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Atmospheric variations of rust spore concentrations during sugarcane growing seasons in Florida
P. C. ROTT (1), M. Kanaan (2), N. Glynn (3), W. G. Gibson (4), J. Haudenshield (5), M. Irey (6), C. LaBorde (7), R. Raid (1), J. Shine (8), J. C. Comstock (2). (1) University of Florida, Belle Glade, FL, U.S.A.; (2) USDA/ARS, Canal Point, FL, U.S.A.; (3) Syngenta Seeds Inc., Longmont, CO, U.S.A.; (4) BASF, Vero Beach, FL, U.S.A.; (5) USDA/ARS, Urbana, IL, U.S.A.; (6) United States Sugar Corporation, Clewiston, F

Orange rust and brown rust of sugarcane are two economically important diseases caused by the obligate biotrophic pathogens <i>Puccinia kuehnii </i>and <i>P. melanocephala</i>, respectively. Most of sugarcane cultivars grown in commercial fields in Florida are currently susceptible to one of these diseases, and fungicides are used to preserve yields. A real-time PCR assay for <i>P. kuehnii</i> and <i>P. melanocephala</i> was used in conjunction with weather-vane spore traps to monitor changes in atmospheric concentrations of spores (as pathogen DNA) through the growing seasons 2012 and 2013 in 6 different locations. Spores trapped on vaseline-coated glass slides were PCR-quantified twice a week. Spore concentrations varied according to the location and the month of the year, ranging from no DNA detected to DNA from the equivalent of thousands of spores. In 2012 and in 2013, high concentrations of <i>P. kuehnii </i>spores started to be trapped end of May or early June in 5 of 6 locations. High concentrations of <i>P. melanocephala</i> spores were also detected in these five locations during the same period in 2012. However, in 2013, high amounts of brown rust spores were already detected from mid-March to early May, suggesting that atmospheric rust spore concentrations vary not only according to climate but also to each disease. Spore data combined with disease and environmental data will be investigated in the future to predict sugarcane rust epidemics, and recommend fungicide applications only when needed.

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