Identification of a Fourth Major Gene Conferring Resistance to Soybean Rust
1986
Hartwig, Edgar E.
Studies were conducted in containment facilities at Frederick, MD to determine the genetic basis of resistance to Phakopsora pachyrhizi Syd. (incitant of soybean rust) carried by the soybean [Glycine max (L.) Merr.] line PI 459025. Previous studies showed that soybean genotypes PI 200492, PI 230970, and PI 462312 each carried a single dominant gene conferring resistance to a specific soybean rust isolate. Genotype PI 200492 gave a near-immune reaction to rust isolate India 73-1 and a susceptible reaction to Taiwan 72-1. Genotype PI 462312 gave a resistant reaction to the India rust isolate and a susceptible reaction to the Taiwan isolate. Genotype PI 230970 and F₄ lines having PI 230970 as a parent gave resistant reactions to both rust isolates. Genotype PI 200492, PI 230970, and PI 462312 gave a susceptible reaction when inoculated with rust isolate Taiwan 80-2. Line PI 459025 was identified as resistant to Taiwan 80-2 as well as Taiwan 72-1 and India 73-1. Line PI 459025 was crossed with each of the three previously identified sources of resistance. The F₁ plants, F₂ populations, and selected F₃ lines were inoculated with each of the three rust isolates to determine their reaction. For each plant evaluated, a leaflet of a single trifoliolate leaf was inoculated with a different rust isolate. The results showed that PI 459025 carried a single dominant gene for resistance to all three rust isolates and that this gene was at a different locus from the three previously identified genes conferring resistance to specific rust isolates. The genotype assigned for rust resistance of PI 459025 is rpp₁ rpp₁ rpp₂ rpp₂ rpp₃ rpp₃ Rpp₄ Rpp₄.
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