Histology of Diplodia pinea in diseased and latently infected Pinus nigra shoots

Abstract

Diplodia tip blight is a serious disease of >30 conifer species worldwide. Symptoms are particularly severe on non-native, two-needled Pinus species, and typically include stunted, necrotic needles and shoots and a general decline of the tree. Latent Diplodia pinea infections occur in current-year shoots of some symptomless pines, and in some apparently healthy current-year shoots of diseased pines. Latent infections also occur in symptomless terminal buds. A histological approach was used to investigate the nature of latent infections in shoot stems and terminal buds of landscape Pinus nigra. Fungal colonization was compared in healthy, diseased and latently infected tissues. A nested-PCR technique that is specific for D. pinea was used to differentiate latently infected tissues from uninfected ones. Latent D. pinea infections were localized in the outer stem cortex, usually in the vicinity of needle scales at leaf axes. In contrast, pathogenic D. pinea infections were characterized by fungal colonization throughout the shoot stem tissues, even very early in symptom development. The presence of necrophylatic periderms in two of the latently infected samples suggests that host defences play a role in the production and maintenance of latent stem infections. Latent infections of terminal buds appeared to originate from the distal bud scales of axillary buds in the terminal bud cluster, and not from the subtending shoot. Fungal tissues were never observed inside asymptomatic, PCRnegative shoots.

High-Resolution Melting Analysis: a new molecular approach for the early detection of Diplodia pinea in Austrian pine

“…This is consistent with other studies in which the more aggressive D. pinea was found to be more common than the less aggressive D. scrobiculata (Palmer 1991;Smith & Stanosz 2006 (Flowers et al 2006).…”

Red pine harvest debris as a potential source of inoculum of Diplodia shoot blight pathogens

“…Smith et al, 1996;Stanosz et al, 1997;Flowers et al, 2006). detected Diplodia species from over half the asymptomatic shoots collected from standing mature red pines in northern Wisconsin.…”

“…Sphaeropsis sapinea) is an important fungal pathogen that causes Diplodia shoot blight, canker, and collar rot. Damage has been reported on at least 35 pine species and many other conifers growing in nurseries, ornamental settings, plantations, and natural stands (Chou, 1987;Flowers et al, 2006;Johnson et al, 1985;Palmer et al, 1988). Another closely related species, Diplodia scrobiculata J. de Wet, B.…”

“…Slippers & M.J. Wingfield, recently has been differentiated from D. pinea (De Wet et al, 2003), but details of its life cycle are believed to be similar. In addition to causing disease, these fungi can persist on or in hosts without causing symptoms (Smith et al, 1996;Stanosz et al, 1997;Flowers et al, 2006). During its asexual reproductive phase, D. pinea produces pycnidia and sporulates on or in dead host organs such as cones, needles, and stems (e.g.…”

Diverse sources of infection and cryptic recombination revealed in South African Diplodia pinea populations

“…Consistent with our results, Dakin et al (2010) reported that all eight isolates of Neofusicoccum australe from asymptomatic Agonis flexuosa were in different vegetative compatibility groups (VCGs), while 26 isolates from a cankered tree included eleven VCG's. This would suggest that wounding is involved in the infection process because it provides an easy entry for D. pinea (Flowers et al 2006). An alternative explanation for the lower diversity of the fungus after hail damage or in cankers could be competition and selection among the endophytic strains.…”