Occurrence and pathogenicity of Corinectria spp. - an emerging canker disease of Abies sibirica in Central Siberia

Abstract

During recent years, a new disease of Siberian fir (A. sibirica) emerged in Central Siberia, exhibiting symptoms of stem/branch deformation, cambium necrosis, and dieback of branches and twigs, the causal agent remaining unknown. The aim was to identify agent of the disease and to investigate its pathogenicity to A. sibirica and Norway spruce (Picea abies). Symptomatic tissues of fir were subjected to pure culture isolation of anticipated pathogen(s). Obtained isolates were subjected to molecular identification, phylogenetic analyses, and pathogenicity tests with A. sibirica saplings, and seeds and seedlings of A. sibirica and P. abies. The study demonstrated that, (i) most commonly isolated fungus from canker wounds of A. sibirica exhibited Acremonium-like anamorphs; (ii) phylogeny demonstrated that investigated fungi belong to genus Corinectria, but are genetically well separated from other worldwide known Corinectria spp.; (iii) one species of isolated fungi has the capacity to cause the disease and kill A. sibirica saplings and seedlings, but also seedlings of P. abies. Guidelines for future research were defined in order to generate needed information on species description, its origin and ecology, and estimation of potential risks upon the eventual invasion of the pathogen to new geographic areas, in particular of Europe.

Figure 1

Map of Eurasia showing distribution range of Picea abies (dark yellow), Abies sibirica (green), and in common for both tree species (light yellow). Spread of the disease during 2006–2017 is shown in purple. The map was produced using Google Earth Pro v. 7.3.2.5776 available at www.google.com/earth/.

Figure 2

Typical symptoms and signs of investigated fungus (presumably Corinectria spp.) on approx. 5-10 mm diameter branch of Abies sibirica (A,B); red fungal fruitbodies (C) (approx. 1 mm in diameter); colony of the fungal strain N1 (NfP5.7) on PDA (D), carrot-agar (E) and MEA (F).

Figure 3

Scanning electron microscopy of conidiophores and microconidia (magnification x 650–3000 times) of the Acremonium – like anamorph fungal strain N1 (NfP5.7).

Figure 4

Phylogeny of several Nectriaceae taxa showing the Bayesian Inference best tree inferred from four genes (ACT, BTUB, ITS & TEF1, but not all sequences were available for all taxa). Support values are indicated at the nodes (BI posterior probabilities/ML bootstrap). Outgroup taxa is Thelonectria discophora. The results of the BI and ML analyses showed a strong support for the clade that includes the Siberian isolates, which are clearly separated from the other Corinectria spp. Siberian isolates were subdivided into two clades; three isolates that clustered together were denoted by X and a single isolate – by Y. The strain of C. tsugae is a type strain.

Figure 5

Extent of necrosis in cambial zone beyond inoculation wounds after the removal of an inoculation chip. Right bottom picture shows control. Diameter at wounding/inoculation point approx. 10 mm.

Figure 6

Seeds of Picea abies after 14 days, a-priori soaked in cultural filtrate, and placed to germinate in sterile 9 cm Petri plates with moist filter paper. A picture on the right shows control.