Zinc Content and Fruit Quality of Pecan as Affected by Application of Zinc Sulfate

Abstract

Pecan [Carya illinoinensis (Wangenh.) K. Koch] is an important nut tree species, and Zn nutrition is critical for its growth and nut production. The aim of this study was to provide a perspective on Zn accumulation in pecan fruit over time and to determine the effects of Zn application on fruit quality. Two concentrations of ZnSO4 (0.4% and 1.6%) were sprayed onto the shuck or the nearest pair of leaflets. Purified water was sprayed similarly as the control. The results show that Zn application to the shuck and leaves increased the Zn concentration and content in embryos. The greater the concentration of the Zn solution sprayed, the greater the Zn concentration in the embryo. The greatest zinc concentration in the embryo was found during the early stage of embryo development. In the treatment during which 1.6% ZnSO4 was sprayed onto the shuck, the Zn concentration in the early embryo was 242.91 mg·kg–1, which was 2.2 times that of the control. Thereafter, embryo Zn concentration decreased gradually until maturity. The treatments could be ranked, from greatest Zn concentration in the mature embryo to least, as follows: 1.6% ZnSO4 on shuck (66.36 mg·kg–1) > 1.6% ZnSO4 on leaflets (64.28 mg·kg–1) > 0.4% ZnSO4 on leaflets (55.51 mg·kg–1) > 0.4% ZnSO4 on shuck (49.67 mg·kg–1) > control (47.34 mg·kg–1). A model was presented that showed Zn was transported from the shuck and leaves to the stalks through the conducting tissue, and then to the embryo through the embryo sac. The application of 0.4% ZnSO4 to the shuck resulted in the greatest oil content (74.05%), which was 10% greater than that in the control. Applications of 0.4% ZnSO4 to the shuck and leaflets resulted in a greater proportion of oleic acid (≈69%) and a lower proportion of linoleic acid (≈20%), palmitic acid (≈6.0%), and linolenic acid (≈1.1%). The results of this preliminary investigation are useful for exploring the mechanism of action for Zn on pecans.