A Major Gene for Resistance to White Pine Blister Rust in Western White Pine from the Western Cascade Range

Abstract

A dominant gene for resistance to white pine blister was indicated by Mendelian segregation in full-sib families of western white pine parent trees selected for phenotypic resistance in six heavily infected stands in the Western Cascades of Oregon and Washington. Seedlings were artificially inoculated three times between 1959 and 1964 and observed for development of stem infection. Segregation at this locus (Cr2) occurred in only two of the six parent populations sampled: one a natural stand, Champion Mine (CM), and the other a plantation of unknown seed origin. At CM, reduced penetrance of this gene was expressed by altered Mendelian ratios (mostly less-than-expected resistant phenotypes) in families of specific combinations of certain parents, indicating the presence of modifier genes with effects that ranged from mild to almost complete suppression of Cr2. Between 1968 and 1994, an apparent shift in virulence at CM caused all of the resistant selections to become infected and die. Recent inoculations of many of the same or related families from these parents, made from grafted ramets in a seed orchard, showed that Cr2 conditions a classical hypersensitive reaction (HR) in needle tissues, the primary infection courts. In the latter tests, seedlings were challenged with wild-type and four other sources of inoculum at and near CM that were also suspected of having wider virulence than wild type. No seedlings segregating for HR that were inoculated with wild type subsequently developed stem symptoms, but the other inocula induced both susceptible and HR needle spots on Cr2- genotypes, and many of these seedlings did develop stem infections. This implied that spore genotypes with specific virulence to Cr2 are carried in these inocula.

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

“…Seedling progeny of field selections and advanced-generation selections have been tested. For the eight species of white pines in western North America, very young seedlings (usually two to four months old) are inoculated and screened for complete resistance, typically due to a hypersensitive response (HR) in the needles [10,12,32,33]. Older two-year old seedlings are usually used to evaluate a fuller suite of resistance related traits [8,31].…”

“…Complete resistance from resistance (R) genes has been documented in four of the nine white pine species native to the US or Canada: sugar pine, western white pine, southwestern white pine, limber pine [10,12,32,33,37]. This resistance appears to restrict the fungus to the needles and has been described as a hypersensitive-like response [11,32,33,38] (Figure 6).…”

Comparative mapping in Pinus: sugar pine (Pinus lambertiana Dougl.) and loblolly pine (Pinus taeda L.)

“…Additionally, linkage analysis has been reported in western white pine (Pinus monticola Dougl. ex D. Don) Ekramoddoullah 2007, 2008; Liu et al 2006) and in sugar pine (Devey et al 1995;Harkins et al 1998) in which the MGR (named Cr1 for sugar pine and Cr2 for western white pine in Kinloch et al 1999) was mapped to a single linkage group using RAPD markers.…”

“…In an attempt to infer the map position of Cr2 in relation to Cr1, primers from two SCARs linked to Cr2 in western white pine (Kinloch et al 1999;Liu and Ekramoddoullah 2008) were used to amplify sugar pine genomic DNA in the three mapping populations (Table 1). Only scar420, yielded PCR product and was subsequently resequenced in sugar pine to discover SNPs for genotyping and linkage analysis.…”

Adaptive response of Pinus monticola driven by positive selection upon resistance gene analogs (RGAs) of the TIR-NBS-LRR subfamily

“…P. monticola species exhibits genetic variation in disease resistance to C. ribicola involving mainly a dominant disease resistance gene (Cr2 - Kinloch et al 1999, Liu et al 2006. Disease resistance and maintenance of genetic diversity in production populations are very important aspects for P. monticola breeding (Dangl et al 2013).…”