Table 1.

Overview of key terms used in tree defence systems

Term	Meaning and references
Biotroph	A specialized pathogenic fungus that feeds off living parenchyma without killing them and usually causes disease. Possesses appressoria or haustoria
Brown rot fungi	Decay fungi specialized in breaking down cellulose in plant secondary cells walls using specialized digestive enzymes, such as cellulase (Schwarze et al., 2000a)
Dynamic reaction zone	A migrating reaction zone that keeps pace with the advancing decay by developing into previously functional sapwood and preceded by drying wood. Typically found in conifers and some angiosperms (Shain, 1995; Barry et al., 2002; Baum and Schwarze, 2002)
Induced systemic resistance	A resistance mechanism in plants triggered by beneficial microbes, e.g. Trichoderma harzianum or Mycorrhiza spp. Priming of whole plant body is through activation of jasmonate and ethylene and by salicylic acid signalling pathways (Pieterse et al., 2014)
Jasmonic pathway	Leads to localized synthesis of jasmonic acid, an SM plant hormone essential for the immune response against necrotrophic pathogens (Pieterse et al., 2014)
Necrotroph	Pathogenic fungi that actively kill host cells as a source of nourishment
Pathogen	A pathogen is a disease-causing organism. A pathogen is interpreted here as the ability to kill or cause parenchyma death or pass reaction zone defences in sapwood. Pathogenicity ranges from low to high along a saprotroph–necrotroph gradient for decay fungi
Pattern-triggered immunity	An innate immune plant recognition system triggered by activating the plasma membrane in response to pathogenic fungi. Part of a two-tiered defence system alongside effector-triggered immunity (Jones and Dangl, 2006)
Phytoalexin	Secondary metabolites produced by parenchyma in response to a plant pathogen or saprotroph
Phytoanticipin	Pre-existing or constitutively produced SMs that interact and inhibit fungal colonization, e.g. in heartwood
Salicylic pathway	Leads to an accumulation of the phenolic SM salicylic acid around the fungal infection or wound site in response to effector-triggered immunity (Betsuyaku et al., 2018)
Saprotroph	A decay fungus that solely lives on dead tissue, especially regarding heart rot decay. Has low pathogenicity (e.g. Fistulina hepatica; Schwarze et al., 2000c)
Soft rot fungi	Similar to a brown rot, these fungi selectively degrade lignin, but the fungal hyphae grow in the cell wall and follow the direction of the microfibrils (Schwarze et al., 2000b)
Static reaction zone	A non-migrating reaction zone formed between sound and discoloured wood in response to fungi or any desiccation-inducing threat. Typically found in angiosperms (Shain, 1995)
Systemic induced resistance	Infection by a pathogen which results in an induced or greater resistance to further challenges by the same pathogen (Bonello et al., 2001)
Vessel-associated cells	Parenchyma in direct association with the vessels that have specialized functions compared with vessel-distant cells (Morris et al., 2018b)
White rot fungi	Decay fungi specialized in breaking down lignin using specialized digestive enzymes, e.g. laccase. A simultaneous white rot can degrade cellulose and lignin at equal rates, whereas a selective delignification white rot primarily involves lignin digestion (Schwarze et al., 2000a)