SEEDLING REACTIONS TO STEM RUST OF LINES OF MARQUIS WHEAT WITH SUBSTITUTED GENES FOR RUST RESISTANCE

Abstract

Lines of the wheat variety Marquis carrying genes Sr6, Sr7, Sr8, Sr9, Sr10, and Sr6 plus Sr7 for resistance to stem rust were produced by the backcross method. The reactions of these lines to 99 North American cultures of 29 races of stem rust and to 8 Australian cultures were determined. Genes Sr6, Sr8, and Sr9 conferred a uniform type of resistance to most of the cultures. Genes Sr7 and Sr10 conferred only moderate resistance to a few cultures. Genes Sr6, Sr8, and Sr9 appeared to confer the same kind of resistance in Marquis after 5 backcrosses as in the source varieties, but Sr7 and Sr10 seemed less effective. Results of the infection studies indicated that Sr7 may be allelic with a gene for resistance in Marquis and that at least two alleles conditioning different rust reactions may occur at the Sr9 locus. The reactions of the lines with Sr6, Sr8, and Sr9 were nearly identical with those of the Chinese Spring substitution lines, Red Egyptian XX, Red Egyptian VI, and Red Egyptian XIII respectively, which presumably have these genes. The data indicated that Sr6 is the same as SrKa1 and Sr9 is the same as SrKb1. The resistance of lines with Sr7, Sr8, and Sr9 was affected only slightly by temperature but the resistance of lines with Sr10 and especially of those with Sr6 diminished at high temperature.