Peroxidase activity in soybeans following inoculation with Phytophthora sojae.

The effects of race-specific resistance as conditioned by Rps genes (rps, Rps1-k, Rps2, Rps3, Rps6) in two genetic backgrounds (Williams & Harosoy) on accumulation of soluble peroxidases were determined by a soybean peroxidase capture assay (SPCA) after inoculation with P. sojae races 2, 7, or 25. Peroxidase activity increased in all isolines during the 72 h after inoculation, but reactions varied depending on time after inoculation, genetic background, Rps gene and P. sojae race. Peroxidase activity was higher in race-specific resistant than in susceptible reactions at 72 h. after inoculation, except for plants with the Rps2 gene which confers a unique form of root resistance in addition to the whole plant race-specific resistance. Williams isolines had larger increases in peroxidase activity than Harosoy isolines when data were averaged across Rps genes, and was most evident when plants were inoculated with race 2. When soybeans were inoculated with race 7 Rps1-k resistant plants had the highest increase in peroxidase activity, but Rps2 susceptible plants had a significantly higher peroxidase activity than plants with rps, Rps3, and Rps6 that were also susceptible. Results from inoculations with race 25 were somewhat different, Rps2 resistant plants had the highest increase in peroxidase activity; however, plants with the Rps3 or Rps6 gene that were also resistant did not have a significantly higher peroxidase activity than susceptible plants with the rps or Rps1-k gene.