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Guido Schnabel

Guido Schnabel was born in Marburg, Germany, and received B.S. and M.S. degrees in agricultural sciences from Justus Liebig University, Giessen, Germany, and a Ph.D. degree in plant pathology from the University of Hohenheim in Stuttgart in 1997. Thereafter, Schnabel was a post-doctoral research associate in the Department of Botany and Plant Pathology at Michigan State University from 1997 to 2000, where he investigated genetic diversity and fungicide resistance in Venturia spp. under the guidance of A. L. Jones. In July 2000, Schnabel began his position as fruit pathologist at Clemson University. Currently he is an associate professor in the Department of Entomology, Soils, and Plant Sciences with a 60% research and 40% extension appointment.

During the last 10 years, Schnabel has published 12 articles in Phytopathology, Plant Disease, and Plant Health Progress dealing with detection, molecular characterization, and management of fungicide resistance in Monilinia fructicola and other Monilinia species. South Carolina and Georgia are ranked consistently as the second- and third-highest peach-producing states in the United States. Thus, it was natural that Schnabel focused his research at Clemson on brown rot of peach caused by Monilinia fructicola and specifically on managing isolates with reduced sensitivity to demethylation-inhibitor (DMI) fungicides that had been discovered in South Carolina peach orchards shortly before he arrived. His first accomplishment was to demonstrate efficacy of fungicides with different modes of action against DMI-resistant isolates of M. fructicola. He also detected DMI resistance in Georgia peach orchards, an example of his excellent cooperation with fruit pathologists in neighboring states. He then turned his attention to mechanisms of fungicide resistance. Schnabel’s lab was the first to discover that overexpression of the DMI resistance gene cyp51 encoding P450 14α-demethylase (a well-known mechanism of DMI fungicide resistance) in M. fructicola was caused by transposons (mobile genetic elements) carrying promoter sequences. After the transposon named “Mona” was found in isolates from Georgia, it was found in DMI-resistant isolates from South Carolina, Ohio, New York, and New Jersey. The study of these mobile elements not only contributed to a better understanding of fungicide resistance in general but also provided a strong basis for the development of rapid molecular identification of fungicide resistance in isolates and populations of plant pathogens. Schnabel developed a simple, PCR-based technique for the detection of “Mona” that allows identification of DMI resistance within hours of sampling. In subsequent laboratory studies, DMI-resistant isolates were shown to be more likely than sensitive isolates to become resistant to the strobilurin group of QoI fungicides. This was especially significant because peach producers often rotate DMI and QoI fungicides. Recently, Schnabel reported on M. fructicola isolates with reduced sensitivity to QoI fungicides in South Carolina and Georgia.

It became obvious that what was lacking in brown rot management was a way for growers to rapidly adjust fungicide applications based on the sensitivity or resistance of M. fructicola in their orchards. Thus, Schnabel and his Georgia colleagues developed a novel fungicide resistance assay kit trademarked as “Profile.” The idea was remarkably simple: The kits contained lip balm tubes filled with agar amended with one of four fungicide active ingredients. Agar disks were sliced off and placed into a Petri dish, inoculated by transferring spores from fruit to the center of the disk, and pathogen growth was assessed after just 24 hours. Based on feedback from county extension agents who field tested the kits, Schnabel modified and expanded the kit in a second version, in which the tubes were replaced with 24-well plates that were inoculated using a sterile toothpick or cotton swab. In addition, a real-time online web application was created that—upon entering the in vivo data—created a sensitivity profile for an orchard with customized fungicide programs for the grower. For example, a benzimidazole may be recommended if isolates are sensitive, or an increased rate of DMI fungicides is recommended if isolates are insensitive to the standard rate. The “Profile” kits are produced in Schnabel’s lab and shipped to trained county agents and specialists in South Carolina and Georgia. The assay was featured in seven popular press and grower magazines, including American Fruit Grower and The Grower. This service provides precise information that has not been available before and which enables producers to adjust spray programs before fungicide resistance causes crop loss. The implementation of this program saved producers an estimated $7–10 million in 2009, when a brown rot epidemic did not occur in the Southeast despite conducive weather conditions. Because peaches receive regular and heavy applications of fungicides, the “Profile” kits reduce pesticide use by preventing application of ineffective fungicides, improve control of brown rot, and minimize the risk of fungicide resistance occurring in orchards where the pathogen is still sensitive to one or more fungicides.

Schnabel shares his research findings with fruit researchers and growers over a wide area. He has a very close partnership with the members of the South Carolina Peach Council. Currently, Schnabel has active collaborations with scientists in Germany, Hungary, China, France, and Greece. He is the co-founder of the International Grey Mold Consortium, which will extend his research results with Monilinia to the related genus Botrytis. Schnabel was a member of the APS Fungicide Resistance Committee (2003–2006) and is a member of the Deciduous Tree Fruit Workers and the International Chemical Control Committee of the ISPP. He has given 28 invited extension presentations and 15 invited research presentations during the past 10 years. His peach disease website ( has had over 10,000 visits since January 2009. He has served as an associate and currently serves as a senior editor for Plant Disease. Schnabel is an excellent candidate for the Lee M. Hutchins Award because of his extraordinary accomplishments that range from the molecular basis for fungicide resistance to technology transfer over an intensive five- to 10-year period.