Variability of the Moroccan sweet chestnut (Castanea sativa Mill.): Contribution of the morphological parameters and qualitative descriptors of the nut

The areas occupied by the common chestnut tree, Castanea sativa Mill. are continuously declining on an international scale. In Morocco, the chestnut trees are present in a restricted geographical area in the North and remains relatively unknown in the rest of the kingdom. This study represents the first contribution to the characterization and the evaluation of phenotypic similarities among Moroccan populations of Castanea sativa Mill. through univariate and multivariate statistical analysis of quantitative parameters and qualitative descriptors of fruits. The analysis was conducted on 13,455 fruits from 299 trees distributed across 31 populations from three regions. Ten qualitative descriptors were evaluated: nut shape (NSh), nut size (NSz), area of pubescence on upper part (AP), area of hilum (AH), shape of border line of hilum and pericarp (BSh), color of skin (CSk), glossiness (Gl), kernel color (CKr), coat adherence to kernel (CoA), and kernel inner-cavity (KC). In addition, the number of fruits/cupule (N/B), the number of fruits/kilo (N/K), and the average weight of fruits (W) were measured along with 11 quantitative parameters: nut length (NL), nut width (NW), nut thickness (NT), hilum length (HL), hilum width (HW), NL/NW, NT/NL, NT/NW, NW/HL, HW/NT, and HW/HL. The results of statistical analysis conducted on the 24 quantitative and qualitative parameters studied (ANOVA and SNK mean comparison test) demonstrated a very highly significant intra and inter-population variability for all the studied parameters. The correlation matrix analysis of the 12 quantitative parameters reveals a strong correlation between the fruit and hilum measurements, specifically NL, NW, NT, HW, and HL. Principal Component Analysis (PCA) and UPGMA analyses have shown the structuring of the 31 populations subdivided into two groups with subgroups, indicating significant diversity. The overall results highlighted a high genotypic variability of Moroccan populations of the chestnut trees and can be used to develop programs that aim to preserve the existing genetic variability of the chestnut tree and establish an in-situ collection of genetic resources in a geographically restricted area in the North of Morocco.