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Title: Bioassay conditions for infection of Pinus radiata seedlings with Phytophthora pinifolia zoospores

item Widmer, Timothy
item Dodge, Stephen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2015
Publication Date: 8/1/2015
Publication URL:
Citation: Widmer, T.L., Dodge, S.C. 2015. Bioassay conditions for infection of Pinus radiata seedlings with Phytophthora pinifolia zoospores. Plant Disease. 99:1204-1209.

Interpretive Summary: The pathogen that causes mortality of Monterey pine in Chile, Phytophthora pinifolia, is a concern to the United States because California is the worldwide genetic resource for this native forest tree and the potential to infect other pine trees. However, very little is known about this pathogen including what conditions are needed for disease to occur. This study showed that wounding of the stem or needles was necessary for infection to occur and that exposure to moisture was also needed. However, infection occurred over a range of temperatures. This research is important in that it develops a standardized test to screen other pines and tree species for infection by this pathogen. This information will be important to researchers, forest managers and regulatory agencies who are looking to study how this pathogen might impact specific environmental areas should it enter the U.S.

Technical Abstract: Phytophthora pinifolia is known to cause a devastating disease on Monterey pines in Chile. Although this pathogen is not yet present in the U.S., there is reason for concern. The main source of Monterey pine genetic material is found in California and there is potential for other important tree species to be hosts. This study described here was conducted to develop a method to produce zoospores and determine optimal conditions for infection to be used in future host range studies. Abundant zoospores were produced when agar plugs containing P. pinifolia mycelia were ground into suspension prior to transfer in a solution of carrot broth. These zoospores then were used to inoculate Monterey pine seedlings under various conditions. Consistent infection occurred when seedlings were wounded by trimming needles prior to inoculation and exposure of inoculated seedling to constant dew for 5 days. Dew chamber temperature (15, 20, or 25 degrees C) did not affect the infection rate. Information obtained from this study will be useful in screening other hosts for susceptibility to P. pinifolia infection.