The latent period of barley leafrust, Puccinia hordei, was studied in a number of cultivars at different development stages and growing conditions.
The relative latent period of the different cultivars was not affected by temperature.
Other environmental factors, like daylength and light-intensity did not seem to have any effect either. The development stage of the plant and the genotype on the other hand influenced the latent period greatly. The latent period became longer for all cultivars tested from the seedling stage onward until a maximum was reached with the young flag leaf at heading. For the most susceptible cultivar, L94, the relative latent period increased from the primary leaf in the seedling stage, set at lOO%, to 117 in the young flag leaf. With the fairly resistant cultivar Vada the relative latent period increased from 123 to 233. The genotypic differences in latent period are very much greater in the adult plants stage than in the seedling stage. This and the fact that the relative latent period of the seedling does not predict the relative latent period of the adult plant very well, necessitates a cautious approach of seedling data.