Effects of calcium treatments on grape fruit quality and anthocyanin content

Abstract：【Objective】In order to find the proper time, concentration and method of calcium fertilization during fruit growth and development for‘Beauty finger'grape (Vitis vinifera L.) , we compared the effects of different calcium treatments (different concentrations, fertilizing methods and application time) on the fruit quality, especially on anthocyanin content in grape. Some previous studies showed that spraying calcium could promote fruit quality and enhance coloration. But the proper time, concentration and fertilizing method are still unknown. Thus, we conducted the study to provide reference for cultivating grape with high quality and high yield.【Methods】This experiment was conducted in the Gan Shan Orchard in the Hunan Agricultural University. Six-year-old‘Beauty finger'vines under rain shelter cultivation were used as materials to study the effects of different calcium concentrations (0, 1.0, 3.0, 5.0 and 8.0 g· L-1) , fertilizing methods (foliar spraying and fruit soaking) and application periods (at the first enlargement period and at the second enlargement period) on grape fruit quality and anthocyanin content. The calcium used in the experiment was Ca (NO3) 2·4H2O with a purity of 98%. Three trees were selected for each treatment (n=3) . Randomized experimental design was used. The fruit were harvested at mature stage to measure the fruit quality attributes, including berry weight, total soluble solids, acidity, and fruit firmness. Fruit samples were also collected 7 to 15 days after the treatment at the second enlargement period to analyze the anthocyanin content and observe fruit color. The sampleswere put in labeled bags in an ice box and taken to the lab immediately. Anthocyanin content was measured during the fruit development period to analyze the effect of calcium on coloration.【Results】The two fertilizing methods in the first enlargement period did not affect the berry weight significantly. Berry weight increased with the increase in calcium concentration, and fruit soaking treatment in the second enlargement period was better than the spraying treatment. The berry weight was the highest under the treatment of fruit soaking in 8 g·L-1 calcium solution in the second enlargement period. Total soluble solids increased first and then declined. Under the treatment of fruit soaking in 5 g·L-1 calcium solution in the second enlargement period, the total soluble solid content was 16.23%, which was significantly higher than the other treatments. In the treatment of foliar spraying with 5 g·L-1 calcium solution in the second enlargement period, total soluble solid content was 15.47%, which was significant lower than in the other treatments. On the contrary, acidity declined first and then increased. The acidity of treatment of fruit soaking in 5 g·L-1 calcium solution in the second enlargement period was 0.26%, the lowest in all the treatments, and spraying treatment with the same calcium solution at the same period had an acidity of 0.31%. The two fertilizing methods in the first enlargement period did not affect the fruit firmness significantly. And under the treatments with 5 g·L-1 calcium solution, both fertilizing methods in the second enlargement period lowered fruit firmness. All the treatments with calcium significantly promoted fruit coloration and anthocyanin accumulation compared with the control. The coloring level and anthocyanin content increased with the rising of calcium concentration until 5 g·L-1 and declined at 8 g·L-1. The anthocyanin content reached the highest of 820.23 nmol·g^-1 under the treatment of soaking in 5 g·L-1 calcium solution in the second enlargement period, which was significantly higher than the foliar spraying treatment with the same calcium solution.【Conclusion】In conclusion, calcium fertilization could significantly improve berry weight, soluble solids and anthocyanin content, and reduce the firmness and acidity of fruit. The fruit quality and anthocyanin content increased with the rising of calcium concentration until 5 g· L-1. In addition, it was found that the effect of calcium treatment was better in the second enlargement period than in the first enlargement period, and that the fruit soaking treatment was better than foliar spraying. Therefore, fruit soaking in 5 g· L-1 calcium solution in the second enlargement period is recommended for application.