Abstract
Growth and plant water relations of seven citrus rootstocks were tested under the arid environment of Qatar. Rootstocks used were Rangpur lime, Volkamer lemon, Citrus macrophylla (Alemow), Yuma Citrange, Citrus amblicarpa, Sacaton Citrumelo and Cleopatra mandarin. Transplants were raised in the greenhouse and when six months old, they were transplanted in the open field and monitored to age of 32 months.
While in the greenhouse, all seven rootstocks showed similar and irregular pattern of increased absolute growth rate (AGR) with age as based on shoot height. The highest values of AGR in the greenhouse ranged between 3.9 mm/day in Sacaton citrumelo to 5.1 mm/day in Yuma citrange. The AGR was significantly reduced during the first year of transplantation, while increased rates were resumed during the second year after transplantation with highest values ranged from 1.6 mm/day in Citrus amblicarpa to 9.3 mm/day in Rangpur lime. Generally, the three rootstocks namely Rangpur lime, Volkamer lemon and Citrus macrophylla exhibited after transplantation an overall better AGR, survival, stem diameter, leaf area, dry matter production and shoot branching than the other four rootstocks.
All tested rootstocks showed limited fluctuations in their water content and water saturation deficit during the day time. The Rangpur lime, Volkamer lemon and Citrus macrophylla have significantly lower number of stomata on their leaves than the other rootstocks - an important asset for plants to reduce water loss and delay, onset of water stress and maximize the period of growth.
It is recommended that raising of transplants in the greenhouse ensures their successful establishment and growth after transplantation in the open field. The two rootstocks Rangpur lime and Volkamer lemon are recommended to be used in Qatar.