Volume 42(5). Published June, 01, 2017 www.jnsciences.org E-ISSN 2286-5314 Hamdi et al. (2017) / Journal of new sciences, Agriculture and Biotechnology, 42(5), 2306-2317 2306 Assessment of the genetic diversity of some local squash (Cucurbita maxima Duchesne) populations revealed by agro- morphological and chemical traits K. HAMDI 1 , J. BEN-AMOR 1 , K. MOKRANI 1 , N. MEZGHANNI 2 , N. TARCHOUN 1 * 1 Laboratory of Vegetable crops/ High Agronomic Institute of Chott Mariem, Sousse, Tunisia 2 National Genes Bank *Corresponding author: nejitarchoun@yahoo.fr Abstract – Tunisia is one of the most important diversity centers for cultivated cucurbits characterized by their adaptation to climatic changes. Many local varieties have resulted from natural or farmers’ selection. The aim of this study was to characterize fifteen local accessions of squash collected from different regions of the country. ‘In situ’ and ‘ex situ’ characterization were undertaken based on 30 parameters related to seeds, growth, flowers and fruit characteristic. This agro-morphological characterization was carried out based on UPOV and IPGRI descriptors. Total sugar, β-carotene pigment, and chemical parameters were also analyzed. Results revealed a considerable genetic variability for most of the agro-morphological parameters. Morphological variation was most apparent in fruit characteristics. In fact, most populations in this study had transverse broad elliptical fruit (75.6%), a medium skin thickness (89.12%), a medium flesh thickness (57.89%) and a big cavity diameter (94.7%). PCA helped to produce a dendrogram which classifies these local varieties into three homogenous groups. Analysis of the biochemical constituents revealed a significant difference between these groups for all the traits, except magnesium content. These results represent the first report on the characterization of squash in Tunisia, which will serve to the management, conservation and use of local genetic resources. Keywords: squash, local varieties, genetic diversity, characterization. 1. Introduction Cucurbita spp., commonly known as cucurbits, includes many economically and nutritionally important vegetable crops cultivated worldwide, such as cucumber, melon, watermelon, pumpkins, gourds, and squashes (Robinson and Decker-Walters, 1997). In this field, China and India are the world leading producers. Squash (Cucurbita maxima Duchesne) is one of the economically and nutritionally important vegetable crops in Tunisia and many other African countries. Local varieties of squash known as populations are largely produced in different regions of Tunisia. This species is often represented by local accessions (Bejaoui, Batati, Kerkoubi, Kalaaoui ...). In 2015, the area of 2523 ha was cultivated, producing 92450 tonnes of fresh fruits from different regions of Tunisia. Ariana, Nabeul, Kasserine, Gafsa and Sidi-Bouzid are the major producing regions, respectively covering production areas of 514, 507, 250, 245 and 250 ha (DGPA, 2015). The cucurbit family displays a rich diversity of many traits, and was among the first to be examined in sex expression analyses, vascular biology studies, and analysis of some fruit ripening mechanisms. Squashes have considerable impact on human nutrition, being appreciated for their medical properties (Shokrzadeh et al., 2010). In addition to the use of their flesh flowers and leaves, their seeds are also consumed as snacks, providing a source of edible oil and protein for human and animal consumption. They also have an array of applications in the pharmaceutical industry. The economic value of Cucurbita spp. as rootstocks for overcoming soil-generated diseases in cucurbits is significant. Squash is an important vegetable, mainly valued for its long storage life fruits, which can be consumed after six months of their harvest (Fita et al., 2007). Cucurbita genus (2n = 2 × = 40), which includes squashes, gourds and pumpkins, has been scarcely studied. It contains some of the earliest domesticated plant species (Smith, 2005). Despite the agricultural and biological importance of cucurbits, knowledge of their genetic diversity and genome has been very limited till now. Genomic characterization efforts have been largely focused on cucumber and melon, and only recently has focus started to be directed to the whole