Autecology of Citrullus colocynthis L. Schrad (Colocynth) in Gonabad desert, Iran

Colocynth (Citrullus colocynthis) is one of the major medicinal plants, naturally growing in deserts of Middle East and North Africa. Extending cultivation of this species is useful for sand dune fixation and livelihood of the local inhabitants. In spite of numerous studies on seed germination, there are still debates on the best methods of breaking seed dormancy for colocynth. Moreover, seed morphology, phonological stages and habitat conditions of this species is almost unravelled. This study was conducted in 2016-2020 at Gonabad desert, Iran. We established five line transects of 200 m and five plots of 4×4 m, and vegetation parameters, phenology and root morphology, soil charactristics of colocynth were measured. The pH varied between 7.0-7.5 in bare soil and 8.0-8.1 under the canopy of colocynth habitat. The soil of study area was classified as slightly saline. Two weeks pre-chilling at 4°C and night -day temperature range from 25-40°C significantly increased seed germination. In our study area, colocynth was detected as a perennial forb with long and ligneous roots (more than120 cm). Its vegetative growth starts in middle of May, seed ripening and shedding occur in October and November. Average fruit volume was 2.62 cm3 and seed number counted in each fruit varied between 250 to 420 by the length of 4-7 and 2-4 mm width. Big size fruits contained the highest seed numbers. The best harvesting time in terms of both economic value and seed viability is ripening of fruits.