59 Characterization of Ustilago segetum causing loose smut of wheat G Kaur 1 , I Sharma 2 and RC Sharma 3 Abstract Isolates of loose smut of wheat caused by Ustilago segetum (Pers.) Roussel tritici Jensen were collected from different cultivars of wheat grown at various locations of North-Western India (Punjab, Haryana, U.P. and Rajasthan). The genetic relationships of molecular variability and and virulence pattern among these races is unknown. In this study, a total of 24 isolates of representing six groups of U. segetum tritici were studied using molecular and virulence data. In total, eighteen random decamer primers and ISSR primers were used to characterize twenty four isolates of the pathogen. The RAPD and ISSR primers were used for polymorphism analysis and generated a total of 206 scorable bands collectively. All the isolates could be precisely differentiated from each other employing these primers and grouped into two distinct clusters. The classifcation at molecular level did not exactly collate with the geographical distribution of the isolates and virulence / pathogenicity. Keywords: Loose smut, wheat, molecular characterization 1 Punjab Agricultural University, Ludhiana-141004 2 Directorate of Wheat Research, Karnal (ICAR) -132001, 3 Dr. Y. S. Parmar University of Horticulture and Forestry, Nauni-173230 Corresponding author: ramindu2000@yahoo.co.in Introduction Loose smut of wheat (Ustilago segetum (Pers.) Roussel tritici) Jensen is distributed worldwide. It is seed-born and the earheads emerging from infected seeds get partially or wholly converted into black powdery mass. The varietal patterns keep changing which lead to change in the pathogens. Several studies have revealed the existence of pathogenic variability in this pathogen (Nielson, 1987, Rewal and Jhooty, 1986). Studying the mechanisms of pathogenicity and source of genetic variation in plant pathogens is critical for the future control of the diseases they cause (Nelson et al., 1994). Knowledge of the pathogen population structure can contribute to resistance breeding efforts and to the development of strategies for the deployment of resistance. The most widely used method for characterizing pathogen population is determining the virulence structure of isolates from the population by evaluating their reactions on a set of differentials. However, virulence analysis used to infer population spectrum because the genes involved in virulence represent a very small fraction of genes in the pathogen genome (Lueng et al., 1993). This measure Changes in pathogen are also refected at molecular level. The objective of present investigation was to determine the genetic relationships among the races of U. segetum tritici collected from wheat based on molecular and virulence data. Materials and Methods Collection and maintenance of pathogen isolates The present investigation was carried out in the laboratories of Seed Technology Centre, School of Agriculture Biotechnology and experimental areas of wheat section, Department of Plant Breeding and Genetics, Punjab Agricultural University, Ludhiana (2008-2011). Twenty four different isolates of Ustilago segetum, collected from various locations of north-western India (Punjab, Haryana, Uttar Pradesh, Rajasthan and Delhi) and from different types of wheat were maintained on highly susceptible variety, WL 711(Table 1). All the isolates were morphologically looking black in colour and powdery. Isolates collected in different years and places were maintained by artifcially inoculating the highly susceptible variety from a single properly bagged infected earhead by standard method of inoculations using dry teliospores (Gothwal and Pathak, 1977). Table 1. Isolates collected from different places in India and types of wheat Isolate Place of collection States in India Type of wheat LS 1, LS 31 Mansa Punjab Triticum aestivum LS 2, LS 30, LS 12 Gurdaspur Punjab Triticum aestivum LS 4, LS 25, LS27 Bathinda Punjab Triticum aestivum LS 5 Mansa Punjab Triticum durum LS 6 Hoshiarpur Punjab Triticosecale LS 7, Ludhiana Punjab Triticum aestivum LS 8 Ferozepur Punjab Triticum aestivum LS 9 Faridkot Punjab Triticum aestivum LS 13 Pantnagar Uttarakhand Triticum aestivum LS 15 Pantnagar Uttarakhand Triticum durum LS 16 Dhaulakuan Himachal Pradesh, Triticum aestivum LS 18 Shriganganagar Rajasthan Triticum aestivum LS 20 Hoshiarpur Punjab Triticosecale LS 22 Hisar Haryana LS 23 New Delhi New Delhi Triticum durum LS 28 Sangrur Punjab Triticum aestivum LS 29 Bathinda Punjab Triticosecale LS 33 Kapurthala Punjab Triticum durum LS 35 Ludhiana Punjab Triticosecale J. Wheat Res. 3(2) : 59 (2011)