The genetic determinants of vigour control and precocity by pear (Pyrus communis L.) rootstocks
The growth habits of fruit trees have a significant influence on their efficiency in commercial production. Small tree stature allows high-density plantings and therefore more efficient land use, while minimising the length of the trees’ juvenile period means the orchard becomes profitable sooner. Vigour control and precocity are therefore two of the most important traits in commercial pear production. Dwarfing rootstocks are used to reduce the size of the scion and enable precocious flowering in many perennial cultivars. Currently there is a lack of Pyrus rootstocks that are vigour-controlling and precocity-inducing. The development of such a rootstock is a major focus in pear rootstock breeding. Marker assisted selection (MAS) could help to shorten this time consuming and costly breeding process. The aim of this PhD project was to examine the genetic determinants of vigour control and early flowering conferred to a scion by Pyrus rootstocks. A segregating population of 421 F1 seedlings from a P. communis ‘Old Home’ x ‘Louise Bonne de Jersey’ (OHxLBJ) cross was grafted with clonal ‘Doyenne du Comice’ scions and used as the core experimental material for this project. High-density genetic maps were constructed for pear using two different high throughput genotyping tools, the Infinium® II 9K apple/pear SNP array and the genotyping-by-sequencing (GBS) approach. QTLs influencing expression of scion vigour and precocity were detected on linkage groups (LG)5 and LG6 of OH and LG6 of LBJ. The LG5 QTL was found in the same genomic region as the dwarfing (DW1) QTL identified in the ‘M9’ apple rootstock. The alignment of the QTL loci of apple and pear showed a high synteny between both loci and may help to identify candidate genes in both genera. The ease of vegetative propagation, a crucial trait for rootstock breeding, was assessed in rooting experiments and small effect QTLs were identified. These results will help to understand the genetic control of vegetative propagation in pear, and may assist in developing markers for MAS for this complex trait.
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