Effect Of Zn?NO₃?₂ And NAA On Peel Anatomical Structure And Mechanism Of Creasing In ‘Hongjiangcheng' Orange

‘Hongjiangcheng' is graft chimaera of sweet orange and red tangerine, is competitive in the export of sweet orange. But serious creasing fruit is often found in the rapid expansion period and mature period, this is a major obstacle in production. The albedo creasing on the surface of the creasing fruit lead the fruit not suitable for transporting and storing. Hence, better control measures and further understanding of creasing physiology is required. The ‘Hongjiangcheng' was used as experimental material with different treatments respectively, 0.1 % Zn?NO₃?₂, 20 mg/L NAA, 0.1 %Zn?NO₃?₂+20 mg/L NAA, water?CK?, during fruit expanding period. The objective of this two-year study was to determine if Zn?NO₃?₂ and NAA influence the creasing incidence,mechanical property of peel development, mineral element content, pericarp structure,morphological features of vessels and fruit quality. We revealed the mechanism of how Zn?NO₃?₂ and NAA affect the creasing incidence. The main results were summarized as follows:?1?Creasing incidences of different treatments were investigated. The results showed:Three kinds of treatments significantly decreased the creasing incidence, and Zn?NO₃?₂+NAA treatment had the best effect, the next was Zn?NO₃?₂ treatment, there was no significant difference between the three treatments. The creasing incidence of same treatment were different in 2014?33.1%? and 2015?10.5%?. The creasing incidences of three treatments were under 20%?2014? and 10%?2015?.?2?The investigation results showed that creasing occured more in the shaded peel.The thickness and hardness of shaded pericarp were less than that of the pericarp exposing to the sun. Three kinds of treatments significantly increase the peel thickness and hardness.The effects of Zn?NO₃?₂ and Zn?NO₃?₂+NAA treatments were the best. The glossiness ofshaded pericarp was more than that of pericarp exposing to the sun. Three kinds of treatments reduced the glossiness of peel. Zn?NO₃?₂+NAA treatments made the peel more rough. The color changing period of ‘Hongjiangcheng' began in early October. The color of shaded pericarp was deeper than that of pericarp exposing to the sun. The green of fruit was deeper before turning-color period and that was lighter after turning-color period under Zn?NO₃?₂ treatment, which is beneficial to the photosynthesis and fruit coloring. NAA treatment made fruit a lighter green during turning-color period, which may delay fruit ripening. Three kinds of treatments had little effect on yellow color. Zn?NO₃?₂ and Zn?NO₃?₂+NAA treatments made fruit smaller and more compact.?3?Effect of each treatment on mineral element content showed that K content of the shaded pericarp was more than that of the pericarp exposing to the sun. Three kinds of treatments significantly improved Ca and Zn content. Zn?NO₃?₂ treatment had the best effect on the increasing of Zn content. NAA and Zn?NO₃?₂+NAA treatments significantly reduced K content.?4? Fruit quality analysis showed that NAA treatment significantly increased the soluble solids content and solid acid ratio, Zn?NO₃?₂+NAA treatment significantly reduced the titrate acid content. There was no significant differences in the weight of single fruit,edible rate, Vc content, and the content of reducing sugar between three treatments and CK.?5?Comparation of peel microstructure of ‘Hongjiangcheng' fruit during different development stages showed that the thickness of the pericarp, sarcocarp, epidermis,subhypodermis was thinner and thinner, but the thickness of the exocarp and the diameter of oil cell was almost constant, the thickness of cuticle was thicker and thicker. The thickness of the shaded pericarp, exocarp, subhypodermis was significantly thinner than that of the tissue exposing to the sun. NAA and Zn?NO₃?₂+NAA treatment significantly increased the thickness of the pericarp, sarcocarp and exocarp. NAA treatment significantly increased the thickness of the shaded subhypodermis.?6?The effects of three treatments on morphological characteristics of the vessels of‘Hongjiangcheng' peel showed that Zn?NO₃?₂ and NAA treatments reduced the proportion of spiral vessels, two-end-inclined vessels, dried vessels, and increased the proportion ofreticulated vessels, two-end-horizontal vessels. Three kinds of treatments made the vessels shorter and thicker, the effect of Zn?NO₃?₂+NAA treatment was the best.