Pathogenicity and Virulence of Root-Inhabiting Ophiostomatoid Fungi on Pinus Species of the Southeastern United States

Abstract

Root- inhabiting ophiostomatoid fungi cause root disease in conifer hosts around the world. A group of ophiostomatoid fungi in the genus Grosmannia Goid. and their Leptographium Lagerb. & Melin anamorphs have been recently associated with declining loblolly (Pinus taeda L.) and longleaf (P. palustris Mill.) pine in the southeastern United States. This dissertation establishes the potential for ophiostomatoid fungal species to cause disease in healthy southern pine. In addition, virulence differences, among the primary ophiostomatoid fungi, were investigated. Six inoculation tests were conducted exploring the relationship root-inhabiting ophiostomatoid fungi have with southern Pinus species. Qualitative and quantitative measurements of the lesion reaction were used to assess the pathogenicity to host species and virulence among fungal species. In young pine hosts, Grosmannia huntii (R.C. Rob. Jeffr.) Zipfel, Z.W. de Beer & M.J. Wingf., Leptographium procerum (Kendrick) M.J. Wingfield, L. terebrantis S.J. Barras & T.J. Perry and L. serpens (Goidanich) Siemaszko caused dark lesions surrounding the point of inoculation. Grosmannia huntii caused the largest average lesion in loblolly and slash (P. elliottii Engelm.) pine. Longleaf pine seedlings and young longleaf pine trees appear to be more resistant to infection and damage, compared to other southern pine species. All ophiostomatoid fungi caused damage in large, mature tree roots following inoculations. Common observations included a darkened, pitch-filled lesion, often accompanied by a severe primary resin response eight weeks following inoculation. Grosmannia huntii caused the largest lesions and root damage. Leptographium serpens was the second most virulent pathogen tested, while L. terebrantis and L. procerum caused less damage. Each root-inhabiting ophiostomatoid fungus is capable of causing local disease symptomlogy and is pathogenic to the southeastern Pinus species tested. Grosmannia huntii and L. serpens are most virulent among the fungi and have the greatest potential for root damage following inoculation.