Interaction between Brenneria goodwinii and Phytophthora species on young Quercus robur seedlings

Abstract The decline of oak stands is a globally recognised phenomenon. Among the causing factors, the most frequently mentioned are pathogens of the genus Phytophthora and bacteria associated with the phenomenon of acute oak dieback. The aim of the study was to conduct a pathogenicity trials on three-year-old English oak seedlings using isolates of Brenneria goodwinii and two different Phytophthora spp. ( P. quercina and P. plurivora ) isolated from declining oaks in south-west Poland in the area of the so-called Krotoszyn Plateau. The analyses carried out showed that there were no statistically significant differences in the development of the bacteria on the trunks of the inoculated trees and the length of the lesions was 0.93 cm on average. The analyses of roots inoculated with pathogens of the genus Phytophthora showed statistically significant differences in all six parameters analysed. In the multiple comparison test, significant differences were found in the control plants, which always differed significantly from the variant in which Phytophthora was inoculated. The highest root loss was observed in the treatment inoculated with both B. goodwinii and P. quercina , and the length of both fine and total roots was about twice as short compared to the ungrafted control. The first symptoms related to the decline of the plant condition (discoloration and wilting of the leaves) were also observed after treatment with B. goodwinii + P. quercina . These results suggest that the combination of both factors contributes to greater damage, but further studies are needed to clarify the interaction between B. goodwinii and Phytophthora spp. in oak dieback.