The Effect of Seed Pretreatment and Foliar Application of Growth Regulators and Potassium Nitrate on Physiological, Biochemical Characteristics, Yield and Yield Components of Borage (Borago officinalis L.)

Seed pretreatment is one of the simple techniques that can increase seed vigor and seedling establishment, and thus plant yield. Seed pretreatment can be done with water (hydropriming), inorganic salts such as potassium nitrate (halopriming), and growth regulators such as salicylic acid (hormone priming) and ascorbic acid (vitamin priming). Another effective factor in producing strong seeds is proper nutrition of the mother plants. Proper nutrition of the maternal plant in the form of foliar sprays with essential elements leads to the production of high-quality seeds, which affects germination and yield. Considering the positive role of seed pretreatment in improving germination rate and seedling establishment, and increasing seed yield of various plants as a result of foliar application of growth regulators and inorganic salts, this experiment was conducted to study the effect of seed pretreatment and foliar spraying with salicylic acid, ascorbic acid and potassium nitrate on improving physiological and biochemical characteristics, yield and yield components of borage.

The experiment was conducted in 2017-2018 cropping year as a randomized complete block design with three replicates at Samian Ardabil Natural Resources and Medicinal Plants Research Farm. The experimental treatments were water pretreatment for 48 hours, seed pretreatment with ascorbic acid (0.85 mM) for 48 hours, seed pretreatment combined with foliar spray with ascorbic acid (0.85 mM), seed pretreatment with salicylic acid (4 mM) for 60 hours, seed pretreatment combined with foliar spray with salicylic acid (4 mM), seed pretreatment with potassium nitrate (20 mM) for 24 hours, seed pretreatment combined with foliar spray with potassium nitrate (20 mM), and control treatment (without seed pretreatment and without foliar spray of the maternal plant). Statistical analyses were performed using SAS software (Ver 9.1) and comparison of means was performed using the Duncan multiple range test at the 1 and 5 percent probability level.

The results showed that although pretreatment of seeds by improving growth, physiological and biochemical characteristics cause increased yield and yield components of borage but, seed pretreatment combined with foliar sprays had a greater effect on increasing yield components and flower and grain yield due to synergistic effects. The use of potassium nitrate as a seed pretreatment in combination with foliar sprays had the greatest effect on increasing the amount of photosynthetic pigments, caused a 2.3-fold increase in total chlorophyll and a 1.8-fold increase in carotenoids compared to the control treatment. The use of ascorbic acid as a seed pretreatment in combination with foliar sprays increased the amount of proline a 2.3 fold, leaf protein a 2.5 fold, and flower yield a 3.8 fold compared to the control treatment. Application of salicylic acid as a seed pretreatment in combination with foliar sprays by increasing the components of seed yield had the greatest effect in increasing grain yield and caused a 3.4-fold increase in grain yield compared to the control. Seed hydropriming showed the highest seed weight among the treatments with a 28% increase in 1,000-seed weight compared to the control treatment.

The results of this study indicate that both seed pretreatment and foliar sprays of maternal plants with growth regulators and chemical stimulants led to an increase in flower and grain yield in borage. This increase was achieved by enhancing the levels of photosynthetic pigments, the quantum efficiency of photosystem II, the accumulation of amino acids like proline, and soluble proteins in the leaves. These treatments also had a positive impact on various yield components. While seed pretreatment alone had a positive effect on borage yield and its components by improving the plant's growth, physiological, and biochemical characteristics, the combined use of ascorbic acid, salicylic acid, and potassium nitrate as seed pretreatment, along with foliar spray, had an even more pronounced positive effect. This was likely due to synergistic effects on the plant's physiological, biochemical, and yield traits.