Effect Of Exogenous Gibberellins On Growth And Physiological Characteristics Of Cucumber Under Suboptimal Temperature And Light Intensity

Cucumber is one of the main plants cultivated in greenhouses, it is always affected by the suboptimal temperature and light during winter and early spring especially. GA₃ is involved in the process of root formation as a kind of plant growth regulator. In order to study the effect of GA₃ on plant growth, physiological characteristics, yield and quality of cucumber, cucumber cv. ‘Zhongnong 26’ was selected, GA₃ was applied to the root of cucumber seedlings at the phase of two fully expanded leaves, and ten days after moving the seedlings to the phytotron which provides the condition of suboptimal temperature and light, the dry weight, root activity and content of MDA, pigment as well as mineral elements were tested; Furthermore, GA₃ was applied to the leaves of cucumber plants at the phase of four to five fully expanded leaves, the effects of application of GA₃ on sunlight greenhouse cucumber cultivation was studied. The main results obtained are as follows:1. Compared with the treatment cucumber seedlings cultured under appropriate temperature and light conditions, the height, stem diameter, leaf area, root diameter, root volume, dry mass, pigment content and nutrient concentration, nutrient accumulation and uptake of whole plant at corresponding nutrient supply levels decreased under suboptimal root-zone temperature. However, plants treated with GA₃ under suboptimal temperature showed greater height, stem diameter, leaf area, root diameter, root volume, dry mass and pigment content compared with plants grown at suboptimal temperature without addition of GA₃. Increasing the plant height, shoot dry mass, root dry mass, total dry mass, nutrient concentration, nutrient accumulation and uptake of whole plant increased progressively with increased nutrient concentration. Compared with plants under low nutrient treatments, a high nutrient supply increased the total dry mass at optimal temperature, suboptimal temperature, and suboptimal temperature in GA₃-treated plants by 30.66%, 19.59% and 21.98% respectively. The N, P and K uptake rate decreased progressively with increased nutrient supply, with plants grown at a suboptimal temperature showing greater reductions. However, a lower reduction was observed in plants treated with GA₃ under suboptimal temperature conditions.2. Foliar applied GA₃ promoted the growth of cucumber compared with the control. Plant height, stem diameter, number of leaves and pigment content, net photosynthetic rate（Pn） as well as contents of N, P, K, Ca, Mg and Fe were increased first and then decreased along with the raise of GA₃ concentration in the experiments. The content of chlorophyll a and b, content of carotenoid and Pn treated with 50mg·L^-1 GA₃ was increased by 27.16%, 24.22%, 22.44%, 29.24% respectively compared with that of control. Application of GA₃ also increased the fruit setting rate, number of fruits and yield per plant significantly. The 24% increase was recorded in yield of cucumber treated with 50mg·L^-1 GA₃（ 18.22 kg per m2） compared with control. In addition the quality of cucumber was improved. The results indicated that the adverse effects of suboptimum temperature and light condition in greenhouse on cucumber in early spring could be alleviated by GA₃. It is also concluded that the best concentration was 50mg·L^-1 for the good quality of cucumber.