High Seedling Mortality of Scots Pine Caused by Heterobasidion annosum s.s.

Tuula Piri,Heikki Nuorteva,Eeva J Vainio,Jarkko Hantula

doi:10.3390/f12091289

Abstract

This study provides new information on the infection biology and pathogenicity of an important root-rot fungus, Heterobasidion annosum sensu stricto (Fr.) Bref., through a detailed examination of the vegetative spread of clonal individuals and their capacity to produce fruiting bodies on young pine seedlings. The seedlings were planted in a clear-cutting area (c. 1.2 ha in size) after a pine generation that showed slight external symptoms of Heterobasidion root rot. The first dead seedlings were found five years after planting and during a nine-year monitoring period; nearly 600 seedlings were killed by H. annosum s.s. in 48 individual disease centers. Based on pairing tests of 482 isolates, 117 different H. annosum s.s. genotypes were identified. On average, 2.9 genotypes occurred in a single disease center. The extensive secondary spread of genotypes within root systems (up to 48 pine seedlings infected by the same genotype) resulted in annually expanding disease centers. In addition, more than half of the seedlings killed by H. annosum s.s. produced perennial fruiting bodies thus providing air-borne inoculum. The risk of spore infection should be taken into account in any type of cutting operation in young pine stands. Moreover, new control measures directed towards the secondary spread of H. annosum s.s. in pine regeneration are urgently needed in order to maintain the productivity of the pine forest on infested sites.

Highlights

Root and butt rot caused by Heterobasidion annosum (Fr.) Bref. sensu lato is one of the most serious diseases of coniferous forests in the Northern Hemisphere [1]
As a result of a visual evaluation of standing pines, c. 8% of generation 1 were classified as infected by H. annosum s.s
The results cannot be directly generalized to pine stands growing under different conditions with different management and disease history, our study showed that a mature pine stand may be severely infected by H. annosum s.s

Summary

Introduction

Root and butt rot caused by Heterobasidion annosum (Fr.) Bref. sensu lato is one of the most serious diseases of coniferous forests in the Northern Hemisphere [1]. Root and butt rot caused by Heterobasidion annosum (Fr.) Bref. Sensu lato is one of the most serious diseases of coniferous forests in the Northern Hemisphere [1]. In Europe, three Heterobasidion species with different host tree preferences are present: Heterobasidion parviporum Niemelä and Korhonen prefer Picea abies (L.) Karsten, H. abietinum Niemelä and Korhonen Abies species and H. annosum sensu stricto (Fr.) Bref. Pinus species but attack many other tree species as well [1,2]. In the Nordic countries, Heterobasidion root rot is caused by either H. annosum s.s. or H. parviporum. In Finland, H. parviporum is widely distributed throughout the country while H. annosum s.s. is more scattered and limited to the south [3].

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