Relationship between occurrence of Phytophthora cambivora on plants in hardy ornamental nursery stocks and detection of the pathogen from water ponds.

Phytophthora cambivora was isolated from rooted bases and roots of Castanea sativa, Chamaecyparis lawsoniana and Cotoneaster spp. as well as from water ponds Located in HNS. In the laboratory trials the species colonised leaf blades and stem parts of 3 tested plant species. Differentiated reaction of tested plant species on P. cambivora was observed.

Phytophthora tropicalis on Hedera helix and Epipremnum aureum in Polish greenhouses.

Phytophthora tropicalis was isolated from Hedera helix and Epipremnum aureum showing discoloration of leaves, necrosis of shoot base, spread upwards and on roots. The species was detected from 7/8 plants of Hedera and 3/4 of Epipremnum. Additionally Botrytis cinerea, Fusarium avenaceum and Rhizoctonia solani were recovered from some of diseased plants. P. tropicalis caused leaf necrosis of 13 plant species and tomato seedlings. The quickest spread of necrosis was observed on leaves of Peperomia magnoliaefolia, Pelargonium zonale and Phalaenopsis x hybridum. The disease developed at temperature ranged from 10 degrees to 32.5 degrees C with optimum 30 degrees C.

Biological control of Phytophthora ramorumon rhododendron.

Phytophthora ramorum was found in Poland in 2000 as the causal agent of rhododendron blight. Besides eradication of diseased plants and rhododendron growing around, chemical and biological control of the pathogen is necessary. In this study in vitro activity of grapefruit extract and chitosan in the inhibition of P. ramorum growth and sporulation and their efficacy in the control of leaf and stem rot development was evaluated. Amendment of V8 juice agar and soil leachate with grapefruit extract resulted in the inhibition of colony growth and sporulation of P. ramorum. Zoosporangia were more susceptible to the extract than pathogen hyphae and chlamydospores. Chitosan only slightly inhibited the colony growth and zoosporngia production. Spraying of rhododendron inoculated with P. ramorum with grapefruit extract at conc. 165 microg/cm3 inhibited 2-3 times the spread of necrosis on stems and leaves. Pre- and postinoculation spraying of rhododendrons with chitosan at conc. of 1000 microg/cm3 suppressed the disease spread about 40%.

Alder phytophthora in Poland: occurrence and plants colonization.

Common alder (Alnus glutinosa) decline has been observed in Poland 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 parts, leaves and seedlings with Phytophthora isolates resulted in the development and spread of necrosis. Studies will be continued in the nearest years.

Plant extracts in the control of Phytophthora cryptogea.

Grapefruit extract at dose 40 micrograms/cm3 inhibited Phytophtora cryptogea linear growth about 50% and almost completely suppressed zoosporangia formation. Drenching of gerbera plants with the extract at dose 165 micrograms/cm3 reduced population density of the pathogen about 70% and this high efficacy was noted at least one month after application. Treatment of gerberas with grapefruit extract resulted in protection of about 50% of plants against the pathogen. Biological activity of purple coneflower extract was lower than extract from grapefruit. Significant decrease of population density of the pathogen during the first 5 days and increase of gerbera healthy stand was observed, however, in peat treated with that extract.

Biological activity of Pythium oligandrum against Phytophthora species.

Influence of Pythium oligandrum as an a.i. of Polyversum on population dynamic of Phytophthora cryptogea in peat and development of Phytophtora rot on gerbera, Lawson cypress and yew-tree were evaluated. Drenching of peat, artificially infested with P. cryptogea, with Polyversum immediatelly after gerbera planting resulted in significant decrease of colony forming units number within 4 weeks. Concentrations of the biopreparate used had no significant influence on its greater, biological activity. Drenching of plants with Polyversum at conc. 0.05 or 0.1%, after planting into peat infested with P. cryptogea or P. cinnamomi, resulted in the strong suppression of Phytophthora foot or root and stem rot of gerbera, cypress and yew-tree.