The disease is caused by three different species of Alternaria.


Alternaria solani:
  • Dark brown spots with concentric rings develop on the leaves, which give target board effect, the most characteristic symptom of the disease (Plate-3a).
  • In humid weather, the affected areas coalesce and form dark brown patches. In severe attacks, affected leaves shrivel and fall down prematurely resulting in early defoliation.


Alternaria alternata:
  • Spots are small, circular scattered, dark brown spots (Plate-3b).
  • Older spots are surrounded by yellow halo.
  • The affected leaves dry prematurely.


A. alternata f.sp. lycopersici:
  • Spots are small, angular, scattered and light brown in colour (Plate-3c).
  • Spots are not surrounded by yellow halo.
  • The symptoms also appear on stems and branches as light to dark brown spots(Plate 3d).


Pathogen (s)
Alternaria solani (Ell. and Mart) Jones and Grout:
    • The mycelium consists of septate, branched, light brown hyphae, which become darker with age. Conidiophores emerge through the stomata from the dead centers of the spot.
    • Conidia are beaked, muriform, dark and borne singly or in chains of two.
    • Five to ten transverse septa and a few longitudinal septa are present in each conidium.
A. alternate (Fr.) Keissler:
    • The conidia occurring on leaflet lesions under field conditions are 1-6 septate.
    • The size of beak range from 3.0 - 10.0 µm with an average length of 7.9 µm.
A. alternata f.sp. lycopersici Grogan Kimble and Misaghi:
    • The conidia occurring on leaflet and stem lesions under field conditions are 1-5 septate measuring 17.0 - 50.0 x 10.0 - 13.0 µm (av. 34.40 x 12.30 µm) and beak length ranged from 3.0 - 7.0 µm with an average of 6.13 µm.
Disease cycle and epidemiology
  • Alternaria species survive in diseased plants debris and can persist for one to two years.
  • Seed borne nature of A. solani has also been reported.
  • Primary infection of lower leaves first takes place through conidia formed on crop debris in soil. Secondary spread of the disease occurs through conidia developed on primary spots.
  • These conidia are blown by wind, water and insects to the neighbouring leaves\ plants.
  • The optimum temperature for infection of A. solani is 28 to 30oC while for A. alternata f. sp. lycopersici and A. alternata, it ranges between 25-30 and 20-25oC, respectively.
  • Maximum dispersal of conidia occurs in advanced stages of disease development and in between 9 am and 12 noon.
  • Collect and destroy the infected plant debris. Follow at least two years crop rotation.
  • Select healthy seed and treat it with captan (0.3%).
  • Remove the foliage particularly in indeterminate type of cvs/hybrids up to 15-20 cm to avoid moist and stagnant air conditions.
  • Spray the crop with chlorothalonil (0.2%) or mancozeb (0.25%) and repeat at 10 to 14 days interval.
Last modified: Monday, 12 March 2012, 6:04 AM