CUCUMIS-MELO L CALLUS RESPONSE TO TOXINS PRODUCED BY MYROTHECIUM-RORIDUM TODE EX FRIES

Studies examining exposure methods and callus type were conducted to d evelop an in vitro selection system using roridin E as a selection age nt. Vacuum infiltration of callus with the toxin solution was the only successful selection method at the concentrations tested. Primary cal lus (callus originating directly from the explant) was not sensitive t o roridin A or E at the concentrations used. Secondary callus (callus produced from primary callus) exhibited a differential response to ror idins A and E similar to that of detached-leaf assays. Electrolyte lea kage studies of callus were not conclusive in establishing the membran e as the site of toxin action or useful for screening tolerance in vit ro. A small percentage of callus from tolerant and susceptible cultiva rs survived repeated exposure to roridin E at 50 mu g.ml(-1).