The worldwide production of mango (Mangifera indica L.) is frequently reduced by severe losses of fruit numbers throughout the growing season, a phenomenon that is referred to as premature fruit drop (Singh et al., 2005).
Mango produces an abundance of male and polygamous flowers, but only a small proportion of the latter group is successfully pollinated and has the potential for setting fruit (Mukherjee, 1953; Singh et al., 1966). Numerous abiotic and biotic factors reduce pollen viability (Issarakraisila and Considine, 1994), the fertilization process of the flower, and embryo survival (Lakshminarayana and Aguilar, 1975), which are all commonly associated with extensive fruit drop in early season (Singh et al., 2005). Fruit that remains attracts a greater share of the available tree resources for continued growth and development. Subsequent fruit drop is induced by any factor reducing carbohydrate availability and thus the demand of the growing fruit is not sufficiently matched by its supply (Wünsche and Ferguson, 2005). This carbohydrate imbalance can occur, for example, by air temperatures below 13 °C or exceeding 36 °C as a result of heavily reduced leaf photosynthesis rates (Issarakraisila and Considine, 1994; Whiley et al., 1999; Yamada et al., 1996).
For mango, principal phenological growth stages are distinguished (Hernández Delgado et al., 2011) according to the general BBCH-scale (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie); however, fruit drop is only described in Stage 7 with “beginning and end of the physiological fruit drop” when fruits have attained 10% or 30% of final fruit size, respectively. The premature fruit drop stages have been named invariably and there is also no common agreement on the number of drop stages as well as the onset and duration of each. Dahshan and Habib (1985) originally described three distinct stages of premature fruit drop of mango and this classification was also used in the review of Singh et al. (2005). The first stage is referred to as “post-setting drop” and ceases 60 d after “fruit set” (BBCH-scale 619). The second stage is termed “mid-season drop,” characterized by a duration of 15 d with lesser intensity than during the “post-setting drop.” The third stage is the “pre-harvest drop” with only moderate losses.
These descriptions of premature fruit drop, commonly found in the literature, represent some considerable limitations. The onset of each fruit drop stage is based on a “fixed” number of days from “fruit set” as used for example in the review of Singh et al. (2005). Fruit set, however, is variably related to: 1) time after all flowers have dried out at the end of bloom (Malik and Singh, 2003); 2) 14 d after full bloom (DAFB) (Notodimedjo, 2000); or 3) size of fruitlets (Lam et al., 1985). The flowering of mango is a very prolonged and sometimes non-synchronized process, especially in the tropics where erratic flowering is common but also in the subtropics flowering can occur from a few days of an individual flower, 1 to 2 weeks within a panicle to up to 1 month within a tree canopy (Goguey, 1997; Mukherjee, 1953; Verheij, 1986). Typically, panicles exhibit a hierarchical flowering pattern from distal to proximal with an overlapping continuum of flowering and fruit development (Mukherjee, 1953; Singh, 1954). The terms “full bloom” and “fruitlet size” are often subjectively assessed by scoring and variably defined and thus do not offer precise occurrences that justify a valid comparison of published fruit set data. The duration of each fruit drop stage is clearly dependent on seasonal, regional, and cultivar-specific variability and therefore the “fixed time after fruit set” definition might be useful for characterizing the annual drop pattern of a given cultivar in one location but is not appropriate when comparing multiple data sets. Consequently, the main objective of this study is to provide a new approach for interpreting and evaluating fruit drop data, attempting to overcome or at least to alleviate the limitations described. Consequently, fruit drop of two mango cultivars was monitored in largely different cropping and management systems over six seasons in the Province Sơn La in North Vietnam and data were tested and validated in a mathematical model.
Unfavorable environmental cues, particularly when temperature extremes coincide with severe drought conditions (Elsheery et al., 2007), are thought to be key triggers for the extensive premature fruit drop patterns in this province. Huong (2010) further suggested poor orchard management, in particular insufficient pest management, as an additional cause of fruit drop for the local mango cultivars Hôi and Tròn predominantly cultivated in this region.
Despite extremely low orchard productivity of ≈1 t·ha−1 (Yên Châu, 2008, Statistical Data of Yên Châu District, Statistical Department, unpublished data), mango trees are often planted either in monoculture or in intercropping systems with mainly maize in the mountainous Province of Sơn La with steep, sloping hillsides. Indeed, tree crops, including mango, provide a more appropriate and sustainable land use system for steep, deforested slope sites (Roberts-Nkrumah, 2000; Young, 1989), because the cultivation of annual crops in monocropping systems under those topographical conditions will lead to reduced soil fertility and severe soil erosion (Clemens et al., 2010). In particular during the juvenile phase of tree crops, intercropping with annuals is a common practice (Musvoto and Campbell, 1995; Roberts-Nkrumah, 2004). However, it has been reported that some plant species enhance mango fruit drop in intercropping systems (Singh et al., 2005).
Crop management strategies such as irrigation or plant growth regulator (PGR) applications may also offer opportunities for fruit drop prevention. Galán Saúco (1997) suggested that the water requirement of mango is ≈100 mm monthly during the fruit development period to ensure good productivity. However, this level is typically lower during early fruit development in the Province of Sơn La (Roemer et al., 2011) with water deficiency particularly prevalent from bloom to midseason drop as a result of the lack of precipitation or irrigation sources. Alternatively, applications of PGRs are commonly used for enhancing fruit retention in many perennial fruit crops, including mango. For example, CPPU increased fruit retention in different mango cultivars and growing regions (Burondkar et al., 2009; Notodimedjo, 2000). Similar effects were shown when GA was applied either alone or in combination with other PGRs (Benjawan et al., 2006; Chen, 1983; Notodimedjo, 2000; Oosthuyse, 1993, 1995; Ram, 1983; Singh, 2009). Moreover, the synthetic auxin NAA is another fruit drop-reducing PGR with a timely different efficacy; fruit retention is less affected when applied around post-bloom rather than at later fruit developmental stages (Chattha et al., 1999; Notodimedjo, 2000).
In summary, the largely equivocal assessment and description of fruit drop in mango render the comparison and interpretation of published data extremely difficult to draw general conclusions and providing horticultural recommendations. We therefore attempt to offer not only a new approach for assessing fruit drop data, based on a simple mathematical model, but also to newly characterize this process that occurs throughout the growing season from first flower to just before harvest. In particular, describing the fruit drop process, we are re-evaluating the appropriateness of existing terminologies in this context and offering more precise benchmarks for onset and duration of each fruit drop stage. For a robust evaluation and validation of our model as well as the interpretation of the seasonal fruit drop continuum, fruit abscission was monitored over several years in varying mango production systems.
AsifM.UsmanM.FatimaB.LaskaniM.I.KhanM.M.2002Fruit set and drop behaviour of three commercial cultivars of mangoPak. J. Agr. Sci.39129131
BenjawanC.ChutichudetP.ChanaboonT.2006Effect of gibberellin (GA3) on fruit yield and quality of Kaew mango (Mangifera indica L.) cv. Srisaket 007 in Northeast ThailandPak. J. Biol. Sci.915421546
BhuyanM.A.J.IrabagonJ.A.1993Effect of fertilizer, potassium nitrate and irrigation on fruit drop of ‘Carabao’ mangoSouth Indian Hort.41315321
BolkerB.M.BrooksM.E.ClarkC.J.GeangeS.W.PoulsenJ.R.StevensM.H.H.WhiteJ.-S.S.2009Generalized linear mixed models: A practical guide for ecology and evolutionTrends Ecol. Evol.24127135
BurondkarM.M.JadhavB.B.ChettiM.B.2009Post-flowering morpho-physiological behavior of Alphonso mango as influenced by plant growth regulators, polyamine and nutrients under rainfed conditionsActa Hort.820425432
ChatthaG.A.AnjumM.A.HussainA.1999Effect of various growth regulators on reducing fruit drop on mango (Mangifera indica L.)Intl. J. Agr. Biol.1288289
ChenW.-S.1983Cytokinins of the developing mango fruit: Isolation, identification, and changes in levels during maturationPlant Physiol.71356361
ClemensG.FiedlerS.CongN.D.Van DungN.SchulerU.StahrK.2010Soil fertility affected by land use history, relief position, and parent material under a tropical climate in NW-VietnamCatena818796
DahshanD.I.HabibS.1985Seasonal changes in endogenous auxin like substances in relation to fruit drop in mangoProc. Egypt. Bot. Soc.4769780
DamourG.VandameM.UrbanL.2009Long-term drought results in a reversible decline in photosynthetic capacity in mango leaves, not just a decrease in stomatal conductanceTree Physiol.29675684
DavenportT.L.2006Pruning strategies to maximize tropical mango production from the time of planting to restoration of old orchardsHortScience41544548
ElsheeryN.I.WilskeB.ZhangJ.-L.CaoK.-F.2007Seasonal variations in gas exchange and chlorophyll fluorescence in the leaves of five mango cultivars in southern Yunnan, ChinaJ. Hort. Sci. Biotechnol.82855862
FAO2006World reference base for soil resources: A framework for international classification correlation and communication. World soil resources report No. 103. Food Agric. Organ
FAOSTAT2012Statistical database of the Food Agric. Organ. 20 July 2013. <http://faostat.fao.org>
GonzálezA.LuP.MüllerW.2004Effect of pre-flowering irrigation on leaf photosynthesis, whole-tree water use and fruit yield of mango trees receiving two flowering treatmentsSci. Hort.102189211
Hernández DelgadoP.M.ArangurenM.ReigC.Fernández GalvánD.MesejoC.Martínez FuentesA.Galán SaúcoV.AgustiM.2011Phenological growth stages of mango (Mangifera indica L.) according to the BBCH scaleSci. Hort.130536540
HuongP.T.2004Impacts of thinning and pre-harvest bagging on growth, yield and fruit’s appearance of mango grown in Sap Vat commune, Yên Châu district, Sơn La provinceJ. Sci. Dev.5234328
IFPRI2002Fruits and vegetables in Vietnam: Adding value from farmer to consumer. Int. Food Policy Res. Inst. Washington DC
IwahoriS.TominagaS.YamasakiT.1988Stimulation of fruit growth of kiwifruit, Actinidia chinensis Planch., by N-(2-chloro-4-pyridyl)-N'-phenylurea, a diphenylurea-derivative cytokininSci. Hort.35109115
LakshminarayanaS.AguilarP.H.1975Effect of orchard heating in reducing parthenocarpic fruit in ‘Haden’ mangoProc. Fl. St. Hort. Soc.88502505
LamP.F.NgK.H.OmarD.TalibY.1985Fruit-drop and growth, respiration and chemical changes in ‘Golek’ mangoMalaysian Agr. Res. Dev. Inst. Bul. Penyelidikan.13814
LarsonK.D.SchafferB.DaviesF.S.1989Effect of irrigation on leaf water potential, growth and yield of mango treesProc. Fl. St. Hort. Soc.102226228
MehouachiJ.SernaD.ZaragozaS.AgustiM.TalonM.Primo-MilloE.1995Defoliation increases fruit abscission and reduces carbohydrate levels in developing fruits and woody tissues of Citrus unshiuPlant Sci.107189197
NotodimedjoS.2000Effect of GA3, NAA and CPPU on fruit retention, yield and quality of mango (cv. Arumanis) in East JavaActa Hort.509587600
Núñez-EliseaR.DavenportT.L.1983Abscission and ethylene production in mango (Mangifera indica L.) fruit cv. Tommy AtkinsProc. Fla. Hort. Soc.96185188
OosthuyseS.A.1993Effect of spray application of KNO3, urea and growth regulators on the yield of ‘Tommy Atkins’ mangoSouth African Mango Grow. Assn Yrbk.135862
OosthuyseS.A.1995Effect of post-bloom aqueous spray application of GA3, NAA, and CPPU on fruit retention, fruit size and yield in Tommy Atkins and Heidi mangoSouth African Mango Grow. Assn. Yrbk.153133
PrakashS.RamS.1984Naturally occurring auxins and inhibitor and their role in fruit growth and drop of mango ‘Dashehari’Sci. Hort.22241248
Roberts-NkrumahL.B.2000The establishment and growth of young mango trees in on-farm hillside trials in Trinidad, W.IActa Hort.509705712
RoemerM.G.HegeleM.WünscheJ.N.HuongP.T.2011Possible physiological mechanisms of premature fruit drop in mango (Mangifera indica L.) in Northern VietnamActa Hort.9039991006
RuizR.García-LuisA.MonerriC.GuardiolaJ.L.2001Carbohydrate availability in relation to fruitlet abscission in citrusAnn. Bot. (Lond.)87805812
SinghR.N.1954Studies on the floral biology and subsequent developments of fruits in the mango (Mangifera indica L.) varieties of Dashehari and LangraIndian J. Hort.116988
SinghR.N.MajumdarP.K.SharmaD.K.1966Sex-expression in mango (Mangifera indica L.) with reference to prevailing temperatureProc. Amer. Soc. Hort. Sci.89228229
SpreerW.OngprasertS.HegeleM.WünscheJ.N.MüllerJ.2009Yield and fruit development in mango (Mangifera indica L. cv. Chok Anan) under different irrigation regimesAgr. Water Mgt.96574584
StinoR.G.El-WahabS.A.M.A.HabashyS.A.KelaniR.A.2011Productivity and fruit quality of three mango cultivars in relation to foliar sprays of calcium, zinc, boron or potassiumJ. Hort. Sci. Ornam. Plant.39198
SukhvibulN.WhileyA.W.SmithM.K.HetheringtonS.E.2000Susceptibility of mango (Mangifera indica L.) to cold-induced photoinhibition and recovery at different temperaturesAustral. J. Agr. Res.51503513
WhileyA.W.SaranahJ.B.RasmussenT.S.WinstonE.C.WolstenholmeB.N.1988Effect of temperature on growth of ten cultivars of mango with relevance to production in Australia. Proc. 4th Austral. Conf. Tree and Nut Crops. p. 176–185
WhileyW.A.SearleC.SchafferB.WolstenholmeN.B.1999Cool orchard temperatures or growing trees in containers can inhibit leaf gas exchange of avocado and mangoJ. Amer. Soc. Hort. Sci.1244651
YamadaF.FukamachiH.HidakaT.1996Photosynthesis in longan and mango as influenced by high temperatures under high irradianceJ. Jpn. Soc. Hort. Sci.64749756
YoungA.1989Agroforestry for soil conservation. CAB International Wallingford UK
YuanR.HuangH.1988Litchi fruit abscission: Its patterns, effect of shading and relation to endogenous abscisic acidSci. Hort.36281292