Submitted to: Government Publication/Report
Publication Type: Government publication
Publication Acceptance Date: 6/10/2008
Publication Date: 6/30/2008
Citation: Smith, L. 2008. Predicting the success of the fungal pathogen Puccinia jaceae var. solstitialis in diverse California habitats and the identification of factors that affect pathogen survival. Government Publication/Report. 12 p. Interpretive Summary: Yellow starthistle is an important alien weed that has invaded over 20 million acres in the western U.S. It is a spiny plant that interferes with grazing livestock and outdoors recreation, it is fatally poisonous to horses, it outcompetes desirable vegetation, and reduces biodiversity. Previously introduced insect biological control agents became established but are not providing sufficient control of the weed. The rust fungus, Puccinia jaceae var. solstitialis, was introduced to California from Turkey in 2003 to help control yellow starthistle. It has since been released in over 40 counties in California. We are evaluating the environmental conditions that limit the establishment and effectiveness of the rust. The rust has had minimal impact on the weed and has become established at less than 20% of the release sites. It appears that the rust is not well adapted to the climate where the weed is most problematic.
Technical Abstract: We measured persistence and incidence of the yellow starthistle rust in each of 80 release plots around the state of California and measured geographical spread using GPS. Urediniospore (infective asexual spore) lifespan in the field was measured at sites representing the Central Valley and Coastal Hills. We observed that dormant teliospores have been produced at some sites and that they are capable of germinating the following winter. We developed a mathematical model of the functional relationship of urediniospore latent period (development time) to temperature. We measured the dormancy requirements and germinability of teliospores (the dormant spores), and developed a degree-hour model derived from laboratory data that accurately predicts when teliospores are primed for germination in the field. Regions where the rust is most likely to be effective were determined by using the CLIMEX program to compare the climate at the originating site of the rust isolate.