Diseases of fruit plantation medicinal and aromatic crops (2+1)

Damping off;foot rot

Causal organism: Pythium aphanidermatum

• Foot rot is also known as collar rot or stem rot or root rot or damping off.It is the most serious disease of papaya. In India, the disease appears during the rainy season and is prevalent throughout the country. It is more common in trees of 2-3 years age.
Symptoms

• In case of nursery plants, damping off symptoms are produced, whereas in adult plants foot rot, collar rot symptoms are produced.
• Foot rot is characterized by the appearance of water-soaked patches on the stem near ground level.
• These patches enlarge rapidly and girdle the stem, causing rotting of the tissues, which then turn dark brown or black. The affected internal tissues give a honey comb like appearance.
• Simultaneously, the terminal leaves of infected plants turn yellow, start drooping and fall off.
• The infected plants cannot withstand strong wind and topple down to die.
• If the disease attack is mild, only one side of the stem rots and the plants remain stunted.
• Fruits if formed are shrivelled and malformed. Gradually the plant dies.
Causal organism

• Mycelium is well developed, coenocytic, hyphae 2.8-7.5 µ in diameter.
• Sporangia are loculate, toruloid and vesicle formed at the time of germination, zoospores, 30-40 in number, are present within the vesicle and are borne on spherical oogonia.
• They germinate by producing a germ tube.
• The sexual spores are the oospores, borne singly which are moderately thick walled
Epidemiology

• A number of factors like inoculum density, soil moisture, temperature, pH, light intensity etc effect the pathogen development.
• One week old seedlings are more susceptible than the one year old trees.
• But stem rot caused by Pythium aphanidermatum is common in plants of 2-3 years age. The disease usually appears during rainy season and severity increases with the intensity of rainfall.
• Optimum temperature of 360c, excessive moisture ,uncontrolled irrigation, heavy rainfall and water logged condition are favourable for disease development. Abundance of moisture around the base is conducive for disease development and its spread.
Disease cycle

• The pathogen is soil inhabitant and capable of growing and surviving on the residue left in the soil where it produces abundant oospores in decaying organic matter.