Exam Revision Flashcards
1
Q
What is a genome?
A
A set of chromosomes within a gamete of a species
2
Q
What does haploid mean?
A
Cell or organism with a single genome
3
Q
What does diploid mean?
A
Cell or organism with paired chromosomes (set from each parent)
4
Q
What is a genotype?
A
Sets of alleles present at each locus in the genome
5
Q
What is allele?
A
One of several alternate DNA sequences that reside at the same locus on the chromosome and controls the phenotype for a particular trait
6
Q
What are gametes in plants?
A
Pollen grains and eggs
7
Q
What does homozygous mean?
A
The 2 alleles at a specific genetic locus are identical
8
Q
What does heterozygous mean?
A
The 2 alleles at a specific genetic locus are not the same
9
Q
What are the two sorts of natural reproductive systems in plants?
A
- Sexual reproduction
- Asexual reproduction
10
Q
What are the two forms of sexual reproduction in plants?
A
- Self-pollinating
- Cross-pollinating
11
Q
What kind of alleles do self-pollinating plants tend to have?
A
Homozygous
12
Q
What kind of alleles do cross-pollinating plants tend to have?
A
Heterozygous
13
Q
What are monoclinous flowers?
A
Flowers with both the male and female parts in the one flower. These can be both self-pollinating or cross-pollinating
14
Q
What are diclinous flowers?
A
The male and female parts of the plant are in separate flowers
15
Q
What are the two flower types?
A
- Monoclinous
- Diclinous
16
Q
What are diclinous flowers separated into?
A
- Monoecious
- Dioecious
17
Q
What does monoecious mean?
A
The male and female flowers are on the same plant
18
Q
What does dioecious mean?
A
The male and female flowers are on different plants
19
Q
What are the 3 self pollinating mechanisms in plants?
A
- Plant must be genetically self compatible
- Plant must have certain mechanisms or structures
- Need synchronous production of the male and female gamete
20
Q
What might stop a plant from being genetically self compatible?
A
Recognition mechanisms stopping the pollen tat lands on the stigma from going down
21
Q
Why must plants have certain mechanisms or structures?
A
To ensure the ovary of the plant will normally be fertilised by its own pollen
22
Q
Why do plants need synchronous production of male and female gametes?
A
The pollen must be produced at the same time the egg is produced to ensure fertilisation
23
Q
What is cleistogamy?
A
When the stigma remains enclosed by floral parts during anthesis to ensure the pollen lands on the stigma rather than nearby plants
24
Q
What is the purpose of cross-pollinating mechanisms?
A
To either minimise the level of inbreeding or to promote outcrossing
25
What are the two ways to minimise selfing in cross-pollinating plants?
- Monoecism
| - Non-Synchronous maturation of anthers and stigmas
26
What are the __ types of cross-pollinating mechanisms?
- Minimise selfing
- Prevent selfing
- Self-Incompatibility
27
How is selfing prevented in cross-pollinating plants?
Dioecism
28
How does dioecism work in cross-pollinating plants?
Prohibits selfing but not brother-sister mating.
29
How does self-incompatibility work?
The styles on the same plant as the pollen will not let the effect of pollen occur
30
How does self-incompatibility work?
The styles on the same plant as the pollen will not let the effect of pollen occur
31
What is self-incompatibility?
A genetic mechanism the stops self fertilisation from occurring to promote diversity and heterogeneity for plant survival
32
Are self-pollinated or cross-pollinating plants more stable?
Self-pollinated. They do not segregate upon selfing
33
What determines the breeding method?
The reproductive system of the crop plant
34
What are the five breeding methods for self-pollinated crops?
- Pedigree Method
- Bulk or Mass selection Method
- Single seed Descent
- Backcrossing
- Hybrids
35
What are the three breeding methods for cross-pollinating crops?
- Recurrent selection
- Synthesis
- Hybrids
36
What is the purpose of the pedigree breeding method?
Aiming to incorporate an attribute(s) into a superior to high yielding line/commercial cultivar
37
What does the pedigree method involve?
- The crossing between two parents of the same species
- Selecting plants from segregating populations of a cross and evaluating the performance of their progeny
- Repeated selection within better progeny
- Continued until F6 or F7 are homozygous lines
38
Why use the pedigree method?
- Allows the breeder to handle large numbers of recombinants with comparative ease
- Useful for the selection of 'readily identifiable' characters in early generations
39
What is hybrid crossing?
- Crosses between species
| - Crosses within a species
40
Why perform a hybrid cross between species?
To gain access to new sources of genetic variability in ice crosses
41
Why perform a hybrid cross within species?
- Cross two homozygous lines to create a heterozygous line
| - To exploit hybrid vigour, especially for yield
42
What is the concept of hybrid vigour?
- This can produce better yield depending on the two cultivars used
- The offspring performs better than its parents
43
What are the disadvantages of hybrids?
They must be brought every season to maintain hybrid vigour
44
What is wide hybridisation?
- Used particularly for the transfer of disease resistance from closely related species.
- Usually done through backcrossing
45
What is the purpose of backcrossing?
To limit ultimate genetic contribution of donor parent to the desired gene only
46
What is backcrossing?
Enables breeders to transfer a desired trait from one variety to another genetically different variety
47
What is mutation in plants?
Physical (radiation) and chemical (EMS) mutagens used
48
What can supplementary breeding methods be used for?
To introduce new sources of genetic variability and to overcome species barriers
49
What are the five supplementary breeding methods?
- Wide hybridisation
- Mutation
- Polyploidy
- Haploidy
- In vitro methods
50
What is qualitative genetic control of characters?
- Simple genetic control
- Often readily observable characters (disease resistance and plant height)
- High heritability
51
What is qualitative genetic control of characters?
- More complex genetic control
- Selection is much more difficult
- The environment and genotype contributes to the phenotype
- Lower heritability
52
What are molecular markers?
A fragment of DNA associated with a certain location within the genome
53
What are molecular markers used for?
The selection of particular traits without having to wait for maturity in some plants
54
What is important about environment selection when producing cultivars?
Have to think about where they will be grown and therefore what they will face there
55
Where do government regulations come into the production of new cultivars?
- Regulations regarding releasing new cultivars
- Requirements for the protection of germ plasm
- Need to be aware of industry requirements
56
How are individual characters selected for?
- Some characters have a minimum or maximum acceptable value
- Anything above or below, has their line discarded
57
What does the soil environment consist of?
A dynamic interplay of physical, chemical and biological factors
58
Does the soil profile buffer change above ground?
Yes
59
What are the physical properties of soil?
- Particles (clay to gravel)
- Pores
- Temperature
60
What effect does pore size have?
- Smaller pores make it harder for microbes to extract water
- Can effect microbe movement and diversity
61
How does temperature effect the soil?
Effects the metabolism and growth of the soil environment
62
What does the soil nutrient status effect?
- The pathogen and the host
| - Can have toxic levels of some elements
63
How can plants effect the chemical properties of the soil?
Can release chemicals into the soil which can be toxic to pathogens
64
What are the five biological properties of soil?
- Bacteria
- Actinomycetes
- Fungi
- Nematodes
- Subterranean fauna
65
What is the soil microbiome?
Where there is a large interplay of bacteria, actinomycetes and fungi in the soil
66
What is the rhizosphere?
Where plants create a nutrient-rick, root habitat for microbes in which they are greatly affected by
67
What are the three relationships in the rhizosphere?
- Symbiotic
- Pathogenic
- Commensalism
68
How do inoculums need to survive?
Between crops
69
How long can plant pathogens survive in plant debris or soil?
- Days to weeks
- Weeks to months
- Months to several years
- Many years
70
How is inoculum spread?
- Via oospores
- Soil water
- Contaminated soil on animals/people
- machinery
- Wind
71
What is fungistasis?
The inability of spores of pathogenic fungi to germinate in the soil
72
Why does funistasis occur?
A lack of nutrients in the soil and chemical inhibitors in the soil produced by plants and weeds
73
How can you overcome fungistasis?
In the right conditions, root exudates from an active rhizosphere can overcome the fungistasis and pathogen can recognise there is a host there
74
How can you control fungistasis?
Rotation of non-host crops to trick the pathogen to become active and let it die
75
What do soil borne pathogens need in order to infect?
A certain amount of inoculum
76
What happens to the pathogen with low levels of inoculum?
Infects the plant but so low that when the plant matures, it hasn't got enough for the pathogen to cause disease
77
What happens when you have high levels of inoculum in the soil?
Plants will become infected quickly which will impact growth and yield
78
How would a pathogen escape antagonists to survive in the soil?
- Resistant structures
- Low temperature growth
- Growth in dry soil
79
How many juvenile stages do nematodes have?
Four
80
What stage of the nematode life cycle will it create cysts in the roots?
Adult
81
What are the two types of soil borne parasites?
- Ectoparasites
| - Endoparasites
82
What are ectoparasites?
Parasites that feed from the outside of the root
83
What is a disadvantage of being an ectoparasite?
They are subject to the extremes of the soil environment, competitors etc.
84
What is a mobile endoparasite?
A parasite that lives within the plant, moves through the plant tissue and feeds off it
85
What is an advantage of being an ectoparasite?
They can move from root to root
86
What are the two forms of endorsement parasites?
- Sedentary
| - Mobile
87
What are endoparasites?
Parasites that enter the root or shoot tissue and feed within the plant
88
What do endoparasites do to the plant?
- They produce chemicals and cause an imbalance in plant cells to make them divide and cause galls
- Move through the plant tissue and cause damage
89
What is a sedentary endoparasite?
A parasite that lives within the root, establishes a feeding site and does not move
90
What are the symptoms of a nematode infection?
- Root knots
- Cysts
- Lesions
91
What are cysts?
A structure full of eggs that survive for a very long time in the soil
92
What are nematode lesions?
Red lesions found in the roots
93
What are root knots?
Like a gall that forms on the roots from large amounts of cell division and enlargement as the nematode feeds
94
What causes the symptoms on plants from nematodes?
- Stimulants
- Secondary metabolic inhibitors
- Enzymes
95
What are the four control methods of nematodes?
- Cultural
- Chemical
- Biological
- Physical Resistant
96
What are the two cultural controls of nematodes?
- Crop rotation
| - Organic amendments
97
What are the three chemical controls of nematodes?
- Fumigants
- Non-volatile nematicides
- Serious health and environmental issues
98
What are the two biological controls of nematodes?
- Resistant and tolerant varieties
| - Antagonistic fungi/bacteria
99
What are the two physical resistant controls of nematodes?
- Healthy propagating material
| - Heat
100
What are the five characteristics of water moulds?
- Zoospores with two flagella
- Thick-walled oospores at the sexual stage
- Vegetative stage is diploid
- Aseptate mycelium
- Cell walls contain gluten and cellulose
101
What does pythiaceae cause?
- Damping off
- Root rot
- Soft rot
102
How do pythiaceae cause damage?
- Sporangium that contain vesicles with zoospores
| - Zoospores either inserted into a resting structure or germinate and infect the roots and get into seedlings
103
What does a pythiaceae infection do?
Kills young seedlings
104
What is phytophthora blight?
An infection that causes root and crown rot and distinctive black lesions on the stems
105
What are the consequences of phytophthora blight?
- Root infection leads to leaf wilt
- Leaf lesions occur
- Lesions on fruit containing white sporangia
106
How can you perform a pathogenicity test in the glasshouse?
Plant a healthy plant into a soil pot with inoculum present
107
How do you control phytophthora blight?
- Manage the soil moisture
- Crop rotation
- Soil amended with organic matter
- Fungicides
108
What are downy mildews?
An infection of the leaves and branches with a downy bloom consisting of specialised branched hyphen structures on the surface
109
What spores do downy mildews produce?
- Asexual, biflagellate zoospores
| - Sexual oospores
110
What does albuginaceae cause?
White rust
111
What happens to gram negative bacteria after washing with alcohol and counterstained with a contrasting dye
They lose their violet dye
112
What does Peronosporaceae cause?
Downy mildew
113
What is white rust of brassica?
Pustules of white powdery sporangia
114
Where are the zoospores of white rust produced?
In a sporangium
115
What are the two types of bacteria?
- Gram Positive
| - Gram Negative
116
What are the five identifications of bacteria?
- Shape and size of cell
- Chemical composition of substances in cells
- Biochemical tests
- Pathogenicity on plants
- Serological and DNA methods
117
How do biochemical tests identify bacteria?
Separates species and subspecies
118
What happens to gram positive bacteria when washed with alcohol?
Retains the primary violet colour
119
Hoe do you test plant pathogenicity?
Pathogenicity is tested on various species and varieties of host plants
120
What are the five infraspecific groups?
- Pathovars
- Races
- Biovars
- Serovars
- Molecular groupings
121
What are pathovars?
Different reactions to host species
122
What are races?
Different reactions to host cultivars of a plant. Some pathogens may be more pathogenic on some cultivars than others
123
What are biovars?
Different reactions to biochemical tests
124
What are servers?
Different reactions to serological tests
125
What are the four main ways of spreading bacteria?
- Water
- Insects
- Animals
- Humans
126
What are the four main ways to control bacterial infections?
- Cultural practices
- Sanitation
- Resistant crop varieties
- Chemicals
127
What are the three cultural practices that should be used to control bacteria?
- Avoid planting in infested soils
- Use healthy seeds or propagation material
- Steam sterilising soil in nurseries
128
What are the two sanitation practices that should be used to control bacteria?
- Decontamination of tools and hands
| - Removal of infected debris and plant material
129
What are the six symptoms of a bacterial infection?
- Spots and blights
- Soft rots
- Wilts
- Scabs and cankers
- Galls
- Stunting
130
How are bacterial spots transmitted?
Through wounds and stomates
131
What is bacterial speck?
- Specks on the fruit
| - Curling of leaves
132
How is bacterial speck transmitted?
Rain and favoured by cool, damp conditions
133
What are soft rots caused by bacterium?
Breakdown of pectin and cellulose in the plant leaf material and stems
134
What is bacterial wilt?
Symptoms resembling water stress due to the vascular systems being compromised
135
What is common scab of potato?
Small, brownish raised spots that enlarge and become corky
136
What are bacterial galls?
The bacterium contains a tumour inducing plasmid that is transferred to the host DNA which leads to the formation of galls
137
What is bacterial stunting?
When bacteria reside in the vascular tissue and uses secondary metabolites in the xylem vascular tissue, causing stunting and impinges growth
138
What are phytoplasma?
Obligate bacterial parasites of plant phloem tissue
139
What are four exotic diseases?
- Fire blight of apples and pears
- Pierce's disease
- Huanglongbing or citrus greening
- Potato zebra chip
140
Why produce GM crops?
- For more efficient breeding procedures than the conventional breeding
- To provide access to new genes/traits not accessible with traditional breeding
- To enhance the expression of existing traits
141
What can we do with genes in GM breeding?
- Incorporate single genes
- Can switch off individual existing genes
- Can more readily combine different genes
142
Why would we switch off a gene in GM breeding?
To help with the processing of some foods by removing toxins to make them safe to consume or to alter their use
143
What plant would we want to reduce the toxins in with Gm?
Cassava
144
What plant would we want to alter the use of with GM
Sunflower to have higher Oleic acid
145
Why do we want to combine genes with GM?
To combine a series of genes into a single cultivar
146
What are two examples of GM being used to combine a series of genes into a single cultivar?
- Multiple resistance genes to a pathogen
| - Genes for insect resistance and herbicide tolerance
147
Why do we want to access new traits/genes with GM?
To help with producing cultivars of crops resistant to herbicides
148
Why enhance the expression of existing traits with GM?
- To insert multiple copies of genes
| - To go beyond limits obtainable by recombination
149
Does GM replace conventional breeding techniques?
No. It comments it by providing a new way to incorporate new genes/gene combinations
150
Will genes function the same as existing genes after GM?
Yes
151
How many waves of GM products are there?
Three
152
What are the three waves of GM products?
- First wave
- Second wave
- Third wave
153
What is the first wave of GM products?
Input traits
154
What is the second wav of GM products?
Output traits
155
What is the third wave of GM products?
Industrial crops
156
What is the purpose of the first wave of GM products?
Aiming to enhance the quantity of product produced
157
How is the quantity of product improved using GM?
- Increased disease, insect or virus tolerance
| - Increased tolerance to stress
158
What is an example of a herbicide resistance created by GM?
Roundup Ready crops
159
What is an example of insect resistance created by GM?
Bt cotton
160
What is an example of disease resistance created by GM?
Virus resistant papaya
161
What is an example of a second wave transgenic plant?
Plant-based long chain omega-3
162
What is an example of a third wave transgenic plant?
Super high Oleic safflower
163
What are five major benefits of GM cotton?
- Improved insect efficacy
- Stacked Bt trait for insect resistance
- Herbicide tolerante
- Reduced pesticide use
- Enhanced yield capture
- Decreased pest management costs
164
What are seven issues associated with GM?
- Concerns with potential gene flow to related species
- Acceptance of GM technology
- Access to GM technology
- Labelling
- Multinational companies
- High cost of technology
- Trade issues/adventitious presence
165
What is a concern for gene flow with GM crops?
Crossing and seed production may occur at a very low rate with a weedy relative
166
What issues are associated with access to GM technology?
Someone may not have the right to the gene they want to use or it may be available at a high price
167
What is Canola grown in rotation with?
Cereals and legumes
168
What was Canola originally introduced not Australia as?
Rapeseed
169
Why was Canola developed?
To suit the different climatic conditions of Australia to Canada
170
What are the main varieties of Canola in Australia?
Brassica napas
171
What are the three main breeding priorities in Canola?
- Yield and adaptation
- Quality
- Disease and insect resistance
172
What is bred for in the yield and adaptation of Canola?
- Days to flowering
- Yield
- Herbicide tolerance
- Hybrids
- Shatter tolerance
173
What quality characteristics is bred for in Canola?
- Low ethic acid in oil
- Low glucosinolates in meal
- High oleic
- Low linolenic
174
What disease is Canola bred to resist?
Blackleg disease
175
What is the structure of an oil?
A triglycerol wiht three fatty acids attached
176
What is the predominant fatty acid in Canola?
Oleic acid (60%)
177
What is blackleg disease in Canola?
Pathogen entering the plant through wounded cotyledons and causing cankering of the stems which leads to the plant rotting away
178
What is the blackleg pathogen?
Ascomycete fungus
179
What are the two forms of blackleg pathogen?
- Teleomorph
| - Anamorph
180
What are the main symptoms of blackleg disease in Canola?
- Stem canker
| - Fruiting bodies on the stem
181
What is the purpose of disease nurseries?
To allow the testing of different varieties of a crop being inoculated naturally by a pathogen
182
What are the two main ways of breeding for blackleg disease in canola?
- Major or single gene resistance
| - Minor or quantitative gene resistance
183
What is the boom and bust cycle?
When there is a boom of resistant cultivar growing but the more it is grown puts more pressure on the pathogen.
After selecting varieties the pathogen can slowly start to effect, you get your bust when infection starts to occur again
184
What are the two management practices for Blackleg resistance?
- Resistance gene management
| - Agronomic management
185
What are the four main processes of resistance gene management?
- Resistance gene pyramiding
- Combination of major and minor resistance genes
- Categorising cultivars into resistance groups
- Gene deployment
186
What are the four main processes for agronomic management of blackleg?
- Field rotation
- Distance to stubble
- Fungicide dressing
- Monitoring isolate frequencies
187
What is triazine tolerance in Canola?
A variety of Canola that is able to resist the effect of triazine herbicide
188
Why use hybrid canola?
They show increased vigour and a yield advantage compared to conventional cultivars
189
What kind of issues arise with using hybrid seeds of canola?
- Companies benefit more
- More cost for companies
- Seed needs to be brought every year
190
Why is shatter tolerance important in Canola?
Want to prevent the seed pods from shattering as he seed is what is required to make canola oil
191
How is shatter tolerance implemented in Canola?
Windrowing of crop before it is fully mature
192
What is the purpose of high stability oils produced from canola?
It is a healthier option over palm oil for deep frying
193
What are molecular markers used for in canola breeding?
- Improve breeding efficiency
- Quality assurance
- Trait confirmation
194
What is non-host resistance?
The inability of a pathogen to recognise specific susceptible genes in the host
195
Why might a pathogen experience non-host resistance?
Because it may be lacking the specific pathogenicity genes required to recognise the host
196
How is a plant susceptible to a pathogen?
It has to have particular gene combinations that the pathogen will recognise
197
What is apparent resistance?
Plants escape or tolerate infection by the pathogen
198
What is disease escape?
The three factors for disease do not coincide
199
What are the three factors for disease?
- Susceptible host
- Virulent pathogen
- Favourable environment
200
What is tolerance in plants?
The ability of the plant to produce good growth even if they are infected
201
What is true resistance?
- Disease resistance genetically controlled by plant resistance gene(s)
202
What are the three forms of host specificity?
- Species - species
- Subspecies - species
- Subspecies - subspecies
203
What is species-species host specificity?
The host range of a pathogen is restricted to certain species of host
204
What is subspecies-species host specificity?
The subspecies or a certain form of pathogen species of a pathogen are restricts to certain host species
205
What is subspecies-subspecies host specificity?
Races of the pathogen which can infect certain cultivars or genotypes
206
How do hosts and pathogens interact?
The host contains genes for resistance while the pathogen contains genes for virulence
207
What are the two genes for resistance in hosts?
- Resistant
| - Susceptible
208
What are the two genes for virulence in pathogens?
- Virulent
| - Avirulent
209
What is the gene for gene hypothesis?
for each genetic locus in the host governing resistance/susceptability, there is a specific and related locus in the pathogen governing avirulence/virulence
210
Is resistance or susceptibility dominant in the host?
Resistance
211
Is virulence or avirulence dominant in the pathogen?
Avirulence
212
What is avirulence?
The negative ability that prevents pathogens from infecting a host which creates resistance
213
What is vertical resistance?
Single gene resistance
214
What is horizontal resistance?
Many-gene resistance
215
What is the efficiency of vertical resistance?
Highly efficient but may mask extreme susceptibility to other races
216
What is the efficiency of horizontal resistance?
Variable but effective against all races of the pathogen
217
What is the stability of vertical resistance?
Liable to sudden breakdown by new physiological races
218
What is the stability of horizontal resistance?
Not affected by changes in virulence genes of the pathogen
219
What is the mechanism of vertical resistance?
Either immune or hypersensitive reaction
220
What is the mechanism of horizontal resistance?
Reduced rate and degree of infection and development and/or reproduction of the pathogen
221
Are there combinations of vertical and horizontal resistance?
Yes
222
What should you know about the pathogen when breeding for resistance?
The capacity of the pathogen to produce new physiological races to overcome disease resistance
223
How can new virulence genes occur?
- Hybridisation and sexual recombination
- Mutation
- Asexual reproduction
224
How are new races identified?
From the inoculation of different host cultivars with different isolates
225
What are differentials in plant breeding?
Genotypes that have known resistance genes in them
226
What genes will be more easily selected for in a breeding program?
Dominant genes based on phenotypic selection
227
What is the definition of infection?
The invasion by and multiplication of a pathogenic microorganism which may produce tissue injury and progress to disease through a variety of cellular or toxic mechanism
228
What is the definition of pathogenesis?
The origin and development of a disease
229
What is the definition of a life cycle?
The stage or successive stages in the growth and development o an organism that occur between the appearance and reappearance of the same stage of the organism
230
What is the definition of a disease cycle?
The chain of events involved in disease development, including the stages of development of the pathogen and the effect of the disease on the host
231
What is a monocyclic disease cycle?
The pathogens complete only one or part of one disease cycle per year
232
What are the three stages of a monocyclic disease cycle?
- Primary infection
- Over seasoning stage
- Primary inoculum
233
What is a polycyclic disease cycle?
Pathogens complete more than one disease cycle per year
234
What are the four stages for a polycyclic disease cycle?
- Primary infection
- Secondary infection
- Over seasoning stage
- Primary inoculum
235
What is secondary inoculum?
The inoculum formed after initial infection/colonisation of the host and causes secondary infections
236
Are there combinations of monocyclic and polycyclic disease cycles?
Yes
237
How does a combination of monocyclic and polycyclic disease cycles work?
There may be distinct phases to they may occur simultaneously
- Asexual and sexual
238
How many stages are there in a disease cycle?
Seven
239
What are the seven stages of a disease cycle?
- Dissemination of inoculum and attachment
- Pre-penetration
- Penetration
- Infection/establishment
- Colonisation
- Reproduction
- Survival over winter or summer
240
What is the dissemination of inoculum and attachment?
The introduction of the pathogen to the host plant
241
How are pathogens disseminated?
- Wind, rain or insects
- Seeds, plant material or pollen
- Anthropogenic
242
How do pathogens attach to a host plant?
Adhesive chemicals keep the microbial cells attached to the host cell surface
243
What is pre-penetration?
- Pathogen adapts to enter host
- Germination of fungal spores
- Germ tube formation and host recognition
- Specialised infection structures form (appressoria)
244
What are appressoria?
Specialised infection structures
245
What is the germination of fungal spores influenced by?
- Humidity
- Spore density
- Duration of host surface wetness
- Temperature
- Light
- pH
- Nutrient availability
- External plant layers
- Host plant exudates
246
What do host exudates do?
May inhibit germination
247
What is penetration?
when pathogens enter the host by indirect or direct penetration
248
What is direct penetration?
When enzymes and specialised structures are used by the pathogen to enter the host
249
What is indirect penetration?
when the pathogen uses wounds or natural openings to enter the host
250
Is penetration of pathogens always successful?
No. It can be stopped by plant defences
251
How does a combination of monocyclic and polycyclic disease cycles work?
There may be distinct phases to they may occur simultaneously
- Asexual and sexual
252
How many stages are there in a disease cycle?
Seven
253
What are the seven stages of a disease cycle?
- Dissemination of inoculum and attachment
- Pre-penetration
- Penetration
- Infection/establishment
- Colonisation
- Reproduction
- Survival over winter or summer
254
What is the dissemination of inoculum and attachment?
The introduction of the pathogen to the host plant
255
How are pathogens disseminated?
- Wind, rain or insects
- Seeds, plant material or pollen
- Anthropogenic
256
How do pathogens attach to a host plant?
Adhesive chemicals keep the microbial cells attached to the host cell surface
257
What is pre-penetration?
- Pathogen adapts to enter host
- Germination of fungal spores
- Germ tube formation and host recognition
- Specialised infection structures form (appressoria)
258
What are appressoria?
Specialised infection structures
259
What is the germination of fungal spores influenced by?
- Humidity
- Spore density
- Duration of host surface wetness
- Temperature
- Light
- pH
- Nutrient availability
- External plant layers
- Host plant exudates
260
What do host exudates do?
May inhibit germination
261
What is penetration?
when pathogens enter the host by indirect or direct penetration
262
What is direct penetration?
When enzymes and specialised structures are used by the pathogen to enter the host
263
What is indirect penetration?
when the pathogen uses wounds or natural openings to enter the host
264
Is penetration of pathogens always successful?
No. It can be stopped by plant defences
265
What is the infection of a host?
When a pathogen enters a host
266
Does a pathogen always cause disease when it infects?
No. It can remain latent depending on favourable environmental conditions and the plant growth stage
267
What is the incubation period?
The time interval between inoculation and the appearance of disease symptoms
268
What are the classes of infectious fungi?
- Biotroph
| - Necrotroph
269
What is a biotroph?
A parasitic fungus that exists in association within a living cell
270
Are biotrophs pathogenic of beneficial?
They can be both
271
What is an obligate biotroph?
Needs to reproduce in the host
272
What are haustoria?
Specialised hypahae that feed off the cells and eventually weaken them
273
What is a necrotroph?
A pathogenic fungus that kills its host cells in advance of the hyphal invasion
274
How do necrotrophs work?
They secrete substances that diffuse ahead of the pathogen, causing cell death where nutrients are then obtained
275
What is the colonisation stage of disease infection?
When the pathogen invades the plant tissues and colonises to grow and reproduce
276
What is localised colonisation?
Discrete infection sites, affecting small areas of the plant
277
What is systemic colonisation?
When infection spreads widely through the host
| It may use the phloem and/or the xylem
278
What is the pathogen reproduction stage of the disease cycle?
- Fungi reproduce sexually or asexually with spores
- Bacteria reproduce through fission within or between host cells
- Virus replicate within nuclei of host cells
279
What is the fungal pathogen survival stage of the disease cycle?
Mechanisms to survive unfavourable environmental conditions between host growing seasons
280
What are the five host-pathogen relationships?
- No relationship
- antagonistic response from the plant
- Antagonistic response from the pathogen
- Mutual antagonism between the plant and pathogen
- Mutual adjustment
281
What is an antagonistic response from the plant?
In response to infectious particles reaching the plant surface, the plant secretes inhibitory compounds into the environment
282
What is an antagonistic response form the pathogen?
When the pathogen can overcome the defence of the host and secrete compounds that damage the plant
283
What is mutual antagonism between plant and pathogen?
Inhibition of death in both the host tissue and pathogenic species
284
What is mutual adjustment?
When there is a compatible cell relationship between the host and the pathogen
285
What is a non-host-specific toxin?
Pathogen effectors induce toxicity and increase disease in broad range of host species expressing non-specific susceptibility genes
286
What is a host-specific toxin
Toxin specific only to the host of the pathogen
287
When does resistance occur?
If the pathogen is blacked at pre-entry, entry or colonisation
288
What can break the response of a plants resistance?
Stress
289
What are the two mechanisms used by plants to defend themselves against pathogens?
- Pre-existing defence mechanisms
| - Induced defence mechanisms
290
What is an induced defence mechanism?
Produced in response to the presence of a pathogen
291
What are the two characteristics of host defence?
- Structural characteristics
| - Biochemical reactions
292
What are three structural pre-existing defences?
- Wax and hairs
- Cuticle
- Thick, tough cell walls
293
What ate two biochemical inhibitors released in pre-existing defences?
- Phenolics
| - Plant defensins
294
What are structural induced defences?
When pathogens penetrate pre-existing structural defences and induce cytoplasmic defence reactions and cell wall defence structures
295
What is hypersensitive response?
Localised induced suicide of host cells at the site of infection
296
What are pathogenesis related proteins?
- Microbial substances in the host that are always present at low levels and unregulated in response to a pathogen
297
What are the two types of resistance mechanisms?
- Local acquired resistance (LAR)
| - Systemic Acquired Resistance (SAR)
298
What is localised acquired resistance?
The induced resistance localised around the point of pathogen infection
299
What is systemic acquired resistance?
Subsequent systemic spread of resistance that reduce the severity of disease caused by all classes of pathogen
300
What is epidemiology?
The study of epidemics and of factors that influence these
301
What is an epidemic?
Any increase of disease in a population
302
What is an endemic?
When the disease is always present
303
What is a pandemic?
Particularly severe epidemics occurring over large areas
304
What influences epidemics?
- Susceptible host plants
- Virulent pathogen
- favorable environmental conditions
305
What are disease progress curves?
They show the progress of an epidemic over time and allows the forecasting of diseases and selection of best control strategies
306
How do you measure the impact of disease?
- Develop descriptive growth stage keys for particular crops
- Develop methods to assess the incidence and severity of the disease
- Develop methods of sampling crop populations for assessment of the amount of disease
- Estimate the effect of disease on crop yield and quality
