1.8.6
PATHOGENIC AND BIOCHEMICAL DIFFERENCES AMONG THE ISOLATES OF TILLETIA INDICA

DV SINGH, SK SHARMA and R AGGARWAL

National Centre for Integrated Pest Management (ICAR), LBS Centre of Biotechnology and Plant Protection, Indian Agricultural Research Institute, Pusa, New Delhi, India

Background and objectives
Tilletia indica (=Neovossia indica) causes Karnal bunt in wheat. The disease is prevalent in India, and also in Afghanistan, Pakistan, Nepal, Iraq, Iran, Mexico and the USA [1]. The disease is of international quarantine significance, and therefore production of disease-free seed is a prime requirement for export. Although sources of resistance to N. indica have been identified, truly resistant varieties have not been developed due to a lack of knowledge of the variability existing in the pathogen.

Materials and methods
Pathogenic variability was assessed based on the coefficient of infection produced by isolates on differential hosts. Biochemical variations among the isolates were determined using biomass produced in potato dextrose broth, except for estimations of total lipids and fatty acid profiles, where teliospores were used.

Results and conculsions
Host-pathogen responses on 10 differential hosts distinguished populations of six isolates into three pathotypes: pathotype I (KB-1, -2 and -4), pathotype II (KB-3 and -5) and pathotype III (KB-6). Isolate KB-2, which was most virulent, showed the highest content of lipid (131.1 mg/g), nitrogen (24 mg/g), protein (15.3%), sugars (35 mg/g) and reducing sugars (0.131 mg/g). Comparatively, KB-6, which was a less aggressive and slower-growing isolate, had the minimum amount of these constitutents. KB-2 could be distinguished from other isolates by the presence of linolenic acid, and KB-6 by the absence of capric and pentadecenoic acids. Polyacrylamide gel electrophoretic analysis reflected variations in soluble protein fractions among the three differently virulent pathotypes of N. indica. In KB-6, 23 bands were resolved, of which 16 were common to all the representative isolates. Esterase isozyme detected in the mycelial extracts revealed the presence of four bands of different Rf values in KB-6. However, isolates KB-2 and KB-5 lacked bands with an Rf value of 0.76. Analysis of peroxidase isozyme showed the presence of six bands in KB-2 and KB-5, but in KB-6 a band of 0.87 Rf was missing, confirming variation within the isolates.

Reference
1. Singh DV, Srivastava KD, Aggarwal R, 1997. In Proceedings of International Symposium on Bunts and Smuts of Wheat, North Carolinia, USA, August 1997.