Development of a core collection in Iranian walnut (Juglans regia L.) germplasm using the phenotypic diversity

• Published in: Scientia horticulturae Vol. 249; pp. 439 - 448
• Main Authors: Mahmoodi, Razieh, Dadpour, Mohammad Reza, Hassani, Darab, Zeinalabedini, Mehrshad, Vendramin, Elisa, Micali, Sabrina, Nahandi, Fariborz Zaare
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.04.2019
• Subjects: Core collection; Diversity; Germplasm; Persian walnut; Phenotypic characteristics; Phenotypic characteristics; Persian walnut; Germplasm; Core collection; Diversity
• ISSN: 0304-4238; 1879-1018
• DOI: 10.1016/j.scienta.2019.02.017

•In a Persian walnut collection with 104 accessions, evaluation of phenotypic diversity showed that among studied genotypes or cultivars there were 53 days of differences in leafing date (from March, 5 to April, 27). Regarding nut and kernel weight and kernel percentage, there were 8.7 g (from 6.60 to 15.33 g), and 5.5 g (2.67–8.21 g) of difference in kernel weight in nut weight respectively. Kernel percent showed a variation of 35 % (from 35.39 to 71.09%). Nut production efficiencies among genotypes and cultivars varied from 0.20 to 11.39 nuts per centimeter square of tree trunk cross sectional area, and from 0.27 to 93.17 nut per meter square of tree scaffold cross area.•Factor analysis showed that in 18 evaluated walnut traits, there were 6 factors explaining together around 80% of the total variance.•Evaluation of traits in walnut primary collection with 104 accessions using the Maximization strategy showed a core subset with 26% of genotypes/cultivars. In this evaluation the variance difference was 38.37%, the mean difference was 9.88%, the coincidence rate was 95.05% and the variable rate was 120.28%.•The difference between the mean of the core and the original collection was non-significant except for the start of pollen shedding and beginning of the pistillate flowers receptivity. In addition, the“Coverage” analysis accounting for the number of variables captured in the core set with respect to the primary collection, showed the complete coverage (100%) of the different phenotypic variables considered in this study. Persian walnut (Juglans regia L.) is a very important nut crop with increasingly attention in the world. It was among the fruit tree species that has been propagated sexually, up to some decades ago. So, there were no or limited cultivars and the breeding works are usually new. In order to release new cultivars, a walnut improvement program started in Iran in 1980s. There was established a walnut collection, with selection of some superior genotypes from the orchards together with some introductions. As, the comprehensive characterization of germplasm is necessary in the breeding programs, in this study a collection of 104 Persian walnut accessions has been evaluated especially in order to create a core or breeding collection with reduced number of accessions and keeping maximum variability. To carry out this work, 18 walnut important traits were evaluated during 2014 and 2015 in the walnut collection of Horticultural Science Research Institute, Karaj, Iran. A wide variation was observed for several important characteristics such as leafing date (from March, 5 to April, 27), nut weight (6.60–15.33 g), kernel weight (2.67–8.21 g), and kernel percentage (35.39–71.09%). Significant correlations were observed between traits. Factor analysis showed that the six major factors affecting traits were explaining 79.9% of the total variance. The analysis, using maximization strategy through a heuristic algorithm, determined a core collection consisted of 27 accessions with similar variability respect to primary collection (mean difference percentage = 9.88% and coincidence rate of range = 95.05%). The parameters showed that this core includes 100% coverage of the primary diversity. According to result the F-test revealed no-significant differences for all traits. In this paper, for the first time, a walnut core collection was established from a primary collection. Conservation of this core collection could be more economic and better manageable for breeding purposes.