Citrullus lanatus cultivation is affected by drought stress. Citrullus species that grow wild and domesticated in arid areas, are considered potential useful donors of drought tolerance traits. Here, we evaluated the response of seed germination, seedling establishment and growth to different water availabilities in eleven landraces of C. amarus, from most of their cultivation range and in one C. lanatus commercial cultivar (‘Sugar Baby’). ‘Sugar Baby’ germinated to lower water potential better than all C. amarus landraces, while seedling establishment was much higher in C. amarus than in C. lanatus. Finally, seedling growth of C. amarus landraces and the C. lanatus cultivar followed different patterns depending on water availability, showing enhanced biomass growth under wet conditions and no changes between dry and wet growing treatments, respectively. The different water use strategies in seed germination and seedling growth found in the two crops highlight drought avoidance strategies linked to the species growing environment in C. amarus, not present in the C. lanatus cultivar. The high seedling establishment, the plastic responses to water availabilities and the strong root system, indicate that genetic resources of C. amarus may have important applications in breeding programmes and in the selection of water-use efficient rootstock lines.
