Genetic diversity and population structure analysis of carob germplasm from Lebanon, Morocco and Spain: uncovering a potential asset for innovative breeding initiatives

Abstract

Carob tree (Ceratonia siliqua L.) is a drought-resistant species endemic to the Mediterranean Basin. It has been cultivated for its highly nutritious edible fruit for centuries. Genetic diversity is considered one of the key requirements for the management and use of plant genetic resources. In this work, we evaluated the genetic diversity and population structure of 169 semi-natural carob individuals from Lebanon, Spain and Morocco based on nine EST-SSR (Expressed Sequence Tags-Simple Sequence Repeat) markers. The eight EST-SSR loci that were polymorphic produced 43 alleles, with Cesi_187 and Cesi_1187 being the most informative loci. The AMOVA and SAMOVA results revealed that most (> 80%) of the genetic variation was within populations, with the remaining < 20% corresponding to among population variability. STRUCTURE analysis suggested the presence of three clusters corresponding to each country; however, some individuals from Morocco and Spain shared the same genetic structure. The PCoA and discriminant analysis of principal components (DAPC) complemented the STRUCTURE results, contributing to a better understanding of the genetic differences among countries. Our findings may enhance the effectiveness of management and conservation strategies, and promote the use of these carob genetic resources in breeding and reforestation programs.