Histology of White Pine Blister Rust in Needles of Resistant and Susceptible Eastern White Pine

Abstract

White pine blister rust, Cronartium ribicola, has plagued the forests of North America for almost a century. Over past decades, eastern white pine (Pinus strobus) that appear to tolerate the disease have been selected and incorporated into breeding programs. Seeds from P. strobus with putative resistance were collected from Oconto River Seed Orchard, Nicolet National Forest, WI. Seedlings were grown for 5 months and artificially inoculated with basidiospores of C. ribicola in two replicated greenhouse experiments. Needles from infected seedlings were fixed, sectioned, and stained with a variety of histological reagents, and rate of mortality for the remaining seedlings was monitored. The most susceptible families suffered 50% mortality in approximately half the time of the more resistant families. Extensive inter- and intracellular hyphae were observed in needles from seedlings of susceptible families, whereas hyphal proliferation was restricted in needles of resistant seedlings. Needles from resistant families had pronounced responses to infection. Phenolics, observed with phloroglucinol-HCl staining, were deposited around infection sites where dense mycelial masses were present. Abnormal host cell growth and rapid cell death in the immediate area of infection were also observed in some eastern white pine families.

Genetic Resistance to Fusiform Rust in Southern Pines and White Pine Blister Rust in White Pines—A Contrasting Tale of Two Rust Pathosystems—Current Status and Future Prospects

“…A slightly higher frequency of complete resistance (Cr4 frequency varying from 0 to 0.139) has been found in limber pine in the portion of the range surveyed to date [12]. No complete resistance has been detected in whitebark pine families evaluated so far [21,39] or in eastern white pine although families, which exhibit HR-like mechanisms, which may contribute to complete resistance in this species, have been identified in eastern white pine [40,41]. Patton [42] originally selected a number of individual disease-free trees from high-hazard sites in the upper Midwest.…”

“…Once rust germ tubes invaded needle tissues through stomata, histochemical analysis revealed that C. ribicola induced a build-up of physical barriers by collapsed cells adjacent to infected sites and deposition of cell wall bound phenolic compounds within the needle [40,99], suggesting this defense reaction may prevent systemic rust spread in partial resistant eastern white pine families. At the molecular level, a few studies revealed several Pinus gene families involved in defense response against C. ribicola infection.…”

A review of Pinaceae resistance mechanisms against needle and shoot pathogens with a focus on the Dothistroma–Pinus interaction

“…These resistance 'markers' can still be used to screen for resistant individuals. Another similar method is to compare the chemical and morphological response of 'resistant' and 'susceptible' plants to inoculation with a given pathogen (Jurgens et al 2003;Luchi et al 2005;Jacobs et al 2009). Host tissue cultures have also been used to determine responses to pathogen recognition (Hotter 1997).…”

“…However, the action of phenolic compounds in defence has been studied in other host-pathogen systems. For example, in WPBR-resistant P. strobus needles inoculated with C. ribicola, phenol-containing vacuoles, that are present constitutively, fragment and release phenolic compounds into the cytoplasm; deposition of phenolic compounds occurs on the host cell wall, leading to encapsulation and death of the fungi (Boyer 1964;Boyer and Isaac 1964;Jurgens et al 2003;Jacobs et al 2009). Despite the finding by Wallis et al (2010) (Bahnweg et al 2000;Wallis et al 2008).…”

“…Furthermore, genomic mapping identified a single dominant allele associated with resistance against C. fusiforme in P. taeda (Fr1, Wilcox et al 1996). HR-like reactions have also been observed in the needles of WPBR-resistant individuals of Pinus armandii Franch and P. strobus; rapid host cell death which stops the progression of the pathogen was observed in the immediate area of infection (Hoff and McDonald 1975;Jurgens et al 2003;Jacobs et al 2009). …”