Field Performance of Melon Seedlings Hardened by Brushing or with Paclobutrazol

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1 Field Performnce of Melon Seedlings Hrdened by Brushing or with Pclobutrzol M.E. Aystuy 1,, L.F. Hernández 1, 2, R.A. Rodríguez 1, J.A. Fernández 3 nd M.A. Cntmutto 1 1 Dpto. de Agronomí, Universidd Ncionl del Sur, Sn Andrés 85, 8 Bhí Blnc, Argentin 2 Comisión de Investigciones Científics (CIC), Prov. de Buenos Aires, 19 L Plt, Argentin 3 Dpto. de Producción Vegetl, Universidd Politécnic de Crtgen, Pseo Alfonso XIII, 52, 323 Crtgen, Spin Keywords: Cucumis melo, estblishment, stem length nd dimeter, folir re, flowers number, yield components Abstrct Excessive hypocotyl growth observed in greenhouse-grown melon (Cucumis melo vr. scchrinus Nud.) seedlings mkes post-plnting estblishment difficult. The objective of this work ws to determine the effect of seedling s chemicl or physicl hrdening on its re-estblishment, growth, development nd production fter trnsplnting. Seedlings of melon were trnsplnted fter being chemiclly or physiclly hrdened t phenologicl stges expnded cotyledon (ECS) or first true lef (FTLS). Chemicl hrdening ws mde by sprying Pclobutrzol (PBZ) t concentrtion of or 3 mg L -1. Mechnicl hrdening were performed by brushing the seedlings one minute once dy during dys t two intensities: or 4 strokes min -1. Experiments nd evlutions were mde on field trils during three consecutive yers. The two chemicl tretments nd the strokes min -1 mechnicl tretment t the ECS hd the sme effect of improving by 7% seedling estblishment in comprison to the control. The 4 strokes min -1 mechnicl tretment did not show ny improvement in the trnsplnt response. Growth nd yield from mechniclly hrdened plnts ws similr to those from control plnts, wheres chemiclly hrdened seedlings spryed with PBZ produced plnts tht hd good post-trnsplnt growth nd higher fruit yield (25%) compred with to the control. The results demonstrted tht, in order to improve the qulity of melon seedlings nd their growth fter trnsplnting, low concentrtion of PBZ hrdening procedure or low intensity brushing t n erly growth stge is recommended. INTRODUCTION Horticulturl seedlings plnted t high density under conditions of optimum humidity nd nutrient vilbility cn become tll with wek stems. Hrdening nd cclimtiztion re techniques developed during the seedling production period to off set this. Hrdening generlly promotes the compct development of the seedlings to withstnd mechnicl dmge during trnsplnt nd resume ctive growth nd produce cceptble yields (Ltimer, 1998). Sprying seedlings with gibberellin biosynthesis inhibitor is frequent growth control technique. Appliction of Pclobutrzol (PBZ), ((2RS, 3RS)-1-(4-clorofenil)-4,4- dimetil-2-(1h-1,2,4-trizol-1-il)pentn-3-ol) t low concentrtions (Ltimer, 1992; Berov nd Sltev, 2) or soking the seeds of greenhouse-grown species in PBZ solutions before sowing my help reduce plnt growth (Mgnitsky et l., 26). For exmple in tomto (Solnum lycopersicum L.) nd cucumber (Cucumis stivus L.) this technique improves seedling re-estblishment fter trnsplnting nd their further development in the field without finding ny residul elements of the product in the fruits (Mgnitsky et l., 26). mystuy@crib.edu.r Act Hort. (ISHS), 211, 898: Proc. V th IS on Seed, Trnsplnt nd Stnd Estblishment of Hort. Crops Eds.: J.A. Pscul nd F. Pérez-Alfoce Act Hort. 898, ISHS

2 Another hrdening technique is mechnicl conditioning. Brushing cn be used to control stem growth nd qulity of seedlings (Ltimer, 1998). In this cse the effect of mechnicl perturbtions in herbceous plnts vries ccording to the species nd cultivr, but cuses height reduction in the plnt. In some cses, yields of mechniclly hrdened seedlings re similr or lower compred with non mechnicl stressed plnts (Wein, 1996). Few studies hve compred field estblishment efficiency fter chemiclly or mechniclly hrdening horticulturl species. Preliminry trils using cultivrs of greenhouse-grown melon (Cucumis melo vr. scchrinus Nud.) plnts showed tht the seedlings hd excessive hypocotyl growth nd, when trnsplnted to the field, they were dmged by wind ction or brsive effects of snd, with significnt losses in finl yield. The objective of this work ws to determine the effect of two seedling hrdening techniques, chemicl nd physicl, on the re-estblishment, growth, development nd production of the seedling fter trnsplnting. MATERIALS AND METHODS The experiments were conducted in field locted in the vlley of Suce Chico river, Coloni L Merced ( S.; W.), in the northern region of Ptgoni, Argentin. Seedlings of yellow-type melon, hybrid Dordo (Petoseed Co.), were trnsplnted fter being hrdened during the nursery period t the phenologicl stges: expnded cotyledon (ECS) or first true lef (FTLS), t moment of full expnded blde lef. Chemicl hrdening ws mde by sprying Pclobutrzol (PBZ) t concentrtion of or 3 mg L -1. Mechnicl hrdening ws performed by brushing the seedlings once dy during dys t two intensities: or 4 strokes (1 stroke: brush pplied bck nd forth) in minute. Control seedlings were trnsplnted without being treted with some of the hrdening techniques previously described. On the first week of December, seedlings were hnd trnsplnted in the field t 1.5 m between rows nd.8 m between seedlings (plnting density: 8.33 plnt h -1 ) Ech row ws drip irrigted nd covered by blck polyethylene sheet (4 µ thickness) of.6 m width. The distribution of the tretments ws done in three rndomized complete block design. The experiments were conducted during three consecutive yers, defined in this work s experiments I, II nd III. In experiment I totl of 9 tretments, the two hrdening techniques nd the control, were evluted. To improve estblishment nd further development of the plnts, ech hrdening technique ws seprted in two successive yers, experiment II (brushing) nd experiment III (PBZ), with 5 tretments ech. For ll tretments, trnsplnted seedlings tht filed to estblish were not replced. Twenty five dys fter trnsplnting, the percentge of plnts fully estblished nd the percentge of seedlings lost during the post-trnsplnting period were determined. The length nd dimeter of the min stem t 6 cm from cotyledonry node, the number of leves nd the lef re were mesured on 3 plnts per tretment nd repetition using lef re meter LI-COR, mod. LI-3 A. Also, the numbers of mle nd hermphrodites flowers were counted. The dry weight of the eril prt ws obtined fter oven-drying the leves nd stems t 6 C for 3 dys. At hrvest time (75 dys fter trnsplnting), the number of fruits per plnt, the fresh weight per plnt nd the verge fresh weight of the fruits were obtined. The ctul yield (emerging from estblished plnts), the lost yield (tking in ccount seedling loss tht potentilly could produce fruits) nd the potentil yield (ssuming % of seedlings estblishment) were clculted for ech hrdening tretment nd controls. Dt were evluted using the vrince nlysis nested in single blocks for estblishment nd morphologicl vribles, while for the yield components evlution ws done in single blocks. The men vlues of the tretments were compred using the Fisher s LSD test protected t 5% (InfoStt, U.N. de Córdob, Argentin). 3

3 RESULTS AND DISCUSSION Seedling Estblishment 1. Control. In experiments I nd III high losses of control plnts (5%), mostly cused by wind, were observed. In experiment II control plnt loss ws of 25% (Fig. 1). Vlues of temperture nd wind speed re shown in Tble Pclobutrzol. The tretment improved seedling estblishment (75 nd 6%) t both concentrtions t ECS nd 3 mg L -1 t FTLS, compred to the controls for experiments I nd III, respectively (Figs. 1c-d). Pclobutrzol would provide the plnt enough tolernce to wter stress becuse it induces morphologicl dpttions such s n increse root to shoot rtio nd decrese lef in re reduction (Fernández et l., 26). Also, n increse in lef stomtl density of tomto seedlings (Berov nd Sltev, 2) nd n increse in the epicuticulr wxes content in potto (Solnum tuberosum L.) leves (Tsegw et l., 25) were observed. Ltimer (1992) reported n increse in the temperture of the leves of trnsplnted seedlings of tomto, suggesting tht PBZ reduces folir trnspirtion. 3. Brushing. The tretment ws effective in experiments I nd II when it ws pplied t low intensity in ECS, incresing implnttion in 74 nd 4%, respectively (Figs. 1-b). Brushing 4 strokes min -1 t FTLS in experiment II cused seedling mortlity fter trnsplnting (Fig. 1b). Although mortlity ws not significnt (29%) it suggested tht high intensity brushing ws risky prctice. Brushing positively ffects resistnce to posttrnsplnting dverse fctors such s wind in tomto seedlings, which resist wind speeds higher thn 4.4 km h -1 (Grner nd Björkmn, 1999). In numericl model of the melon stem Hernández et l. (26) found tht flexion reduces length nd increses rigidity nd strengthens hypocotyl since mechnicl stimuli ct on the surfce but cn rech the vsculr tissue. Adpttion to flexion chieved by brushing would reduce the lck of control of wter loss through cuticle (Ltimer nd Beverly, 1994). Growth nd Development of Estblished Plnts 1. Pclobutrzol. Plnts obtined from seedlings hrdened with PBZ were more compct nd robust, chieving high degree of lnd covering nd good production of flowers (Figs. 2C nd A). The length nd width of the min stem hd n increse of pproximtely 2 nd 4%, respectively. In experiment I, the number of leves nd lef re were 4 nd 13%, respectively higher thn control plnts. In experiment III, these vribles showed n increse of 3% compred with the control, but they were 5% lower thn those observed in Experiment I. Twenty five dys fter trnsplnting, the number of hermphrodite flowers incresed 3% in ll the tretments with PBZ both yers. The dry weight of the eril biomss of these plnts were between 5 nd 25% higher compred with the control plnts in experiment I nd III, respectively (Tble 2). Wng et l. (1985) determined tht PBZ induces higher levels of chlorophyll content, soluble proteins nd minerl elements in pple (Mlus domestic Borkh.) seedlings. Also, the development of n dditionl lyer of the plisde prenchym observed in leves of melon seedlings treted with PBZ (Aystuy, unpublished dt), suggested tht photosynthetic ctivity nd the bility of recovering their own wter blnce might be incresed (Berov nd Sltev, 2). In ndromonoic melons it hs been found tht the increse in hermphrodite flowers ws cused by the inhibiting effect of PBZ on the gibberellin biosynthesis (Wien, 1997b). 2. Brushing. The tretment did not ffect ppernce nd development of estblished plnts (Figs. 2B nd A). A widening (2%) of the min stem ws observed in both experiments (I nd II) (Tble 2). Grner nd Björkmn (1999) determined tht fter trnsplnting mechniclly treted tomto plnts they resume growth nd bloom t the sme time of the controls. In similr trils crried out with broccoli (Brssic olerce vr. itlic L.) plnts, 14 or 21 dys fter trnsplnting the weight of the eril prt hd higher regrowth rte thn the non-treted plnts (Ltimer, 199). 31

4 Yield 1. Pclobutrzol. When pplied in ECS (experiment I nd III), it led to n increse of 24% in the fresh weight of fruits per plnt compred to controls. The number of fruits per plnt hd n increse of 2 nd 3% compred to the control with the two PBZ concentrtions pplied in FTLS nd to ECS, respectively. The men fruit fresh weight ws similr to tht of the control (Tble 3). Mgnitskiy et l. (26) observed in cucumber plnts treted with PBZ tht the verge weight of the fruits ws lower due to reduction of 4% in their length, while no vritions were observed in tomto fruits. In this species, ppliction of PBZ ccelertes the formtion of fruits nd increses their erly production (Berov nd Zltev, 2). Our results re in greement with report by Dikshit et l. (24) who found tht fter 3 dys from trnsplnting tomto seedlings showed 4% more of fruits in the first cluster nd higher number of flowers in the second cluster. Tomto seedlings spryed with 14 mg L -1 of PBZ did not show yield chnges in while with concentrtions of 6 nd 9 mg L -1 of PBZ the plnt dry weight showed yield reduction of 4 nd 6% fter 9 dys compred with the controls (Ltimer, 1992). Yield loss, considering the estblishment, ws lower in ll the plnts from seedlings hrdened with PBZ, compred to those of the control ones, producing higher vlues for potentil nd ctul yield when PBZ ws pplied to ECS (Tble 3). 2. Brushing. Applied t ECS with n intensity of strokes min -1, fresh weight nd fruit number in the estblished plnts ws similr to those of the controls. In the rest of the brushing tretments reduction of 27 nd 38% in these vribles compred to the controls, in experiments I nd II, respectively ws observed. The tretments tht produced reduction in the number of fruits per plnt showed men fresh weight 25% higher (Tble 3). In experiment I, yield loss ws lower in plnts from brushed seedlings t low intensities t ECS compred to controls. In this experiment the highest ctul yield ws chieved. In experiment II the ctul yield ws similr to the control (Tble 3). In generl, no yield chnges hve been observed in crop plnts when brushing ws pplied during seedling production (Ltimer, 1998). Brushing did not ffect the weight of broccoli inflorescences (Ltimer, 199), the yield of cucumber, wter-melon (Citrullus lntus Schurb.) or summer sqush (Cucurbit pepo L.) (Ltimer nd Beverly, 1994). Brushing on tomto seedlings did not ffect erly production or the first fruits developed in the plnt (Grner nd Bjorkmn, 1999), while in eggplnt (Solnum melogen L.) brushing cused 2% reduction in the men fruit weight (Beverly nd Ltimer, 1994). CONCLUSIONS Hrdening melon seedling t ECS with PBZ ( mg L -1 ) or by brushing t rte of strokes min -1 during dys, results in n pproprite plnt re-estblishment fter trnsplnting compred to non-hrdened seedlings. Plnts from seedlings hrdened by brushing showed similr growth nd yield response to those which hd not been mechniclly treted. Seedlings hrdened with PBZ showed good post-trnsplnting growth which ws reflected in higher crop yield compred to the control. Literture Cited Berov, M. nd Slte, Z. 2. Physiologicl response nd yield of pclobutrzol treted tomto plnts (Lycopersicon esculentum Mill.). Plnt Growth Regultion 3: Beverly, R.B. nd Ltimer, J.G Drought nd mechnicl conditioning of tomto nd eggplnt trnsplnt hve little effect on subsequent yield. Proceedings of the Florid Stte Horticulturl Society 7: Dikshit, S., Bennett, R.J., Precheur, M.D., Kleinhenz, M.D. nd Riedel, R.M. 24. Trnsplnt qulity, disese control nd yield in fresh mrket tomto s ffected by pclobutrzol nd commercil biologicl control gents. Act Hort. 631: Fernández, J.A., Blenztegui, L., Bñon, S. nd Frnco, J.A. 26. Induction of drought tolernte by pclobutrzol nd irrigtion deficit in Phillyre ngustifoli during the nursery period. Scientie Horticulture 7(3): Grner, L.C. nd Björkmn, T Mechnicl conditioning of tomto seedlings 32

5 improves trnsplnt qulity without deleterious effects on field performnce. HortScience 34: Hernández, L.F., Aystuy, M.E. nd Cntmutto, M.A. 26. Computtion of Mechnicl Stress in Melons (Cucumis melo L.) Hypocotyls during Trnsplnt Preconditioning by Brushing. Act Hort. 718: Ltimer, J.G Drought or mechnicl stress ffects broccoli trnsplnt growth nd estblishment but not yield. HortScience 25: Ltimer, J.G Drought, Pclobutrzol, bscisic cid nd gibberellic cid s lterntives to dminozide in tomto trnsplnt production. J. Amer. Soc. Hort. Sci. 117: Ltimer, J.G Mechnicl conditioning to control height. HortTechnology 8: Ltimer, J.G. nd Beverly, R.B Conditioning ffects growth nd drought tolernce of cucurbit trnsplnts. J. Amer. Soc. Hort. Sci. 119: Mgnitskiy, S.V., Psin, C.C., Bennett, M.A. nd Metzger, J.D. 26. Effects of soking cucumber nd tomto seeds in pclobutrzol solutions on fruit weight, fruit size, nd pclobutrzol level in fruits. HortScience 41(6): Mitchell, C.A Recent dvnces in plnt response to mechnicl stress: Theory nd ppliction. HortScience 31: Tsegw, T., Hmmes, S. nd Robbertse, J. 25. Pclobutrzol-induced lef, stem nd root ntomicl modifictions in potto. HortScience 4(5): Wng, S.Y., Byun, J.K. nd Steffens, G.L Controlling plnt growth vi the gibberellin biosynthesis system- I. Biochemicl nd physiologicl ltertions in pple seedlings. Physiol. Plnt. 63: Wein, H.C Chpter: 2, Trnsplnting. In: The physiology of vegetble crops: CAB Interntionl, Wllingford, Inglterr. Wein, H.C. 1997b. Chpter: 9, The Cucurbits: Cucumber, Melon, Sqush nd Pumpkin. In: The physiology of vegetble crops: CAB Interntionl, Wllingford, Inglterr. Tbles Tble 1. Higher, men nd lower wind speeds nd higher, men nd lower tempertures from trnsplnting until fter 25 dys trnsplnting, in the three experiments. Wind speed (km h -1 ) Temperture ( C) Mximum Men Minimum Mximum Men Minimum Experiment I Experiment II Experiment III

6 34 Tble 2. Effect of hrdening methods on morphologicl nd reproductive vribles of melon plnts in three experiments. Abbrevitions: EC: expnded cotyledons; FTL: first true lef. Brushing Pclobutrzol Tretment strokes min -1 strokes min -1 4 strokes min -1 mg L -1 mg L -1 3 mg L -1 Stges of hrdening EC FTL EC FTL EC FTL EC FTL EXPERIMENT I Stem length (cm) b b b b b d c d bc Stem dimeter (cm) b bc.53 b d.57 bc.75 c.64 cd Lef number b b b bc d 32.8 bcd cd 34.8 bcd Lef re (cm 2 ) bc 636 b 813 bcd 694 bc e 918 bcde 1.15 de 1.4 cde Mle flowers number b bc d 28.5 bcd 29.5 cd 3. d Perfect flowers number b 7.8 bc bc c 8.33 bc 13. d 8.33 bc Aeril dry weight (g) b b 6.65 b c 8.71 bc 11.8 c 9.93 bc EXPERIMENT II EXPERIMENT III Stem length (cm) c b d 53.5 b Stem dimeter (cm) b.58 b.65 c.62 bc c.79 b.9 c.82 b Lef number b 43.8 b b 45.8 b Lef re (cm 2 ) b 2.77 b 3.8 b 2.87 b Mle flowers number bc b c 62.5 c Perfect flowers number c 2.66 b 28.8 d c Aeril dry weight (g) c 19.3 b 25.3 c 2.45 b 1 In row, between hrdening tretments within ech experiment, mens followed by the sme letter re not significntly different t P>.5. 34

7 Tble 3. Effect of hrdening methods on yield components nd rel yield of melon plnts in three experiments. Abbrevitions: EC: expnded cotyledons; FTL: first true lef. Brushing Pclobutrzol Tretment strokes min -1 strokes min -1 4 strokes min -1 mg L -1 mg L -1 3 mg L -1 Sttes of hrdening EC FTL EC FTL EC FTL EC FTL EXPERIMENT I Fruit fresh weight (kg plnt -1 ) bcd 5.15 cd 4.45 b 4.56 bc bcd 6.66 e 5.58 d 6.67 e 5.68 d Fruit number per plnt 3.9 b 2.82 b b 4.13 cd 3.88 cd 4.31 d 3.71 c Men fruit fresh weight (kg plnt -1 ) 1.66 b 1.85 b 2.17 c 2.3 c 2.15 c 1.66 b 1.62 b Potentil yield (t h -1 ) bcd cd 37. b bc bcd e d e d Lost yield (t h -1 ) c bc.63 bc 7.6 bc c bc Actul yield (t h -1 ) d b bc e 32.9 cd e d EXPERIMENT II EXPERIMENT III Fruit fresh weight (kg plnt -1 ) c 5.26 c 3.64 b 4.11 b b 6.31 b 6.85 b 5.96 b Fruit number per plnt 2.9 d 2.47 c 1.8 b 2.8 b c 3.68 b 4.25 bc 3.65 b Men fruit fresh weight (kg plnt -1 ) b 2.4 b 1.99 b 2.9 b Potentil yield (t h -1 ) 41.9 c c 3.32 b b b b 57.5 b b Lost yield (t h -1 ).48 b b 7.19 b 7.96 b c b Actul yield (t h -1 ) c c b 27.6 b b 32.6 b b 4.69 b 1 In row, between hrdening tretments within ech experiment, mens followed by the sme letter re not significntly different t P>

8 Figurese ) Totl loss of plnts (%) c EXPERIMENT I Brushing bc bc bc c) c EXPERIMENT I Pclobutrzol bc b) 6 EXPERIMENT II Brushing Totl loss of plnts (%) b b b b d) EXPERIMENT III 6 Pclobutrzol c b strokes min -1 strokes min -1 4 strokes min -1 3 mg L -1 mg L -1 mg L -1 Fig. 1. Effect of hrdening techniques on the totl loss of plnts t 25 dys fter trnsplnting in the three experiments. In ech experiment, hrdening ws pplied t expnded cotyledon (ECS) correspond columns t left nd t first true lef (FTLS) correspond columns t right. Blck columns re control. Within ech experiment, columns with sme letters were not different t P>.5 level. Fig. 2. Twenty-five-dy melon plnts fter trnsplnting where size nd covering re observed on the blck polyethylene mulching A- Plnts from non-hrdened seedlings; B- Plnts from hrdened seedlings by brushing nd C- Plnts from hrdened seedlings by Pclobutrzol. 36