Department of Botany, Visva-Bharati, Santiniketan 731235, India

Background and objectives
Although sugarcane is an important and commercial crop in India, studies on its pathology have not gained importance significantly. The present paper attempts to study the metabolic behaviour of bacterial and fungal pathogens of sugarcane in the presence of different carbon sources.

Materials and methods
Enzymes of the glycolytic pathways, tricarboxylic acid cycle and glyoxylate pathway were assayed from cell-free extracts of ten strains of bacterial and ten strains of fungal pathogens of sugarcane after growing in vitro in different carbon sources. Bacterial strains belonged to Xanthomonas albilineans causing leaf scald disease, Pseudomonas rubrilineans causing red stripe disease and Pseudomonas rubrilineans pv. spindulifoliens causing spindle rot disease. The fungal strains belonged to Colletotrichum falcatum causing red rot, Fusarium auriculiformis causing wilt disease, Peronosclerospora sacchari causing downy mildew and Ustilago scitaminea causing whip smut disease of sugarcane. Enzymes were assayed following published procedures [1, 2].

Results and conclusions
Of the glycolytic pathways, the Embden-Meyerhof-Parnas and pentose phosphate pathways are available to all the strains of bacterial as well as fungal pathogens, as evidenced by high specific activity of the key enzymes (phosphofructokinase and 6-phosphogluconate dehydrogenase) in the cell-free extracts of midlog cultures of these organisms grown in presence of glucose, galactose or sucrose in media. Key enzymes of the Entner-Doudoroff pathway were detected only from CFE of cultures of bacterial strains as well as their isolates direct from the infected materials and were not detected from any of the fungal isolates. This enzymatic property of the bacterial isolates can be utilized for diagnostic purposes during isolation of bacterial pathogens. Substantial activity of isocitrate dehydrogenase in all the strains of bacterial and fungal pathogens indicated a constitutive operation of the tricarboxylic acid cycle in these organisms. All the bacterial as well as fungal isolates exhibited activity of isocitrate lyase, a key enzyme of the glyoxylate pathway when grown in culture media with acetate as the sole source of carbon. But the other carbon sources tested, glucose, galactose or sucrose, failed to induce the activity of isocitrate lyase. This indicates the inducible nature of isocitrate lyase in sugarcane pathogens.

1. Mandal NC, Chakraborty PK, 1993. Current Microbiology 26, 247-251.
2. McFadden BA, 1969. Methods in Enzymology 13, 163.