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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY AND MANAGEMENT OF INVASIVE WEEDS IN THE WESTERN UNITED STATES

Location: Exotic and Invasive Weeds Research

Title: Latent period and viability of Puccinia jaceae var. solstitialis urediniospores; implications for biological control of yellow starthistle

Authors
item Fisher, Alison
item Woods, Dale - CDFA
item Smith, Lincoln
item Bruckart, William

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2007
Publication Date: October 22, 2007
Citation: Fisher, A.J., Woods, D.M., Smith, L., Bruckart, W.L. 2007. Latent period and viability of Puccinia jaceae var. solstitialis urediniospores; implications for biological control of yellow starthistle. Biological Control 45:146-153.

Interpretive Summary: Yellow starthistle is an invasive rangeland weed that infests over 14 million acres in California and it is currently spreading. In 2003, a rust fungus was introduced to California for biological control of yellow starthistle. A field and laboratory study of spore viability was conducted to determine the potential of using infected plant material for redistribution of inoculum into new areas. Viability of spores declined over a period of ten weeks when stored in the laboratory and over a period of three weeks when stored outside. Based on these results, introductions of harvested infected plant material would have to be done quickly to offset losses in spore viability. Results of this study suggest that infecting spores are not likely to remain viable through the summer and fall dry season. Overwintering spores therefore, serve as the inoculum source when yellow starthistle seedlings germinate in the winter. The potential number of spore generations that occur per year was also measured. Approximately six spore generations can be expected to occur each year in central-northern California under suitable conditions for disease.

Technical Abstract: Since the introduction of Puccinia jaceae var. solstitialis into California in 2003, multiple urediniospore generations have been observed, along with teliospores and pycnia, on yellow starthistle (Centaurea solstitialis). A field and laboratory study of urediniospore viability was conducted to determine the potential of using infected plant material for redistribution of inoculum into new areas. To better understand the life history of P. j. solstitialis, urediniospore viability was measured during the summer and fall when the host plant is usually senescent. Latent period (time from inoculation to pustule eruption) after field and laboratory inoculations was measured in order to determine the potential number of urediniospore generations that occur per year. Viability of urediniospores stored in the laboratory gradually declined over a period of ten weeks; spore hydration increased germination. Based on the results obtained in this study, introductions of harvested infected plant material would have to be done quickly to offset losses in urediniospore viability. Urediniospore viability in the field decreased exponentially 86% near the coast and 97% in the Central Valley three weeks after production, and was negligible (0-0.2%) thereafter. Latent period ranged from four to five weeks at cool winter temperatures to two to three weeks at warm summer temperatures in both the laboratory and field. Results of this study suggest that urediniospores are not likely to remain viable through the summer and fall dry season. Teliospores, therefore, serve as the inoculum source when YST seedlings germinate in the winter. Approximately six urediniospore generations can be expected to occur each year in central-northern California under suitable conditions for disease.

Last Modified: 9/23/2014
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