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

Sigatoka leaf spot

Causal organism:Cercospora musae (Zimm.)
First observed in Java, it has also been reported to cause severe losses in banana crop in countries like Columbia, Mexico, Jamaica, Panama, and India. In India it occurs in Andra Pradesh, Assam, Bihar, Karnataka, Kerala, Maharashtra.etc
Symptoms

• Light yellow or brownish green narrow streaks which enlarge in size developing into linear, oblong, muddy brown to black spots.
• In central portion necrotic circular spots appear on older leaves. The spots lead blight formation and splitting of leaf lamina, complete leaf drying followed by defoliation.


Etiology

• Conidia are elongated, narrow and multi septate borne on conidiophore
• Perithecia is dark brown to black. asci are oblong, ascospores septate, hyaline, obtuse, ellipsoid with upper cell slightly broader.
• Ascospores are sexual spores.

Mode of survival and mode of spread

• Primary source of inoculum: dormant mycelia present in infected debris.
• Secondary source of inoculum: Air borne conidia

Epidemiology

• Warm temp 23 - 250c, rainy or humid weather ;
• Poor or badly drained soils situated in shady areas ;
• Closer spacing, heavy weed or grass cover and neglected crops favours disease development
Life cycle

• The pathogen survives in dry, infected leaves fallen on the field soil.
  
• It spreads through air borne conidia and ascospores
  
• Conidia are formed in humid weather throughout the year but their release and germination depends on atmospheric humidity and moisture condition.
  
• Spores are dispersed by rain water splashes and by wind. Ascospores are shot out violently through the ostiole due to wetting of perithecia and dispersed by air currents. They are responsible for long distance spread of the pathogen while conidia are generally the most important means of local spread.
  
• The infection by both type of spores produce the same type of spots and subsequent development of the disease.
  
• Sigatoka spreads fast in a humid weather or periods of high rainfall at 230 -250c. Negligible infection occurs at a temperatures 210c- even if the humidity is optimum.
  
• In dry weather with high day temperature and little dew during night ,the disease fails to spread. Soils with poor drainage and low fertility favour the disease.
  
• Conditions which are conducive for increased humidity in the plantation are favourable for the disease. Thus thick planting, presence of weeds and increased number of suckers promote disease development.
  
Management

• Removal and destruction of infected leaves followed by treatment with Bordeaux mixture 1% +linseed oil 2% solution spray is recommended
• Spray with oil based copper fungicides has also been found effective. Carbendazim (0.1%)or Mancozeb (0.25 %) spray with spreading agents like teepol is also recommended
• Propiconazole spray (0.1%) with spreading agent effectively manages the disease.