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

Black rot of grapes

Causal Organism: Guignardia bidwelli (Ell.) Viala & Ravaz.

• The disease after its introduction in France during 1880’s, spread to all grape growing areas of Europe. In India, the disease has been observed in Madurai district.
  
• Black rot is more destructive in warm and humid areas than in the cooler and drier ones.
  
• The disease has been recently been observed on certain purple varieties and it is less common on the seedless and Pachha draksha varieties.
Symptoms

• The disease appears on fruits as light, brownish, soft, circular spots which increase in size and the entire berry is discoloured.
• The decaying berries begin to shrivel within a week and transformed into hard, black, shrivelled mummies.
• On the leaf, circular red spots appear and later the margins become black. Minute black dots representing fruiting bodies of the fungus are arranged in a ring near the outer edge.
Causal Organism
Guignardia bidwelli (Ell.) Viala & Ravaz.

• The mycelium is hyaline when young and turns brown after full maturity.
• Perithecia are globose, ostiole not prominent; asci are clavate, thick walled.
• Each Ascus contains 8 ascospores which are bicelled but cells are unequal in size. Ascospores are hyaline, sub-ovoid or elliptical, slightly flattened on one side .
Mode of spread and survival

• Perithecia develop on mummified grape berries and the ascospores discharged when mummies are wet.
• Ascospores produce germ tube and penetrate directly through the cuticle.
• Primary infection occurs on young leaves and fruit pedicles.
• Pycnidia are rapidly produced. Pycnidiospores spread through meteoric water.
• They may survive the winter and germinate in the following season.
Epidemiology

• Frequent rains and humid climate are conducive for disease development.
  
Management

• Diseased berries and leaves should be collected and destroyed.
• Spraying of Bordeaux Mixture (1.0%) or Ferbam (0.2%) or Captan( 0.2%), Chlorothalonil (0.2%) should be done when the new shoots are 15-25cm long and repeated before bloom and also 10-15 days after bloom.