Citrus greening or HLB, caused by Candidatus Liberibacter asiaticus (CLas), is the most fatal and quickly spreading citrus disease worldwide (Garnier and Bove, 1983; Gonzalez et al., 2012; Jagoueix et al., 1994). Citrus [Citrus ×sinensis (L.) Osbeck] trees affected by this disease decline in productivity and produce deformed and inedible fruit (Hall and Gottwald, 2011). Currently, there is no known cure for HLB (Raithore et al., 2015), and it has spread throughout the entire state of Florida with an estimated 80% of citrus trees affected (Singerman and Useche, 2015).
Due to the threat of reduced production and negative economic impacts, there is an urgent need for strategies to manage HLB without severely depleting our resources including water. Water is a limiting factor in crop production, particularly in Florida with predominantly sandy soils in citrus-producing regions. During the last six decades, water demands for irrigated crops have increased (Maupin et al., 2014). In the United States, irrigated agriculture consumes more than 80% of total water used and contributes to more than 45% of the total agricultural production costs (Schaible and Aillery, 2012). Recently, the Southwest Florida Water Management District has reported that more citrus growers are exceeding their monthly and yearly permitted water allocations (Ferguson, 2015).
In addition to plant characteristics associated with plant age, health, and structure, SF is impacted by environmental factors including air temperature and soil water availability. Soil water availability is mainly affected by a series of factors including soil physical and chemical properties (e.g., soil texture, structure, organic matter content, and topography), climate factors (e.g., temperature, solar radiation, and rainfall), and vegetation cover. Soil water availability may also affect evapotranspiration by reducing water uptake (Morgan et al., 2006). However, studies investigating relationships between soil moisture and SF can be confusing. Various studies have reported a limited effect of soil moisture on crop SF (Granier et al., 2000; O’Brien et al., 2004). Conversely, others have reported a negative relationship between soil moisture and SF (Holscher et al., 2005).
In Florida, citrus groves are typically planted in areas with sandy soils with low water-holding capacities and organic matter contents. Irrigation strategies that allow growers to increase fruit production without depletion of water resources must be documented and practiced. Scientists are facing tremendous challenges for increasing water efficiency in citrus production systems as a consequence of HLB (Kadyampakeni et al., 2014). Improved water-use efficiency may be achieved by using the proper irrigation schedule (Fereres and Soriano, 2007).
Improving irrigation management is a vital factor in developing sustainable agricultural practices (Fernandez et al., 2008). In addition, there are increasing concerns about the availability of water that must be used in agricultural production (Fereres and Gonzalez-Dugo, 2009; Fernandez et al., 2008). During the last few decades, environmental concerns over water scarcity have stimulated research to invest into new irrigation technologies and more efficient scheduling approaches (Fernandez et al., 2008). Various methods for irrigation scheduling under different crops have been tested. Many of them rely mainly on nondestructive SF measurements (Fernandez et al., 2008; Jones, 2004). Thus, SF measurements play an important role in understanding the dynamics of plant water flow in irrigated crops (Smith and Allen, 1996). The use of nondestructive SF and Ψ measurement methods are exceptionally suited for determining crop water status in irrigation scheduling studies (Ballester et al., 2013).
Investigating improved irrigation practices for HLB-affected trees has not been conducted in Florida or other areas where greening occurs. It has been documented that HLB-affected trees have lower root densities than healthy trees (Hamido et al., 2016; Kadyampakeni et al., 2014), reducing the ability of the tree to take up water and nutrients from dryer soils compared with healthy trees. Thus, field scale experimentation is needed to determine if current citrus irrigation practices need to be changed for citrus trees with HLB. The combination of experiments and demonstrations in a wide range of soils and areas of the state would improve the applicability and adoption of improved irrigation management recommendations. Thus, the objective of this study was to determine the impact of irrigation scheduling on growth and water relations of HLB-affected citrus trees.
BallesterC.CastelJ.TestiL.IntriglioloD.S.CastelJ.R.2013Can heat-pulse sap flow measurements be used as continuous water stress indicators of citrus trees?Irrig. Sci.3110531063doi: 10.1007/s00271-012-0386-5
ChenD.WangY.LiuS.WeiX.WangX.2014Response of relative sap flow to meteorological factors under different soil moisture conditions in rainfed jujube (Ziziphus jujuba Mill.) plantations in semiarid Northwest ChinaAgr. Water Mgt.1362333
Dynamax1990Dynagage installation and operation manual. Dynamax Houston TX
DomingoR.Ruiz-SanchezM.C.Sanchez-BlancoN.J.TorrecillasA.1996Water relations, growth and yield of Fino lemon trees under regulated deficit irrigationIrrig. Sci.16115123
FereresE.Gonzalez-DugoV.2009Improving productivity to face water scarcity in irrigated agriculture p. 123–143. In: V.O. Sadras and D.F. Calderini (eds.). Crop physiology: Applications for genetic improvement and agronomy. Academic Press San Diego CA
FergusonJ.F.2015Southwest Florida Water Management District 2014 estimated water use report: Southwest Florida Water Management District
FernandezJ.E.GreenS.R.CaspariH.W.Diaz-EspejoA.CuevasM.V.2008The use of sap flow measurements for scheduling irrigation in olive, apple and Asian pear trees and in grapevinesPlant Soil30591104
GarnierM.BoveJ.M.1983Transmission of the organism associated with citrus greening disease from sweet orange to periwinkle by dodderPhytopathology7313581363
GasqueM.MartiP.Beatriz GraneroB.González-AltozanoP.2016Effects of long-term summer deficit irrigation on ‘Navelina’ citrus treesAgr. Water Mgt.169140147
GonzalezP.Reyes-De-CorcueraJ.EtxeberriaE.2012Characterization of leaf starch from HLB-affected and unaffected-girdled citrus treesPhysiol. Mol. Plant Pathol.797178
GranierA.LousteauD.BredaN.2000A generic model of forest canopy conductance dependent on climate, soil water availability and leaf area indexAnn. For. Sci.57755765
HamidoS.A.MorganK.T.MahmoudK.A.2016Citrus huanglongbing impact on citrus trees biomass and nutrients uptake. In: Annual soil science society conference. Division: Nutrient management and soil and plant analysis. 24 Feb. 2017. <https://scisoc.confex.com/scisoc/2016am/webprogram/Paper99487.html>.
HandiqueU.EbelR.C.MorganK.T.2012Influence of soil-applied fertilizer on greening development in new growth flushes of sweet orangeProc. Fla. State Hort. Soc.1253639
HolscherD.KochO.KornS.LeuschnerCh.2005Sap flux of five co-occurring tree species in a temperate broad-leaved forest during seasonal soil droughtTrees19628637
JagoueixS.BoveJ.M.GarnierM.1994The phloem-limited bacterium of greening disease of the proteobacteria is a member of the alpha subdivision of the proteobacteriaIntl. J. Syst. Bacteriol.44379386
KadyampakeniD.M.MorganK.T.SchumannA.W.Nkedi-KizzaP.ObrezaT.A.2014Water use in drip- and microsprinkler-irrigated citrus treesSoil Sci. Soc. Amer. J.7813511361
MaupinM.A.KennyJ.F.HutsonS.S.LovelaceJ.K.BarberN.L.LinseyK.S.2014Estimated use of water in the United States in 2010: U.S. Geological Survey Circular 1405. 22 Dec. 2016. <http://dx.doi.org/10.3133/cir1405>.
MorganK.T.BarkatakyS.KadyampakeniD.EbelR.C.RokaF.2014Effects of short term drought stress and mechanical harvesting on sweet orange tree health, water uptake and yieldHortScience49835842
MorganK.T.ObrezaT.A.ScholbergJ.M.S.ParsonsL.R.WheatonT.A.2006Citrus water uptake dynamics on a sandy Florida EntisolSoil Sci. Soc. Amer. J.709097
NadezhdinaN.NadezhdinV.FerreiraM.I.PitaccoA.2007Variability with xylem depth in sap flow in trunks and branches of mature olive treesTree Physiol.27105113
O’BrienJ.J.OberbauerS.F.ClarkD.B.2004Whole tree xylem sap flow responses to multiple environmental variables in a wet tropical forestPlant Cell Environ.27551567
PierceL.L.RunningS.W.1988Rapid estimation of coniferous forest leaf area index using a portable integrating radiometerEcology6917621767
RaithoreS.DeaS.PlottoA.BaiJ.MantheyJ.NarcisoJ.IreyM.BaldwinE.2015Effect of blending Huanglongbing (HLB) disease affected orange juice with juice from healthy orange on flavor qualityLebensm. Wiss. Technol.62868874
SAS Institute2007SAS system for Windows release 9.1.3. SAS Institute Cary NC
SchaibleG.D.AilleryM.P.2012Water conservation in irrigated agriculture: Trends and challenges in the face of emerging demands EIB-99 U.S. Department of Agriculture Economic Research Service
SingermanA.UsecheP.2015Impact of citrus greening on citrus operations in Florida. 19 Jan. 2017. <http://www.crec.ifas.ufl.edu/extension/economics/pdf/Impact%20Citrus%20Greening%20web.pdf>.
Systat Software2009SigmaPlot 12.3. Systat Software Inc. San Jose CA
XuX.TongL.LiF.KangS.QuY.2011Sap flow of irrigated Populus alba var. pyramidalis and its relationship with environmental factors and leaf area index in an arid region of Northwest ChinaJ. For. Res.16144152
YinG.ZhouG.WangX.ChuG.HuangZ.2003A study on sap flux density of two eucalyptus (Eucalyptus ueophylla) plantation in southeastern China by heat-pulse methodActa Ecol. Sin.2319841990