Managing certain recently named Lr genes in breeding wheat for resistance to Puccinia recondita f. sp. tritici in South Africa

Abstract

Five new or locally unexploited Lr genes were evaluated as sources of resistance to leaf rust (Puccinia recon- dita Rob. ex Desm. f. sp. tritici) of wheat (Triticum aestivum L.) in South Africa. The expression of Lr36, Lr41 and Lr42, as well as the provisionally named genes 'Lr39 and ‘Lr40’, their reaction to different temperatures and inheritance in two South African wheat cultivars were determined. Lr36 in line C78.10 was more effective at higher temperatures whereas Lr39 (line KS86WGRC02) and Lr40 (line KS89WGRC07) conferred lower infection types at 15°C than at 25°C. Except for more pronounced flecking at 15°C, temperature had no detectable effect on the expression of Lr41 in line KS90WGRC10. An interaction between temperature and pathotype showed that Lr42 in line KS91WGRC11 was less effective to certain pathotypes at lower temperatures. According to seedling infection types in the F₂ and BC₂F₁, Lr36, Lr39 and Lr40 were inherited as partially dominant genes in Karee and Palmiet. With these backgrounds, Lr39 and Lr40 produced similar infection types. Lr41 was partially dominant in Karee, but similar, highly resistant infection types suggested complete dominance in Palmiet. Lr42 was partially dominant to pathotype UVPrt13 in Palmiet, but recessive to UVPrt9 in Karee. The results obtained in this study provided information for the establishment of reliable selection criteria for Lr gene management during wheat leaf rust resistance breeding.