|Aegerter, Brenna - UC DAVIS|
|Gordon, Tom - UC DAVIS|
|Smith, Dale - CDFA|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 18, 2008
Publication Date: January 1, 2009
Citation: Fisher, A.J., Aegerter, B.J., Gordon, T.R., Smith, L., Smith, D.M. 2009. Puccinia Jaceae Var. Solstitialis Teliospore Priming on Yellow Starthistle. Phytopathology. 99 (1): 67-72. Interpretive Summary: Yellow starthistle is an invasive alien weed in the western United States. In 2003, the yellow starthistle rust fungus was been introduced to California for biological control of yellow starthistle. Since its introduction, the full life cycle of the fungus has been observed; however, there are few populations that have permanently established in California. To determine the role of dormant spores in the life cycle of the fungus, spore emergence, priming, and germination were evaluated in the field. A laboratory experiment was used to determine spore priming requirements and a mathematical model was used to determine if laboratory results could be used to predict when spores germinated in the field. Spore production coincided with plant senescence in late summer, but was inconsistent, suggesting low spore production may contribute to local extinctions in some areas. In the field, spores germinated in January during both years. A degree-hour model derived from laboratory data accurately predicts when spores are primed for germination in the field.
Technical Abstract: Following the introduction of Puccinia jaceae var. solstitialis to California for biological control of yellow starthistle (Centaurea solstitialis, Asteraceae), teliospores, pycnia, and multiple urediniospore generations have been observed in the field. Because urediniospores have a relatively short life span in the field, functioning teliospores are expected to be necessary for the permanent establishment of P. j. solstitialis in the California. To determine if conditions in California were conducive to this, teliospore emergence and priming were evaluated in the field. A factorial experiment in laboratory with five incubation times and three incubation temperatures was used to determine teliospore priming requirements. Teliospore production coincided with 24 plant senescence in August and September at two sites in two years; fewer teliospores were produced in 2006 suggesting inconsistent teliospore production may limit population growth and contribute to local extinctions in some areas. When teliospores were primed in the field, germination was low through the fall, and abruptly peaked in January during both years. In the laboratory, teliospore germination increased as incubation time increased from two to six weeks and temperatures decreased from 12 to 4°C. A degree-hour model derived from laboratory data accurately predicts when teliospores are primed for germination in the field. Based on the results obtained in this study, it is apparent that teliospore germination can occur over a range of priming conditions. However, lower temperatures and longer incubation periods are superior in breaking teliospore dormancy.