The Screening of Persian Walnut Genotypes Based on the Quantitative and Qualitative Characters and the Investigation of Genetic Diversity among Promising Samples Using ISSR Marker

Persian walnut (Juglans regia L.) belongs to the family of Juglandaceae and is one of the most important nut crops in Iran. Until recently, all of the fruitful walnut trees grown in Iran are seedling originated and thus, they exhibit a significant variation, especially in nut and kernel characteristics. Therefore, the identification of the promising genotypes based on the phenotypic traits is essential in breeding programs. The aims of the current work were to evaluate 119 Persian walnut trees in different western regions of Iran based on nut and kernel characteristics, and then to detect genetic relationships among desirable genotype using ISSR marker.
  In this research, 119 Persian walnut genotypes collected from different parts of the west of Iran were evaluated based on nut characteristics. Based on the primary evaluation, 30 superior genotypes that had desirable characters in nut and kernel properties, such as nut and kernel weight, kernel percentage, kernel removal from the nut, kernel plumpness, and kernel filled were selected and then, the genetic variation among them was evaluated using 10 ISSR primers.
  The preliminary evaluation of 119 walnut genotypes illustrated that most of the evaluated genotypes showed high variability for the measured traits related to nut and kernel. Among the nut and kernel characters, the kernel shriveling showed the highest coefficient of variation (114.02%), while the lowest CV was related to the nut diameter (8.68%). Among walnut genotypes, both nut and kernel weight varied from 7-19.8 g and 2.8-9.20 g, respectively. The genetic relationship among 30 promising genotypes with ten ISSR primers indicated a considerable level of variability. All of the ISSR primers were polymorphic and produced a total of 79 alleles among the 30 genotypes, which 77 alleles were polymorphic. The size of the amplified fragments ranged from 200 bp to 1700 bp. The number of the observed alleles for each locus ranged from 3 (HB10) to 13 (UBC-807), with an average of 7.7 alleles per locus. Polymorphic index content (PIC) was observed to be highest (0.82) in the UBC-807 locus, while the HB10 locus had the lowest value (0.51) with an average of 0.75 among ISSR locus. The Jaccard’s genetic similarity coefficient ranged from 0.31 to 0.85 among the genotypes. The cluster analysis performed based on ISSR data using UPGMA, divided the genotypes into seven major groups.
  Finally, the results of this study showed that there was high variability among walnut genotypes in terms of quantitative and qualitative characteristics of the nut and the kernel. In this study, the average nut and kernel weight among walnut genotypes varied. The difference in nut and kernel properties of germplasm under the same geographical conditions may be the result of genotypic factors. The results indicated that some genotypes (16, 4, 24, 26, 11, and 17) had desirable traits in the nut and kernel. Moreover, the Persian walnut is of most important horticultural crops grown in Iran. Therefore, these genotypes can be propagated according to the vegetative methods and used for commercial cultivation or utilized for traditional breeding and advanced biotechnology studies to achieve superior progenies.