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Association mapping of agro-morphological traits in European hazelnut (Corylus avellana)
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More than half of European hazelnut (Corylus avellana) production occurs in Turkey. Despite this dominance, the yield of Turkish cultivars has remained stagnant over the past 10years with Italian yield nearly double that in Turkey. This difference is due to Turkey's unique cultivation system; hazelnuts are grown in bushy clusters (ocak system), not as single trees. Current hazelnut breeding efforts are shifting toward the development of materials for single plant orchards which are much higher yielding; thus, there is a need to explore germplasm for relevant agro-morphological traits and to determine their genetic control. The objectives of this study were to examine data for 44 such traits in 390 hazelnut accessions: 16 cultivars, 232 landraces and 142 wild individuals from nine provinces in Turkey and to map the loci associated with these characteristics using simple sequence repeat markers. Comparison of cultivars, landraces and wild hazelnut accessions revealed the effects of domestication and selection on the crop and indicated that useful alleles for traits such as cropping and reduced alternate bearing may exist in the wild germplasm. A total of 145 quantitative trait loci (QTL) were detected with the largest proportions identified for involucre (26%) and inflorescence (14%) morphology. Several markers co-localized with more than one trait including markers for male catkin abundance which were shared with plant vigor and height. Similarly, markers for female flower abundance co-localized with suckering and alternate bearing. Such markers and their linked QTL should be studied in more detail as they might help breeders select for plant vigor, decreased suckering and increased flower production: traits which will be extremely useful for Turkey's transition to single plant orchards.