Variability of seedling vigour in Persian walnut as influenced by the vigour and bearing habit of the mother tree

SummaryObservations on dwarf and precocious (early maturing) seedlings of Persian walnut (Juglans regia L.) in nurseries, and the consistency of their growth under orchard conditions, encouraged us to study the genetic nature and variability of morphological traits related to seedling vigour. In the present study, two trials were conducted using open-pollinated offspring of six and 18 half-sib families in 2006 and in 2007, respectively. Significant variation was found both within and between families in terms of seedling height, stem diameter, the number of nodes, and internode length in both 45-d-old and 1-year-old seedlings. Moderate to high heritability (0.39 - 0.88) was estimated by between-family variance, implying that the majority of phenotypic variations were under additive genetic control. Seedling height was positively correlated with seedling diameter (r = 0.87), the number of nodes (r = 0.86), and the length of the internodes (r = 0.89), indicating that measuring only seedling height was adequate to identify families that produce dwarf seedlings. The shortest seedlings were generally observed in the offspring of low-vigour and cluster-bearing families. The relevance of early maturing seedlings in developing genetically dwarf walnut rootstocks and/or cultivars is discussed. In conclusion, we suggest a recurrent selection programme for the selection of dwarf and easy-to-root genotypes, in order to exploit their advantages in a high-density orchard system.