Abstract
BackgroundThe vigour and precocity of trees highly influences their efficiency in commercial production. In apple, dwarfing rootstocks allow high-density plantings while their precocious flowering enables earlier fruit production. Currently, there is a lack of pear (Pyrus communis L.) rootstocks that are equivalent to the high yielding apple rootstock ‘M9’. For the efficient breeding of new Pyrus rootstocks it is crucial to understand the genetic determinants of vigour control and precocity. In this study we used quantitative trait loci (QTLs) analysis to identify genetic loci associated with the desired traits, using a segregating population of 405 F1 P. communis seedlings from a cross between ‘Old Home’ and ‘Louise Bonne de Jersey’ (OHxLBJ). The seedlings were grafted as rootstocks with ‘Doyenne du Comice’ scions and comprehensively phenotyped over four growing seasons for traits related to tree architecture and flowering, in order to describe the growth of the scions.ResultsA high density single nucleotide polymorphism (SNP)-based genetic map comprising 597 polymorphic pear and 113 apple markers enabled the detection of QTLs influencing expression of scion vigour and precocity located on linkage groups (LG)5 and LG6 of ‘Old Home’. The LG5 QTL maps to a position that is syntenic to the apple ‘Malling 9’ (‘M9’) Dw1 locus at the upper end of LG5. An allele of a simple sequence repeat (SSR) associated with apple Dw1 segregated with dwarfing and precocity in pear and was identified in other pear germplasm accessions. The orthology of the vigour-controlling LG5 QTL between apple and pear raises the possibility that the dwarfing locus Dw1 arose before the divergence of apple and pear, and might therefore be present in other Rosaceae species.ConclusionWe report the first QTLs associated with vigour control and flowering traits in pear rootstocks. Orthologous loci were found to control scion growth and precocity in apple and pear rootstocks. The application of our results may assist in the breeding process of a pear rootstock that confers both vigour control and precocity to the grafted scion cultivar.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0620-4) contains supplementary material, which is available to authorized users.
Highlights
The vigour and precocity of trees highly influences their efficiency in commercial production
We present the results for a Quantitative trait locus (QTL) analysis of these traits using a high density genetic map based on single nucleotide polymorphism (SNP) markers anchored to the ‘Bartlett’ v1.0 European pear genome assembly [27]
We found that the proximal marker flanking the Dwarfing locus 1 (Dw1) locus in apple segregates for dwarfing and precocity in pear, and that the 116 bp pear allele linked to low vigour in the rootstock mapping population is carried by the dwarfing pear rootstock ‘Pyrodwarf’
Summary
The vigour and precocity of trees highly influences their efficiency in commercial production. For the efficient breeding of new Pyrus rootstocks it is crucial to understand the genetic determinants of vigour control and precocity. Commercial apple (Malus x domestica Borkh.) production relies on the use of dwarfing rootstocks to reduce scion vigour and promote early flowering in young trees [1, 2]. To develop a series of pear rootstocks, it is necessary first to develop an understanding of the mechanisms involved in vigour control and precocity in pear and the genetic determinants of the desired traits. Lliso et al [5] found significantly higher concentrations of carbohydrates in fruit and roots of trees on dwarfing rootstocks than on more vigorous ones, suggesting that dwarfing rootstocks promote heavier flowering and crop load and thereby reduce vegetative growth. Foster et al [11] observed that key flowering genes from the Flowering Time (FT) locus family were up-regulated in dwarfing rootstocks, which would promote flowering and reduce shoot extension growth
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