This study was conducted in order to evaluate and compare the morphological traits of species leaflet, genotypes and inter-species hybrids of walnut tree in the Research Center of Kamal-Shahr, Karaj, Iran, Horticultural Research station, Seed and Plant Improvement Institute. Morphological characteristics are one of the first and most widely used markers that have always been considered by botanists in the past. In this regard, morphological traits of leaf have a special place in the classification of plants. The importance of morphological characteristics is such an extent that the study of them can be helpful to process genetic diversity in plants. Using these markers, species and even clones within a species can be distinguished from one another.
Evaluation of traits from following genotypes was performed with sampling in the summer from the leaves that were grown fully: eight genotypes of black walnut (N1, N2, N3, N4, N5, N6, N7, N8), seven cultivars / genotypes of Iranian walnut (Seer Damavand, Jamal, Chandler, Hartley, Pedro, Ronde de Montignac, B21 and K72), five genotypes of inter-specific hybrids (J. hindsii × J. nigra) and four genotypes of inter-specific hybrids (J. hindsii × J. regia) and a genotype of J. hindsii species. In total, 14 traits were evaluated including 7 quantitative traits (length and width of leaves (a and b), leaf width (e), leaflet length (f), petiole length (c), number and leaf area) and 7 qualitative traits (shape of the leaflet, leaf edge, leaf and petiole color, time of opening leaf bud, having wool, time of falling leaf and main petiole durability).
The results indicated that there was much morphological diversity among above species and hybrids. Statistical results showed that this species can be distinguished with selected traits.
The highest leaf area was belonged to B21 genotype of Iranian walnut species with 336.3 cm2 and the lowest leaf area was measured for N8 genotype of black walnut with 76.2 cm2. The average of quantitative traits for leaf samples showed that Iranian walnut cultivars had the maximum mean of leaf length and width and black walnut had the minimum length and width of leaf. The mean of maximum width and length of leaflet was observed in Iranian walnut and the lowest leaflet width was observed in paradox (J. hindsii x J. regia) inter-specific hybrid. The minimum of leaflet length were measured in black walnut. Among the evaluated species, the minimum and maximum number of leaflets was achieved in Iranian walnut and J. hindsii species, respectively. Genotypes were studied and grouped using cluster analysis and based on quantitative and qualitative characteristics of leaves. The genotypes were separated into three distinct clusters. The first cluster includes: six different genotypes of Black Walnut, J. hindsii species and inter-specific hybrids of Royal and paradox, a second cluster includes the cultivar of Iranian walnut and third cluster includes (B21) genotypes of Iranian walnuts.