The Cucurbitaceae family, which originates in Africa, is known for its ability to grow in arid regions worldwide. Within this family, the colocynth (Citrullus colocynthis), common in arid regions including Israel, is characterized by high adaptability to water scarcity conditions. In this study, we aimed to characterize the physiological traits that confer drought tolerance in wild watermelon, compare them with those of cultivated watermelon, and examine whether such traits can be used to improve the cultivated species.
In a pot experiment, the physiological responses of the shoot to soil water content were similar between the species, but the wild plants exhibited higher photosynthetic efficiency. The root-to-shoot ratio in the wild plants increased under drought, mainly due to a reduction in shoot biomass rather than an increase in root biomass. In another experiment, examining the effect of rooting depth (one meter), it was found that in response to drought, the wild plants developed a branched root system in deeper soil layers, whereas the cultivated plants’ roots remained confined to the upper soil layer. This system increased the root surface area but not root biomass. We demonstrated that at advanced stages of drying, the physiological activity of the wild plants depended on the water content in the deeper soil layers.
This ability, to enhance water uptake from deeper soil without additional carbon investment in root biomass, represents a promising target for the improvement of cultivated watermelon and its adaptation to climate change.
