Document Type : Research Paper - Olericulture
Authors
1 Horticultural Sciences and Engineering Department; respectively, Faculty of Crop Sciences, Sari Agricultural Sciences and Natural Resources University, Sari
2 Department of Horticulture, Sari University of Agricultural Sciences and Natural Resources, Sari, Iran.
Abstract
1. Introduction: Broccoli is a one of the vegetables that has a very high nutritional value and it is cultivated in many countries all around the world. Due to the intensification of climate change, sudden drops in temperature during the winter in northern countries pose a serious threat to some vegetable species, including broccoli. In this study, an experiment was conducted to investigate the effect of sucrose, potassium silicate, and Bordeaux mixture on increasing the tolerance of broccoli seedlings to the frost stress.
2. Materials and Methods: The experiment was conducted in a completely randomized design with eight treatments, three replications, and three samples per each replication. The treatments included: control, sucrose1%, potassium silicate 0.2%, Bordeaux mixture 0.2%, sucrose + potassium silicate, sucrose + Bordeaux mixture, potassium silicate + Bordeaux mixture, and sucrose + potassium silicate + Bordeaux mixture.
3. Results and Discussion: The effect of the treatments on the growth of broccoli seedlings one week after exposure to low temperature stress, including stem height, leaf number, shoot dry weight, root fresh weight, and root dry weight, was not statistically significant. The highest concentration of chlorophyll b (1.647 mg/g fresh weight) was obtained in the Bordeaux mixture treatment which along with the combined treatment of sucrose + potassium silicate + Bordeaux mixture were the only treatments that showed a significant superiority compared to the control. The highest transpiration rate among the tested treatments was observed in the sucrose + Bordeaux mixture treatment, which did not show a significant difference compared to the three-component treatment of sucrose + potassium silicate+ Bordeaux mixture, but showed a significant superiority compared to the other treatments. The foliar application of Bordeaux mixture caused a higher stomatal conductance compared to the control after a temperature stress of minus 2 Celsius degrees, but the other treatments did not show a significant difference compared to the control. In terms of the non-photochemical quenching (Y(NPQ)), the highest Y(NPQ), was observed in the control and potassium silicate treatments, which was significantly higher than all other treatments. Meanwhile, the lowest level of this index was observed in the potassium silicate+ Bordeaux mixture treatment, which did not show a significant difference compared to the sucrose + potassium silicate, sucrose + potassium, and silicate+ Bordeaux mixture treatments. The highest level of antioxidant activity was observed only in the sucrose treatment and the sucrose + potassium silicate and Bordeaux mixture treatments, which were superior to all other treatments without any significant difference among them. In terms of total phenolic content, only the sucrose+ Bordeaux mixture treatment showed a significant superiority compared to the control, and the other treatments did not show a significant difference from the control. In the trait of soluble sugar content, the sole potassium silicate and the three-component treatments were better than the control, and the other treatments did not show a significant difference compared to the control. The highest ion leakage was observed in the sucrose + Bordeaux mixture treatment, which was higher than the control and all other treatments. The lowest ion leakage was also observed in the sucrose + potassium silicate and potassium silicate+ Bordeaux mixture treatments, although the difference between them and the control and potassium silicate-only treatments was not significant. The highest level of proline was observed in the sucrose+potassium silicate treatment, which was significantly superior to all other treatments.
4. Conclusion: Sucrose+potassium silicate treatment improved the defense system of the plant against freezing stress by increasing the amount of carotenoid and proline, and as a result of these activities, the antioxidant of the whole plant and higher chlorophyll also increased. Also, this treatment showed low ion leakage and low non-photochemical quenching, which can show higher freezing tolerance. Another favorable treatment was Potassium Silicate+Bordeaux mixture which produced a higher assimilation rate, although this photosynthetic production did not affect the biomass, but since the ion leakage was low and caused the lowest Y(NPQ), it can be said that the plant in this treatment receive lower stress. Overall, considering all the evaluated traits, the top-performing treatment in this experiment was the potassium silicate+ Bordeaux mixture treatment, followed by the sucrose + potassium silicate treatment.
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