2018 ASHS Annual Conference

Peach Tree Short Life (PTSL) is a complex disease syndrome caused by different biotic, climatic, and edaphic factors. The PTSL disease etiology is associated with the presence of high population densities of ring nematode (Criconemoides xenoplax Raski syn. Mesocriconema xenoplax (Raski) Loof and de Grisse). The resulting injury and physiological response to nematode feeding increases susceptibility of peach trees to bacterial canker (Pseudomonas syringae pv. syringae van Hall) or cold injury, or an interaction of both. The genetic basis of tolerance/susceptibility to PTSL in peach is not well understood. Thus, four different F₂ families, derived from a cross between a PTSL susceptible rootstock Nemaguard and tolerant rootstock Guardian^®, were evaluated for PTSL tolerance in the field, and genotyped using Genotyping by Sequencing (GBS). A meta-analysis approach was used to refine QTL positions detected in family specific genetic linkage maps, and revealed a total of six metaQTLs that largely drive PTSL resistance, two on each linkage groups (LG)1, 4 and 6. All metaQTLs except PTSL.meta-1.2 showed significant effects on PTSL. Individuals heterozygous for PTSL.meta_1.1, with a haplotype originating from both Guardian^® and Nemaguard, exhibited the best phenotypic performance. Both metaQTLs on LG4 exhibited the best PTSL field performance when the haplotype derived from Guardian^® was in a homozygous state. Candidate gene analyses in the metaQTL genomic regions detected over 180 resistance genes, including genes associated with resistance to bacterial diseases. A denovo Guardian^® genome assembly revealed multiple duplications in resistance genes, most of them in PTSL.meta_4.1 and PTSL.meta_4.2 regions, suggesting a disease resistance hot spots on chromosome 4 of the peach genome. MetaQTLs identified in this work suggested that genomic regions associated with PTSL response in peach are associated with response to bacterial canker as a main cause of death after nematode infection weakens a peach tree.