Suppression of stripe rust and leaf rust resistances in interspecific crosses of wheat

Stripe rust and leaf rust caused by Puccinia striiformis (Ps) Westend. and P. triticina (Pt) Eriks., respectively, are important foliar diseases of wheat worldwide. Breeding resistant wheat cultivars is the preferred strategy to control these diseases. Genes for resistance when introgressed from alien species or wheats of lower ploidy are frequently diluted effectiveness in the hexaploid wheat background or are completely suppressed. The objective of this study was to examine the expression of wheat stripe rust and leaf rust resistances derived from wild emmer wheat and Aegilops tauschii when combined in synthetic hexaploid lines. Eight amphidiploid wheat lines, synthesized by crossing five tetraploid wheats (AABB), viz. Triticum carthlicum var. darginicum, T. carthlicum var. fuligioscum, T. dicoccoides var. fuligioscum, T. durum with five lines of Ae. tauschii (DD), were evaluated in the seedling stage for resistance to five pathotypes of stripe rust caused by Ps and four pathotypes of leaf rust caused by Pt. Resistance in one or both parents was frequently suppressed in synthetic hexaploid lines, indicating the presence of suppressor genes in both Ae. tauschii and T. carthlicum var. darginicum. Specific suppression of resistance genes in the parental genotypes and to pathotypes of Ps and Pt were also observed. The presence and specificity of the suppressors for rust resistance obtained in this study provides useful knowledge for developing cultivars resistant to both rusts utilizing such genetic stocks in wheat breeding programs.