Phytophthora citricoia dominated among 11 genera and fungal species isolated from Rhododendron brachycarpum, R. catawbiense, R. impeditum and R. sepedonicum. In greenhouse trial isolates from Abies concolor, Chamaecyparis lawsoniana, R. catawbiense, R. impeditum and Thuya occidentalis caused dieback of rhododendron. Inoculation of leaf blades with isolates of the pathogen from 4 cultivars resulted in the spread of necrosis about 0.63 mm/hr. P. citricola was pathogenic to all tested rhododendron cultivars.

Common alder (Alnus glutinosa) decline has been observed in most of European countries since 1993. In Poland decline of alder trees has been observed during the last 6 years. Alder Phytophthora was recorded, however, only from one sampling area in the middle of the country. Species of Armillaria, Fusarium, Mucor, Penicillium and Trichoderma were also isolated from diseased trees. Inoculation of alder stem pans, leaves and seedlings with Phytophthora isolates resulted in the development and spread of necrosis. Studies will be continued in the nearest years.

Phytophthora citricola was isolated from diseased seedlings of European beech and Silver fir taken from the most of surveyed nurseries. Fusarium species, Pythium ultimum and Rhizoctonia solani were also found in diseased plant tissues.Isoates of P. citricola fro mboth plants and additionally from heather and rhododendron colonised leaf blades, needles and stem parts of beech and fir. In greenhouse trials on inoculated 1-year-old seedlings necrosis spread about 2 mm/24 hr on beech stems whereas on fir about 1.5 mm/24 hr.

From Hedera helix and Epipremnum aureum showing necrosis of shoot base spread upwards and on leaves Phytophthora tropicalil was isolated. The species was obtained from ⅞of Hedera and ¾ of Epipremnum diseased shoot and root parts. Additionally, Botrytis cinerea, Fusarium avenaceum and Rhizoctonia solani was recovered from some of affected plants. The chosen 2 isolates colonised petioles and leaf blades of both host plants. P. tropicalis caused necrosis of leaves of 11 tested cultivars of H. helix and 13 other pot plant species and seedlings of tomato. The fastest spread of necrosis was observed on leaves of Peperomia magnoliaefolia, Pelargonium zonale and Phalaenopsis x hybridum. The development of disease was observed at temperatures ranged from 10 to 32.5°C with optimum 30°C.

Genotypic differentiation among 10 isolates of Phytophthora cinnamomi Rands and 24 isolates of Phytophthora citricola Sawada from 12 different plant species grown in Polish ornamental nurseries was determined. DNA was extracted from pure pathogen cultures and amplified by the PCR technique using ISSR and RAPD primers. 9 primers were used to amplify P. cinnamomi and 8 to amplify P. citricola DNA. The analyzed amplification products were between 300 and 2300 bp. The genotypical differentiation was from 17 to 35% in P. cinnamomi and from 10 to 60% in P. citricola. Isolates from host plants of the same family showed, with some exceptions, similar levels of differentiation.