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Plant Pathology and Microbiology

Plant Pathology and Microbiology / Pest Management and Detection / Research Highlights / Exploring the sooty blotch and flyspeck complex on apples - Gleason Laboratory

Exploring the sooty blotch and flyspeck complex on apples - Gleason Laboratory

Sooty blotch and flyspeck (SBFS) is a fungal complex that colonizes the waxy cuticle of apple fruit. The blemishes caused by SBFS prevent apples from being sold as fresh fruit, causing financial losses for growers. The conventional strategy against SBFS is non-stop chemical warfare: 3 to 8 fungicide sprays from late spring through harvest.

To manage SBFS in a more environmentally friendly way, we need a better understanding of the fungi that cause it. After 175 years of study, five SBFS species had been described using traditional morphology-based techniques. Collaboration between Mark Gleason’s and Tom Harrington’s lab applied techniques of molecular genetics to help unravel the identity of fungi in the SBFS complex. By combining DNA sequence analysis with morphological descriptions, Jean Batzer (a former PhD student and now postdoc in Gleason’s lab) found 30 putative SBFS species in 9 Midwest orchards. This was a 6-fold increase in the number of known SBFS pathogens!

This exciting result set the stage for progress in several directions. A M.S. student, Katie Duttweiler, recently proved that a RFLP-based method could help to identify SBFS rapidly and efficiently by minimizing agar-plate isolations. This breakthrough opens the door for field studies of the environmental biology of SBFS. A visiting M.S. student from University of Costa Rica, Mercedes Díaz, completed a 30-orchard survey from 10 eastern U.S. states, revealing distinct patterns of geographic distribution among SBFS fungi and discovering 20 to 30 new SBFS species.

We are collaborating with mycologists and plant pathologists around the world to find out the full extent of SBFS diversity. Ongoing projects with Guangyu Sun (Northwest A&T University, Shaanxi Province, China), Bernhard Oertel (University of Bonn, Germany), Pedro Crous (Centraalbureau voor Schimmelcultures, Utrecht, The Netherlands), Mirko Ivanović (University of Belgrade, Serbia), and Emerson del Ponte (Federal University of Rio Grande do Sul, Brazil) will provide missing pieces of this puzzle.

We are also refining a SBFS warning system that can save 2 to 3 fungicide sprays per season, but has performed inconsistently in the Midwest. Our preliminary results indicate that substituting relative humidity for leaf wetness duration as an input to the warning system should improve the system’s reliability. Field testing of the warning system, including trials with cooperating commercial growers, have continued for nearly 10 years. We are also testing the feasibility of incorporating remotely estimated weather data in order to make the warning system cheaper and easier for growers to use.

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