Anthracnose of SOYABEAN-Part-2

>> Sunday, August 22, 2010

Disease Cycle

 In every infectious disease a series of more or less distinct events occurs in succession and leads to the development and perpetuation of the disease; this chain of events is called disease cycle. As the infectious disease, anthracnose has a cycle are as follows: 


 This pathogens, usually is a seed borne fungus, and also in crop residues.
 Primary inoculation occurs through conidia or mycelium that was dormant in seed or plant debris, mycelium may be active in plant debris.
 Air-borne conidia also cause secondary inoculation which is produced after primary infection.
 Pathogens from crop residue may causes disease by means of any contact ness of the host.

Conidia produce germ tube with only in the presence of water and form an appresorium and penetrate the host tissue directly.
 In the beginning, the Sharpe hyphae grow rapidly, intercellular as well as intra-cellular, but cause little or no visible discoloration or other symptom.

Establishment of infection:

Incase of seed-borne, the fungus causes primary infection on the seedlings automatically because it was already present in the seed through over wintering.
 But secondary infection may occur in any later stage, of course at susceptible stage of the host, by conidia which are produced in accervuli transmitted through air or insects.
 Develops a relation with host tissue and recurs nutrients from the tissue and also damages or discolor the host tissue.


 Invasion of Colletotrichum may occur through intercellular, intracellular and sub-epidermal cell etc.
 May invade a small number of seeds without causing any apparent injury to them.


Mycelium produces the asexual fruiting body that is known as acervuli in the favorable condition.
 The fungus produces colorless, one-celled, ovoid, cylindrical sometimes curved or dumbbell-shaped conidia in acervuli.
 Masses of conidia appear pink or salmon colored.
 The acervuli are sub epidermal and break out through the surface of the tissue i.e. conidia push up and rupture the cuticle.


 The conidia disseminates passively.
 The conidia are released and spread only when the acervuli are wet and are generally contact with insects, other animals, tools and so on.
 Spores are splashed by irrigation or rain water to near by plants.
Over wintering:

 This fungus over winters in infested seed as well as in infected crop residues.
 They are in the soil as saprophyte.
 They can over winters as mycelium or as conidial form on the seed.

Factor affecting disease development:

 Development of anthracnose is favored during periods of moderate temperatures.
 High humidity or wet weather


• To destroy the crop refuse completely.
• Seed treatment with organo-mercurials helps to eradicate the external seed-borne inoculation.
• Fungicidal sprays (benomyl, captan, iprodione, bordeaux mixture)
• at 15 days intervals helps to reduce the disease incidence.
Difolatan (0.3%) and Dithane M-45 (0.2%) are effective when sprayed at fortnightly interval.  
• To collect seeds from healthy disease free area.
• To rotate crops and till areas where anthracnose occurred to bury inoculum and prevent a build-up of the pathogen.


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