RPP-gene Pyramiding Confers Higher Resistance Level to Asian Soybean Rust

Abstract

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 aim of this study was to evaluate sister lines with different pyramided Rpp gene for resistance to Phakopsora pachyrhizi and identify which combination of Rpp genes had higher levels of resistance under field conditions. All Rpp-pyramided lines showed higher levels of resistance, with significant reductions in sporulation levels (SL), number of uredinia per lesion (NoU), and frequency of lesions with uredinia (%LU), compared to the resistance sources PI200487 (Rpp5), PI200492 (Rpp1), PI230970 (Rpp2), PI459025A (Rpp4), PI506764 (Rpp3, 5), PI587880A (Rpp1-b), PI594538A (Rpp1-b), and PI594723 (Rpp1-b). Rpp-pyramided lines carrying Rpp1-b + Rpp1-b, Rpp2 + Rpp1-b, Rpp4 + Rpp1-b, and single gene Rpp1-b were classified as “highly 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.