Biochemical Basis of the Resistance of Sugarcane to Eyespot Disease

Helminthosporoside is the host-specific toxin produced by Helminthosporium sacchari, the organism causing eyespot disease on sugarcane. Clones of sugarcane susceptible to the toxin posses a membrane protein that binds the toxin. Membranes of resistant clones do not bind the toxin. In this study, a binding protein from a susceptible clone was compared with its counterpart from a resistant clone. The protein from the resistant clone did not bind the toxin unless it was first treated with mild detergent. The two proteins are antigenically identical, have the same molecular weight, and each contains four subunits. They differ slightly in their electrophoretic mobility and vary with respect to four different aminoacid residues. The basis of resistance of clone H50-7209 to eyespot disease is directly associated with the structurally altered membrane-binding protein.