Effects of Pine Bark Extracts and Pine Bark Powder on Fungal Pathogens, Soil Enzyme Activity, and Microbial Populations1

Pine bark extracts and pine bark powders were evaluated in vitro and in greenhouse experiments for effect on fungal growth and infectivity, soil enzyme activity and soil microbial populations. Agar media were formulated using powdered fresh or composted pine bark and pine bark extracts prepared by refluxing pine bar powder with acid, neutral, and alkaline solutions Growth of Rhizoctonia solani, Sclerotium rolfsii, Fusarium oxysporum f. sp. vasinfectum, Phytophthora parasitica, Alternaria solani, and Sclerotinia sclerotiorum was reduced on agar containing either fresh or composted pine bark powder, whereas growth of the nonparasitic fungus Penicillium citrinum was enhanced. Growth of parasitic fungi on media containing pine bark extracts was varied. However, extracts prepared using alkaline solutions reduced the growth of more of the fungi tested and to a greater extent than extracts prepared with neutral or acid solutions. In greenhouse experiments, emergence of lentil (Lens culinaris) was significantly increased by the addition of fresh or composted pine bark powder to soil inoculated with either R. solani or S. rolfsii. Increases in soil trehalase activity were correlated with increases in total populations of indigenous fungi and specifically with species of Penicillium and Paecilomyces. Pine bark powder decreased fungal growth in vitro and reduced disease incidence in greenhouse experiments while altering soil fungal populations. Analysis of soil trehalase activity provides a simplified means for monitoring soil fungal populations leading to a more complete understanding of soil microbial ecology.