Damping of seedling

this is important video to related plant pathology

1. Damping off Of seedling

2. Damping-off is a term applied to a very common trouble in which seedlings are attacked by soil-inhabiting fungi usually just at the soil level on to hypocotyl or upper taproot causing partial or complete rot and the seedlings suddenly topple over in a characteristic manner. Of the various species of soil-inhabiting fungi responsible for damping-off of seedlings, Pythium debaryanum ranks first in importance, in relation to this disease as a damping-off parasite green houses and nursery seed beds are ideal places for outbreaks of damping-off if moisture and temperature conditions are favourable . Damping off Of seedling

3.  Symptoms The fungus attacks the seedlings at or near the surface of the ground, ac­cording to the moisture level and depth of planting, on the hypocotyl or taproot The cell wall of the rapidly growing seedlings is generally thin, and as such the tissue is particularly vulnerable. In a very short time the pathogen causes upon invasion, rapid killing and rot of cells and collapse of the tissue rapid killing and rot of cells and collapse of the tissue to such an extent that the seedlings suddenly fall over 

4. Damping-off of seedlings actually occurs in two stages: Pre-emergence stage This is the stage when the young seedlings are killed before they reach the surface of the soil when the hypocotyl has just emerged. The radicle and the plumule are destroyed as soon as they come out of the seed coat.  (ii) Post-emergence stage. During this stage the seedlings are out on the surface of the soil and on being infected by the pathogen they topple over and lie on the surface of the soil.

5. Causal Organism Pythium debaryanum Hesse, is the common cause of damping-off The non-septate somatic hyphae of the organism may survive both intra- and intercellularly without any haustoria. The sex organs, oogonia and antheridia, usually appear at a later stage than sporangia and may arise within or outside the substratum. Normal Infected

6. Oospore germination Germ tube Host infection Sporangia Zoospore Encysted Zoospore Germ tube Mycelium with host Gametangia Plasmogamy + karyogamy Oospore Oospore in plant debris Active Phase Dormant Phase Damping off Of seedling

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