Importance of local and long-distanceHeterobasidion irregulareaerial basidiospore dispersal for future infection centres in thinned red pine plantations in Quebec

Abstract

Heterobasidion irregulare is a basidiomyceteous forest pathogenic fungus which causes a root disease capable of killing large trees. Infection probability is proportional to the density of aerial basidiospores infecting freshly cut stumps. The purpose of this study was to quantify for the first time H. irregulare aerial basidiospore density in southern Québec and to determine the importance of a local basidiospore load from a nearby infested plantation. Spore counts from automated rotary arm spore collectors were assayed using a ribosomal ITS TaqMan real-time PCR detection assay. Cumulative basidiospore deposits on a 30-cm stump were estimated to be highest in the infected plantation with 2.37 basidiospores per stump, with decreasing count of 0.52 basidiospores at a 500-m distance and 0.46 basidiospores at a 1.5-km distance. At 5 km from the infected plantation, the number of basidiospores deposited on a stump was 0.22, a value similar to those at distances of 25 and 140 km. Since a single Heterobasidion basidiospore may travel as far as 500 km, the level detected at 5 km may represent the background basidiospore load resulting from long-distance dispersal, and basidiospores from a nearby infected plantation are unlikely to be an added risk of infection to plantations located more than 5 km away. Long distance aerial basidiospore dispersal will remain for now the most important constant source of infectious H. irregulare in Québec. Despite the very low risk level per stump in this study, the large number of trees thinned annually warrants that stump treatment with Rotstop® C is still the best strategy, especially in valuable plantations.Key words: basidiomycetes, basidiospore deposition, biological control, forest pathology, ribosomal ITS, root rot, Rotstop RÉSUMÉHeterobasidion irregulare est un champignon pathogène forestier capable de tuer des arbres de grand diamètre et le risque d'infection est proportionnel à la quantité de basidiospores aériennes qui se déposeront sur les souches des pins rouges fraîchement coupées. Le but de cette étude était de quantifier pour la première fois la densité de basidiospores aériennes dans le sud du Québec et déterminer l'importance de basidiospores locales provenant d'une plantation infectée située à proximité. Le comptage des basidiospores capturées par un collecteur à bras rotatif s' est fait à l'aide de PCR en temps réel avec des sondes TaqMan visant l'ITS de l' ADN ribosomique. Le compte cumulatif de basidiospores sur une souche de 30 cm était maximal, soit 2,37 basidiospores par souche, dans la plantation infectée, suivi de 0,52 basidiospores à 500 m de distance et de 0,46 basidiospores à 1,5 km. À 5 km de la plantation infectée, le nombre cumulatif de basidiospores était de 0,22, une valeur semblable à celles se trouvant à 25 et 140 km. Puisque les basidiospores de Heterobasidion sont reconnues pour voyager sur des distances allant jusqu'à 500 km, le nombre cumulatif de basidiospores à 5 km peut être considéré comme le niveau basal résultant de la propagation ...

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

“…During their 8-week study, spore totals ranged from 0 to 3.48 m −2 h −1 compared to 0 to 1.26 m −2 h −1 for spores collected in Minnesota. The number of basidiospores collected at an infected plantation we studied in Wisconsin was higher than that of [24] with a highest weekly value of 3.48 m −2 h −1 compared to 149.33 m −2 h −1 in our study. This high number we detected was due to the placement of collectors in a stand with many basidiocarps nearby.…”

“…Spore trapping methods followed those used to trap H. irregulare basidiospores in Quebec [24,25]. Two automated rotary arm spore collectors (Aerobiology Research Laboratories, Ottawa, ONT, Canada) were programmed to spin 4 min every 60 min, with rods (1.5 mm × 1.5 mm × 3 cm) placed in the rotary arms that were coated with a 7% silicone-hexane solution.…”

“…The majority of previous spore deposition studies used the wood-disk exposure method, which measure differently than those that utilize rotary arm spore collectors. Wood disks measure the amount of infectious basidiospores per m 2 compared to rotary arm spore collectors that measure the number of basidiospores per m 3 [24]. The aerial basidiospore density would likely be more than the number of basidiospores landing on a stump.…”

Volumetric Spore Traps Are a Viable Alternative Tool for Estimating Heterobasidion Infection Risk

“…Still, DR levels were generally low compared to those reported in the literature from similar European ecosystems [19,39]. DRs of Heterobasidion irregulare spores measured in the autumn in infected Pinus resinosa plantations in Québec [40] and Wisconsin [41] were within the range of values registered in the same season in conifer stands in present work. The above studies from North America used rotary arm spore collectors coupled with differing qPCR platforms and master mixes, which indicates that results obtained by different approaches can be comparable.…”