Location: National Clonal Germplasm Repository
Project Number: 2072-21000-049-05-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2017
End Date: Aug 31, 2018
1. Test the dwarfing ability of genotypes selected by R. Bell by double grafting. 2. Evaluate additional pear wild relative species for tree architecture traits associated with dwarfing rootstock potential. 3. Validate association of microsatellite marker identified for the Dw1 locus in apple, and recently associated with dwarfism in pear with dwarfism. 4. Detect associations between genotypes obtained with the 55K Pear SNP Axiom array and tree architectural traits and dwarfing potential.
Cuttings of pear clones identified in 2013-14 from the NCGR collection, plus additional selections with compact tree habit and wide branch angles will be grafted onto commercial pear seedling rootstocks. Rootstock selections already known to be either dwarfing or vigorous will be included as controls. Scion cultivars ‘Bartlett’ and ‘Bosc’ will be simultaneously grafted onto the interstem pieces. This “Interstem Bioassay’ will be tested for the ability to identify accessions with rootstock dwarfism potential. Grafted trees will be grown in pots for the first growing season. Data to be collected following the first year of growth will include shoot length, stem cross-sectional area, internode length in the middle of the stem, number and angle of lateral shoots. During the mid-growing season 2017 (July-August), additional data will be collected on tree architecture for the NCGR pear species collection, including trees previously identified by Bell as having dwarfing potential. Data to be collected will include mid-stem internode lengths, primary tree branch angles, and date that shoot elongation growth ceases. Genotypic data at the apple Dw1 homologous locus in pear will be obtained by using the SSR marker Hi01c04. The data will be evaluated for the presence of an allele, 116 bp, previously found to be associated with low vigor in scions and of another allele, 121 bp, associated with precocity in pear. The candidate accessions will be genotyped with the 55k Pear SNP Axiom array by Montanari. This SNP-based genotypic data and the tree architecture data collected by Postman will be used by Montanari to attempt detection of marker-trait associations, and shared with the pear curator to upload to GRIN.