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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, from 1997 to 2000, Schnabel was a post-doctoral research associate in the Department of Botany and Plant Pathology at Michigan State University, where he investigated genetic diversity and fungicide resistance in Venturia species under the guidance of Alan L. Jones. In July 2000, Schnabel began his position as fruit pathologist at Clemson University. Currently, he is a professor in the Department of Agricultural and Environmental Sciences with a 60% research and 40% extension appointment.

His research and extension program is geared toward helping farmers cope with disease problems. To understand the impact of his outreach program, it is important to reflect at least some on his outreach­supported research program. During the last 15 years, Schnabel has published more than 80 peer-reviewed articles, most in Phytopathology and Plant Disease, dealing primarily with detection, molecular characterization, and management of fungicide resistance in Monilinia, Botrytis, Alternaria, and Colletotrichum species. Some highlights of his research include the discovery of the molecular mechanism of DMI resistance in M. fructicola. He found that overexpression of the CYP51-encoding P450 14-a demethylase (a well-known mechanism of DMI fungicide resistance) was caused by transposons (mobile genetic elements) carrying promoter sequences. 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 then cloned and characterized Qol and SDHI fungicide target genes in the same and other fungi and is currently using next generation sequencing (RNAseq) to find yet unknown genetic determinants of SDHI fungicide resistance.

About 5 years ago, evidence for dwindling fungicide performance for gray mold control emerged in strawberry farms. Schnabel has since studied intensely the fungicide resistance phenotypes and genotypes of hundreds of B. cinerea isolates from blackberry and strawberry fields in the Carolinas and other states. He found multifungicide-resistant strains in virtually all fields examined with variable resistance profiles. He also found that resistance was frequently qualitative in nature and based on target gene alterations. Schnabel also reported at the IPPC in Beijing and later in the journal Phytopathology the presence of MDR1 and MDR1h in fludioxonil-resistant phenotypes. Both genotypes were associated with point mutations in the mrr1 transcription factor causing overexpression of multidrug efflux pump AtrB.

It became obvious that what was lacking in brown rot and gray mold management was a way for growers to rapidly adjust fungicide applications based on sensitivity of M. fructicola and B. cinerea in their orchards and fields. Thus, Schnabel developed a fast and accurate pathogen-collection and testing protocol for fungicide resistance monitoring. Using 24-well plates filled with various media amended with discriminatory doses of fungicides, he can quickly test the sensitivity of a pathogen population to 11 fungicides of seven chemical classes. Inoculation is done by transferring spores from cotton swabs containing spores from fruit or blossoms to the center of the disk using a toothpick. Growth is assessed after just 72 hours. He created a real-time online web application that—upon entering the in vivo data—creates customized recommendations for the growers.

He designed two different test protocols, one for M. fructicola and one for B. cinerea, and both are produced in Schnabel’s lab. They were originally used to serve South Carolina and Georgia growers, but the service soon became so popular among specialists and growers that, in 2014, growers from 10 states, including Maryland, Pennsylvania, Virginia, West Virginia, North Carolina, South Carolina, Florida, Georgia, Arkansas, and Connecticut used the service. The service provides precise information that has not been available before and enables producers to adjust spray programs before fungicide resistance causes crop loss. The service was featured in several popular press and grower magazines, including American Fruit Grower, Citrus + Vegetable, and The Grower. Schnabel is frequently invited to talk about his resistance profiling service and to give insights into resistance management at local and regional meetings, such as regional In-Service Training for Agents, the Southeastern Regional Fruit and Vegetable Conference in Savannah, Georgia, and the Southeastern Strawberry Expo in Raleigh, North Carolina. He was an invited keynote speaker at the International Horticultural Society meeting in Melbourne, Australia, to talk about his outreach program.

The implementation of this program saved peach producers an estimated $7 to 10 million in 2009 and 2013, and it is estimated that strawberry growers using this service prevent yield loss of about 10% on average every year due to improved gray mold control. The monitoring service reduces pesticide use by preventing application of ineffective fungicides and reduces the risk for continued selection of resistant populations. A poll among users indicated that, besides improved disease management, growers benefited also from the educational component of the program.

During the past 15 years, Schnabel published 129 extension publications and gave 138 extension talks (56 of which were invited talks). His peach disease website ( has had more than 150,000 visits since January 2009. Schnabel is an excellent candidate for the Excellence in Extension Award because of his extraordinary accomplishments and entrepreneurship in his research-supported outreach program that range from the molecular basis of fungicide resistance to the determination of location­specific resistance profiles to technology transfer to manage resistance development for dozens of growers in multiple states.