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POSTERS: Pathogen dispersal and survival

Development of a controlled-environment assay for studying tar spot in corn
Carlos Cecilio Gongora-Canul - Purdue University. Damon Smith- University of Wisconsin-Madison, Darcy Telenko- Purdue University, Nathan Kleczewski- University of Illinois, Daren Mueller- Iowa State University, Jorge Valle-Torres- Purdue University, Alison Robertson- Iowa State University, Martin Chilver

Tar spot is an emerging threat to U.S. corn production. In the United States, Phyllachora maydis has been the only pathogen associated with the tar spot outbreaks. No reliable, high throughput phenotyping protocol is available to study aspects of the ecology, epidemiology, and management of tar spot under controlled conditions. This study focused on developing a controlled-enviroment assay to facilitate P. maydis research. Dried corn leaves with tar spot symptoms were surface sterilized and blended to release asci and ascospores from stromata. Spores were then suspended in water and Tween 20 and concentration adjusted to 30,000 spores ml-1. Corn plants at the V5 growth stage were inoculated in a greenhouse by spraying the spore suspension directly onto the upper and lower surfaces of leaves until runoff. Plants were left inside a humidity chamber at 95% RH for five days at 14 h/10 h day/light. Plants were taken from humid chamber and put under greenhouse conditions at an average of 20oC. Initial chlorotic symptoms began to develop four days after inoculation, and 12 days later, severity reached 5% on individual leaves. Stromata developed between 25-30 days post inoculation. The pycnidial anamorph (Linochora) of P. maydis, was microscopically confirmed in black stromata and no ascospores were observed in microscopic examinations of these lesions. Experiments will continue to refine and develop a reliable method for inoculation in controlled environments.