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1. DEFENCE MECANISM IN PLANT
DR. RAJBIR SINGH
Assistant Professor
Department of Plant Pathology
Gochar Mahavidyalaya, Rampur Maniharan, Saharanpur (UP), India
Affiliated to Ch. Charan Singh University, Meerut (UP), India
Email: rajbir25805@yahoo.com, rajbirsingh2810@gmail.com
Cell No. 91-9456613374

2. Defense Mechanism
(A). Structural defense mechanism-
act as physical barrier
• Pre-existing – already present
(a). Role of wax & cuticle – hydrophobic surface
(b). Epidermal layer – make difficult / impossible of direct
penetration
Exp. Salicic acid – P. gresia

3. (c). No. & structure of natural opening
(i) . Narrow opening – Szinkum - X. citri
(ii). Size & internal structure of lenticels – small
lenticels in apple - inhibit infection
(iii). Hydathodes – bacterial infection
(d). Seed coat – physical & biological barriers
(e). Internal physical barriers-
(i). Sclerenchyma - extended

4. 2. Defense structure formed in response to infection
(a). Histological defense
(i). Formation of cork layer
(ii). Abscission layer
(iii). Tyloses formation
(iv). Deposition of gum
(b). Cellular defense structure
(i). Swelling of cell wall
(ii). Sheathing of mycelium
(C). Cytoplasmic, necrotic or hypersensitive reaction
In weak pathogen- clump of hypha, nucleus stretched & break down

5. (B). Biochemical Defense Mechanism
(1). Pre-existing biochemical defense
(a). Inhibitor released by plants in its environment
tomato- resistant to Botrytis cineria
(b). Inhibitors present in the pl. cell before infection
Common scab of potato- resistant varieties have chlorogenic
acid (phenolic compound) in the lenticels
(c). Defense through deficiency of nutrients essential for pathogen
Apple scab- res. Var. – lacking of amino acids /growth factor

6. (2). Induced biochemical defense
(a). Phenolic compounds - (i). Chlorogenic acid
(ii). Caffeic acid
(iii). Scopolatin
(b). Phytoalexins – produced in the host after infection
(i). Pisatin (ii). Orchinol (iii). Ipomeamarone
(3). Defense through inactivation of pathogen enzymes
(4). Defense through detoxification of toxins

7. Thank You