Genetic control of uredial development of stem rust in orchardgrass

Abstract

Genetic control of uredial development of stem rust, Puccinia graminis Pers., in orchardgrass, Dactylis glomerata L., was demonstrated in the following three experiments:
1. Five clonal lines of orchardgrass which were presumed to be nulliplex, simplex and duplex for resistance gene to race IIc or Ic were inoculated with the two races of stem rust. Uredia were observed to develop on nulliplex and simplex plants, but not on duplex plants. Large elongated uredia, parallel to leaf vein, were observed on nulliplex plants, while small and round uredia, often surronded by chlorotic or necrotic area, were observed on simplex plants.
2. A duplex clonal line which were duplex for resistance gene to races Ic and IIc and its immediate progenies after self-pollination were inoculated with the two races of stem rust. Genic constitutions of immediate self-pollinated progenies (S₁) for resistance to stem rust were revealed by further progeny tests. Uredium development was observed on nulliplex and simplex plants but not on duplex and triplex (or quadruplex) plants. Large uredia were observed on nulliplex plants.
3. A clonal line which was triplex for resistance gene to races III_C and III_W (Puccinia graminis Pers. f. sp. phlei-pratensis Stak. & Piem.), duplex for resistance gene to races I_C and II_C, simplex for resistance gene to race IIT and nulliplex for resistance gene to race II_N, was inoculated with the above-mentioned six races. Uredia developed in nulliplex and simplex cases, but not in duplex and triplex cases. Large uredia were observed only on nulliplex plants.
From the results of these experiments, it was evident that the uredial development of stem rust was under genetic control in orchardgrass. Gene dose effects on resistance were demonstrated. These results suggested possibility of estimating genotypes for resistance to stem rust from phenotypic responses to the fungus.