Rpp-Gene pyramiding confers higher resistance level to Asian soybean rust

Asian soybean rust (ASR) causes large reductions in soybean yield, affecting the entire grain market. With low fungicide efficiency, the use of resistant cultivars can be an economical, safe, efficient, and sustainable control alternative. However, the great variability and aggressiveness of ASR and the use of Rpp genes are limited. Thus, gene pyramiding is a promising strategy for the development of cultivars with high resistance to a greater number of isolates. Thus, the objective of this study was to evaluate sister lines, previously evaluated by Meira et al. (2022). https://doi.org/10.1007/s10681-020-02667-x), presenting different Rpp-pyramided genes for resistance to Phakopsora pachyrhizi to clarify the pyramiding effect of two originally developed Rpp-pyramided lines compared to two existing lines or lines possessing only a single Rpp of resistance under field conditions. Rpp-pyramided lines 52117-1 (Rpp2 + Rpp1-b), 52117-57 (Rpp2 + Rpp1-b), 52117-59 (Rpp2 + Rpp1-b) + 52117-60 (Rpp2 + Rpp4) showed high resistance levels compared to resistant sources and resistance control, carrying a single Rpp gene PI 200487 (Rpp5), PI 200492 (Rpp1), PI 230970 (Rpp2), PI 459025A (R pp4), and PI 506764 (Rpp3 + Rpp5) with significant reductions in sporulation levels (SL), number of uredinia per lesion (NoU), and frequency of lesions with uredinia (%LU). Only, the line 52117-54 (Rpp2 + Rpp1-b), and 52117-63 (Rpp2 + Rpp4) showed resistance level smaller than PI 594723 (Rpp1-b) and similar resistance levels than PI 230970 (Rpp2), respectively. Rpp-pyramided lines carrying Rpp2 + Rpp1-b (52116-54, 52116-74, 52117-21, 52117-59 and 52117-60), and Rpp2 + Rpp4 (52117-60), and single gene Rpp1-b were classified as "highly resistant" and "resistant". Furthermore, one sister line, 52117-57 (Rpp2 + Rpp1-b), showed immunity under field conditions. The Rpp-pyramided genes are an alternative for achieving high resistance levels against ASR.