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A collection of fifty‐three samples representing diploid and tetraploid species of the genus Avena was tested for resistance to three races of crown rust (Puccinia caronata avenue) and two races of stem rust (P. graminis avenae). Resistance to some races of the two rust species was confined to one sample of subsp. strigosa and two samples of subsp. barbata of A. strigosa. Sample no. 20, representing subsp. barbata, alone possessed resistance to all the races of both rust species. This material had previously been shown to be resistant to six races of smuts (Ustilago spp.). Genotypes possessing combinations of resistance to a wide range of pathogens appear to be very rare, and intra‐specific variation in respect of these characters is so great, that taxonomic classification cannot be used with any degree of certainty to discover sources of resistance to disease. The discovery of widespread resistance in a sample of the tetraploid subsp. barbata offers possibilities of the direct transference of genes to the cultivated species, thus dispensing with the need to synthesize amphidiploid bridging forms. The reaction of the hexaploid variety, Richland, to stem rust proved to be sensitive to temperature. Resistance mechanisms which are subject to environmental influences are considered to be less effective in combating the evolution of new races of the pathogen.

A collection of fifty‐three samples representing diploid and tetraploid species of the genus Avena was tested for resistance to three races of crown rust (Puccinia caronata avenue) and two races of stem rust (P. graminis avenae). Resistance to some races of the two rust species was confined to one sample of subsp. strigosa and two samples of subsp. barbata of A. strigosa. Sample no. 20, representing subsp. barbata, alone possessed resistance to all the races of both rust species. This material had previously been shown to be resistant to six races of smuts (Ustilago spp.). Genotypes possessing combinations of resistance to a wide range of pathogens appear to be very rare, and intra‐specific variation in respect of these characters is so great, that taxonomic classification cannot be used with any degree of certainty to discover sources of resistance to disease. The discovery of widespread resistance in a sample of the tetraploid subsp. barbata offers possibilities of the direct transference of genes to the cultivated species, thus dispensing with the need to synthesize amphidiploid bridging forms. The reaction of the hexaploid variety, Richland, to stem rust proved to be sensitive to temperature. Resistance mechanisms which are subject to environmental influences are considered to be less effective in combating the evolution of new races of the pathogen.