Effect of Plant Age and Inoculum Concentration on Leaf Freckles and Wilt of Corn1

The effect of plant age and inoculum concentration on disease reactions in corn (Zea mays L.) was determined following inoculation with Corynebacterium nebraskense Schuster, Hoff, Mandel, and Lazar, the causal organism of the leaf freckles and walt of corn. Resistant and susceptible corn materials were simultaneously inoculated at four different age groups and at four inoculum concentrations for each group. Plant age or maturity played a vital role in differentiating resistant from susceptible lines when the syringe injection technique was used. Susceptible materials were not greatly influenced by plant age. On resistant lines, however, the disease ratings were strongly influenced by plant age. In resistant materials, infection decreased with increased plant maturity, but with the susceptible genotype the greatest infection occurred in plants inoculated at tasseling. Inoculum concentration was a critical factor only in young plants. However, optimum concentration was difficult to define because the results were variable. In tasseling plants, higher concentrations were tolerated without affecting disease reaction.