Crop Genebank Knowledge Base

Management strategies

Safe transfer of germplasm

Forage grasses

Guidelines

Bacteria

Bacteria - forage grass

Contributors to this page are: CIAT, Colombia (Maritza Cuervo, Cesar Medina, Jose Luis Ramirez, Socorro Balcazar, Josefina Martinez, Daniel Debouck); ILRI, Ethiopia (Jean Hanson, Janice Proud, Juvy Cantrell).

Bacterial Blight of forage grasses

Scientific names

Xanthomonas campestris pv. graminis (Egli et al.) Dye
Xanthomonas campestres pv. phlei

Significance

Affects the value of the forage grass.

Symptoms

Wilting and drying up of the tillers or the whole plants accompanied or not by leaf necrosis; no growth of new shoots after mowing; yellow stripes turn necrotic along the leaf; distorted growth of the leaves out of the sheath or difficulty of cobs (ears, heads) to emerge; young leaves have a pale colour.

In the Lolium multiflorum yellow droplets form inside the hollow of the stem.

Hosts

Arrhenatherum elatius, Dactylis glomerata, Festuca arundinacea, Festuca pratensis, Phleum pretense, Brachiaria spp., Lolium multiflorum, Lolium perenne.

Geographic distribution

Widespread in the tropics and sub-tropics

Biology and transmission

Bacterial wilt settles in the xylem vessels. The disease can only settle through lesions from which it extends to the xylem. It goes counter sap-flow down to the base of the plant and infects the neighbouring tillers.

Considerable damage may occur after long periods of hot and dry weather, while in cool and wet periods hardly any diseased plants are found. The pathogen may be identified by isolation and biochemical tests. Specific antibodies used in immunofluorescence and ELISA had a high degree of sensitivity and specificity against the target bacterium. The two methods were used for screening pure cultures and detecting bacteria directly in plant tissue extracts. Their application revealed the presence of low numbers of bacteria in symptomless plants and a discontinuous distribution within the plant.

Cultures of Xanthomanas campestris pv graminis showed no loss of virulence following freeze-drying and revival.

Inoculation of seeds, and inoculation of plants for seed production, X. campestris pv. graminis was shown to be seed-transmitted. The level of infection in seeds was, however, too low to produce plants with disease symptoms.

The spread inside the crop is caused by the infected cutter bar of forage harvesters which can carry the pathogen for several months.

Detection/indexing method in place at the CGIAR Center

at CIAT: None
at ILRI: None
at ICRISAT: Agar plate method

Treatment/control

Hot water treatment at 56ºC for 30 minutes

Procedure followed at the centers in case of positive test

Seeds treated as above to kill bacteria

References and further reading

Seed Health General Publication Published by the Center or CGIAR

Frison EA, Bos L, Hamilton RI, Mathur SB, Taylor JD. (eds). 1990. FAO/IBPGR Technical Guidelines for the Safe Movement of Legume Germplasm. Food and Agriculture Organization of the United Nations, Rome/International Board for Plant Genetic Resources, Rome.

Miles JW, Maass BL, do Valle CB; with the collaboration of V. Kumble. eds. 1996. Brachiaria: Biology, Agronomy and Improvement. Cali, Colombia: Centro Internacional de Agricultura Tropical, Tropical Forages Program and Communications Unit; Campo Grande, Brazil, Empresa Brasileira de Pesquisa Agropecuaria, Centro National de Pesquisa de Gado de Corte, 1996. 288 p. CIAT Publication; no. 259