Viability of Puccinia horiana Teliospores Under Various Environmental Conditions

Bonde, M. R., Palmer, C. L., Luster, D. G., Nester, S. E., Revell, J. M., and Berner, D. K. 2014. Viability of Puccinia horiana teliospores under various environmental conditions. Plant Health Progress doi:10.1094/PHP-RS-13-0117. Puccinia horiana Henn. is a quarantine-significant fungal pathogen and causal agent of chrysanthemum white rust (CWR). The pathogen and disease were first discovered in the United States in 1977 and quickly eradicated. During the early 1990s, CWR reemerged in several instances, but in each instance was declared eradicated. However, since approximately 2004 CWR has reappeared at an accelerated frequency. This has suggested that either P. horiana is entering the country more frequently from foreign locations or that P. horiana is now established in the field, implying that spores are capable of surviving winter conditions in plant debris or soil. As a result of the possibility that the pathogen has become established in the United States, we initiated several lines of research. The objectives of the study reported here were: (i) develop a better and more sensitive method to measure teliospore longevity; and (ii) determine if the pathogen is able to survive northeastern winters as viable teliospores. Results from the study showed that teliospores survived in the greenhouse a maximum of 28 days in dry soil and 7 days in moist soil. In a growth chamber simulating winter temperature conditions in the northeastern United States, teliospores survived a maximum of 35 days. It was concluded that P. horiana teliospores are not able to survive through typical northeastern U.S. winters.