Sooty Blotch and Flyspeck of Apple

Our lab is a world leader in the study of the ecology, evolutionary biology, diversity, and management of fungi in the sooty blotch and flyspeck (SBFS) complex. These fungi cause economic losses for growers in many countries by blemishing the epicuticle of apple fruit. Our goals are to 1) help growers to manage SBFS more cost-effectively, 2) characterize  worldwide diversity in the complex, 3) clarify SBFS ecology and evolutionary origins, and 4) discover genetic and adaptive changes that occurred during the evolutionary transition from plant parasitism to epiphytism. Together with many U.S. and international collaborators, we summarized progress in understanding SBFS in a recent Feature Article in Plant Disease (Gleason et al., 2011).

Apple with sooty spotsAssistant Scientist II Dr. Jean Batzer has been working on SBFS in my lab for 17 years; she is the top expert in the world on SBFS ecology and morphology. Jean has led many surveys to discover patterns of diversity and biogeography in the complex; with former visiting scientist Mercedes Diaz Arias and Dr. Sun Guangyu and colleagues at Northwest A&F University in Yangling, China, we have documented over 80 species in the complex from apples and a diversity of other wild and cultivated plant hosts, making SBFS perhaps the most diverse disease complex ever documented. A key to our rapid progress in species discovery was linking phylogenetic analysis to traditional morphological characterization.

In collaboration with Dr. Pedro Crous of CBS, Utrecht, The Netherlands, Jean is currently identifying sub-groups of the U.S. SBFS fungi. In cooperation with Drs. Bernhard Oertel and Thomas Feldmann of the University of Bonn, Germany, Jean is helping to identify SBFS islolates from German orchards using DNA and morphological description.

Katie Duttweiler, a M.S. candidate, is evaluating an RFLP-based method to streamline identification of SBFS fungi. This technique could open the door for ecological and management studies by allowing researchers to identify SBFS fungi directly from mycelium scraped off apple peels, avoiding cumbersome and time-consuming agar plate bioassays. Katie is also gathering weather data and SBFS occurrence data from orchards in Iowa, North Carolina, and Wisconsin to refine the existing SBFS warning system.

Mercedes Diaz, a M.S. candidate at University of Costa Rica, is doing her M.S research on SBFS in our lab. She is examining the diversity and biogeography of SBFS fungi in the eastern U.S. Using colonies isolated from apples in 30 orchards across 10 eastern U.S states, Mercedes is describing SBFS genetic diversity in the region by parsimony analysis of sequences from the ITS and LSU regions of rDNA, and characterizing morphology of these isolates.

Apple with sooty spotsTwo undergraduate research interns mentored by Jean Batzer in 2005-2006, Fabien LeCorronc (ESMISAB, Brest, France) and Benjamin Peterson (ISU), conducted in vitro studies of growth and morphological responses of a wide range of SBFS fungi to nutrition (percent apple juice). This information will be combined in a manuscript with studies on in vitrotemperature responses by the same fungi, conducted by former M.S student Sandra Hernández (graduated 8/05) and our collaborator, Dr. Patty Mc Manus of the University of Wisconsin.

New projects on SBFS include an investigation of the timing of appearance of colonies of various SBFS fungi on apples in Iowa orchards (by M.S. student Adam Sisson), and speciation of SBFS fungi in the genus Pseudocercosporella (by M.S. student Nenad Tatalović).

A 2-year (2006-2007) field project, in collaboration with Dr. McManus, is exploring the impact of apple tree pruning and fungicide-spray volume on SBFS suppression when using the SBFS warning system to extend the spray interval between first and second cover. In addition, Nenad Tatalović will evaluate the effectiveness of remotely estimated wetness-duration data (SkyBit, Inc.) for implementing the SBFS warning system during the 2006-2008 growing seasons.

A collaboration with Dr. Guangyu Sun, a fungal geneticist at Northwest Sci-Tech University, Yangling, People's Republic of China, began in 2002. After isolating SBFS fungi from apples in commercial orchards in Shaanxi Province in central China, Dr. Sun's team is performing PCR and sequencing of the ITS and LSU regions of these isolates. We will then attempt to fit Dr. Sun's SBFS assemblage into the phylogenetic trees created by Jean Batzer for the Midwest U.S. One publication has already emerged from this collaboration (Sun et al., 2006,Mycotaxon 95:277-280).