Alternaria Rot

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What is Alternaria Rot?

It is the fungal disease cause by Alternaria and found mostly on all citrus family. It primarily affects leaves, twigs and fruit rot causing economic losses.

Susceptibility– Oranges, Lemons, Grapefruit and Mandarin are mostly susceptible.

Causal organism– Alternaria citri

Symptoms–

  • The leaf is characterized by small brown to black spots with prominent yellow halo
  • The spots expand and produces circular and irregular necrotic regions. These regions are same at both side of leaves and have a paper like texture.
  • The internal damage on the affected fruits starts much earlier and may vary from species to species-
  • In lemon the pulp becomes greyish brown, soft and slimy.
  • In oranges, grapefruits and mandarins, the affected internal tissue turns black giving a common name to the disease as Black rot or Black Centre rot.
  • In Mandarin, lesions often develop on the side of the fruit and the infected skin appears brown and hence the name, Brown spot of mandarins.
  • In some cases, affected fruits appears small spots to large crater with corky appearance.

Fig- Symptoms on fruits and leaf

Source- Timmer et. al., 2003 Alternaria diseases of citrus – Novel pathosystems

Mode of spread-

  • Rain and overhead irrigation act as short distance dispersal.
  • Wind act as a long-distance dispersal.
  • The dead and decay portion of plant act as a host which should be removed and disposed properly.

Favorable Condition –

Management-

Cultural MethodsChemical Control
Avoiding bruising of fruits especially during harvesting.Wider spacing and skirting of trees allow better ventilation reduces severity of diseases Removal of infected twigs, leaves and fruits from the vicinity of an orchard.The disease can be controlled by spraying (Azoxystrobin 11% + Tebuconazole 18.3% SC) @ 0.6ml per liter water.  Thiophonate methyl 70% WP @ 2g per liter of water. 

Source –

Book – Handbook of Horticulture.

Lavern W. Timmer, 1 Tobin L. Peever, 2 Zvi Solel3 and Kazuya Akimits, Alternaria diseases of citrus – Novel pathosystems, Phytopathol. Mediterr. (2003) 42, 99–112