Zinc is essential for the healthy growth and reproduction of all organisms (Broadley et al., 2007) and plays a key role in catalytic, regulatory, and structural functions in plants, including carbohydrate metabolism, photosynthesis, and sugar and starch synthesis (Hacisalihoglu et al., 2003). The apple is among the four most popular fruits in the world, and as an essential fruit for human health, high fruit quality is important. Zn deficiencies affect production and quality of all crops, particularly major staple crops; apple cultivars tend to be highly susceptible to Zn deficiency, and the symptoms associated with Zn deficiency have been well documented (Alloway, 2008). Similar to other micronutrients, Zn is not a mobile element within the plant, thus deficiency symptoms are first observed in the youngest leaves (Fageria et al., 2003). Zn deficiency results in reduced leaf and shoot size and photosynthetic rates, ultimately influencing the apple yield and quality (Wang and Jin, 2005; Yan et al., 2010). About 50% of the cultivated soils of the world (Sadeghzadeh and Rengel, 2011), and 51.1% of the soils in China are Zn deficient (Zou et al., 2008). The amelioration of Zn deficiency through soil Zn application is limited by many factors, such as the high soil pH, low soil moisture, and low organic matter (Sarkar and Wynjones, 1982; Sarong et al., 1989), which negatively impact the absorption and upward transport of Zn in the roots; therefore, this method of application requires a long treatment duration, and the effects are not always obvious (Swietlik, 1999). In contrast, Zn application on the aerial parts of plants is an effective, rapid, and economic method for ameliorating Zn deficiency (Swietlik, 2002a).
As Zn application is widely practiced, many cultivation areas show no Zn deficiency. However, it has remained unclear whether continuing the supply of Zn could increase fruit quality. Although many fruit trees were found to be Zn deficient based on leaf Zn analysis (12–13 mg·kg−1 dry weight of leaves), these trees exhibited no Zn deficiency (Swietlik, 2002a). Furthermore, the orchards grown on Zn-amended fields produce fruit of varying quality as a consequence of differences in the Zn nutrition status (Alloway, 2008); thus, it is essential to study the relationship between Zn and apple quality.
Many researchers reported that Zn nutrition is closely related to fruit quality. In Brazil, the foliar application of ZnSO4 and the use of Zn tablets increased the size of coffee beans [Coffea arabica (Poltronieri et al., 2011)]. In Iran, combining the placement of ZnSO4 in holes at the base of the trees with foliar applications increased the Zn concentration of apple fruit tissue from 0.7 to 1.5 mg·kg−1 (Malakouti, 2001); the foliar application of Zn also increased the number and yield of fruit compared with the control treatment (Roosta and Hamidpour, 2011). However, studies about the effects on fruit quality of different forms of foliar Zn applied at different stages of apple tree growth are very few. A single foliar spray of fulvic- and humic-based Zn compounds was equally or more effective than ZnSO4 at being absorbed by vegetative apple seedling tissue (Neilsen et al., 2005), but whether the sugar alcohol zinc is effective has not been clear. Recently, sugar compounds containing Zn have been advocated for use with little information to support their use. The goal of the present study was to compare the effects of the application of ZnSO4 and sugar alcohol Zn sprays separately at different developmental stages on apple fruit quality and make sure that whether continuing the supply of Zn could increase fruit quality of apple trees with no zinc deficiency symptoms.
AllowayB.J.2008Zinc in soils and crop nutrition. 2nd ed. International Zinc Assn. Brussels Belgium
Commission Internationale d’ Éclairage1931Proceedings of the eighth session Cambridge England Bureau Central de la CIE Paris France
DingM.PengS.Z.ZhaoJ.M.2006Nearly 53 years climatic changes at tai'an and its impacts on the development of fruitsJ. Taishan Univ.287073
FageriaN.K.SlatonN.A.BaligarV.C.2003Nutrient management for improving lowland rice productivity and sustainabilityAdv. Agron.8063152
GijsenH.J.QiaoL.FitzW.WongC.H.1996Recent advances in the chemoenzymatic synthesis of carbohydrates and carbohydrate mimeticsChem. Rev.96443474
HacisalihogluG.HartJ.J.WangY.H.CakmakI.KochianL.V.2003Zinc efficiency is correlated with enhanced expression and activity of zinc-requiring enzymes in wheatPlant Physiol.131595602
HippsN.A.DaviesM.J.2001Effects of foliar zinc applications at different times in the growing season on tissue zinc concentrations, fruit set, yield and grade out of culinary apple treesActa Hort.564145151
LiX.X.1994Fresh fruit and vegetable quality and analysis method (in Chinese). China Agricultural Press Beijing China
MalakoutiM.J.2001The effects of balanced fertilization and zinc application on improving apple yield, quality, and reducing browning incidenceActa Hort.564153158
NeilsenG.H.HogueE.J.NeilsenD.BowenP.2005Postbloom humic- and fulvic-based zinc sprays can improve apple zinc nutritionHortScience40205208
NeilsenG.H.NeilsenD.2002Effect of foliar Zn, form and timing of Ca sprays on fruit Ca concentration in new apple cultivarsActa Hort.594435443
NeilsenG.H.NeilsenD.2003Nutritional requirements of apple p. 276–302. In: D.C. Ferree and I.J. Warrington (eds.). Apples: Botany production and uses. CABI Oxfordshire UK
ObradorA.NovilloJ.AlvarezJ.M.2003Mobility and availability to plants of two zinc sources applied to a calcareous soilSoil Sci. Soc. Amer. J.67564572
PoltronieriY.MartinezH.E.P.CeconP.R.2011Effect of zinc and its form of supply on production and quality of coffee beansJ. Sci. Food Agr.9124312436
RoostaH.R.HamidpourM.2011Effects of foliar application of some macro- and micro-nutrients on tomato plants in aquaponic and hydroponic systemsSci. Hort.129396402
SadeghzadehB.RengelZ.2011Zinc in soils and crop nutrition p. 335–375. In: M.J. Hawkesford and P. Barraclough (eds.). The molecular and physiological basis of nutrient use efficiency in crops. Wiley-Blackwell Oxford UK
SarongL.Q.BouldinD.R.ReidW.S.1989Total and labile zinc concentrations in water extracts of rhizosphere and bulk soils of oats and riceCommun. Soil Sci. Plant Anal.20271289
StilesW.C.ReidW.S.1991Orchard nutrition management. Cornell Coop. Ext. Ithaca NY
WangH.JinJ.Y.2005Photosynthetic rate, chlorophyll fluorescence parameters, and lipid peroxidation of maize leaves as affected by zinc deficiencyPhotosynthetica43591596
YanZ.G.ZhangY.Z.ZhangY.H.WangY.A.ZhangF.S.ShuH.R.2010Effects of zinc fertilization on the dynamics accumulation and distribution of dry matter and zinc in apple treesPlant Nutr. Fert. Sci.1614021409(In Chinese)
ZouC.GaoX.ShiR.FanX.ZhangF.2008Micronutrient deficiencies in crop production in China p. 127–148. In: B.J. Alloway (ed.). Micronutrient deficiencies in global crop production. Springer Dordrecht The Netherlands