Red rot of sugarcane

Host: Sugarcane (Saccharum officinarum L.)
Pathogen: Colletotrichum falcatum Went. Teleomorph = Glomerella tucumanensis (Speg.) Arx and Muller

Distribution

The disease was first described from Java by Went in 1893. It is widely distributed throughout the sugarcane-growing countries of the world. Red rot of sugarcane is prevalent in all the cane-growing states of India. The disease was very widespread and virulent in North Bihar and the eastern parts of the United Provinces during 1939 and 1942. It was so destructive that it almost whipped out the sugarcane plantations in these areas and threatened the sugar industry.

Symptoms

Small, red-colored elongated spots develop on the midrib of leaves. Spots are with a red margin and white or yellow center. Later, many spots unite to cover the whole midrib of leaves. On the outer side of the stems, red blotches appear.

red rot of sugarcane
Sugarcane stems and leaves showing symptoms of red rot

Infection in the stems being internal, the presence of the disease is not visible externally. Upon splitting a diseased cane during the early stages of the disease, it will be found that the fibro-vascular bundles near the base are reddish in color.
The host tissue reacts vigorously to the presence of the fungus. The protoplasm changes color and a gummy dark-red material oozes out of the cells filling the intercellular spaces. The soluble pigment present in this ooze, is absorbed by the cell wall producing the characteristic red rot appearance.

Red rot of sugarcane
Split inter nodes of sugarcane showing red-rot disease (Photo provided by Dr. Harendra Singh, ACF from his farm)

Diseases of sugarcane
Cross section (left) and vertical section of cane showing reddened pith regions


Pathogen

Colletotrichum falcatum
Acervulus of Colletortichum falcatum
Red rot is caused by the fungus Colletotrichum falcatum Went. The perfect stage of this fungus is Glomerella tucumanensis (Speg.) Arx and Muller, which belongs to ascomycetes.

Systematic position

  • Class: Deuteromycetes
  • Order: Melanconiales
  • Family: Melanconiaceae

C. falcatum being intercellular, forms branches in the parenchymatous pith. The hyphae are septate, thin, branched, and contain oil droplets.
On the rind as well as on the midrib of leaves, hyphae produce numerous pin-head like black structures, the so-called 'acervulus'. The acervulus bears long and thick septate setae along with short, clavate, unicellular conidiophores. Numerous small falcate, unicellular, thin-walled (measuring 16-48 μm × 4-8 μm) conidia are born on these conidiophores. On germination, conidia produce a single germ tube, which penetrates the host by means of appressorium.

Disease cycle

The pathogen can survive and produce acervulus in the soil, however, the disease is primarily seed-born. Primary infection occurs through the infected setts. Conidia born in the acervulus on the midrib of leaves and rinds disperse through the water and cause secondary infection. Conidia penetrate the host through the wounds or root primordia by means of a germ tube. Waterlogging, rain, and humidity favor conidia formation and secondary infection.


Control measures

  • Careful selection of red rot-free seed setts is recommended for planting.
  • Seed should always be taken from disease-free nurseries examined regularly by the cane protection staff.
  • Before planting, each seed sett should be carefully examined, and those setts that show reddening should be discarded.
  • In no case should ratoons of sugarcane be kept in the red-rot-affected fields.
  • Treating seed with fungicides like Arasan (0.25 percent.) is often effective.
  • Use of sugarcane varieties resistant to red rot is also recommended. Some of the resistant varieties are: Co. 975, 1148, 1158.
  • The possibility of an epidemic is very much minimized with the practice of long crop rotations (2 to 3 years) where planting is done in plots.

See also



Content first created on 20-09-2020
last updated on 06-10-2024