Resistance to Phakopsora pachyrhizi in Soybean PI 587905 Maps to the Rpp1 Locus and Exhibits Variable Dominance Associated with Plant Ontogeny

Abstract

Soybean rust, caused by Phakopsora pachyrhizi Sydow, results in significant soybean (Glycine max (L.) Merr.) yield losses worldwide. The purpose of this research was to confirm the inheritance, gene action, and genomic location of resistance to P. pachyrhizi in soybean accession PI 587905. Two independent populations (F₂-derived F₃ lines and F₂ plants) were inoculated with P. pachyrhizi in a greenhouse and assayed in a field, respectively, in southeastern Paraguay. Both the field F₂ and the greenhouse F₂-inferred segregation ratios fit the 1:2:1 ratio expected for segregation of a single gene (P > 0.05). Unlike previous studies, gene action differed according to ontogeny. Among seedlings in the greenhouse, gene action was dominant, but in the field assay among adult plants, the gene exhibited incomplete dominance. Molecular markers were used to map the resistance gene in PI 587905 to the Rpp1 locus. This information should be useful to plant breeders for developing and selecting resistant cultivars.

KEYWORDS:

• dominant gene action
• genetic map
• resistance
• Rpp1 genes
• soybean rust

Additional information

Funding

This research was funded by the USDA, Agricultural Research Service, in house research projects, 6402-21220-012-00D, 1920-22000-041-00D, and 3611-22000-021-00D. Funds were also received from the ARS National Plant Disease Recovery Systems Program in support of this research. Research in Paraguay was facilitated by Specific Cooperative Agreements with the Instituto Paraguayo de Tecnología Agraria (#58-6402-0-139FN) and the Cámara Paraguaya de Exportadores de Cereales y Oleaginosas (#58-6402-0-135F). Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.