The correlation analysis between quality characteristics and fruit mineral element contents in ‘Fuji' apples

Abstract:【Objective】To probe into the relationship between the contents of fruit mineral elements andquality features of the‘Fuji'apple. To screen major mineral elements of the fruit affecting fruit quality fea-tures, and set up optimum proposals of fruit mineral elements for good fruit qualities. To provide a theoretical basis for reasonable orchard soil and foliar fertilizer applications for increasing fruit quality and reduc-ing the physiological diseases of each county selected based on its Chinese location and climate condi-tions for apple production, related to the‘Fuji'apple.【Methods】We selected 51 counties with apple pro-duction, which had three commercial apple orchards where‘Fuji'apples were primarily planted, and thetrees were 15 to 20 years old, and had high and stable yields over the past 5 years. Each orchard selectedhad an area of over 0.6 hm2, which resulted in a total of 153 orchards being selected. Fruit were pickedduring the local commercial harvest(late October to early November), 10 fruits were picked from the treecanopies in the southeast and southwest at 1.5 m above the ground, with a total of 60 fruits selected fromeach orchard during 2010 to 2011. The fruit in each orchard was randomly divided into two groups, onebased on an analysis of the fruit quality(mean fruit weight, fruit shape index, firmness, soluble solid content, titratable acid content and red color area), and the other analysis based on the mineral elements con-tent(N, P, K, Ca, Fe, Zn and B). The partial least squares regression(PLS) method was used to analyze themodel effect and weight analysis impact of the fruit mineral element contents to fruit quality, to screen outmajor factors of fruit mineral elements influencing the different fruit qualities, and to set up the regressionequation of the fruit qualities and major fruit mineral elements. Linear programming was used to obtain op-timum proposals of the fruit mineral elements to achieve good‘Fuji'apple qualities.【Results】The mineralelements content and quality characteristics in‘Fuji'apple fruit had the biggest differences in the different produce regions in which the maximum content of nitrogen, iron, zinc and boron in the‘Fuji'fruit were12.06, 6.17, 7.7, and 10.08 times greater than the minimum respectively, the differences for titratable acid and the SSC/TA ratio were 2.33 and 2.16 times respectively. The correlation coefficient between thefruit mineral element contents and qualities showed that the nitrogen content of fruit had a significantlynegative correlation with the soluble solid, SSC/TA ratio and Red color area, while the Calcium and ironcontent in the fruit were significantly positively correlated with the soluble solid and SSC/TA ratio. Themodel effect and weight analysis showed that the content of nitrogen and iron in the fruit had a greater in-fluence and was followed by phosphorus, potassium and calcium for the integral fruit quality. The variableimportance for projection(VIP) technology of PLS was used to select the main fruit mineral elements af-fecting the fruit quality characteristics respectively, such as the mean fruit weight was primarily affectedby nitrogen, phosphorus and potassium, and the soluble solid was primarily affected by nitrogen, calciumand iron, while the red color area was primarily affected by nitrogen, potassium, calcium, iron and zine.The regression equation between fruit quality and mineral element contents showed that the mean fruitweight had the greater positive effect coefficient with a content of phosphorus and potassium, and thegreater negative effect coefficient with a content of nitrogen in the fruit. Moreover, the soluble solid hadthe largest negative effect coefficient with nitrogen and largest positive effect coefficient with calcium andiron in the fruit. Linear programming was used to obtain the optimization range of the fruit mineral ele-ment contents for the mean fruit weight≥ 250 grams, fruit shape index≥ 0.86, firmness≥ 8.8 kg∙cm-2, sol-uble solid content≥ 13.8%, titratable acid content≥ 0.21% and red color area≥ 90%, in which the fruitmineral element contents were 0.25% in nitrogen, 0.07%-0.12% in phosphorus, 0.7%%-1.2% in potassium, 700 mg∙kg^-1 in calcium, 105-184 mg∙kg^-1 in iron, 4.3-9.0 mg∙kg^-1 in zinc, and 16.8-43 mg∙kg^-1 inboron respectively.【Conclusion】The maximum content of soluble solid and titratable acid were 1.5 timesmore than the minimum, and nitrogen, iron, zinc and boron were 6 times more than in the‘Fuji'applefruit in the different produce regions. It is therefore a key technological measure to decrease the content ofnitrogen, increase the content of iron, phosphorus, potassium and calcium in the fruit for improving theoverall qualities of th‘eFuji'apple.