Evaluation of variability to drought and saline stress through the germination of different ecotypes of carob (Ceratonia siliqua L.) using ahydrotime model

Carob is a valuable leguminous species for its productions but also for forestation of arid and degradedareas threatened by soil erosion and desertification processes. However, large-scale cultivation of thisspecies is hampered by the difficult propagation by cuttings or seeds. Researches to evaluate genotypetolerance to saline and drought stress during germination and first plant establishment, are also inhibitedby the scarce seed germination.In this study, carob seeds, from wild and domesticated carob genotypes collected in a representativearea of the Mediterranean basin (Sicily, Italy), were subjected to germination tests under isotonic solu-tions of polyethylene glycol (PEG) and sodium chloride (NaCl) at -0.5, -1.0, -1.5 MPa. Before germinationtests, a 20 min pre-treatment with 96% sulphuric acid was necessary to overcome seed coat dormancywhich does not permit germination.Differences in drought and salinity tolerance were determined in the different genotypes during ger-mination. All genotypes exhibited a higher sensitivity to drought stress as compared to salinity stress.The observed differences in some genetically inherited germination characteristics (i.e. base b(50)s andhydrotimes) suggest genetic differences even in seeds of individual old trees situated in close areas, aspreviously found in other countries of the Mediterranean basin.A greater sensitivity to stress was determined during early radicle growth, an essential feature for earlyplant establishment in marginal dry areas.In this paper, a protocol to test germination under simulated stress conditions (drought and salinitystress) was established. Including in the analysis other parameters representative of early embryo growth(i.e. radicle elongation), this protocol may be useful to select genotypes for breeding programs towardsthe selection of tolerant cultivars or rootstocks. It may be also applied to other leguminous species witha difficult germination.