Marssonina leafspot disease of poplar under elevated ozone: pre-fumigated host and in vitro studies

The effects of O-3 On leafspot disease of poplar were assessed for the path ogen (Marssonina tremulae Lib.) in isolation and combined with the host Pop ulus trichocarpa T&GxPopulus balsamifera Duroi non L. in enclosed chamber f umigation experiments. O-3 exposure of 150 nl l(-1), 8 h day(-1), for 7 day s and 200 nl l(-1), for 8 h, had no effect on colony growth in vitro, altho ugh O-3 enhanced conidiospore germination (150/200 nl l(-1), over 8/5-6.5 h ) and increased significantly the numbers of germtubes produced (150 nl l(- 1), over 8 h). Pre-fumigation of host plants (100 nl l(-1), 8 h day(-1), fo r 30 days) increased significantly the size of lesions on old leaves, but d ecreased these significantly on young leaves. Spore germination was signifi cantly increased on leaves of all ages after a 15-day chronic exposure (100 nl l(-1), 8 h day(-1)), but decreased significantly after acute exposure t o 200 nl l(-1), over 8 h. (C) 1999 Elsevier Science Ltd. All rights reserve d.