Pinus monticola pathogenesis-related gene PmPR10-2 alleles as defense candidates for stem quantitative disease resistance against white pine blister rust (Cronartium ribicola)

White pine blister rust, caused by the invasive fungus Cronartium ribicola, has been responsible for extremely high mortality of native western white pine (Pinus monticola) and other five-needle pines in natural stands throughout western North America. The presence of this non-native fungus has also led to greatly restricted use of western white pine for reforestation. A few families of defense proteins have been found as functional candidates involved in tree resistance to rust infection. Here we report genetic variation of a gene encoding a family 10 pathogenesis-related (PR) protein (PmPR10-2) in open-pollinated seed families with different levels of stem quantitative disease resistance (QDR). Six novel alleles and five common genotypes were identified inside the PmPR10-2 locus: these genetic variations included 33 single nucleotide polymorphisms (SNPs) throughout the gene regions and copy variation of a rare octanucleotide simple sequence repeat (SSR), 5′-AATTATTT-3′, in the gene intron. PmPR10-2 exhibited a moderate level (average r2 = 0.42) of linkage disequilibrium. Two-thirds of the identified SNPs and the SSR marker were significantly associated with stem QDR levels. The PmPR10-2 genotype (H3:H3) exhibited the highest level of stem QDR (P < 0.01). Cost-effective and co-dominant SSR markers were developed and used for genotyping the PmPR10-2 locus using simple PCR, providing a potential molecular tool for accelerating screening efforts of white pine resistance against C. ribicola.