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Hunt for sources of rust resistance in the bioenergy crop, switchgrass (Panicum virgatum L.).
S. R. Uppalapati (1), Y. Ishiga (1), D. Serba (1), L. J. Szabo (2), M. C. Saha (1), K. S. MYSORE (1). (1) The Samuel Roberts Noble Foundation, Ardmore, OK, U.S.A.; (2) Cereal Disease Laboratory, USDA-ARS, St. Paul, MN, U.S.A.

Several fungal pathogens have been identified on ornamental and native strands of switchgrasss (<i>Panicum virgatum</i> L.). Diseases of switchgrass have been largely neglected and pathogens could become the major limiting factors to biomass quality, and yield of switchgrass; especially when planted in monocultures. Leaf and stem rust caused by <i>Puccinia emaculata</i> is a major emerging disease in switchgrass research fields of Oklahoma. To identify genetically diverse source(s) of rust resistance, we evaluated half-sibling families from upland (Summer and Cave-in-Rock) and lowland (Alamo and Kanlow) switchgrass populations in both field growth chamber assays. Our results revealed a high degree of genetic variation within and among switchgrass populations. Alamo in general showed moderate resistance to <i>P. emaculata</i>, while Summer was highly susceptible. These results suggested a potential for improvement of rust resistance via the selection of the resistant individuals within the population. In addition, we have also initiated programs to identify and incorporate traits that confer nonhost rust resistance. Using forward-genetics screen in <i>Medicago truncatula</i>, we identified an <i>irg1</i> (<i>inhibitor of rust germ tube differentation1</i>) mutant that failed to promote pre-infection structure differentiation of <i>P. emaculata</i> due to complete loss of the abaxial epicuticular wax crystals and reduced surface hydrophobicity. An update on integrated approaches undertaken to mitigate rust disease and will be discussed.<p><p>Keywords:

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