Development of DNA markers for breeding walnut from quantitative trait loci associated with phenology characters

Walnut is one of the most important nut crops belonging to the Juglans genus and showing a monoic flower structure. Cultivar breeding programs in walnut takes long time due to its long juvenile period. Molecular studies are very important to shorten this long breeding period. Genetic linkage maps and quantitative trait locus (QTL) analysis are important tools in the development of markers associated with important phenotypic characters. These molecular markers can increase breeding efficiency by shortening the breeding period in walnut. Bud burst and leafing time are among the important selection criteria in walnut breeding. In order not to be damaged by the late spring frost, walnut varieties with late bud burst and leafing time are preferred. In this study, we aimed to determine QTL regions associated with bud burst and leafing time in walnut by using previously constructed high-density genetic maps of Chandler and Kaplan-86 together with four-year phenotypic data, and to develop DNA markers that can be used in breeding from the determined QTL regions.QTL analyzes of 11 other important phenological traits for walnut were also performed this study. As a result, in the "Chandler × Kaplan-86" populationa total of 43 and 33 QTLs for 12 traits were determined in Chandler and Kaplan-86 linkage maps, respectively. No QTL was detected related to dichogamy. Major QTL related to bud burst and leafing time was detected on LG4 in both Chandler and Kaplan-86 maps.For bud burst time, the highest LOD score in Chandler and Kaplan-86 maps was 47.9 and 40.2, respectively, and the highest phenotypic variation was 78.7% and 76.1%, respectively. For leafing time, the highest LOD score in Chandler and Kaplan-86 maps was 38.9 and 31.5, respectively, and the highest phenotypic variation was 68.8% and 63.5%, respectively. Three SSR and DArT primers developed from the closest regions of major QTLs were tested for validation in 160 walnut varieties and genotypes. As a result, it is determined that thesethree SSR and DArT markers had no effect on bud burstand leafing time. Key words: Walnut, J. regia, QTL, phenology