STUDIES ON SUNFLOWER RUST: IV. TWO GENES, R1 AND R2 FOR RESISTANCE IN THE HOST

Abstract

Crosses were made between rust-resistant sunflower plants, from sources 22, 88 and 307, and susceptible inbred lines or varieties. The resistance in all three sources was derived from wild annual sunflowers from Renner, Texas. Seedlings of progenies from the crosses segregated in a ratio of three resistant to one susceptible, when one parent was resistant to the rust cultures used, and in a ratio of fifteen resistant to one susceptible when both parents were resistant. There appears to be a dominant gene for resistance, R1, in source 22, and a non-allelic dominant gene for resistance, R2, in source 88 and 307. Occasional aberrant ratios may be due to unidentified genes exerting minor effects in the host plants, variations in environmental factors, or the interaction of these with specific cultures of rust.