Comparative Efficacy of State-of-the-Art and New Biological Stump Treatments in Forests Infested by the Native and the Alien Invasive Heterobasidion Species Present in Europe.

Martina Pellicciaro,Silvia Ongaro,Paolo Gonthier,Guglielmo Lione

doi:10.3390/pathogens10101272

Abstract

The Heterobasidion annosum species complex includes major fungal pathogens of conifers worldwide. State-of-the-art preventative stump treatments with urea or with commercial formulations of the fungal biological control agent Phlebiopsis gigantea (i.e., Rotstop®) may become no longer available or are not approved for use in many areas of Europe infested by the three native Heterobasidion species and by the North American invasive H. irregulare, making the development of new treatments timely. The efficacy of Proradix® (based on Pseudomonas protegens strain DSMZ 13134), the cell-free filtrate (CFF) of the same bacterium, a strain of P. gigantea (MUT 6212) collected in the invasion area of H. irregulare in Italy, Rotstop®, and urea was comparatively investigated on a total of 542 stumps of Abies alba, Picea abies, Pinus pinea, and P. sylvestris in forest stands infested by the host-associated Heterobasidion species. Additionally, 139 logs of P. pinea were also treated. Results support the good performances of Rotstop®, and especially of urea against the native Heterobasidion species on stumps of their preferential hosts and, for the first time, towards the invasive North American H. irregulare on stumps of P. pinea. In some experiments, the effectiveness of Proradix® and of the strain of P. gigantea was weak, whereas the CFF of P. protegens strain DSMZ 13134 performed as a valid alternative to urea and Rotstop®. The mechanism of action of this treatment hinges on antibiosis; therefore, further improvements could be possible by identifying the active molecules and/or by optimizing their production. Generally, the performance of the tested treatments is not correlated with the stump size.

Highlights

Heterobasidion annosum (Fr.) Bref. sensu lato (s.l.) is a complex of species comprising fungal plant pathogens causing root rots, butt rots and wood decay in coniferous forests of the Northern Hemisphere [1,2]
The aims of this study were to compare the efficacy of Proradix®, the cell-free filtrate (CFF) of P. protegens strain DSMZ 13134, the strain of P. gigantea MUT 6212 collected on P. pinea in the H. irregulare invasion area in central Italy and screened for its biocontrol potential [40], the biological control agent Rotstop®, and the chemical control agent urea as stump treatments in forests of A. alba, P. abies, P. pinea, and P. sylvestris each infested by their own host-associated Heterobasidion species (i.e., H. abietinum, H. parviporum, H. irregulare, H. annosum s.s., respectively)
Stumps of A. alba treated and sampled were as follows: 24 control stumps sprayed with sterile water, stumps treated with Proradix®, with CFF, 23 with P. gigantea MUT 6212, 22 with Rotstop® and 21 with urea

Summary

Introduction

Heterobasidion annosum (Fr.) Bref. sensu lato (s.l.) is a complex of species comprising fungal plant pathogens causing root rots, butt rots and wood decay in coniferous forests of the Northern Hemisphere [1,2]. Annual economic losses caused by H. annosum s.l. in Europe were estimated at EUR 790 million [1] and occur in association with the decrease in wood production and the reduction in wood quality, which are reported as directly correlated to the incidence of the pathogens [3]. Heterobasidion spp. infect their hosts through basidiospores or mycelium. Once the root system of the stump is colonized, the mycelium of Heterobasidion spp. spreads to the neighboring heathy trees by means of root contacts and grafts [2]. This second method of spreading is acknowledged as secondary infection. Stumps created during thinnings and cuttings play a crucial role as starters for new infection foci

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