Synthesis and New Observations on Needle Pathogens of Larch in Northern Finland

Risto Jalkanen

doi:10.3390/f7010025

Abstract

Needle pathogens of larch (Larix spp.) in the Nordic countries are under-studied. Their incidence in Finland tends to be low and local, and this may be a function of enemy release, since species of larch were introduced to the region. Here, the ecology and incidence of larch needle pathogens and the abiotic factors that also affect larch in northern Finland are reviewed. Field observations and related laboratory analyses during the past 35 years have mainly been obtained near the Kivalo Research Area within the Arctic Circle, Finnish Lapland. The relatively recent introduction of Hypodermella laricis is a primary focus. This pathogen is not only new to Nordic countries, but can cause severe outbreaks, defoliation and crown-thinning in the canopies of all ages of most planted larch species worldwide. Symptoms of H. laricis clearly differ from those of Mycosphaerella laricina; the latter has affected Larix sibirica at high latitudes for decades. The effects of Meria laricis, Lophodermium laricinum, various rust fungi, and wind and frost are also discussed.

Highlights

Native larch (Larix spp.) grows largely in cool zones of the Northern hemisphere
The first record of H. laricis in northern Europe was in 2007, when larch needle blight broke out in a 60-year-old European larch stand in Kivalo Research Area [7]. It spread to most stands of the Kivalo area, most of which consisted of Siberian larch (Figure 1); Dahurian larch became infected, but tamarack has remained healthy, at least to date
Rovaniemi, 2 June 2009; (b) Salix pentandra trees or bushes can be detected when heavily infected by Melampsora laricis-pentandrae, Tervola, 5 August 2005; (c) A shoot of Alnus incana heavily infected by Melampsora laricis-pentandrae, Tervola, 5 August 2005; (c) A shoot of Alnus incana infected by Melampsoridium hiratsukanum in Kivalo Research Forest, Rovaniemi, 2 September 2013

Summary

Introduction

Native larch (Larix spp.) grows largely in cool zones of the Northern hemisphere. Its environments are mainly mixed or pure boreal forests, where it often forms the northern or alpine conifer tree line. About 10 different larch species of this highly hybridizing genus have been recognized [1] None of these species is native to Finland, larch is known to have grown during the more continental climate of the Eemian interglacial period about 130,000–115,000 years ago in the territory of current. Larix is commonly considered to be a tolerant genus against pests, diseases and abiotic factors, especially in Nordic environments, where larch has a short history as an introduced genus and, a rather restricted co-evolution with pests and pathogens. A needle-inhabiting ascomycete, Hypodermella laricis Tub., which is new to the whole of Fennoscandia, was recorded in northern Finland [7] Hartig) Miq., has occurred for decades in northern Finland, this presented a good opportunity to provide an update on the situation concerning fungal pathogens and common abiotic factors among larch needles in northern Finland

Experimental Section

Results and Discussion

Other Needle Cast Fungi

Abundant

Wind and Frost

Conclusions