USE OF FOLIAR-APPLIED UREA TO INHIBIT THE DEVELOPMENT OF SEPTORIA-NODORUM IN SPRING WHEAT

This study was carried out to provide more detailed information about the toxicity of foliar-applied urea on the development of the fungus Septoria nodorum Berk. in wheat, and to examine the interaction between urea and infection on the formation of yield components and grain protein properties. Greenhouse and field experiments involved spring wheat cv. Ruso, which is very susceptible to leaf and glume blotch caused by S. nodorum. Urea solution effectively prevents the development of Septoria infection when applied before inoculation. An agar-plate assay indicated that urea solution > 5% strongly inhibits colony growth. Urea seems to be phytotoxic only if leaf tissue is wetted for an extended period with the solution in the greenhouse. This phytotoxicity would explain the observed decrease in number of grains per ear, ear weight, 1000-grain weight, as well as in residue protein and in SDS sedimentation volume. However, no phytotoxicity and negative effects on yield components and protein properties were observed after urea spray under field conditions. Urea application caused a 0.01-0.04 pmol/100-mu-l increase in abscisic acid concentration in plant tissue.