Efficacy of various Hypholoma spp. and Phlebiopsis gigantea as biocontrol agents against root rotting fungi Armillaria ostoyae
Master of Science
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Conifer plantations are thinned to maximise production of high-quality timber for lumber, fire wood, and utility poles. However, thinning increases susceptibility to pathogens such as Armillaria ostoyae, a native basidiomycete species that causes root rot. Armillaria root rot is detrimental to the forestry industry as it is responsible for substantial revenue loss due to tree mortality in both establishing and mature stands. Thus, finding an effective means to inhibit or reduce its impacts and spread is critical for the industry. Past studies have suggested that biocontrol treatments based on competing basidiomycete species (i.e., Hypholoma spp. and Phlebiopsis gigantea) show promise. The objectives of my study were to: (1) determine the ability of several species and strains of Hypholoma spp. and Phlebiopsis gigantea to function as biocontrol agents against two Armillaria ostoyae strains by examining their in-vitro interactions during competition trials, and (2) examine the ability of H. fasciculare to survive and grow during the winter months at different soil depths in a number of Simcoe County, Ontario forests to determine its potential as a biocontrol treatment for Armillaria root rot in northeastern temperate forest regions. Several strains of Hypholoma fasciculare, H. sublateritium, H. capnoides, and one strain of P. gigantea were grown in both solo (absence of competition) and paired (competing with one of two strains of A. ostoyae - high virulence and low virulence) conditions to examine impacts of competition on radial growth. The solo and pairings were grown and monitored on 2 % malt agar and pine wood infusion medium at 15oC. Radial growth was measured and compared between solo and paired conditions, and macroscopic and microscopic interactions were qualitatively assessed. Hypholoma fasciculare strain Pinnel B was identified as a potential candidate to develop as a biocontrol agent against Armillaria root rot. Radial growth was the highest from the H. fasciculare strain Pinnel B when paired with either of the A. ostoyae strains. Characterisation of the interactions at macroscopic and microscopic levels indicated that it was most effective at inhibiting A. ostoyae growth. Soil temperatures and snow depth were monitored from November 4, 2017 to May 13, 2018 at thinned and non-thinned red pine (Pinus resinosa) plantations located in Simcoe County, Ontario, Canada. Pine blocks inoculated with H. fasciculare were buried in pine plantations from February 1, 2018 to May 13, 2018 at 30 and 100 cm depths to examine how winter soil temperatures, soil depth, and snow presence impacted growth. Soil temperatures at the 30 cm depth were consistently colder than at 100 cm (F1,6 = 63.46, p < 0.001). Hypholoma fasciculare continued to grow over the winter months (F1,36 = 50.41, p < 0.001). Soil depth did not impact growth rate (F1,18 = 1.87, p = 0.188). Mean growth rates were 0.25 ± 0.11 and 0.31 ± 0.10 mm per day at 30 and 100 cm depths, respectively. While snow depths were significantly lower in non-thinned plantations, this had little impact on soil temperatures. This study will aid in the development of a H. fasciculare biocontrol treatment against Armillaria root rot given H. fasciculare’s ability to continue to grow underground throughout the winter months, a period during which Armillaria ostoyae has a reduced growing rate.