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Plant Pathology (2000 – 2005)

Tim WIDMER


The plant pathology lab first began operation on January 4th, 2000, at the European Biological Control Laboratory (EBCL) near Montferrier-sur-Lez, France. As the plant pathologist, my primary objective was to discover new pathogens on target weeds for potential use as biological control agents against invasive weeds in the U.S. The isolated organisms are then screened for their pathogenicity by testing Koch's postulate. Once the organisms have been proven to be pathogenic, they are tested for their efficacy against the target weed and tested under different conditions (temperature, dew period, plant age) to define their maximum potential. Host range studies to determine if the pathogen is specific are then necessary in order to gain approval for release.
I travelled primarily around the Mediterranean region since the invasive weeds we target are believed to be native in this area. I primarily searched in Russia, Greece, Turkey, Italy, and France. We developed cooperations with different institutes from these countries and have always searched for new collaborations.The primary target weed was yellow starthistle (YST), Centaurea solstitialis. I isolated several pathogens that had not previously been reported. One fungus, identified as Phoma exigua, was found on dying plants in Russia. In cooperation with the  Zoological Institute in St. Petersburg, Russia, I conducted host range studies of this fungus. I also found another fungus that has yet to be identified but could show some promise. I have also done some work related to a toxin produced from an Alternaria sp. isolated from YST leaves. I was also interested in studying the YST plant and understanding why it is such a problematic weed in the U.S. but not in its native range.
Another one of my weed projects was Arundo donax (giant reed). I isolated several Fusarium spp. from the rhizomes of giant reed but further tests did not show any significant pathogenicity. Thus, I did not pursue this project any further. However, I isolated several bacteria from the shoot tips of giant reed that could show some promise. This bacteria could be in relation to a fly larvae that is often observed within the shoot tip.
Other weeds which I have isolated fungi and bacteria from include Tamarix spp. (saltcedar), Cardaria draba (hoary cress), Chondrilla juncea (rush skeletonweed), Galium aparine (Bedstraw), Convolvulus arvensis (field bindweed) and Taeniatherum caput-medusae (medusahead rye).
Ms. Fatiha Guermache is the full-time technician in the laboratory. She is involved directly in all of my projects and has extensive background in tissue culture and molecular biology. Ms. Nathalie Laurent also joined the laboratory for some time, and worked on pathogen screening of isolated organisms and using antagonists to control Phytophthora Pod Rot on cacao. (2003)