Exploration of morphological diversity to select naturally occurring promising walnut (Juglans regia L.) genotypes from the North-Western Himalayan region

A comprehensive evaluation of the morphological variation of naturally occurring Persian walnut (Juglans regia L.) in the North-Western Himalayan region of Indian Himalayas was carried out during 2021–2023. In the present investigation, 60 walnut genotypes from 12 distinct sites were analyzed for quantitative and qualitative (UPOV-TG/125/6) traits of tree, leaf, and nut to determine the diversity and select promising walnut genotypes. The results showed considerable morphological variation among the genotypes, where tree height (Th), circumference at breast height (Cbh), crown length (Cl), branching height (Bh), nut weight (Nwt), nut length (Nl), nut thickness (Nt), and total nut yield (Tny) varied significantly from 8.50 to 23.00 m, 90.00 to 370.00 cm, 4.00 to 12.00 m, 3.00 to 16.00 m, 6.60 to 37.30 g, 25.51 to 36.19 mm, 23.64 to 39.60 mm, and 32.00 to 85.00 kg, respectively. Among tree traits, Th exhibits a significant positive correlation with Cbh, Bh, Cl, number of branches (Nb), crown width, and Tny, and among nut traits, Nwt has a positively significant correlation with Nl, nut width (Nw), and Nt. The results of the principal component analysis indicated that characteristics such as Th, Bh, Nw, Nl, and Nwt contributed to a significant proportion of the observed phenotypic variation and reduced the examined traits to four main principal components alone, which accounted for 71.22 per cent of the overall variance. The genotypes were grouped into four distinct groups by subjecting them to cluster analysis. The genotypes DML-I, DML-II, GSN-I, DKD-I, CHK-III, and CHN-V were identified as superior/promising on the basis of mean data, multivariate analysis (PCA) and selection index involving valuable traits with regard to wood and nut traits. Further investigation of these genotypes using the new genomic breeding approaches is highly desirable considering their beneficial role in walnut breeding.