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Effects of Anhydrous Ammonia on Mycelium and Sclerotia of Phymatotrichum omnivorum. C. M. Rush, Graduate research assistant, Department of Plant Sciences, Texas A&M University, College Station 77843; S. D. Lyda, professor, Department of Plant Sciences, Texas A&M University, College Station 77843. Phytopathology 72:1085-1089. Accepted for publication 19 January 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1085.

Anhydrous ammonia (NH3) was toxic to mycelium and sclerotia of Phymatotrichum omnivorum. Mycelium was much more sensitive than sclerotia to NH3, and a 1-min exposure to 4 μg NH3/ml was lethal. Mycelium in naturally infected root pieces was killed within 24 hr by exposure to 56 μg/ml NH3. Shorter exposures resulted in increased survival of mycelium in roots. NH3 concentrations below 21 μg/ml were not toxic to sclerotia in vitro even after a 48 hr of exposure. Toxicity at 28 μg/ml was proportional to exposure period, giving 3, 23, 34, and 59% of kill of sclerotia after 1, 12, 24, and 48 hr. Exposure of sclerotia to NH3 concentrations of 42, 56, or 84 μg/ml for 12 hr resulted in 100% kill in vitro. Higher concentrations of NH3 were required to achieve toxicity to sclerotia in situ; 138 and 276 μg/g resulted in 35 and 79% kill, respectively. Electrolyte leakage from mycelium increased in proportion to NH3 concentration after the first 15 min. Mycelial respiration was highly sensitive to NH3, and was inhibited 55% by 4μg/ml and 82% by 8 μg/ml.