Effects of Anhydrous Ammonia on Mycelium and Sclerotia ofPhymatotrichum omnivorum

Abstract

Anhydrous ammonia (NH3) was toxic to mycelium and sclerotia of P. omnivorum. Mycelium was much more sensitive than sclerotia to NH3, and a 1-min exposure to 4 .mu.g NH3/ml was lethal. Mycelium in naturally infected root pieces was killed within 24 h by exposure to 56 .mu.g/ml NH3. Shorter exposures resulted in increased survival of mycelium in roots. NH3 concentrations below 21 .mu.g/ml were not toxic to sclerotia in vitro even after a 48 h of exposure. Toxicity at 28 .mu.g/ml was proportional to exposure period, giving 3, 23, 34 and 59% of kill of sclerotia after 1, 12, 24, and 48 h. Exposure of sclerotia to NH3 concentrations of 42, 56, or 84 .mu.g/ml for 12 h resulted in 100% kill in vitro. Higher concentrations of NH3 were required to achieve toxicity to sclerotia in situ; 138 and 276 .mu.g/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 4 .mu.g/ml and 82% by 8 .mu.g/ml.