Study On The Difference Of Calcium Content In Apples Varieties And The Method Of Supplementing Calcium In ’honeycrisp’

Apple（Malus domestica）is a plant of the genus Malus in the Rosaceae family.It is one of the fruit trees with the widest cultivation area and the largest yield in the world.China is an important country in the world for apple production.Calcium is one of the important mineral elements in the process of growth and development of apples.Calcium deficiency can cause damage to the cell membrane function of the apple fruit,leading to disorders of cell metabolism,and causing physiological disorders of apple fruit such as bitter pit,water heart disease,and acne.This ultimately has a severe impact on fruit quality.Therefore,this thesis compares the differences in calcium content in the pulp and peel of five different apple varieties including‘Honeycrisp’,‘Nagano Fuji No.2’,‘Qin cui’,‘Pink lady’and‘Hong lu’at different developmental stages,as well as does preliminary analysis of the mechanism of the difference in calcium content.At the same time,different calcium fertilizers and calcium fertilizer mixed with hormones（IAA and GA₃）were sprayed at the young fruit stage to screen out the calcium fertilizer with better calcium supplement effect and appropriate hormone concentration by using‘Honeycrisp’apple as the test material.The analysis of the mechanism of the difference in calcium content in different apple varieties and the effect of different calcium fertilizers and calcium fertilizers mixed with hormone on the‘Honeycrisp’fruit are of guiding significance for efficient use of calcium in terms of the breeding and production of apples.The main findings are as follows:1.The calcium content in the pulp of‘Honeycrisp’,‘Nagano Fuji No.2’,‘Qin cui’,‘Pink lady’and‘Hong lu’continued to decrease with the growth and development of the fruit,but increased in the later stage of growth and development.The calcium content of the pulp during the ripening period was‘Pink Lady’>‘Nagano Fuji No.2’>‘Honeycrisp’>‘Qin cui’>‘Hong lu’.In the entire period of growth and development,the calcium content of‘Pink lady’and‘Nagano Fuji 2’in the peel was significantly higher than‘Honeycrisp’,‘Qin cui’and‘Hong lu’.2.The longitudinal section of the main vascular bundles of sepals showed that the structure of the main vascular bundles of the sepals of different apple varieties at the young fruit stage was relatively complete.With the expansion of the pulp cells,the xylem ducts of the main vascular bundles of the sepals of different apple varieties were fractured and dislocated to different degree,and the extent of damage increased at the mature stage,which may seriously affect the absorption of calcium in apple fruits.Cross-section of the main vascular bundles of sepals showed that the proportions of phloem and xylem of different varieties are quite different.The areas of phloem of‘Honeycrisp’,‘Qin cui’and‘Hong lu’were relatively high,which may be beneficial to the transportation of sugar.While,the xylem areas of‘Pink Lady’and‘Nagano Fuji No.2’were relatively high,which may be beneficial to the transportation of mineral elements such as calcium and magnesium.3.At the young fruit stage,the relative expression levels of the calcium transport related genes（Md ACA8,Md ACA11,Md CAX1,Md CAX3,Md CNGC2,Md TPC1,Md GLR2）of‘Pink Lady’and‘Nagano Fuji No.2’were relatively high while the relative expression levels of calcium transport-related genes in‘Honeycrisp’,‘Qin cui’and‘Hong lu’were relatively low.In the swelling phase,the expression of calcium transport related genes in‘Honeycrisp’was the lowest,and the expression of calcium transport related genes in‘Nagano Fuji NO.2’and‘Pink lady’were more similar,with higher expression levels than others.During the mature period,the calcium transport related genes of‘Pink lady’and‘Hong lu’were expressed at a higher level than others.4.In 2019,the sugar alcohol calcium was experimentally selected as a kind of calcium fertilizer with better calcium supplement effect.The calcium content of the fruit treated with800 times the sugar alcohol calcium solution was 200%higher than that of CK.In the treatment of amino acid calcium mixed with hormone,the calcium content of apple fruit treated with 800 times solution of amino acid calcium mixed with 20mg/LGA₃,20mg/LIAA and 30mg/LIAA was significantly higher than that of the control groups and other combined hormone treatments.In 2019,all different treatments increased the single fruit weight of‘Honeycrisp’fruit to different degrees.The content of sorbitol in different treatments was significantly lower than that of CK,and there was no significant difference between different treatments.For the treatment in 2020,the calcium supplementation effect of the sugar alcohol calcium 800 times liquid and the sugar alcohol calcium 800 times liquid mixed with20mg/L GA₃ and 20mg/LIAA respectively was the best,and the calcium content increased by 95%,126%,and 121%respectively compared to CK.Compared with CK,the calcium content of fruits treated with 800 times of amino acid calcium solution mixed with20mg/LGA₃ and 20mg/LIAA increased by 30%and 72%,respectively.Compared with CK,the calcium content of fruits treated with 0.5%calcium nitrate and 0.5%calcium chloride increased by 45%and 35%,respectively.Except the treatment by the 0.5%calcium chloride,other treatments significantly increased the single fruit weight of the‘Honeycrisp’fruit.In2020,all different treatments have remarkably improved the hardness of the fruit skin,and the extensibility of the fruit skin has been significantly enhanced compared with CK.The content of sorbitol for different treatments was significantly lower with different extent than that of CK,which was consistent with the treatment in 2019.