Marcadores moleculares

Genetics and Resistance

Molecular Marker Analysis of Soybean Plant Introductions with Resistance to Phytophthora sojae
S. G. Gordon, K. Kowitwanich, W. Pipatpongpinyo, S. K. St. Martin, and A. E. Dorrance
First, second, third and fifth authors: Department of Plant Pathology, The Ohio State University, Wooster, OH 44691; and fourth author: Department of Horticulture and Crop Science, The OhioState University, Columbus, OH 43210. Accepted for publication 11 August 2006.

ABSTRACT Gordon, S. G., Kowitwanich, K., Pipatpongpinyo, W., St. Martin, S. K., and Dorrance, A. E. 2007. Molecular marker analysis of soybean plant introductions with resistance to Phytophthora sojae. Phytopathology 97:113-118. Molecular analysis of sources of resistance to plant pathogens should expedite andconfirm novel gene discovery and consequently the development of disease resistant cultivars. Recently, soybean plant introductions (PIs) were identified that contain putative novel Rps genes for resistance to Phytophthora sojae. The number of resistance genes that confer resistance to P. sojae isolates OH17 (1b,1d,2,3a,3b,3c,4,5,6,7) and OH25 (1a,1b,1c,1k,7) was then determined in several of the PIs.The objective of this study was to determine if the Rps genes present in these PIs were associated with eight described Rps loci that have been mapped on soybean molecular linkage groups F, G, J, and N. Nine F2:3 soybean populations were genotyped with simple sequence repeat (SSR) markers linked to previously mapped Rps loci. The nine PI populations all had SSR markers associated (P < 0.01) withresistance to P. sojae isolate OH17 in the Rps1 region. Rps1c is a likely candidate in eight PIs but novel genes may also be possible, while novel genes may confer resistance in one PI to P. sojae isolate OHI7. Two or more Rps genes, including some that are potentially novel, confer resistance to P. sojae isolate OH25 in eight of the populations. However, based on the response to these twoisolates, virulence already exists for at least some of the novel genes identified in this study. Additional keywords: Glycine max, host resistance.

Single, dominant R-genes to plant pathogens often occur in multigene clusters in many of the plant genomes that have been studied (23), including soybean (Glycine max L. Merr.) (1,2,4,13,14,19,20,32). In rice (Oryza sativa L.) and Arabidopsis thaliana (L.)Heynh., whose entire genomes have been sequenced, these resistance gene clusters are made up of active Rgenes as well as numerous R-gene-like sequences (23). In soybean, these gene clusters consist of multiple R-genes that confer resistance to different pathogens, such as the Rps2 (resistance to Phytophthora sojae Kauf. and Gerd.) and Rmd (resistance to powdery mildew) loci on molecular linkagegroup (MLG) J (25); or to different isolates or strains of the same pathogen, such as the tightly linked loci that confer resistance to Soybean mosaic virus on MLG F (17). Numerous resources now exist for soybean genetic analysis, including both classical and molecular markers as well as genetic linkage maps (16,29). The most recent integrated genetic map of soybean is derived from five mappingpopulations and contains 20 linkage groups spanning more than 2,500 cM, defined by simple sequence repeat (SSR), restriction fragment length polymorphism (RFLP), random amplified DNA (RAPD), amplified fragment length polymorphism (AFLP), and classical markers (24,29). These markers are an important resource for both basic and applied research, including investigations to characterize the resistanceto soybean pathogens (18). P. sojae causes root and stem rot of soybean, and is a welldescribed pathosystem (10). Fourteen resistance genes to P. sojae (Rps) have been described and mapped to eight loci in the soybean genome (Rps1 to Rps8) (7,8,12,17) (Fig. 1). Rps1 and Rps7
Corresponding author: A. E. Dorrance; E-mail address: dorrance.1@osu.edu
DOI: 10.1094 / PHYTO-97-0113 © 2007 The American...