Genetic variability in Bipolaris sorokiniana isolates causing spot blotch of wheat in India

Spot blotch caused by Bipolaris sorokiniana (Sacc. in Sorok) Shoem, anamorphic state, syn. Helminthosporium sativum Pamm. King and Bakke, [syn. Drechslera sorokiniana (Sacc.) Subram. and Jain], teleomorphic state Cochliobolus sorokiniana (Ito and Kurib.) Drechsl. ex Dastur., is one of the most important foliar diseases of wheat in warmer wheat growing areas (Dubin and Van Ginkel, 1991; Duveiller and Gilchrist, 1994). Pathogen infects leaves, stems, crowns and roots, causing infected tissues to become necrotic. Pathogen has a world wide distribution, but is more aggressive under high humidity and temperature. Historically, B. sorokiniana has been described as a variable fungus with many morphological and physiological variants (Christensen, 1925; Christensen and Davis, 1937; Tinline 1960; Oliveira et al., 1998; Nelson and Klyne, 1962; Mehta 1981; Valim-Labres et al., 1997). Variability has been attributed to heterokaryosis and parasexuality mechanisms (Tinline, 1962). Untill now, however, no clear physiological races of B. sorokiniana have been characterized on wheat, despite limited genotypeisolate interactions (Hetzler, 1992).