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CROP ECOLOGY, MANAGEMENT & QUALITY

Evaluation of Soybean Cultivars with the Rps1k Gene for Partial Resistance or Field Tolerance to Phytophthora sojae

^a Dep. of Crop Sciences, Univ. of Illinois, Urbana, IL 61801
^b USDA-ARS and Dep. of Crop Sciences, UIUC, Urbana, IL 61801

^* Corresponding author (ghartman{at}uiuc.edu)

Phytophthora root rot, caused by Phytophthora sojae Kaufmann and Gerdeman, primarily attacks the roots of soybean [Glycine max (L.) Merr.] plants. Partial resistance and field tolerance in 14 commercial glyphosate [N-(phosphonomethyl)glycine] tolerant soybean cultivars with the Rps1k resistance gene were studied. Partial resistance to compatible P. sojae races 28 and 30 was evaluated by the agar layer technique. Relative to the percentage of the control, all of the commercial cultivars with the Rps1k had reductions in top mass and plant height that were not significantly different from the partial resistant check ‘Conrad’ that had 83% top mass and 77% plant height reduction; two of the 14 commercial cultivars had significantly lower root mass (28 and 31% lower) than Conrad (84%). In addition, there was no significant difference in disease ratings (root or whole plant) of the 14 commercial cultivars with the Rps1k compared with Conrad. Field tolerance, studied in six field experiments at Urbana, IL, during 2002–2004, was identified when there were no significant differences between the yield of inoculated treatments with or without mefenoxam [methyl N-(methoxyacetyl)-N-(2,6-xylyl)-D-alaninate] fungicide seed treatment or between inoculated and noninoculated treatments. There were no significant cultivar x inoculation x fungicide treatment interactions found in any of the field experiments, and a significant cultivar x inoculation treatment interaction was found in only one field experiment. Therefore, most of the cultivars appeared to be tolerant to P. sojae. It should be noted that field tolerance was not distinguished from partial resistance in the field component of this study.

Abbreviations: MG, maturity group • PRR, Phytophthora stem and root rot