Citrus black spot is a fungal disease caused by G. citricarpa Kiely [anamorph Phyllosticta citricarpa (McAlpine) van der Aa]. This disease was first described in Australia in the 1890s and has since been found in the humid subtropical regions of Sub-Saharan Africa, Asia, and South America (Paul et al., 2005). Europe has classified G. citricarpa as an A1 quarantine disease (absent from the region) and fruit with CBS are not allowed into the European market (Paul et al., 2005). Almost all commercial citrus cultivars are susceptible to CBS, with sweet oranges, especially mid- to late-harvested cultivars such as Valencia, being the most susceptible. Although CBS does not affect the internal fruit quality, external peel blemishes can render the fruit unmarketable and cause extensive premature fruit drop (Hincapie et al., 2014).
In North America, CBS was first discovered on ‘Valencia’ oranges in Southwest Florida in Mar. 2010 (Schubert et al., 2012). As of this writing, the disease has been found in three counties: Collier, Hendry, and Polk. The infected groves in these counties have been designated restricted quarantine areas (USDA-APHIS, 2012). However, for the Polk County discovery, no subsequent CBS detections have occurred since the initial find in Nov. 2012. The USDA’s pest risk assessment concluded that infected fruit are not a likely vehicle to spread CBS and infected fruit can be shipped to all U.S. states provided grade standards are met and the fruit have been treated according to specific protocols, including washing, brushing, surface disinfesting, imazalil, and/or thiabendazole application and waxing (USDA-APHIS, 2010, 2012). However, previous reports indicated that postharvest thiabendazole or imazalil treatment had no significant inhibition on CBS development (Agostini et al., 2006; Lucon et al., 2010). Infected fruit may develop lesions after packing and shipping that could eventually exceed USDA grade standards, causing economic losses from rejection at destination markets (Canale et al., 2011).
Hot water treatments have been widely evaluated and used to control postharvest decay, reduce physiological disorders, and improve storage quality of a variety of horticultural products (Fallik, 2004). It is an environmentally friendly procedure with increasing acceptability in commercial packinghouses. Ritenour et al. (2003) found that dipping ‘Ruby Red’ and ‘Marsh’ grapefruit from Florida in 59 °C water for 10 s resulted in an approximate 90% reduction in stem-end rot (Lasiodiplodia theobromae) incidence. Porat et al. (2000a, 2000b) found that a short-duration, hot water brushing (56 °C for 20 s) not only reduced surface microorganism and natural decay on citrus fruit, but also induced defensive mechanisms in fruit against decay organisms. Pavoncello et al. (2001) reported that hot water treatment of ‘Star Ruby’ at 62 °C for 20 s increased resistance against green mold (Penicillium digitatum) as well as induced the accumulation of heat-shock proteins, chitinases, and β-1,3-glucanase in grapefruit peel tissue. Fallik (2004) concluded that the reduction in disease development on fruit treated with hot water was mainly due to the induction of plant disease-resistance compounds as well as the reduction in microorganism population on the fruit surface.
In addition, heated solutions have been reported to enhance fungicide effectiveness for postharvest decay control, allowing lower fungicide concentrations to be used on fruit. For example, D’Aquino et al. (2006) showed that dipping citrus fruit in heated (50 °C) imazalil or pyrimethanil solution required 8-or 16-fold lower fungicide concentration, respectively, than treatments at 20 °C for control of P. digitatum or Penicillium italicum. There is currently no report of hot water treatment or heated fungicide treatment to delay CBS lesion development on citrus fruit after harvest.
The objective of this study was to investigate whether hot water or heated fungicide treatments can reduce CBS lesion development on ‘Valencia’ orange fruit. The effects of heat treatments on mycelial growth of G. citricarpa in vitro and the potential changes in fruit quality caused by hot water treatments were also investigated.
AgostiniJ.P.MackenzieS.J.AdaskavegJ.E.2006Effect of fungicides and storage conditions on postharvest development of citrus black spot and survival of Guignardia citricarpa in fruit tissuesPlant Dis.9014191424
BaldassariR.B.BrandimarteI.deAndradeA.G.de SouzaD.C.G.MorettoC.de GoesA.2007Induction of the precoce expression of Guignardia citricarpa symptoms in fruits of pera-rio sweet orange. Rev. Bras. FruiticJaboticabal-SP29269275
BrodrickH.Y.RabieC.J.1970Light and temperature effects on symptom development and sporulation of Guignardia citricarpa Kiely, on Citrus sinensis (Linn) OsbeckPhytophylactica2157163
CanaleM.C.BenatoE.A.CiaP.HaddadM.L.PascholatiS.F.2011In vitro effect of UV-C irradiation on Guignardia citricarpa and on postharvest control of citrus black spotTrop. Plant Pathol.366356361
D’AquinoS.SchirraM.PalmaA.AngioniA.CabrasP.MigheliQ.2006Residue levels and effectiveness of pyrimethanil vs imazalil when using heated postharvest dip treatments for control of Penicillium decay on citrus fruitJ. Agr. Food Chem.5447214726
ErH.L.RobertsP.D.MaroisJ.J.van BruggenA.H.C.2013Potential distribution of citrus black spot in the United States based on climatic conditionsEur. J. Plant Pathol.137635647
HincapieM.WangN.Y.PeresN.A.DewdneyM.M.2014Baseline sensitivity of Guignardia citricarpa isolates from Florida to azoxystrobin and pyraclostrobinPlant Dis.98780789
John-KaruppiahK.RitenourM.A.BrechtJ.K.McCollumT.G.2004Short-duration, hot water treatment for the control of chilling injury and postharvest decay in citrusPro. Fla. State Hort. Soc.117403407
KorfH.J.G.SchutteG.C.KotzéJ.M.2001Effect of packhouse procedures on the viability of Phyllosticta citricarpa, anamorph of the citrus black spot pathogenAfr. Plant Prot.72103109
LuconC.M.M.GuzzoS.D.de JesusC.O.PascholatiS.F.de GoesA.2010Postharvest harpin or Bacillus thuringiensis treatments suppress citrus black spot in ‘Valencia’ orangesCrop Prot.29766772
MilesA.K.WillinghamS.L.CookeA.W.2004Field evaluation of strobilurins and a plant activator for the control of citrus black spotAustral. Plant Pathol.333371378
NevarezL.VasseurV.DebaetsS.BarbierG.2010Use of response surface methodology to optimize environmental stress conditions on Penicillium glabrum, a food spoilage mouldFungal Biol.114490497
PaulI.van JaarsveldA.S.KorstenL.HattinghV.2005The potential global geographical distribution of citrus black spot caused by Guignardia citricarpa (Kiely): Likelihood of disease establishment in the European UnionCrop Prot.24297308
PavoncelloD.LurieS.DrobyS.PoratR.2001A hot water treatment induces resistance to Penicillium digitatum and promotes the accumulation of heat shock and pathogenesis-related proteins in grapefruit flavedoPhysiol. Plant.1111722
PoratR.DausA.WeissB.CohenL.FallikE.DrobyS.2000aReduction of postharvest decay in organic citrus fruit by a short hot water brushing treatmentPostharvest Biol. Technol.18181187
PoratR.PavoncelloD.PeretzY.WeissB.CohenL.Ben-YehoshuaS.FallickE.DrobyS.LurieS.2000bInduction of resistance against Penicillium digitatum and chilling injury in Star Ruby grapefruit by a short hot-water brushing treatmentJ. Hort. Sci. Biotechnol.75428432
RappussiM.C.C.BenatoE.A.CiaP.PascholatiS.F.2011Chitosan and fungicides on postharvest control of Guignardia citricarpa and on quality of ‘Pêra Rio’ orangesSumma Phytopathol.373142144
RitenourM.A.KaruppiahK.J.PelosiR.P.BurtonM.S.McCollumT.G.BrechtJ.K.BaldwinE.A.2003Response of Florida grapefruit to short-duration heat treatments using vapor heat or hot water dipsProc. Fla. State Hort. Soc.116405409
RitenourM.A.BurtonM.S.McCollumT.G.2005Effects of pre- or postharvest gibberellic acid application on storage quality of Florida ‘Fallglo’ tangerine and ‘Ruby’ red grapefruitProc. Fla. State Hort. Soc.118385388
SchubertT.S.DewdneyM.M.PeresN.A.PalmM.E.JeyaprakashA.SuttonB.MondalS.N.WangN.Y.RascoeJ.PictonD.D.2012First report of Guignardia citricarpa associated with citrus black spot on sweet orange (Citrus sinensis) in North AmericaPlant Dis.9681225
ShellieK.C.ManganR.L.2002Cooling method and fruit weight: Efficacy of hot water quarantine treatment for control of Mexican fruit fly in mangoHortScience37910913
SmilanickJ.L.MichaelI.F.MansourM.F.MackeyB.E.MargosanD.A.FloresD.WeistC.F.1997Improved control of green mold of citrus with imazalil in warm water compared with its use in waxPlant Dis.811112991304
USDA-APHIS2010Risk assessment of Citrus spp. Fruit as a pathway for the introduction of Guignardia citricarpa Kiely the organism that causes citrus black spot disease. 9 Dec. 2010. <http://www.aphis.usda.gov/plant_health/plant_pest_info/citrus/downloads/black_spot/cbs-risk-assessment.pdf>
USDA-APHIS2012Quarantine for Guignardia citricarpa Kiely causal agent of citrus black spot (CBS). 16 Mar. 2012. <https://www.aphis.usda.gov/plant_health/plant_pest_info/citrus/downloads/black_spot/DA-2012-09-federalorder.pdf>
YunZ.GaoH.LiuP.LiuS.LuoT.JinS.XuQ.XuJ.ChengY.DengX.2013Comparative proteomic and metabolomic profiling of citrus fruit with enhancement of disease resistance by postharvest heat treatmentBMC Plant Biol.134459
ZhangJ.2007The potential of a new fungicide fludioxonil for stem-end rot and green mold control on Florida citrus fruitPostharvest Biol. Technol.463262270
ZhouY.DengL.ZengK.2014Enhancement of biocontrol efficacy of Pichia membranaefaciens by hot water treatment in postharvest diseases of citrus fruitCrop Prot.638996