Morphological variation among Persian walnut (Juglans regia) genotypes from central Iran

Fifty-eight mature Persian walnut (Juglans regia) seedlings growing at six sites in the mountainous regions of Taft, in central Iran, were evaluated to determine their morphological variation and to identify promising individuals. The traits investigated included phenological characteristics, such as budbreak and nut maturity time, and nut characteristics, such as nut and kernel weight, kernel ratio, and shell thickness. Yield efficiency and fruit-bearing habit were also investigated. The average fruit characteristics: nut weight, kernel weight, kernel ratio, and shell thickness were in the range of 6.0-15.2 g, 2.6-9.1 g, 38.4-79.6%, and 0.4-1.4 mm, respectively. The promising genotypes were AA 33 , AA 35 , AA 115 , AA 116 , and BA 150 . These trees had larger nuts (AA 116 ), heavier nuts (15.2 g, AA 33 ), heavier kernels (9.1 g, AA 33 and AA 115 ), higher kernel ratio (79.6%, AA 35 ), and later budbreak (BA 150 ). A few significant correlations were found between nut weight and nut length (0.57), nut width (0.68), nut thickness (0.67), kernel weight (0.75), and shell thickness (0.32); whereas a negative correlation was detected between shell thickness and kernel ratio (-0.34). The data correlation matrix was subjected to principal component analysis, a technique that reduced the dimensionality of the data set and revealed the dominating variables. Cluster analysis of the selected genotypes detected three cluster groups. However, no significant relationship was found between morphological diversity and site geography. The promising selected genotypes identified in central Iran will be further exploited by walnut breeding programmes for their tree and nut characteristics.