Gatunki Phytophthora i Pythium w glebie i w korzeniach dębu szypułkowego na terenach popowodziowych w Nadleśnictwie Wołów

Phytophthora and Pythium species (Oomycota) are known to be serious pathogens of forest trees. Little is known, however, about their presence in Polish oak forests and their role in the oak decline, especially in the flooded areas. The aim of this study was (1) to detect and compare populations of microorganisms from Oomycota and fungi in roots and soil of healthy and declining pedunculate 30−126 years old oak stands, which had been flooded by the Odra River for three months in 1997 and one month in 2010, (2) to demonstrate the relationship between different chemical factors of soil and the occurrence of microorganisms, and (3) to assess the contribution of Oomycota to oak decline. Study was carried out in Wołów Forest District (south−western Poland). Microorganisms were isolated from fine (1−5 mm in diameter) roots and non−rhizosphere soil collected from 0−50 cm horizon. Isolation procedure from roots included surface sterilization and plating the root segments on the nutrient agar. An oak leaf baiting method was used for isolation of Oomycota from soil. Identification of microorganisms was based on morphology and sequencing of the ITS1/2 rDNA. Oomycota was represented by: Globisporangium, Phytophthora and Pythium and fungi mostly by: Aspergillus, Chaetosphaeria, Cylindrocarpon, Mortierella, Mucor, Penicillium, Trichoderma and Umbelopsis. Globisporangium attrantheridium (syn. Pythium attrantheridium) occurred locally and was found in roots of only one flooded oak. This is the first record of this species on oak and in Poland. G. intermedium, P. gibbosa/P. gregata, P. plurivora and Pythium sp. were found in soil of flooded and non−flooded (control) oak stands. The organisms occurred in podzolized brown soils, brown alluvial soils and gley soils that had most nitrogen (21−60 mg/kg), various amounts of calcium (61.1−347.6 mg/100g) and moderate acidity (pH=3.85−4.2). There was often a significant association between exposure to flood and the health status of oak trees assessed by the scale of defoliation. Oomycota seemed to be only moderately associated with increased tree defoliation as a symptom of oak decline.