The Responses of Selected Garden Roses (Rosa x Hybrida) to Drought and Salt Stresses

Water shortage and poor water quality are critical problems for agriculture in many regions of the world. Roses (Rosa ? hybrida L.) are some of the most common garden plants in the world. Despite their popularity, however, they can present challenges to gardeners, particularly in relation to their responses to environmental stresses, such as those caused by arid and semiarid regions. The objectives of the present study were to investigate the tolerance of selected garden roses by evaluating their growth and physiological responses under drought and salt stress conditions.

Four experiments were conducted to evaluate 25 garden rose cultivars, including 22 Earth-Kind? rose cultivars. In Expt. 1, four garden roses were subjected to two watering treatments: well-irrigated and cyclic drought stress. ?RADrazz? was the most drought tolerant among the cultivars investigated. With lower gas exchange and greater reduction in flower numbers at low substrate moisture content (SMC), ?Marie Pavie? was the least drought tolerant. In Expt. 2, two Earth-Kind? rose cultivars were subjected to four constant SMC of 10, 20, 30, and 40 % by utilizing an automatic irrigation system. Plants at 30 and 40 % SMC maintained the highest shoot and root dry weight (DW), flower number, midday leaf water potential, and photosynthetic rate. Plants had excellent performance at 30 % SMC and acceptable growth and quality at 20 % SMC. The 10 % SMC led to significant growth reduction, poor quality, and 25 % mortality. In Expt. 3, six garden rose cultivars were subjected to three salinity levels at electrical conductivity (EC) of 1.5 (control), 4.0 or 8.0 dS?m^(-1). ?New Dawn? was considered to be the most salt tolerant, while ?Caldwell Pink?, ?Marie Pavie?, and ?The Fairy? were the least salt tolerant with their greater reductions in flower number and shoot DW. In Expt.4, 18 Earth-Kind? rose cultivars were subjected to two salinity levels at EC of 1.2 (control) and 10.0 dS?m^(-1). By comparing the growth and physiological responses at high saline solution among the 18 cultivars, ?Belinda?s Dream?, ?Climbing Pinkie?, ?Mrs.Dudley Cross?, ?Reve d?Or?, and ?Sea Foam? were the most salt tolerant, while Cecile Brunner?, ?Else Poulsen?, ?Madame Antoine Mari, ?Perle d?Or, ?Spice?, and ?Souvenir de St. Anne?s? were the least salt tolerant among the cultivars investigated.