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Expression of Two Wheat Leaf Rust Resistance Gene Combinations Involving Lr34. Sébastienne C. Drijepondt, Grain Crops Research Institute, Bethlehem 9700, South Africa. Z. A. Pretorius, and F. H. J. Rijkenberg. Grain Crops Research Institute, Bethlehem 9700, South Africa, and Department of Microbiology and Plant Pathology, University of Natal, Pietermaritzburg 3200, South Africa. Plant Dis. 75:526-528. Accepted for publication 24 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0526.

The effects of temperature and different isolates of Puccinia recondita f. sp. tritici on the expression of leaf rust resistance genes Lr33, LrT3, and Lr34 and gene combinations Lr33 + Lr34 and LrT3 + Lr34, all in Thatcher wheat background, were studied in seedling and adult plants. In reaction to isolates 3SA122, 3SA132, and 3SA135, the expression of low infection type by the individual genes and the two combinations in the seedling stage was best expressed at 7 C. These low infection types were largely negated at 15, 20, and 25 C. All three individual host genes, as well as the two combinations, expressed race-specific characteristics. Enhanced seedling resistance attributable to the combination of Lr genes was observed only with certain isolates. Infection types displayed on flag leaves suggested that levels of enhanced resistance were more easily detected in adult plants. Leaf rust infection types in adult plants were not as influenced by elevated temperatures as seedlings. In adult plants, the low infection types were best observed at 15 C. The effectiveness of gene combinations involving Lr34 depends on the second gene, the rust culture used, environment, and growth stage of the host plant.

Keyword(s): resistance enhancement.