Quantifying the Impacts of Systemic Acquired Resistance to Pitch Canker on Monterey Pine Growth Rate and Hyperspectral Reflectance

Abstract

Pitch canker, caused by Fusarium circinatum, is a disease affecting Monterey pine (Pinus radiata) and many other pine species throughout the world. The impact of pitch canker on Pinus radiata may be limited by systemic acquired resistance (SAR), a phenomenon that elevates resistance to a pathogen after initial challenge by that pathogen or another microorganism. Allocation of resources to defense, as a consequence of SAR, is presumed to reduce resources available to support growth and reproduction, but specific fitness consequences associated with SAR in P. radiata have not been measured. To quantify impacts of SAR on growth rate, a 2ˆ2 factorial experiment was established in which trees were either primed for SAR or unprimed, with half the trees in each of those two groups being inoculated with the pitch canker pathogen and the other half not inoculated. Priming for SAR was accomplished by inoculating one branch with F. circinatum and removing inoculated branches prior to subsequent challenge inoculations (= disease treatments). Disease treatments included three inoculations that were removed for measurement of lesion length, and three additional inoculations that remained on the tree as a representation of persistent disease. Control trees were mock inoculated with water. Main effects of priming and disease did not result in significant effects on growth rate. Based on hyperspectral canopy reflectance data, diseased trees were associated with higher difference vegetation index values and biomass. The absence of a negative impact on growth rate associated with SAR suggests that induction of resistance may have utility as a tool for management of pitch canker in plantations.

Exposure to a pine pathogen enhances growth and disease resistance inPinus radiataseedlings

“…We found elevated host resistance to occur both when seedlings were grown in infested sand and when exposure to inoculum resulted from emergence through infested leaf litter, as would occur under natural conditions. Likewise, no negative effect on growth was detectable over a 1-year period when 2.5-year-old trees were induced for resistance by inoculation with F. circinatum (Reynolds et al, 2016). Enhanced defence under low nutrient conditions has been shown to reduce growth in many systems (Bostock, 2005;Walters & Heil, 2007), but no such cost of induced resistance (asymptomatic root infections) was apparent in our study.…”

“…However, previous studies indicate that the association may be benign under some circumstances, without any detectable effects on host fitness (Reynolds, Gordon, & McRoberts, 2016;Swett et al, 2016). Given the parasitic nature of the association, the fungus may be expected to reduce growth.…”

Priming of inducible defenses protects Norway spruce against tree‐killing bark beetles

“…Acquired resistance to fungal infection was first demonstrated in the 1990s in Norway spruce, where wounding and fungal inoculation made trees more resistant to a subsequent massive fungal infection (Christiansen et al, 1999). Increased tree resistance following conditioning with fungal infection, mechanical wounding, or stem application of the phytophormone methyl jasmonate (MeJA) has since been described in several other conifer species, including Scots pine (Pinus sylvestris), loblolly pine (Pinus taeda), ponderosa pine (Pinus ponderosa), and Monterey pine (Pinus radiata; Franceschi, Krekling, & Christiansen, 2002;Heijari, Nerg, Kainulainen, Vuorinen, & Holopainen, 2008;Martin et al, 2002;Reynolds, Gordon, & McRoberts, 2016;Swett & Gordon, 2017). Application of MeJA has also been shown to increase resistance to bark beetle attack 1 year after application in Norway spruce (Erbilgin, Krokene, Christiansen, & Gershenzon, 2006).…”

Environmentally friendly methods for controlling pine pitch canker

“…Induction of resistance has been observed in young plantations and natural forests of P. radiata and is known to be a key process in the interaction between pines and F. circinatum (Gordon et al, 2011;Reynolds et al, 2016). Repeated infection of the same tree resulted in progressively shorter lesions (Table 1), implying an effect of prior infection on susceptibility.…”

“…An additional practical issue of IR in pines relates to the identification and selection of genotypes able to effectively enhance their resistance after induction (Gordon & Reynolds, 2017). The absence of a negative impact on growth rate associated with IR (Reynolds et al, 2016) suggests that IR may have utility as a tool for the management of PPC in plantations.…”