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Plantwise Technical Factsheet

sugarcane smut (Sporisorium scitamineum)

Host plants / species affected
Saccharum officinarum (sugarcane)
List of symptoms/signs
Inflorescence  -  black fungal spores
Stems  -  witches broom
Symptoms

The most obvious symptom of S. scitamineum infection is the long, whip-like sorus that emerges from the growing point and frequently extends above the tops of the infected plant. Sori may also be produced from side shoots originating from lateral buds. For much of its life cycle, however, the fungus is systemic in the plant and produces no identifiable symptoms except for a 'grassy' appearance in severe cases. This appearance results from the production of numerous weak, spindly stalks in place of the usual vigorous canes. In rare instances, S. scitamineum infection has been observed in the flowering panicle, but this is not of economic importance since commercial sugarcane is harvested before flowering.
 

Prevention and control

Regulatory Control

In most sugarcane-growing countries of the world, strict quarantine regulations govern the importation of sugarcane vegetative propagation materials or true seed. Most of these countries require proof of hot-water treatment of stalk pieces followed by treatment with a fungicide and insecticide. This is to ensure that a number of bacterial, viral and fungal diseases, including S. scitamineum, will not be brought in. Some countries, Australia and the USA in particular, require additional quarantine in sequestered locations until the cane has been grown for one generation before releasing it for commercial propagation.

Sanitary Methods

Roguing of stalks with S. scitamineum sori has been practised at various times and locations, but since the systemic infection may be present for months without producing a sorus, roguing is only effective in reducing the field inoculum level.

Hot-water dip of cane pieces before planting is effective in ensuring clean seed. A short hot-water treatment of 52°C for 30 minutes, or a long hot-water treatment of 50°C for 2 hours, are both adequate in eliminating S. scitamineum from sugarcane pieces. This practice is now standard procedure in many plantations.

Fungicides

Fungicide treatments with one of several different compounds have been tried, but are not generally practised because fungicides do not prevent infection by airborne teliospores.

Resistant Sugarcane Varieties

Breeding for resistance to S. scitamineum is the control method most widely practised. Nearly every sugarcane-growing area has a breeding programme in which selection for S. scitamineum resistance is an important factor. The programme usually involves repeated inoculation of new varieties with S. scitamineum over several generations to determine the level of resistance. Since many different characteristics are thought to be involved in resistance (bud anatomy, bud scale fungitoxic substances, plant physiological characteristics), breeding for resistance results in progeny with a range of resistance levels. Furthermore, the infection is not apparent until sori appear, which may take months. Consequently, development of new resistant varieties is expensive and time consuming. The existence of different S. scitamineum races means that sugarcane varieties that appear resistant in one country may not be resistant in another.

Biological Control

Although several species of fungi have been shown to attack S. scitamineum (see Notes on Natural Enemies), biocontrol has not been shown to provide effective control of smut in commercial sugarcane production.

Impact

The following information on economic impact was taken from Ferreira and Comstock (1989).

It is difficult to make a precise assessment of the economic importance of S. scitamineum since most estimates of yield loss are based on observation and experience rather than rigorous experimentation. It is certain, however, that losses may be quite severe in susceptible varieties under conditions suitable for disease development. There are reports of yield losses of 50-73%. In addition to cane yield losses, S. scitamineum also appears to reduce cane quality. Decreases in both sugar extractability and recovery, as estimated by reductions in juice purity, have been reported. S. scitamineum is also known to cause decreases in the number of millable stalks as well as in stalk diameter. In Hawaii, highly susceptible varieties showed cane yield losses of 10-15% in severely infected commercial ratoon fields, while losses in sugar processing were an additional 5-7%.

Descriptions of S. scitamineum epidemics in various countries suggest that severe disease losses are associated with hot dry climates where crops may experience water stress. Additionally, crop age and growth stage at the time of infection appear to be important since infection becomes more severe as the number of ratoons increases. S. scitamineum does not always pose a serious problem where it occurs. One unexplained aspect of the disease is that both incidence and severity appear to be cyclical. Severe epidemics are often followed by periods when smut can be quite difficult to find. To date there has been no reasonable explanation of this behaviour.

 

Related treatment support
Pest Management Decision Guides
Saleem, M. U.; Khan, Y. S.; CABI, 2013, English language
Saleem, M. U.; Khan, Y. S.; CABI, 2013, Urdu language
 
External factsheets
PlantVillage disease guide, PlantVillage, English language
BSES Factsheets, BSES Limited, English language
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