PLPA 30003 final exam study guide

_______ cells divide primarily by mitosis

Eukaryotic

A relationship between organisms where one benefits and the other is harmed

Parasitism

________ is a directional growth as a mechanosensory response to touch

Thigmotropism

Necrosis is a _______ of disease

Symptom

Gram-positive bacteria stain ______ during gram staining

Purple

______ plants cannot be infected by the pathogen

Immune

_________ is a gram-negative bacterium and a significant disease of apple and pear causing die-back

Erwinia amylovora

________ is a genetically-determined increase in stress tolerance as a result of natural selection over generations

Adaptation

An _______ is a specialized cell that fungi produce to penetrate the plant cuticle

Appressorium

Name the three components of the disease triangle

Environment, host, pathogen

Which of the following is true of high-throughput sequencing methods for plant pathogen diagnostics compared to traditional methods

They can comprehensively detect a broad range of pathogens, including unknown ones

What plant pathogen was responsible for the Irish potato famine in the mid-1800s

Phytophthora infestans

Horizontal gene transfer in bacteria is a key driver of microbial evolution and adaptation. Which method of horizontal gene transfer is most common between bacteria

Conjugation

Which best describes an organism that can extract nutrients from dead tissue?

Saprophyte

Describe a non-host plant

Lacks a critical component of pathogen growth, or completely inhibits the pathogen

Which of the following best describes the difference between frost and freeze injury in plants

Frost forms ice outside the plant and is generally less damaging than freeze injury

Bacterial plant pathogens typically enter plants trhough:

Natural openings or wounds

Which of the following is most commonly associated with interveinal chlorosis, or yellowing of leaf tissue between the green veins

Viruses or abiotic deficiencies

Describe downy mildew

Oomycete, has signs on the underside of the leaf, requires high humidity, and is a biotroph

Which of the following best distinguishes a xylem-limited disease from a phloem limited disease

Xylem-limited pathogens disrupt one-way flow and cause wilt, while phloem-limited pathogens interfere with sugar transport and lead to yellowing and stunting

Which of the following best distinguishes a polycyclic disease from a monocyclic one?

Polycyclic diseases produce secondary inoculum, allowing multiple infection cycles within a single season

• Produces several toxins

• Epiphytes and plant pathogens

• Causes angular leaf spots

• Can cause galls or wilts

• When grown on low-iron media, produces a fluorescent pigment

Pseudomonas

• Few species

• Gram positive

• Causes important wilts, blights, and cankers

Clavibacter

• Related to rhizobium

• Commonly found on pome, stone fruits, grapes

• Soft and rhizosphere inhabitant

• Cause growth regulator abnormalities

Agrobacterium

• Symptoms are angular leaf spot and chlorotic halo

• Colonies are yellow due to the production of a yellow pigment

• Most species are plant pathogens

• Few cause blights and cankers

Xanthomonas

• Fastidious

• Lives exclusively in xylem tissue and inside mouthparts of vector

• Causes scorch diseases

• Causal agent of Pierces Disease

Xylellum

• Common pathogen of plants in Rosaceae

• Native to North America. Most destructive disease of pear

• Kills flowers, twigs, may girdle trunks

Erwinia amylovora

Describe the fundamental steps of basic PCR and the essential components. Then explain how it aids in plant disease diagnostics

The fundamental steps of basic PCR are denaturation, annealing and extension. This is achieved with the use of primers and enzymes. Primers isolate the target DNA. During denaturation, the DNA is heated and separated into single strands. Annealing, cooling and primers bind to their complementary sequences on the single-stranded template. Extension, heated again and polymers extend and multiply the DNA. PCR aids in plant disease diagnostics as it is sensitive to pathogen presence, quick, and not reliant on unreliable ID techniques such as morphology. PCR is very accurate and allows diagnosticians to make effective recommendations for disease control

What are Koch’s postulates for establishing proof of pathogenicity? Why is it not sufficient to simply isolate an organism from infected tissue and assert that it is the pathogen?

Association, isolation, inoculation, re-isolation

It is not sufficient to simply isolate an organism from infected tissue and assert that it is the pathogen as it is possible to isolate an epiphytic organism that is simply living on the plant and not causing disease.

Koch originally stated three postulates the fourth was added later. Why do you think it was added

The fourth postulate (re-isolation) was added later as different pathogens can cause similar symptoms. Re-isolation rules out contamination or coincidence

Explain why insecticides are sometimes used to protect high-value crops from infection by phytoplasmas, but are not used for fire blights

Insecticides are used to protect high-value crops from infection by phytoplasmas because these diseases are vectored by non-beneficial insects such as leaf hoppers or other hemipterans. Phytoplamas are able to live in the mouthparts of these insects and are transmitted to vascular tissue when the insect feeds. Fire blight on the other hand can be spread by wind-blown rain events when bacterial ooze is present. Therefore, solely using insecticides is not effective at controlling the disease. Furthermore, fire blight is transmitted via pollinators. An important organism in fruit production of apples and pears

Which feature distinguishes Oomycetes from true fungi

Diploid vegetative hyphae

What role do haustoria play in Oomycetes like Phytophthora infestans

Extract nutrients while the host cell remains alive

Which mycotoxin is also known as vomitoxin

Deoxynivalenol

The Bordeaux mixture was first developed to control

Downy mildew of grape

Magnaporthe oryzae, the Rice Blast pathogen, possess G-protein coupled receptors which sense environmental cues to know when and where to form appressoria. Which of the following is not a cue sensed by these receptors

The presence of stomata

Which genus produces both antibiotics and mycotoxins, depending on species

Penicillium

What is the significance of chasmothecia in powdery mildew?

They are survival structures producing ascospores

Plant pathogens that cause powdery mildew are classified as

Ascomycota

Which of the following describes a critical difference between rust fungi and smut fungi in terms of their life cycles?

Rust fungi have multiple spore-producing stages, while smut fungi typically have fewer

Which of the following is a distinguishing feature of a plant disease caused by oomycetes compared to fungal pathogens?

Oomycetes produce motile zoospores that aid in the spread of the disease in wet conditions

________ are produced inside sac - like fungi

Ascospores

_______ _______ produces aflatoxins, which are potent liver carcinogens

Aspergillus flavus

Teleomorph is a term for ascomycetes used to describe the _______ stage or _____ reproduction cycle

perfect, sexual

Mycotoxins are ______ metabolites of fungi

Secondary

________ ________ causes Sudden Oak Death and can also infect ornamentals like rhododendron

Phytophthora ramorum

Conidia are asexual spores produced by ________

Ascomycetes

______ Rust fungi require one host to complete their life cycle

Autoecious.

Heteroecious rust fungi require multiple hosts to complete their life cycle

_______ are the only true fungi that produce flagellated spores

Chytrids

__________ lack a true mycelium and reproduce by budding, like yeasts

Chytridiomycota

Peach leaf curl is caused by the fungus ______ _______

Taphrina deformans

Oomycete sexual spore

Oospore

Oomycete asexual spore

Sporangia/Zoospores

Oomycete overwintering structure

Oospore

Oomycete ploidy (nuclear condition of hyphae)

Diploid (2N)

Two examples of Oomycota pathogens

Phytophthora infestans and Pythium spp.

Ascomycota sexual spore

Ascospore

Ascomycota asexual spore

Conidium/conidia

Ascomycota example of overwintering structure

Cleistothecia

Ascomycota ploidy (nuclear condition of hyphae)

Haploid (n)

Two examples of ascomycota pathogens

Fusarium oxysporum f. sp. lycopersici and Venturia inaequalis

Basidiomycota sexual spores

Basidiospores

Basidiomycota asexual spore

Uredospore

Basidiomycota overwintering structure

Teliospores

Basidiomycota ploidy (nuclear condition of hyphae)

Dikaryotic (n + n)

Two examples of Basidiomycota pathogens

Puccinia graminis and Ustilago maydis

Haploid cells (1N)

Plasmogamy

Fusion of two parent cells without the nuclei merging. Produces a Dikaryotic cell

Dikaryotic cell

Karyogamy

Fusion of two haploid nuclei to form a single diploid nucleus. Forms diploid 2N cell

Diploid (2N) cell

Meiosis

Cell division that forms 1N haploid cells

List 3 differences between Oomycetes and true fungi. Use correct terminology

1. Oomycetes have a cell wall that is made of glucans/cellulose. True fungi cell wall is composed of chitin

2. Oomycetes produce flagellated zoospores that are motile in free water. Fungal spores are not flagellated

3. Oomycetes have coenocytic or non-septate hyphae. Fungi have septate hyphae

List 3 examples of non-pathogenic basidiomycetes

Jelly fungi, stinkhorns, puff balls

Mycotoxins create both health and economic risks. List one major mycotoxin, the primary crop it’s associated with, and one key health effect. Next, explain two ecological or environmental factors that influence mycotoxin production by fungi in the field. Propose two cultural/management practices a grower could take to reduce this risk, for each action explain the biological reason why it works.

One major mycotoxin is Deoxynivalenol or DON. DON is primarily associated with grain crops. One key health effect is that is causes vomiting and feed refusal in pigs and other livestock. Two ecological or environmental factors that influence mycotoxin production by fungi are drought and hotter than usual climates associated with global warming/climate change. Two cultural/management practices that a grower can take to reduce the risk of mycotoxins are 1. monitoring and spraying fungicides. Fungicides work by targeting the chitin present in fungal cell walls. Spraying fungicides allow for crops to have limited or no presence of fungal pathogens. Another cultural/management strategy is to burn plant material if mycotoxins are present in a field. While it is a costly process, most crops affected by mycotoxins are not useable. Burning fields inhibits the spread of mycotoxin producing fungi and prevents the fungi from overwintering

Explain the workflow of how spore traps and qPCR are used to monitor downy mildews

Spore traps are used in agricultural systems to capture downy mildew sporangia. The traps works by sucking up particulate matter in the surrounding air. qPCR or real time/qualitative PCR is then used on the contents collected in the spore traps. If spores from the downy mildew are detected then the farmer then knows that it is time to use a fungicide that targets the oomytcete

Basidiomycete spore types in order

Basidiospores, Pycnidiospores, Aescospores, Urediniospores, Teliospores

Puccinia graminis disease cycle. Urediniospores are repeating.

Teliospores produces

Basidium/basidiospores