Effect of temperature and uredinium density on urediniospore production, latent period, and infectious period ofPuccinia hordeiOtth

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Abstract
The effect of 5 temperature regimes and 10 uredinium densities on urediniospore production, latent period, and infectious period of a New Zealand isolate of P. hordei Otth on ''Zephyr'' barley [Hordeum vulgare] was investigated. Increasing ambient temperature in the range 10.degree.-25.degree. C decreased the length of the latent period and increased total urediniospore production during the infectious period. In all cases the spore production curve was negatively skewed. The length of the infectious period was not significantly affected by temperatures of 10.degree.-20.degree. C, but it was less at 25.degree. C. Increasing uredinium density from 1/cm2 to 161/cm2 leaf area decreased uredinium size, urediniospore production per uredinium and lengths of infectious and latent periods, but spore production per unit area of uredinium and the rate of uredinium eruption were both increased. Terminology of the rust infection cycle is discussed in relation to bases for quantification and comparison between laboratories.