A study on the relationship between occurrence of bitter pit and contents of main nutritional elements in‘Ruiyang’apple

Abstract: 【Objective】The study explored the relationship between incidence of bitter pit in‘Ruiyang’apple and the contents of main nutrient elements in order to provide a theoretical basis and guidance for the prevention of the disorder in apple production.‘Ruiyang’fruit (Malus domestica) from different or- chards with different bitter pit incidences in Baishui county and fruits with different incidence severity in the same orchard were collected in October 2019. The relationships between the occurrence of bitter pit and the contents of main nutritional elements in‘Ruiyang’apples fruit were analyzed after main nu- trient elements were determined.【Methods】The contents of total and water-soluble macronutrients (N, P, K, Ca, Mg) in fruit collected from different orchards and fruit with different severity of bitter pit in the same orchards were determined. In October 2019, ripe fruit used for the test were collected from three orchards in Kexian Village (N 35°13′30′′, E 109°24′7′′), Baishui Apple Experimental Demonstra- tion /Station (N 35°12′26′′, E 109°32′49′′), and Lingao town (N 35°12′37′′, E 109°26′21′′) in Baishuicounty, Weinan city, Shaanxi province. Five-year-old plants on M26 rootstock were at a space of 2 m×4 m and under routine management. After cutting off the pedicel, all the fruit samples were taken back to the laboratory, washed twice with distilled water and then with deionized water, air dried, and cut into 1 cm2 slices, which were fully mixed and weighed. The samples were placed in a 105 °C oven for 15 min- utes and then exposed to 80 °C until their weight became constant. The dried samples were ground into powder and passed through a 0.5 mm plastic sieve, and then sealed in plastic bags and stored in a dryer. The contents of mineral elements in the fruit were determined. Standard solutions were prepared and stored in a 4 °C refrigerator. The contents of Ca and Mg were determined with an atomic absorption spectrophotometer (Hitachi ZA3000, Japan); the contents of N and P were determined with a flow ana- lyzer (Systea FLOWSYS, Italy); and the content of K by a flame photometer (Sherwood M410, UK). The analyses were conducted with three replicates. The correlations between bitter pit incidence and the contents of main nutrient elements were analyzed.【Results】Significant positive correlations existed be- tween the occurrence of bitter pit in different orchards and total N, N/Ca ratio, water-soluble N, and the ratio of water-soluble N against water soluble Ca. In the same orchard, significant positive correlations existed between the severity of bitter pit and total N and K/Ca and N/Ca ratios, while a significant nega- tive correlation was found between bitter pit severity and the total Ca content in fruit. There was a sig- nificant positive correlation between the water-soluble N/P and N/Ca ratios, and between water-soluble N and Mg contents. There were significant negative correlations between the water-soluble P/Mg and Ca/Mg values in the fruit, and between the water-soluble P and Ca contents and P/Ca ratio in fruit.【Conclusion】The occurrence of bitter pit in‘Ruiyang’apple was closely related to the elements such as N and Ca as well as to N/Ca ratio, total K/Ca ratio, water-soluble P and Mg and ratios of N/P, P/Ca, P/Mg and Ca/Mg in the same orchard. Therefore, in apple cultivation, balanced application of relevant nutrient elements should be ensured. However, more experiments are needed to explore the mechanisms of bitter pit occurrence in apple fruit and find out the control methods.