Anthracnose of SOYABEAN-Part-2

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: 

Inoculation:

 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.
Penetration:

 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:

 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.

Reproduction:

 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.


Dissemination:

 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



Control:

• 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.