Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2006
Publication Date: N/A
Interpretive Summary: This study evaluated the effects of temperature and light on growth of an important pathogen of oak trees and nursery crops, Phytophthora ramorum. P. ramorum is a fungus whose distant relative caused the Irish potato famine in the mid 1800s. It is a destructive pathogen of oak trees in California, and there are fears that the pathogen will move to new areas. Understanding the range of temperatures over which the pathogen can grow will help determine how wide its range may eventually become. We found that the fungus will grow over a very wide range of temperatures, ranging from near-freezing to very hot. The fungus grew best at cool temperatures. Exposure to visible and near ultraviolet light reduced growth and spore production by P. ramorum, which is in contrast with the effects of light on some other fungi. Knowing the effects of temperature and light on growth and sporulation of the fungus will help scientists understand more about the biology of P. ramorum and under what conditions it will produce spores that enhance its virulence and survival ability.
Technical Abstract: Phytophthora ramorum (Werres), a recent introduction to the US, is causing concern for the hardwood forests and the nursery industry. In an effort to identify some of the environmental parameters regulating growth and sporulation, a laboratory study of 4 US and 3 European (EU) isolates was undertaken. Temperature limits for growth on V8 media were 2 deg and 28 deg C, for chlamydospore production 8 deg and 28 deg C , and for sporangia production 10 deg and 30 deg C (<30 deg C for EU isolates). Optimal temperatures varied within the range of 16-26 deg C for growth, 14-26 deg C for chlamydospore production, and 16-22 deg C for sporangia production. A negative linear relationship was observed between growth/spore production by US isolates and near-UV radiation (50-300 'W/cm2)/visible radiation (250-1500 'W/cm2). EU isolates were exposed to 200 'W/cm2 near-UV, only, which significantly reduced growth of one of three isolates and had no significant effect on spore production. P. ramorum appears to be tolerant of a broad range of environmental conditions which implies that it is capable of establishment in a wide geographic area.