Survival of Heterobasidion irregulare on red pine discs in cold temperatures

Abstract

Disease foci of the conifer root and butt decay pathogen Heterobasidion irregulare are typically initiated following germination of spores deposited on freshly cut stumps, followed by expansion by tree to tree spread through root contacts and grafts. Although most abundant in autumn, inoculum of H. irregulare is also available during some cold winter periods in northern portions of the eastern United States. In both laboratory and field experiments, fresh stem discs of red pine (Pinus resinosa) were inoculated with H. irregulare conidia to test the null hypothesis that the pathogen would not survive prolonged exposure to cold temperatures experienced during winters in those regions. After exposure to cold for various periods of time, discs were incubated and then observed for presence of the Spiniger state of the pathogen. In each of two laboratory trials, the fungus survived on red pine discs incubated at ≤−20°C for 90 days. The field experiment was conducted during each of two winters at two infested red pine plantations. Inoculated discs were deployed periodically beginning in early winter and retrieved after various periods of time until spring. The Spiniger state of the pathogen was frequently observed on discs after laboratory incubation, even after field exposure of up to 6 months, during which temperatures ≤−25°C were sometimes recorded. Whether viable due to growth from inoculum initially placed on the discs, or natural inoculum deposited on discs exposed in the infested plantations, winter temperatures did not eliminate survival of the pathogen on this natural substrate. The potential for survival on stump surfaces during sub‐freezing temperatures during which application of stump protectants in water is impractical should be considered in evaluating the potential risk from H. irregulare to economically and environmentally valuable conifer forests of northcentral and northeastern North America.

Detecting Heterobasidion irregulare in Minnesota and Assessment of Indigenous Fungi on Pines

“…The most commonly isolated substrate was from stumps (76), followed by dead and dying trees (69), sporophores (33), and downed trees and slash (5). Additionally, the majority of samples were collected and isolated from red pine (140) followed by white pine (37), and then white spruce (6). White spruce was selected due to Heterobasidion being reportedly found on these species in Itasca State Park and also being reported as a host to H. irregulare in Wisconsin [15].…”

“…Currently, the known geographic range of H. irregulare in eastern North America is from eastern Texas through the southeastern United States and north to Wisconsin in the Great Lakes Region, New England, and Eastern Canada [6]. Heterobasidion irregulare is part of the species complex Heterobasidion annosum sensu lato (s.l).…”

Antagonistic interactions between native fungi of Minnesota and the root rot pathogen Heterobasidion irregulare

“…Tree species that are under the greatest threat in Minnesota are plantation grown red and white pine (Pinus strobus) (Minnesota Department of Natural Resources, 2021). The distribution of H. irregulare in eastern North America extends from western Texas through the southeastern United States, and north to Wisconsin, in the Great Lakes Region, New England and eastern Canada (Myers et al, 2018). It is also noted by Myers et al that the actual known distribution of H. irregulare is discontinuous and this disease has not been found in some of the northern portions of the United States and Canada in the vast area occupied by coniferous forests.…”

“…Tree species that are under the greatest threat in Minnesota are plantation grown red and white pine ( Pinus strobus ) (Minnesota Department of Natural Resources, 2021). The distribution of H. irregulare in eastern North America extends from western Texas through the southeastern United States, and north to Wisconsin, in the Great Lakes Region, New England and eastern Canada (Myers et al., 2018). It is also noted by Myers et al.…”