Abstract
The growing area of European hazelnut (Corylus avellana L.) is increasing, as well as the number of producing countries, and there is a pressing need for new improved cultivars. Hazelnut conventional breeding process is slow, due to the length of juvenile phase and the high heterozygosity level. The development of genetic linkage maps and the identification of molecular markers tightly linked to QTL (quantitative trait loci) of agronomic interest are essential tools for speeding up the selection of seedlings carrying desired traits through marker-assisted selection. The objectives of this study were to enrich a previous linkage map and confirm QTL related to time of leaf budburst, using an F1 population obtained by crossing Tonda Gentile delle Langhe with Merveille de Bollwiller. Genotyping-by-Sequencing was used to identify a total of 9,999 single nucleotide polymorphism markers. Well saturated linkage maps were constructed for each parent using the double pseudo-testcross mapping strategy. A reciprocal translocation was detected in Tonda Gentile delle Langhe between two non-homologous chromosomes. Applying a bioinformatic approach, we were able to disentangle ‘pseudo-linkage’ between markers, removing markers around the translocation breakpoints and obtain a linear order of the markers for the two chromosomes arms, for each linkage group involved in the translocation. Twenty-nine QTL for time of leaf budburst were identified, including a stably expressed region on LG_02 of the Tonda Gentile delle Langhe map. The stability of these QTL and their coding sequence content indicates promise for the identification of specific chromosomal regions carrying key genes involved in leaf budburst.
Highlights
Corylus avellana L. is the major species of interest for alimentary use within the Betulaceae family
The purpose of our study was: (i) to develop SNP markers, discovered by a GBS approach, to saturate the genetic simple sequence repeat (SSR)-based map constructed by Beltramo et al (2016) [29], (ii) to obtain linkage maps using a bioinformatic approach to disentangle the two linkage groups of Tonda Gentile delle Langhe that had been merged into a single large ‘pseudo-linkage’ group, due to the occurrence of a reciprocal translocation, (iii) to confirm QTL associated with the time of leaf budburst, described in Beltramo et al (2016) [29], and (iv) to detect candidate genes involved in regulation of the time of leaf budburst
Tonda Gentile delle Langhe (TGdL) has an earlier phenology than Merveille de Bollwiller (MB); the TGdL tree is less vigorous and more susceptible to big bud mite (Phytoptus avellanae) than MB, and the two cultivars differ for nut traits
Summary
Corylus avellana L. is the major species of interest for alimentary use within the Betulaceae family. The worldwide production of in-shell hazelnuts is estimated to be 835,000t (average 2012–2016). The growing area has increased from 607,500 ha in 2010 to 661,500 ha in 2016 (+8.9%), [1] due to a worldwide growth in demand, as the health benefits of nut consumption. SNP mapping and QTL analysis in Corylus avellana L. is increasingly recognized [2] and the marketing of processed products has enlarged, with most of the production used by the confectionary industry. The world hazelnut consumption is estimated to be about 390,000 t of shelled nuts (average 2011–2015) [3]. Turkey and Italy remain the major producing countries (80% of the world crop), hazelnut cultivation has spread in recent years to new growing areas including the southern hemisphere
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