Agronomical evaluation of local Tunisian almond cultivars and their breeding prospects

Almonds have been cultivated in Tunisia since ancient times. Due to increasingly severe dry conditions, the local almond gene pool has significantly decreased since the 1980's. In order to rescue the remaining almond germplasm and to investigate the existing agronomical variation in Tunisia, a survey was undertaken several years ago to identify and preserve the traditional almond cultivars. In this study, 52 local almond cultivars and ecotypes were evaluated for three consecutive years, and 18 different tree, kernel and nut traits were observed. Results show a great diversity of almond ecotypes and cultivars in Tunisia. Kernel weight and size and adaptation to dry conditions are the most interesting qualities of this local germplasm. However, self-incompatibility, early flowering and the presence of double kernels are the most common obstacles for using this germplasm in breeding. Furthermore, principal component analysis was used to identify morphological variation patterns and to classify the genotypes. In this analysis, the first three retained principal components were found to explain more than 56% of the total variance. The main nut traits, such as length, thickness and size, were strongly associated with the first principal component. However, shell retention, shelling percentage and kernel weight had the highest loadings for the second principal component. Finally, cluster analysis revealed four groups for the almond cultivars studied, but no discrimination among genotypes according to their origin was observed. Results show the great pomological variation of local Tunisian almond cultivars and their breeding value for increasing Tunisian almond production and as source of drought resistance.