Susceptibility of Small-Diameter Norway Spruce Understory Stumps to Heterobasidion Spore Infection

Tālis Gaitnieks,Astra Zaļuma,Kristīne Kenigsvalde,Indulis Brauners,Tuula Piri,Dārta Kļaviņa

doi:10.3390/f10060521

Tālis Gaitnieks, Astra Zaļuma + Show 4 more

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https://doi.org/10.3390/f10060521

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Abstract

Heterobasidion spp. cause economically important losses in conifer forests in the Northern Hemisphere, especially in Norway spruce stands. Freshly cut stumps are the main route for Heterobasidion spp. infection. Even small stumps of spruce seedlings are known to be susceptible to spore infection, however, very little is currently known about the susceptibility of small stumps of understory spruce to Heterobasidion spore infection. To determine the frequency of spore infections among stumps of understory trees, we analyzed 756 Norway spruce stumps in eight sample plots in eastern Latvia. Understory trees 35–68 years of age, with a stump diameter of 2–10 cm, were felled 33–48 weeks before sampling. In total, 514 (68%) of the spruce stumps were infected by Heterobasidion spores. The infection frequency among the plots varied from 56% to 86%. Both infection frequency and stump surface area occupied by Heterobasidion positively correlated with stump diameter, but neither correlated with the time span elapsed between felling and sampling. Colonization of trees by a competitor fungus, Phlebiopsis gigantea (Fr.) Jülich, was observed in 30 (4%) of investigated stumps, but did not have any effect on the frequency of Heterobasidion infections. Our data show that Norway spruce stumps can be highly susceptible to Heterobasidion spore infection. In order to control airborne Heterobasidion infections, stump treatment should be considered during the sporulation period of Heterobasidion spp.

Highlights

Heterobasidion root rot causes considerable silvicultural and economical losses in coniferous forests of the Northern Hemisphere
In all eight sample plots, stumps of understory spruce trees were infected by Heterobasidion spores
The stump infection rates in the present and previously mentioned studies are not fully comparable due to possible differences in environmental conditions, as well as in the spore load of both Heterobasidion and competitive fungi at the time of cutting, our study shows that stumps of suppressed spruce trees might be extremely prone to Heterobasidion infection

Summary

Introduction

Heterobasidion root rot causes considerable silvicultural and economical losses in coniferous forests of the Northern Hemisphere. High damage is caused in Norway spruce (Picea abies (L.) Karst.) stands, because Heterobasidion mycelium can extend for 8–11 m up the stem, decaying the most valuable wood assortments [4,5]. In addition to the reduction of timber yield and quality, Heterobasidion root rot is a major cause of growth reduction in Norway spruce stands [6,7,8]. In Latvia, Norway spruce covers 17% of the total forest area [11] and ca. In 40–120-year-old spruce stands, decay volumes comprise 19.7–91.8 m3 ha−1 , which corresponds to 6%–16% of the total stand volumes [12]. The most serious damage occurs in fertile soils, mainly on abandoned agricultural lands, where 52% of spruces are decayed on average [13]

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