Host resistance involves an interaction between the plant and the pathogen.
We investigated when both single Rps genes and partial resistance were effective against P.sojae. Figure 4 illustrates the results of these experiments.
We inoculated soybean varieties with partial resistance and found that there was a significant reduction in stand when the plants came into contact with P. sojae at 0, 1, 2, 3, 4, and 5 days after planting. When plants with partial resistance were inoculated after the plants had emerged (7 to 14 days), there was no effect on stand. In contrast, plants with the Rps1k gene that were inoculated with a race of P. sojae that could not kill plants with this gene had 95 to 100% germination when inoculated at 0, 1, 2, 3, 4, 5, 7, and 14 days after planting. This study indicates that plants with an Rps gene(s) that is effective against populations of P. sojae in a field will be effective at the time of planting.
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| Figure 4. The soybean variety Conrad (high levels of partial resistance) was inoculated with zoospores of P.sojae. When inoculations took place 0, 2, 3, and 4 days after planting, the stand was greatly reduced. However, when plants were inoculated 5 to 14 days after planting, the stands were not significantly different. |
However, for varieties that have partial resistance as the main defense component, the resistance will not be effective until that plant has emerged and is photosynthesizing.
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Figure 5. Soybeans were inoculated at 0, 3, 5, 7, 10, and 14 days after planting with Phytophthora sojae. Conrad, a variety with partial resistance, had reduced plant emergence when inoculated early. The Resnik variety with a Rps gene had no disease develop following inoculation with this race. |
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