Diseases of Fruit Plantation Medicinal and Aromatic Crops

Black rot

Causal organism: Pellicularia koleroga
Classification
• Class- Basidiomycotina
• Order- Polyporales,
• Family- Thelephoraceae.
• Koleroga noxia Donk, Pellicularia koleroga Cke., are the different synonymous given to this fungus.
• Also called Koleroga is considered to be the second importance disease of coffee in India. Pathogen attacks on both the Arabica & Robusta coffee, but severe incidence of the disease was seen on Arabica coffee cultivars. Black rot disease has been reported from almost all the coffee growing regions of Karnataka, Kerala and Tamil Nadu coming under the coverage of heavy South-West monsoon.

Symptoms

• The black rot pathogen infects leaves, developing berries and young shoots.
• The most striking symptoms are the blackening & rotten of infected leaves, developing berries and young twigs.
• Infected leaves get detached from branches & remain hanging within slimy fungal strands.
• On green berries characteristic blackening starts from one side and spreads gradually in a narrow band.
• Close examination reveals the presence of characteristic threads of mycelia running along the twigs, petioles and spreading mostly on the lower surface of the leaves.
• When infected leaves and berries become dry, they reveal the presence of white web consisting of closely interwoven mycelium.
• Defoliation and berry drop from the infected branches occur in advanced stage of the disease.
Crop loss

• Damage caused by this fungus varies from place to place & season to season.
• However, in severely diseased areas a loss of 10-20% of crop for the whole estate and 70-80%or even more of an individual bush has been recorded.
• Foliage loss that leads to severe die-back and destruction of wood for the next season bearing should also be taken into account while estimating the crop loss.

Favourable factors/Epidemiology

• Continuous rain with out long dry spell,
• saturated atmosphere with 95-100% RH,
• thick overhead shade, plants sheltered from sunlight and aeration in valleys,
• Frequent or continuous mist during the monsoon are the favourable factors for the out break of the disease.

Initiation of disease

• Early symptoms appear on the bushes infected during the previous season.
• Under favourable conditions infection starts at the place where the leaves come in contact with branches that harbour the sclerotia.

Spread of disease

• Primary spread of the fungus is mostly by contact from leaf & bush to bush through vegetative mycelium.
• Infected leaves get detached and carried by wind to other plants and cause further infection.
• Secondary spread occurs through basidiospores either by wind or rain.

Collateral hosts

• This fungus not only infects several forest plant species but also a few economically important horticultural crops such as orange, pear, fig etc.

Management

• Black rot is effectively controlled by combining physical, cultural methods.
• Cultural management
• Maintenance of good drainage, free circulation of air and sunlight
• Thinning of the overhead branches in the black rot endemic blocks before the onset of the monsoon.
• Centering and cleaning of the bushes by removing criss-cross branches, dead & dry branches, suckers and dry leaves of the shade trees fallen on the canopy of the bush before applying pre monsoon sprays.
• Removal and destruction of infected leaves and berries along with the mycelial threads in the initial stage under wet conditions.
• Chemical control
• Adequate coverage of Bordeaux mixture (1.0%) spray on both surfaces of leaves and developing berries just before the onset and during the break in monsoon rains.
• Several systemic & prophylactic fungicides like carbendazim (%), carboxyl ( %) & captafol(% ) have been found effective.