Chromosomal Regions Associated with Peach Tree Short Life Syndrome

The "disease syndrome" Peach Tree Short Life (PTSL) involves environmental (temperature, soil conditions, pruning) and biotic (ring nematode, and secondary pathogen) factors. PTSL is characterized by premature tree death, resulting in substantial economic losses. In previous work, the rootstock Guardian (R) 'BY520-9' was selected for its tolerance of PTSL. To investigate the genetic and molecular basis for this tolerance, Nemaguard, a PTSL susceptible rootstock, and Guardian (R) selection 3-17-7 were crossed. The F-1 plants were self-pollinated to create segregating F-2 populations. The trees were rated annually from 2004 through 2008 for their response to PTSL. 176 microsatellite/Simple Sequence Repeat (SSR) markers, each mapping to a specific chromosomal location on the Prunus reference nuclear genome, were used to screen the two parents and F-1-11. Only 53 markers showed polymorphism among the parents, and were heterozygous in F1-11. These SSRs were then screened on the F-2-11 population (N=100). Segregation data for PTSL-response and SSR marker inheritance were complied and subjected to Analysis of Variance to determine differences in Genotypic Means (GMs). Nine SSR loci correlate with a response to PTSL and are distributed on four linkage groups (e. g., Linkage Group-1, LG-2, LG-4 and LG-6). Four of the nine loci (EPDCU5100, pacita27, UDA008 and UDA029) appear to account for most of the variance in the trait based upon their large GMs (>2.5). After creating a molecular map from the segregation data, analysis identified a quantitative locus (QTL) on LG2 that was important in all five years of the study. In addition, this chromosomal interval contained three of the four SSR marker loci that accounted for the majority of the variation. These results identify regions of the peach genome where genes controlling PTSL susceptibility and tolerance reside, thus helping to define the genetic basis for response to PTSL as a complex but tractable trait.