Improving Physiological Characteristics of Grafted Cucumber under Drought Stress

Plants are constantly faced with abiotic and biotic stresses during their whole life. Abiotic stresses are various adverse environmental factors, including drought, high salinity, heavy metals, cold or heat shock, and ozone. Resulting in dehydration and osmotic stress, drought has caused a dramatic reduction in crop production globally. Grafting can reduce the content of Malondialdehyde (MDA); prevent the accumulation of reactive oxygen species (ROS); increase activities of antioxidant enzymes; and maintain fresh and dry weights, grain yield, and relative water content in a variety of plants in response to drought stress. On the other hand, a range of abiotic and biotic elicitors can confer tolerance to drought stress in plants. Grafting of herbaceous fruit vegetables can reduce detrimental effects of biotic and abiotic challenges and cultural practices. Grafting can increase yield of cucurbits, initiate shoot growth, aid in resistance against nematodes and viruses, withstand high and low temperatures, improve nutrient and water absorption, resist against high concentration of salt, drought and waterlogging stresses. Grafting elite commercial cultivars onto selected vigorous rootstocks is a special method of adapting plants to counteract environmental stresses. Grafting is currently regarded as a rapid alternative tool to the relatively slow breeding methodology for increasing the environmental-stress tolerance of fruiting vegetables. Potential approach to reduce losses in production and improve water use efficiency under drought conditions in high-yielding genotypes would be to graft these varieties onto proper rootstocks capable of reducing the effect of water stress on the shoot and to increase tolerance to abiotic stresses. Cucumber (Cucumis sativus L.) is one of the main greenhouse vegetable crops widely grown in Saudi Arabia. The total greenhouse area for cucumber production in 2013 was 2605 hectares produced 236,087 tons. Major factor influencing growth and yield of cucumber is water quantity. The effects of different rootstocks on plant growth, yield, fruit quality and water consumption in cucumber was studied. The highest yield was obtained from 9075 (19.02 kg m2), which was 24.5 and 23.5% higher than in the non-grafted and self-grafted treatments, respectively. The plant height also increased with the use of rootstocks. The increase in the dry weights of the leaves and fruits depended on rootstocks. They concluded that grafting improved plant growth and yield depending on the rootstock genotype. Grafting has the potential to be as a strategy to increase the tolerance of plants to promote water use efficiency (WUE). The present study was aimed to evaluate the grafting biochemical and physiological effects on inducing drought stress resistance in cucumber. This experiment was conducted in complete randomized design with three replications and treatments are included grafted and ungrafted plants, and water potential level 0 (control), -0.4 and -0.8 MP. The Isfahan endemic cucumber specious as a scion with the hole method grafted on Ferro rootstock. The physiological and growth traits were measured. Photosynthesis (stomata conductance, photosynthesis, water use efficiency), growth (root and stem growth), and antioxidants (SOD, POD, protein) parameters, and transpiration were measured. Result indicated that grafting with increasing root nutrient absorption and its development drought stress resistance improved. Although, grafting reduced potassium content. Grafting and the interaction of rootstock ×scion impressed many morphological and physiological characteristics. Under stress condition, some features improved plant water relationship, growth and development. Gas exchange indices like photosynthesis, transpiration and stomatal conductance were lower in grafted plant compare to ungrafted plants. Proline content was significantly increased in grafted treatments compare to ungrafted ones. Higher potassium under -0.8 MP in grafted plants showed the maintenance osmotic stability and potassium hemostasis were the draught stress mechanism in resistant rootstocks. Finally, grafting as an efficient method to increase cucumber yield and improve drought resistance recommend. These results suggest that the use of drought tolerant Cucurbita rootstock can improve cucumber photosynthetic capacity under drought stress and consequently crop performance. The results revealed that grafted plants had better vegetative growth than  ungrafted (control) ones. Furthermore, photosynthetic parameter, antioxidant activity and fresh and dry weight of stem and leaves were improved, but grafting had no significant effect on fruit quality and yield. In conclusion it is recommended that grafting procedure in some crops include cucumber should be done only after assuring the benefits and risks of grafted seedlings.