Seasonal Patterns of Spore Deposition of Heterobasidion Species in Four Forests of the Western Alps

Abstract

Patterns of spore deposition by Heterobasidion species were studied between the spring of 1998 and December 2000 in four forests in the western Alps using woody traps. The maximum spore deposition rate (DR) ranged from 169 to 1,550 spores m(-2) h(-1). Although spores were captured from February to October at most sites, inoculum concentration consistently peaked in the late summer or early fall. In one of the four study sites, similar patterns of DR were recorded in 2 years of sampling. A significant correlation (r = 0.654, P = 0.001) was found between DR and the average minimum air temperature in the 4 weeks before sampling. Approximately 1,200 spores were isolated and identified at the species level by polymerase chain reaction-based methods. Single-spore isolates were consistently clampless, indicating the sampled airspora was almost exclusively composed of haploid basidiospores. No significant variations of basidiospore frequencies were detected for either H. abietinum or H. annosum among sampling periods. However, the frequency of H. parviporum spores was always significantly higher in the summer. These findings suggest different patterns of sporulation among Heterobasidion species.

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

“…Edmonds and Driver (1974) also used an automated rotary arm spore collector and found deposition rates between 3 to 70 basidiospore m -2 h -1 in an infected Washington State forest, values that can be compared to our highest weekly values of 3.1 m -2 h -1 in the infected plantation and 0.4 m -2 h -1 1.5 km away in the fourth week of October. Similarly, Gonthier et al (2005) found deposit rates on fresh wood disks ranged from 169 to 15 550 m -2 h -1 in Italian alpine forests where disease incidence ranged from 30% to 50%. Punter (1970) measurements on fresh wood disks in Ontario found values between 0.1-2.1 basidiospores m -2 h -1 .…”

“…Rotary arm collectors give the number of basidiospores per m 3 , whereas fresh wood disks indicate the actual number of viable infectious basidiospores per m 2 . The number of infections on a stump is lower than the actual number of basidiospores landing on the stump for various reasons (Gonthier et al 2005), including environmental factors, virulence of fungal isolates, competition with other fungi, and the ability of the host to fence off the colo- 1 Values in brackets indicate spore deposition per m -2 h -1 for the 7-day period. 2 n/a: not available.…”

“…Rishbeth (1959) reported that aerial basidiospore viability varied between 1% and 5%. It is not known how many basidiospores are needed to actually initiate an infection on a fresh stump but extrapolation of Gonthier et al (2005) data suggests that a deposition rate of 5 basidiospores m -2 h -1 is needed to initiate infection on stumps. Applied to our experimental design, this would represent approximately 356 basidiospores per 30-cm stump over six weeks.…”

“…Eastern Canada is still at the beginning of a possible regional epidemic and the probability of new infections would be described as proportional to the density of aerial basidiospores (Stambaugh et al 1962, Gonthier et al 2005. In Europe, the probability of infection on a freshly cut stump can be as high as 100% in many countries (Vollbrecht et al 1995).…”

Integrating mechanistic disturbance models and stand dynamics of Norway spruce

“…The vulnerability of the forests to root rot is increasing in warmer climate due to longer growing season and increasing metabolic rate of the fungi leading to increased sporulation and mycelial growth (e.g. Gonthier et al, 2005;La Porta et al, 2008;Müller et al, 2014). The effect of strong winds on forests is expected to increase due to the shorter frozen soil period that currently improve tree anchorage during the winter months (Blennow et al, 2010;Kellomäki et al, 2010;Gregow et al, 2011).…”