Plant Resistance And Defece

Question 1

Structural defences

Answer 1

Pre existing- hairs, stomata,surface coating, cell wall

Induced by pathogen- thick cell wall (bacteria and virus), outer parenchyma trap pathogens, callous deposition fungus repair and prevent penetration

Histological- cork, xylose, gum, abscission layers

Question 2

Metabolic defences

Answer 2

Pre existing chemicals- tannins, dienes, phenolic compounds, inhibit plant cells
- missing factors are ressential nutrients, receptors for toxins and recognition factors

In response to pathogens
Phenolics- chlorogenic acid
Phytoalexins- only present in disease tissue, induced by elicitors, production suppressed by the pathogen eg. Isoflavanoids

Question 3

Genetics of resistance

Answer 3

Host- resistance and susceptibility genes

Pathogen- virulence genes

Question 4

Phenols to quinones

Answer 4

Polyphenoloxidase

Question 5

Phenols to oxidised phenols and polymers

Answer 5

Peroxidase

Question 6

PAL to phenol, phytoalexin, lignin

Answer 6

This

Question 7

Other defences

Answer 7

Resistant substances, production of cyanide, detoxification of toxic products, induced resistance

Question 8

Induced resistance

Answer 8

Can be local or systemic

Use pathogen proteins such as peroxidase or proteinase inhibitors

Question 9

Hypersensitive reaction

Answer 9

Induces cellular and metabolic defences

Increased respiration, cell death, production of phytoalexins, accumulation of phenols, loss of membrane permeability

Question 10

Horizontal resistance

Answer 10

Polygenic, doesn’t confer protection, difficult to quantify

Question 11

Vertical resistance

Answer 11

Monogenic, strong hypersensitive response, prevents infection

Question 12

Phytopethora facts

Answer 12

Zoosporic perfect fungus, wide host range, causes root, bud, tuber, seed rots and foliage blight

Question 13

Phytopethora diseases

Answer 13

P. Cacterum- Lilly foot rot and apple trunk rot, wide host range, variable symptoms

P. Cinnamonia- avocado, cinnamon, chestnut rot, wide host range but sample symptoms

P.fagoniae- narrow host range

P.infestans- potato blight

Question 14

P infestans

Answer 14

Larger genome than other species -240kb
Genome contains many transposons
Symplast genes- RXLR proteins, 60% more in infestans, cause hypersensitive response

Apoplast, many more hydrolases, like proteases

Ooomycete- water mould

Infects at all developmental stages- usual mid season

Spreads rapidly

Question 15

Infestans disease cycle

Answer 15

Fungus can spread from tubers to potatoes via air borne spores.

Spores take 7-10 hours in moist and warm conditions to grow and spread

Question 16

Infestans control

Answer 16

Practices- avoid night time irrigation, buy clean tubers, good storage

Chemicals- treat with preventative and eradicating fungicides

Crop monitoring and disease forecasts

Resistant varieties such as Snowden and Atlanta, not completely resistant though

Question 17

Potato blight symptoms

Answer 17

Starts with light to dark green circular or irregular leaf spot.

Turns into brown greasy wound on plant

Infected tubers appear distorted and purple in colour
Inside tubers have a dark red grainy appearance

Distinctive odor