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Genetics

Transfer from Tripsacum dactyloides to Corn of a Major Gene Locus Conditioning Resistance to Puccinia sorghi. R. R. Bergquist, Plant pathologist, Pfister Hybrid Corn Company, El Paso, IL 61738; Phytopathology 71:518-520. Accepted for publication 20 October 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-518.

A dominant gene for resistance to common rust of corn (which is caused by Puccinia sorghi) was found among progeny of Zea mays × Tripsacum dactyloides-BC⁸-[S] After four additional backcrosses to susceptible Corn Belt inbred lines, selected populations were selfed and testcrossed to a rust-susceptible recurrent parent to establish F₂ and testcross populations for genetic study. In greenhouse and field tests, F₂ generations segregated 3 resistant:one susceptible. Backcross generations to a susceptible parent segregated 1:1. The new gene, designated Rp₁^Td, occurs within 0.3 map units of Rp₁^d on chromosome 10. In a testcross of F₁ progreny to a susceptible tester, five of 3,763 testcross progeny were susceptible (ie, lacked both Rp₁^d and Rp₁^Td). Plants with genes Rp₁^d and Rp₁^Td in repulsion were exposed in Hawaii to natural inoculum of P. sorghi that is virulent to plants with Rp₁^b, Rp₁^d, or Rp₁^k. The resistance provided by the Rp₁^d/Rp₁^Td combination was effective, although some small uredia appeared on the lower leaves of mature plants.