Effects of Melampsora leaf rust disease and chronic ozone exposure on poplar

The combined and separate impacts of Melampsora sp. infection and chronic O -3 (100 nl l(-1), 8 h per day, for 17 days) on poplar health (Populus trich ocarpa T&GxPopulus balsamifera Duroi non L.), were assessed in a closed cha mber fumigation experiment. Incidence and severity of Melampsora infection was increased significantly by O-3 Comparisons with non-infected control pl ants showed that Melampsora and O-3 alone had a minor impact on tree health , although their combined effect was severe. By day 17, O-3 had significant ly increased leaf injury and the percentage of senescing leaves. Melampsora significantly reduced stem height throughout the exposure. Melampsora infe ction and O-3 together substantially increased leaf injury and significantl y decreased stem height and biomass, live leaf and total leaf biomass plus whole shoot biomass. They also significantly decreased the area of upper le aves and the ratio of stem weight/stem length, but increased significantly both leaf weight/stem weight and leaf number/leaf weight ratios. (C) 1999 E lsevier Science Ltd. All rights reserved.