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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 Rp1Td, occurs within 0.3 map units of Rp1d on chromosome 10. In a testcross of F1 progreny to a susceptible tester, five of 3,763 testcross progeny were susceptible (ie, lacked both Rp1d and Rp1Td). Plants with genes Rp1d and Rp1Td in repulsion were exposed in Hawaii to natural inoculum of P. sorghi that is virulent to plants with Rp1b, Rp1d, or Rp1k. The resistance provided by the Rp1d/Rp1Td combination was effective, although some small uredia appeared on the lower leaves of mature plants.

Additional keywords: maize, race-specific resistance.