Resistance and tolerance in juvenile interior Douglas‐fir trees Pseudotsuga menziesii var. glauca artificially inoculated with Armillaria ostoyae

Abstract

Plants utilize two general strategies to cope with pathogen attack. They either limit or resist the pathogen (termed 'resistance') or they cope with the disease by surviving and growing (termed 'tolerance'). Both strategies tend to increase plant fitness; however, there are possible costs, trade-offs and interactions associated with each strategy. This study focused on five half-sib interior Douglas-fir families [Pseudotsuga menziesii var. glauca (Beissn.) Franco] that were putatively classified as either resistant or susceptible to Armillaria ostoyae in a previous greenhouse study of seedling families challenged with A. ostoyae. We compared their survival rates in the greenhouse study with results of juvenile trees from the same five families that were artificially inoculated in field conditions. Both resistance and tolerance appeared to be operating in the field test trees, and a possible trade-off between resistance and tolerance was detected. Significant differences were detected among the five families for stem radial growth following infection at the tree root collar. Compared with the putatively susceptible families, resistant families had smaller lesions and lower proportional root collar girdling. Tolerant families generally had larger lesions but demonstrated better growth when diseased than resistant families. One tolerant family that was a good survivor in the greenhouse survival study presented vertically shaped lesions that were large in area but had greatly reduced proportional root collar girdling. While a second family showed tolerant traits in the field study, its poor survival in the greenhouse study agreed with the large horizontally spreading lesions associated with high root collar girdling in the field study trees. Survival rankings of the five families in the greenhouse study mostly agreed with results from the field study based on the proportion of collar girdling among families. These host responses are discussed with respect to stability, quantity and quality of stands and products.

Resistance and tolerance of Douglas‐fir seedlings to artificial inoculation with the fungus Ophiostoma pseudotsugae

“…The resistance and tolerance rankings to O. pseudotsugae in the families we tested were not similar to the rankings of five of the same families inoculated with Armillaria root disease (Cruickshank & Jaquish, 2014); however, that was a small sample of families for comparison. Evidence from elsewhere suggests that plant resistance and tolerance rankings to multiple pests may not align completely (Leimu & Koricheva, 2006b) or that it is uncommon for families to be top performers in all traits.…”

“…In this study, family resistance came at no detectable cost to trees before induction, but there was a cost after inoculation with O. pseudotsugae that may last for some time. Cost of resistance to Armillaria root disease in five infected 22-year-old Douglas-fir families accumulated long after fungal infection (Cruickshank & Jaquish, 2014). For seedlings, the implication of defence costs described above might indicate that having some tolerance to damage would be preferable when height growth is critical.…”

An evolutionary ecology perspective to address forest pathology challenges of today and tomorrow

“…Breeding strategies combining both resistance and tolerance mechanisms therefore appear to be the most desirable (Walters et al 2012). This requires an accurate assessment of resistance and tolerance traits and their interactions (Simms and Triplett 1994), as investigated in the Douglas fir-Armillaria ostoyae pathosystem (Cruikshank and Jaquish 2014).…”

“…The idea that "nothing in forest pathology makes sense except in the light of evolution," paraphrasing Dobzhansky, could now seem obvious and not deserving of further development (Varki 2012). Many recent articles dealing with forest pathology indeed have an evolutionary background (e.g., Hansen and Goheen 2000;Pinon and Frey 2005;Kinloch et al 2008;Garbelotto et al 2010;Hayden et al 2011;Cruikshank and Jaquish 2014;Franceschini et al 2014). However, we contend that an evolutionary perspective is still not sufficiently emphasized and applied to the management of forest diseases.…”

Resistance and tolerance of Douglas‐fir seedlings to inoculation with the fungal root pathogen Coniferiporia sulphurascens

“…British Columbia initiated an Interior Douglas-fir tree breeding programme in 1982 with the view to producing improved and genetically diverse seeds for planting on productive forest land in south-central BC https:// www2.gov.bc.ca/gov/conte nt/indus try/fores try/manag ing-ourfores t-resou rces/tree-seed/fores t-genet ics/tree-breed ing-impro vemen t/inter ior-dougl as-fir. The reporting of resistance by interior Douglas-fir to Armillaria root disease (Cruickshank & Jaquish, 2014;Cruickshank et al, 2010) generated interest in the potential for also breeding this species for root disease resistance/tolerance, and possibly for resistance/tolerance to other biotic and abiotic stresses.…”