been demonstrated in a number of cases as mentioned in the earlier chapters

Biological Control of Weeds
-the use of natural microorganisms that infect and damage or kill weeds
-microorganisms are generally fungi pathogenic to specific weeds.
-they must be extensively tested for efficiency and specificity
What are some advantages to RESISTANCE BREEDING? Disadvantages?
Advantages:
-least expensive
-easiest
-safest
-most effective

Disadvantages
-long period
-pathogen adaptation and tolerance
-limitation of resources
What are the 4 steps in BREEDING A DISEASE RESISTANT CULTIVAR?
1) obtaining a source of resistance
2) transferring the resistance to a breeding line
3) evaluating the line for disease resistance, yield and quality
4) releasing seeds or plant material to growers
What are some classical resistance breeding methods?
-backcross breeding (recurrent selection)
-pure line breeding (pedigree selection)
-hybrid crops
-population screening
-tissue culture
-cell culture
-protoplast fusion (allows transfer from wildtype to commercial lines)
-doubled hapliod (by using colchines: find targeted genes, then duplicate so you end up with targeted diploid shit
What are MOLECULAR MARKERS?
-instead of assaying for the phenotype, selection in segregating generations is based on the markers
-molecular markers have become increasingly popular for selection in breeding programs
What are some advantages to Molecular Marking as opposed to Phenotypic?
-molecular markers greatly facilitate identification of the interest trait, linkage, mapping and gene cloning
-not affected by environment
-detectable in single plants and in all stages
-relatively low cost
-resistance can be selected for in the absence of the pathogen
What are some frequently used techniques in MOLECULAR MARKING?

RAPD
RFLP
AFLP
SNP
SSR
SCAR
Random
Amplified
Polymorphic
DNA
*****************************
Restriction
Fragment
Length
Polymorphism
******************************
Amplified
Fragment
Length
Polymorphism
******************************
Single
Nucleotide
Polymorphism
******************************
Short
Sequence
Repeats
******************************
Sequence
Characterized
Amplified
Regions
What are some applications of resistance varieties?
-using more than one effective R-gene at a time
-gene pyramiding
-multiline varieties and cultivar mixture
-polygenic partial resistance
What is INTEGRATED PEST MANAGEMENT (IPM)?
-the attempt to prevent pathognes, insects, and weeds from causing economic crop losses by using a variety of management methods that are cost effective and cause the least damage to the environment
-plant disease and/or pests can never be eliminated, only managed at an economically acceptable level
-many pests play beneficial roles in the environment
-the economic, social, and political consequences o pest problems should be considered
-it is important to seek and utilize knowledge and techniques from all crop production and protection disciplines in the management of pests
What are the goals of IPM? 5
-please farmers
-please environment
-reduce the incidence of disease to acceptable levels (disease threshold)
-reduce the risk of losing the efficacy of a single method
-largely protect the environment
List and give 4 examples of important R-GENE CLASSES
1) Protein Kinase (eg:Pto)
2) LRR-TM-Kinase (eg:Xa21)
3) LRR-TM (eg:cf-2,4,5,9)
4) NBS-LRR (eg:RPM1, RPS2)