Plant Resistance And Defece Flashcards
Structural defences
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
Metabolic defences
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
Genetics of resistance
Host- resistance and susceptibility genes
Pathogen- virulence genes
Phenols to quinones
Polyphenoloxidase
Phenols to oxidised phenols and polymers
Peroxidase
PAL to phenol, phytoalexin, lignin
This
Other defences
Resistant substances, production of cyanide, detoxification of toxic products, induced resistance
Induced resistance
Can be local or systemic
Use pathogen proteins such as peroxidase or proteinase inhibitors
Hypersensitive reaction
Induces cellular and metabolic defences
Increased respiration, cell death, production of phytoalexins, accumulation of phenols, loss of membrane permeability
Horizontal resistance
Polygenic, doesn’t confer protection, difficult to quantify
Vertical resistance
Monogenic, strong hypersensitive response, prevents infection
Phytopethora facts
Zoosporic perfect fungus, wide host range, causes root, bud, tuber, seed rots and foliage blight
Phytopethora diseases
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
P infestans
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
Infestans disease cycle
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