Seedling and adult plant resistance to leaf rust in the wheat cultivar Tugela

Abstract

The South African bread wheat cultivar Tugela has consistently displayed effective field resistance to leaf rust, caused by Puccinia recondita Rob. ex Desm. f. sp. tritici. Based on its pedigree and adult plant reaction to leaf rust, it has been assumed that Tugela contains the Lr34 gene for resistance to P. recondita f. sp. tritici. Evaluation of wheat seedings at 10°C and 20°C suggested that Tugela has two genes for resistance, one of which is only expressed at 10°C. Tugela primary leaf infection types at 10°C and measurement of latent period, uredinium density and uredinium size on flag leaves strongly resembled those on RL6058 (Thatcher/Lr 34). To determine the number of Lr genes and confirm the presence of Lr34, Tugela was crossed with Thatcher (leaf rust susceptible) and RL6058. F₂ and F₃ populations from each cross were tested as seedlings for segregation of resistance to pathotype UVPrt3 at 10°C. Two dominant genes were indicated by the segregation ratios of Tugela × Thatcher F₂ plants (χ² _15:1 = 0.56) and F₃ families (χ² _7:8:1 = 0.67). The presence of Lr34 was confirmed in all 590 Tugela × RL6058 F₂ seedlings tested. Tugela × Thatcher F₂ plants, inoculated with pathotype UVPrt9 during flag leaf and ear emergence stages of growth, indicated segregation of a single gene (χ² _3:1 = 0.19) for resistance when tested at low glasshouse temperature. All Tugela × RL6058 adult F₂ plants were resistant in this environment. Field tests with F₃ families from both crosses confirmed glasshouse results. This study indicated that Tugela contains Lr34 and an unidentified Lr gene.

Keywords:

• Lr genes
• Puccinia recondita f. sp. tritici
• Triticum aestivum