Association analysis of some physiological traits in Persian walnut under drought stress by SSR markers

Walnut has a high economic value because of the good quality of wood and fruits. So this species has been harvested since many years ago till today and has been introduced as a protected species. The performance of Juglans regia increases in wet years, but reduces in dry years, hence paying attention to physiological and morphological parameters in order to identify the genomic regions related to drought resistant is important for breeding programs in walnut. In this study, genetic diversity by SSR markers has been evaluated. Also, the association of used primers with physiological and morphological traits were analyzed before and after drought stress. 10 SSR primer pairs generated 53 alleles in 62 walnut seedlings. All locies showed significant difference (p≤0.01) from the Hardy-Weinberg. Dendrogram of the Neighbour-Joining method showed that 62 walnut seedlings divided to four main groups. Analyses of population structure by Structure 2.3.1 software identified two sub populations (k=2). Based on association mapping analysis, by using MLM (mixed liner model) method, transpiration, conductance and photosynthesis have been controlled by WGA9 and WGA69 locies in normal condition. In stress condition WGA1 loci showed relationship with CO₂ concentration that was covered %75 of variations of this trait. The results of this study can be used in breeding programs of Juglans regia to identify drought resistant varieties.