Lecture 2 Flashcards by Amiel Encomienda

What are the diseases caused by bacteria

) Fire Blight (apples)
) Crown Gall
) Citrus Canker
) PSA V (virulent)

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What bacteria causes Fire Blight

Erwinia amylovora

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What does Erwinia amylovora affect

pears and apples

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How does Erwinia amylovora affect plants

produces enzymes and toxins that cause necrosis (death of tissue or organ) and death of young shoots
- severe cases, death in trees

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How is Erwinia amylovora (fire blight) spread

Pollinating insects

water splash

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What are ideal conditions for fire blight

spring
16 C
anywhere under right conditions

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true or false; NZ cannot export apples to Australia due to Fire blight (Erwinia amylovora)

true

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What causes Myrtle Rust (fungus)

Puccinia psidii

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Where was Puccinia psidii first reported in and when

Brazil
1984
guava

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true or false; Puccinia psidii have a wide range of hosts including commercial Eucalyptus species in Brazil

true

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true or false; Puccinia psidii arrived in Australia in 2010 and was not eradicated

true

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What do the rust spores of Puccinia psidii look like

thick brown walls

enabling them to survive UV in the upper atmosphere

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Why is possible that NZ will also be invaded by Puccinia psidii in the future

due to Westerly winds from Australia

- Puccinia psidii is very small and can travel very quickly

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What causes Citrus canker

bacteria

Xanthomonas axonopodis pathovar citri

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What are the symptoms of Xanthomonas axonopodis pathovar citri (Citrus Canker)

Infected trees display

raised brown lesions
with water soaked margins
yellow halo on leaves, fruit and stem

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What happens when the lesions caused by citrus canker is wet

lesions ooze bacteria that spread short distances by water splash

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What distributes Xanthomonas axonopodis pathovar citri

Citrus canker:

water splashes (short distance)
Strong winds and rain (long distance)
people (spread the disease by moving infected plants, or fruit)

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What are the effects of Citrus canker on yield

low vigor
reduced fruit quality
reduced fruit quantity

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in 2005 what hurricane spread citrus canker in America

hurricane Wilma

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What causes Pierce’s disease (bacteria)

Xylella fastidiosa

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Where is Xylella fastidiosa a major concern

USA

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how is Pierce’s disease caused (Xylella fastidiosa)

caused by fastidious bacterium Xylella fastidiosa

- which invades and blocks plants xylem vessels

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How is Xylella fastidiosa transmitted

sharpshooters (sucking leafhopper insects)

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Where are the symptoms of Xylella fastidiosa (Pierce’s disease) seen

Leaves
flowers
canes

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How does Pierce's disease affect the leaves

- Chlorotic spots spread as the centre dries out and becomes brittle - concentric zones develop - leaves fall prematurely

How does Pierce's disease affect the flowers

- fruit set is reduced | - berries dry up

How does Pierce's disease affect canes

- wood fails to mature - produce 'green islands' of tissue - bud break is delayed in the following season

Plants affected by Pierce's disease die in about....

1-5 years

What kind of plant does Pierce's disease infect (likely)

grapevines

true or false; Xylella fastidiosa is present in NZ

false; it is not | so it is a bio-security threat

What conditions does Xylella fastidiosa like to establish itself

hot areas | - less prevalent where it is cold

What causes Psa V

Pseudomonas synringae p.v actinidiae | - kiwi fruit bacterial canker

What conditions are Psa V likely to develop

- Spring - Autumn - cool temps - high humidity - rain - 10-20 degrees

Where was Psa V first discovered and when

Japan | 1980s

What are the primary symptoms of a plant infected by Psa V

- spots with halo | - curling, brown infected buds

What are the secondary symptoms of Psa V

red/orange exudatem (substance secreted by plant) shoot die back cane collapse

How is Psa V spread

- windborne pollen - strong winds - heavy rainfalls - animals and humans

What organisation monitors Psa V in NZ

KVH organisation

true or false; about 37% kiwi fruit orchards are infected

true

true or false; 600 ha Hort 16A gold ripped out till April 2012

true

How is the Psa V controlled

``` Chemicals plant health and healthy stock no overhead irrigation inspections disinfection of pruning and picking equipment ```

What do you call the new cultivated Psa V resistant kiwifruit

Gold3 | - which can be grafted

What is Agrobacterium tumefaciens

natural genetic engineer - causes Crown Gall disease: woody plants including peach, apples, roses and vines

What kind of pathogen is Agrobacterium tumefaciens

biotrophic pathogen | - that genetically modifies the host plant

Where is Agrobacterium attracted to

wounded roots by plant phenolics

How does Agrobacterium infect a plant

- attaches to wounded plant cells and transfers T-DNA from Ti plasmid to host nucleus - induces the production of tumor like swellings (galls) on roots or base of the stem

What are the tumor cells induced by (Agrobacterium infection)

- induced by a gene on the Ti plasmid | - to produce OPINES (amino acid derivatives) used as an energy source by the bacterium

What is Rhizobium

A beneficial plant bacteria

What type of relationship does Rhizobium make with the roots of certain plants (clover, lupin, peas)

symbiotic relationship

What does Rhizobium produce that benefits the plant

produces root nodules in which nitrogen fixation takes place | - this association has benefits on both the plant and the bacterium

true or false; Rhizobium is closely related to Agrobacterium

true

What is the difference between the jobs of Rhizobium and Agrobacterium

Rhizobium is beneficial whilst Agrobacterium is a pathogen

What are the steps of how a Rhizobium infects the roots of a plant

1.) Roots emit chemical signals to attract bacteria 2.) Bacterial signals stimulate root hairs to elongate & form an infection thread. 3. ) Bacteria penetrates root cortex; root cells divide; vesicles containing bacteria (bacteroids) bud into cortical cells 4. ) Cortex and pericycle cells continue to divide and fuse to form the nodule 5. ) Nodule continues to grow; vascular tissue grows into nodule (allows movement of N (nitrogen) into the plant)

What is Nitrogen fixation

- When the nitrogenase enzyme (rhizobium) enables the 'fixation of nitrogen' to ammonium compounds - ammonium compounds benefit the plant - Some NH4+ diffuses into the soil/water and is converted into N- containing organic compounds (by other bacteria and plants)

What are mollicutes

bacteria without cell walls

What are the effects of mollicutes on plants

- stunting - yellowing - eventual decline & death - redding of leaves

What caused the cabbage tree decline

- caused by phytoplasma - prokaryote without cell wall - obligate parasites cannot be cultured

How is the cabbage tree disease spread

vectors are plant and leaf hoppers(phloem feeders)

What causes Coconut lethal yellowing

phytoplasma as well

Where was coconut lethal yellowing prevalent

-first noted in Florida 1955; killed 75% palms over the next 13 years

What are the two examples of mollicutes

- cabbage tree disease | - coconut lethal yellowing

How does bacteria usually enters its host

``` natural openings (stomata) wounds ```

How are bacteria controlled

- copper based pesticides and/or anitbiotics - elimination of inoculum sources (eg. seed contamination in annual crops) - genetic resistance are the most effective means of control

What are the distinguishing factor of Mollicutes

- small in size - lack cell walls - instead have a triple layered membrane

What are a group of Mollicutes

Phytoplasma | - plant pathogens associated with insect vectors

Who is Ross Beever

a mycologist, that identified that phytoplasma was the causal agent of Cabbage Tree Sudden Decline

What is an obligate parasite

cannot complete its life cycle without a suitable host

true or false; Coconut lethal Yellowing has been identified in Florida in 1955 and was responsible for the loss of 75% of the palms in 13 years

true

Lecture 2 Flashcards

Aim: - understand the impact and importance of bacterial plant pathogens - disease caused by bacteria (4 examples) - agrobacterium (natures genetic engineer) - Rhizobium (beneficial plant bacteria) - Mollicutes (2 examples)