Growth, assimilate partition and yield of melon charenthais under different shading screens

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1 Comunicção científic / Scientific communiction PEREIRA FHF; PUIATTI M; FINGER FL; CECON PR Growth, ssimilte prtition nd yield of melon chrenthis under different shding screens. Horticultur Brsileir 29: Growth, ssimilte prtition nd yield of melon chrenthis under different shding screens Frncisco Hevilásio F Pereir 1 ; Mário Puitti 2 ; Fernndo L Finger 2 ; Pulo Roerto Cecon 2 1 UFCG-CCTA, R. João Leite 517, Centro, Poml-PB; 2 UFV-Depto. Fitotecni, Viços-MG; fhfpereir@hotmil. com; mpuitti@ufv.r; ffinger@ufv.r; pulocecon@dpi.ufv.r ABSTRACT In this experiment we evluted the growth, prtition of ssimiltes nd yield of melons type hyrid Chrenthis Fleuron under different shding nets. The experiment ws conducted t Federl University of Viços, from Novemer 24, 23 to Mrch 11, 24. The tretments consisted of four growth environmentl conditions, s follows: control (full sun), nd under Aluminet 3%-O, Cromtinet 3%-O, Somrite 3%, with reduction of photosynthetic ctive rdition (PAR) of 3.85%, 35.9% nd 32.%, respectively. The experiment ws rrnged in complete rndom design with four replictes. For the periodiclly evluted chrcteristics we used su divided prcel 4 x 7 with the growing conditions in the prcel nd the evlutions on the su prcel (, 14, 28, 42, 56, 7 nd 84 dys fter trnsplnttion). Among the shding nets, overll growth ws superior under Aluminet 3%-O, with similr plnt height, length nd numer of internodes, numer of leves per plnt, lef dry weight, totl nd commercil yield of fruits nd greter lef re per plnt compred to control t full sun. The low numer of dily rdition (4.47 hours) nd the good growth nd yield of the melon when shded y 3.85% with Aluminet 3%-O, re indictives tht this culture does not require elevted levels of rdition s mentioned efore. The growth of melon under prtil restriction of light is promising, opening opportunities to production in new environments s groforestry systems nd ssocited cultivtions. Keywords: Cucumis melo, light, lef re, dry weight, yield. RESUMO Crescimento, prtição de ssimildos e produção de frutos de melão chrentis somredo por diferentes mlhs Ojetivou-se vlir o crescimento, prtição de ssimildos e produção de frutos de melão tipo Chrentis hírido Fleuron em cultivos somredos por diferentes mlhs. O experimento foi conduzido n Universidde Federl de Viços, no período de 24/11/23 11/3/24. Os trtmentos form constituídos de qutro mientes de cultivo: controle (pleno sol) e so s mlhs Aluminet 3%-O, Cromtinet 3%-O e Somrite 3%, com reduções n rdição solr fotossinteticmente tiv (RFA) de 3,85%, 35,9% e 32,%, respectivmente. O delinemento experimentl foi inteirmente csulizdo, com qutro repetições. Pr s crcterístics vlids periodicmente utilizou-se o esquem de prcel sudividid 4 x 7 com os mientes locdos ns prcels e s vlições periódics (, 14, 28, 42, 56, 7 e 84 dis pós o trnsplnte) ns suprcels. Dentre os mientes somredos, o cultivo so Aluminet 3%-O foi o que mis se destcou por ter presentdo resultdos equivlentes o controle qunto à ltur de plnt, comprimento e número de entrenós, número de folhs por plnt, mss sec de folh e produção totl e comercil de frutos e superdo esse qunto à áre folir por plnt. A ix insolção médi diári (4,47 h) e o om desempenho em crescimento e produção do meloeiro, qundo somredo em 3,85% pelo Aluminet 3%-O, são indictivos de que o melão não é um cultur ltmente exigente em luz como se tem pregodo. O cultivo do meloeiro so restrição de luz mostrou-se promissor rindo perspectivs pr o cultivo em sistems groflorestis ou em cultivos ssocidos. Plvrs-chve: Cucumis melo, luz, áre folir, mss sec, produtividde. (Receido pr pulicção em 23 de ril de 29; ceito em 3 de junho de 21) (Received on April 23, 29; ccepted on June 3, 21) Melon (Cucumis melo L.) is n herceous nnul plnt tht develops well under dry, sunny nd hot wether conditions (Fontes & Puitti, 25). The physiologicl processes responsile for growth nd yield in ny cultivted plnt re directly ffected y the climtic conditions (Wien, 1997). The solr rdition is the primry source of energy, eing responsile for keeping photosynthetic processes. Nevertheless, the excess of rdition my dmge the photosynthetic pprtus, since the efficiency of photosynthesis cn e severlly reduced when some plnts re exposed to elevted levels of rdition, ffecting the overll growth nd yield (Mrtinez, 1996). This phenomenon of photosynthesis reduction y the excess rdition is nmed photo inhiition (Tiz & Zeiger, 24). Since the solr rdition is fundmentl for the crop growth nd yield, such interctions hve een oject of mny reserches, with the gol to identify if the intensity nd light qulity interfere on the morphologicl nd physiologicl processes. The melon species require elevted rdition nd temperture to grow, ffecting photosynthesis, respirtion, photorespirtion, trnspirtion nd stomtic conductnce, fctors tht re responsile for the suitle growth nd Hortic. rs., v. 29, n. 1, jn. - mr

2 FHF Pereir et l. high yields (Nknsh et l., 1996; Silv & Cost, 23). However, the generl elieve is tht melon requires high temperture nd rdition levels; which most of the time, is conditioned to low cost growth condition, without studies to evlute the physiologicl processes under these climtic conditions. In Cntloupe nd Honey Dew fields, the rdition sturtion point usully reches levels etween 1, nd 1,2 μmol m -2 s -1 (Kitroongrung et l., 1992; Vlntin et l., 1998); this rdition intensity is well elow tht of tropicl environment, which cn rech vlues ove the 1,8 μmol m -2 s -1 (Nknsh et l., 1996). Some reserches were conducted to determine the effect of shding on the qulity of melons (Nishizw et l., 1998; Nishizw et l., 2). However, there exist only scrce pulictions in which the uthors evluted the effect of shding in order to otin mximum growth nd yield with optimum source/sink rtio. Relted to the wtermelon, Nknsh et l. (1996) found tht the highest yield ws otined with full sun rdition (1,2 μmol m -2 s -1 PAR, mesured t noon), when compred to 5% shded condition (6 μmol m -2 s -1 PAR, mesured t noon). However, the uthors concluded tht under tropicl conditions the rdition cn e superior to 1,8 μmol/m/s PAR, which is ove the rdition otined in this experiment, llowing the growth of wtermelon in groforestry systems nd ssocited crops. Cltyud et l. (2), lso reserching the wtermelon, found tht the highest yield ws otined under shding conditions t 8 μmol m -2 s -1 PAR, mesured t noon, when compred to the yield t full sun with 1,8 μmol m -2 s -1 PAR, mesured lso t noon. This reserch ws conducted to evlute the vritions on the growth of Chrenthis melon plnts, regrding the iomss ccumultion nd fruit yield under shded net conditions. MATERIAL AND METHODS The experiment ws set up in field, on the Federl University of Viços, Mins Geris Stte, from Novemer 24, 23 to Mrch 11, 24, using the hyrid melon Fleuron, type Chrenthis, from the group Cntloupensis. The crop ws grown in soil clssified s Cly Red-Yellow, Câmico, phse terrce, with clyey texture, with the following chemicl chrcteristics: ph in H 2 O (1:2.5)= 5.8; P= 58.5 nd K= 76. mg dm -3 ; C= 4.; Mg=.8; Al=.; H + Al= 6.63; SB= 4.99; CTC effective = 4.99; CTC totl = 8.62 cmol c dm -3 nd OM= 3.33 dg kg -1. The climtic conditions during the period of the reserch re presented on Tle 1. The experiment consisted of four tretments s follows: control (full sun) nd under shding nets Aluminet 3%-O, Cromtinet 3%-O nd Somrite 3%, reducing the PAR y 3.85%, 35.9% nd 32.%, respectively. The nets were instlled in open greenhouses with the dimensions of 2 x 4 x 36 m (height x wide x length). The experiment ws rrnged in complete rndom design with four replictes. Ech plnt chrcteristic ws evluted t every 14 dys, utilizing sudivided prcel scheme 4 x 7, where the environmentl conditions were considered s prcels nd the evlutions t, 14, 28, 42, 56, 7 nd 84 dys fter trnsplnting s su prcels. Before trnsplnting, the soil preprtion consisted of plowing, hrrowing nd open plnting furrows spced 1. m prt on eds uilt to height of 2 cm nd width of 4 cm. The furrows were fertilized ccording to the chemicl nlysis using the recommendtions for the melon crop (Silv & Cost, 23) s follows: 24 kg h -1 of P 2 O 5, 19 of K 2 O (1% from the totl), 15 of N (1% from the totl), 2 of mgnesium sulfte, 2 of orx, 15 of zinc sulfte nd 3 kg h -1 of mmonium molydte. During the crop cycle, plnts were fertirrigted with N nd K, strting fter seven dys from trnsplnting, with totl of 135 kg of N nd 171 kg of K 2 O h -1 split in ten weekly sections t rtes of 5% in the first two weeks nd 1% ech week until 7 dys fter trnsplnting. Sowing ws conducted in greenhouse, on Novemer 24, in 128-cell polystyrene try filled with the commercil sustrte Plntmx with one seed per cell. The plntlets were trnsplnted with three true leves t 1. x.3 m finl spce. The experimentl unit consisted of four 4.5-m long rows, totlling the re of 18 m 2. The two inside rows were considered useful for the nlysis, excluding the externl plnts. Throughout the whole cycle, the plnts were conducted in the verticl position nd with one min stem per plnt. Weed control, irrigtion nd disese control were done s recommended y Silv & Cost (23). In order to evlute the growth nd ssimilte prtition, reproductive nd vegettive eril prts of the plnts were hrvested every 14 dys, eginning t trnsplnting up to 84 dys fter trnsplnting (DAT), totlizing four plnts composing ech tretment. We evluted the length of the min stem, numer nd length of internodes, numer of leves per plnt, re nd dry mtter of the leves nd dry mtter of stem, roots nd fruits. The lef re ws determined using lef meter LI-31 (Li-cor, NE) nd the dry weight (g/plnt) ws otined fter drying the fresh mtter in n oven with ir circultion t 7 o C. The totl dry mtter ws otined y the sum of dry mtter of leves, stems, roots nd fruits. To evlute the totl production we hrvested ripe fruits from five plnts, when the skin color ws chnging from green to greenish-yellow, with the scission lyer well formed (Menezes et l., 2). A totl of ten hrvests ws executed from Ferury 27 to Mrch 11. We considered fruits hving commercil qulity those presenting minimum ttriutes of qulity, fresh mss nd without externl defects or disese symptoms for the mrket (Filgueirs et l., 2). All sttisticl nlysis were performed using SAEG (UFV) softwre. For the growth nd ssimilte prtition sigmoid curve model ws djusted (logistics nd gompertz) nd for the comprison of fruit yield we dopted the Tukey test t 5% proility. RESULTS AND DISCUSSION There ws significnt (p<.5) effect mong the growing environments for ll 92 Hortic. rs., v. 29, n. 1, jn.- mr. 211

3 Growth, ssimilte prtition nd yield of melon chrenthis under different shding screens A B Plnt height (cm) Ŷ=286.93/[ EXP(-.1416T)] R²=.986 Ŷ=294.35/[ EXP(-.1629T)] R²=.9964 Ŷ=262.81/[ EXP(-.1242T)] R²=.9975 Ŷ=286.81/[ EXP(-.1381T)] R²= Length of internodes (cm) Ŷ=7.12/[ EXP(-.1431T)] R²=.996 Ŷ=7.41/[ EXP(-.1593T)] R²=.9964 Ŷ=6.72/[ EXP(-.1459T)] R²=.9953 Ŷ=6.45/[ EXP(-.132T)] R²= C D Numer of internodes Ŷ=42.71/[ EXP(-.937T)] R²=.9931 Ŷ=41.58/[1+7.5 EXP(-.1163T)] R²=.9948 Ŷ=4.35/[ EXP(-.939T)] R²=.9928 Ŷ=38.93/[ EXP(-.153T)] R²=.9996 Lef re per plnt (cm 2 ) Ŷ=9,993.82/[1+1, EXP(-.269T)] R²=.9979 Ŷ=1,15.69/[ EXP(-.1828T)] R²=.9942 Ŷ=1,23.46/[ EXP(-.914T)] R²=.995 Ŷ=7,143.34/[ EXP(-.1134T)] R²= E F Lef numer per plnt Ŷ=6.78/[ EXP(-.1586T)] R²=.9764 Ŷ=59.81/[ EXP(-.1274T)] R²=.9913 Ŷ=51.21/[ EXP(-.1116T)] R²=.9958 Ŷ=47.26/[ EXP(-.124T)] R²= Totl dry weight (g plnt -1 ) Ŷ=239.34/[ EXP(-.973T)] R²=.99 Ŷ=215.8/[ EXP(-.1114T)] R²=.9829 Ŷ=168.49/[ EXP(-.118T)] R²=.9692 Ŷ=121.35/[ EXP(-.1133T)] R²= Figure 1. Growth chrcters nd dry mss ccumultion in melon plnts hyrid Fleuron in cultivtion environments control ( ), Aluminet (*), Cromtinet (+) nd Somrite ( ) (crcteres de crescimento e cúmulo de mss sec em plnts de melão hírido Fleuron nos mientes de cultivo Controle ( ), Aluminet (*), Cromtinet (+) e Somrite ( )). Viços, UFV, 23/24. the morphologicl chrcteristics nd ssimilte prtition (Figure 1 nd 2). Also, there ws significnt effect of the environments over totl nd commercil fruit production (Figure 3). Increses of plnt height up to 37.6 DAT for Aluminet, 36.7 DAT for the control, 39.9 DAT for Cromtinet nd 39.9 for Somrite were detected, tending to n symptotic mximum vlue with higher numer on Aluminet (294.2 cm), control ( cm), followed y Cromtinet ( cm) nd Somrite ( cm) (Figure 1A). The gretest length nd numer of internodes were otined for the control nd Aluminet net, showing tht oth chrcteristics re importnt for the estlishment of plnt height (Figures 1B nd 1C). The est performnce for plnt height ws otined with the control nd Aluminet, ecuse of the comined effect etween length nd numer of internodes, which cn e ttriuted to the higher vlues of solr rdition otined t respective growth environments (Tle 1). One of the importnt chrcteristics of the Aluminet cloth re the twisted luminum fiers, llowing 15% more light diffusion to the shded environment. As consequence, the Aluminet cloth ffects less the photosynthetic process nd plnt growth (Polysck Industries, 23), mking possile higher growth in height compred to the other screens. Prior reserch hs shown tht the growth of melon under high rdition intensity incresed the plnt growth due to etter synthesis nd lloction of ssimiltes (Silv & Cost, 23). Reserching the Cntloupe melon, Crneiro Filho (21) otined longer stems nd internodes under full sun conditions compred to the plnts kept in Hortic. rs., v. 29, n. 1, jn.- mr

4 FHF Pereir et l. A B Lef dry weight (g plnt -1 ) Ŷ=49.99/[ EXP(-.1877T)] R²=.9946 Ŷ=48.69/[ EXP(-.17T)] R²=.9969 Ŷ=46.32/[ EXP(-.1252T)] R²=.9887 Ŷ=29.88/[ EXP(-.1551T)] R²= Stem dry weight (g plnt -1 ) Ŷ=31.42/[ EXP(-.187T)] R²=.9892 Ŷ=27.61/[ EXP(-.1713T)] R²=.9928 Ŷ=21.37/[ EXP(-.1616T)] R²=.9925 Ŷ=16.21/[ EXP(-.1672T)] R²= C D Root dry weight (g plnt -1 ) Ŷ=1.8/[ EXP(-.1545T)] R²=.9815 Ŷ=.91/[ EXP(-.1339T)] R²=.9886 Ŷ=.89/[ EXP(-.1437T)] R²=.9671 Ŷ=1.1/[ EXP(-.1159T)] R²= Fruit dry weight (g plnt -1 ) Ŷ= EXP[-2, EXP(-.132T)] R²=.9895 Ŷ= EXP[-1, EXP(-.1254T)] R²=.9756 Ŷ=99.9 EXP[-1, EXP(-.121T)] R²=.9492 Ŷ=74.64 EXP[-2, EXP(-.1274T)] R²= Figure 2. Growth chrcters nd dry mss ccumultion in melon plnts hyrid Fleuron in cultivtion environments control ( ), Aluminet (*), Cromtinet (+) nd Somrite ( ) (crcteres de crescimento e cúmulo de mss sec em plnts de melão hírido Fleuron nos mientes de cultivo Controle ( ), Aluminet (*), Cromtinet (+) e Somrite ( )). Viços, UFV, 23/24. Tle 1. Climtic conditions during the experiment under full sun (control) nd under shding nets Aluminet 3%-O, Cromtinet 3%-O nd Somrite 3% (ddos climáticos coletdos durnte condução do experimento so condições de pleno sol (controle) e nos mientes so s mlhs Aluminet 3%-O, Cromtinet 3%-O e Somrite 3%). Viços, UFV, 23/24. Wether conditions Control Aluminet Cromtinet Somrite Air temperture (ºC) Minimum Mximum Soil temperture (ºC) Minimum Mximum Reltive humidity (%) Minimum Mximum PAR (μmol m -2 s -1 ) Hours of full sun Rin (mm) 1,28 1,28 1,28 1,28 1 PAR = Photosyntheticlly ctive rdition (rdição fotossinteticmente tiv). plstic greenhouse. The soil temperture lso hs influence on the growth of melon. In this study, the soil temperture in the control environment ws higher (Tle 1), which my hve fvored higher ccumultion of root dry mtter, in comprison to Aluminet, Cromtinet nd Somrite environments (Figure 1). Consequently, the increse in root growth fvors the elevtion of the plnt height. In cucumer, the increse of soil temperture from 2 to 3 o C (JeWook et l., 23) nd from 12 to 36 o C (Dsklki & Burrge, 1997) resulted in tller plnts due to higher growth nd ccumultion of dry mtter in the root system. The lnce etween the ir minimum nd mximum tempertures is lso importnt for the plnt growth. The optimum temperture for the melon growth rnges from 18 to 33 o C (Fontes & Puitti, 25). Under the Aluminet cloth, the temperture ws within the optimum rnge for the melon crop (Tle 1). Tempertures elow 18 o C cn reduce the trnsloction of ssimiltes from the leves (source) to other prts of the plnts (sink), including the stem s oserved y Mitchell & Mdore (1992). For tempertures ove 33 o C the plnt respirtion ecomes high impiring the development of the plnts (Fontes & 94 Hortic. rs., v. 29, n. 1, jn.- mr. 211

5 Growth, ssimilte prtition nd yield of melon chrenthis under different shding screens Yield (t h -1 ) Figure 3. Totl nd commercil yield of melon fruits hyrid Fleuron grown under cloth nets (produção de frutos totl (PT) e comercil (PC) de melão hírido Fleuron em cultivo so mlhs). Viços, UFV, 23/24. Puitti, 25). Silv & Cost (23) found tht the reduction of light intensity hd negtive influence on the growth of melon plnts. Nevertheless, even with the reduction of PAR, under the Aluminet cloth, the increse in diffuse light, in this kind of net, could modulte morphologicl chnges on the fr red wvelength, etween 7 nd 8 nm (Lrcher, 2). In wtermelon, n elevtion of plnt height nd length of internodes were verified when the plnts were sujected to higher proportions of fr red in reltion to red. This trend of higher growth ws reverted when the fr red ws suspended, ut keeping the tretment with red light, showing possile regultion y the phytochrome (Decoteu & Htt-Grhm, 1997; Htt- Grhm & Decoteu, 1997). Increments of lef re were detected up to 36.9 DAT for Aluminet, 34.6 DAT for the control, 45.9 DAT for Cromtinet nd 42.2 DAT for Somrite, tending to n symptotic mximum vlue of 11, cm 2 for Aluminet, followed y 9, cm 2 for the control, 9,997.5 cm 2 for Cromtinet nd 7,79.6 cm 2 for Somrite (Figure 1D). The lef re for the Aluminet ws lso fvored y the expnsion of the lef lmin compred to the control plnts, since the numer of leves etween them ws similr (Figure 1E). The vlues for lef re per plnts were similr etween the control Totl (CV=14,53) Commercil (15,3) Control Aluminet Cromtinet Somrite nd the Cromtinet environments. Although, higher numer of leves ws present in the control plnts, under the Cromtinet, igger lef lmins were present, compensting the lower numer of leves per plnt (Figures 1D nd E). Under the Somrite cloth, in ddition to the reduction of lef numer per plnt, there ws less expnsion of the lef lmin compred to the Aluminet, control nd Cromtinet environments (Figures 1D nd E). The est performnce for plnt lef re ws determined under the Aluminet shde, due to the comined effect of higher lef lmin expnsion nd numer of leves per plnt. Such effects cn e ttriuted to the etter equilirium etween the mximum nd minimum ir tempertures nd y the increment of 15% on the diffuse light compred to full sun (Polysck Industries, 23). As previously discussed for the plnt height, the equilirium etween minimum nd mximum ir tempertures, the increse of diffuse light cn modulte chnges in the plnt morphology. It is well known tht prt of the diffuse light under the Aluminet cloth is composed y wvelengths t fr red, etween 7 nd 8 nm (Lrcher, 2). The higher proportion of fr red compred to red seems to regulte the elongtion of the stem, ut lso the expnsion of the lef lmin y the phytochrome (Tiz & Zeiger, 24). The phytochrome hs two sites of sorption of light, t red (pr) nd t fr red (pfr). When the plnts re sujected to higher quntity of fr red, there occurrs conversion of the phytochrome from pfr to pr, nd the rtio pfr to totl phytochrome diminishes. According to Tiz & Zeiger, 24), the eventul reduction of this rtio, increses the synthesis of gierellins, which enhnces cell expnsion nd division. This kind of morphologicl modultion seems to hve occurred in plnts grown under the Aluminet cloth, llowing etter light use y the plnts, resulting in higher ccumultion of dry mtter (Figure 1F). The morphologicl responses induced y the light qulity, re lso depending on the cultivr, s oserved for the expnsion of lmin lef nd numer of leves mong different cultivrs of lettuce grown under Aluminet 3%-O nd Cromtinet 3%-O nets (Aurre, 23). The smller lef re from the control plnts compred to Aluminet my e relted to the plnt strtegy of reducing the exposing res to conditions of excessive irrdince, which could result in higher energy expending to keep the physiologicl processes of plnt protection, such s the synthesis of crotenoid pigments nd enzymes involved in the photo oxidtive rections (Lrcher, 2). The lower vlues of lef re under Cromtinet nd Somrite seem to e relted not only to the reduction of light intensity, s well s to the light qulity. According to Tiz & Zeiger (24), rtificil conditions tht fvor the increse of lue light in detriment of red light reduction, my lower the cell rte division nd cell elongtion. Crneiro Filho (21), working with melon found smller lef re nd numer of leves under lower light intensities. The uthors concluded tht the light ws not sufficient to promote the synthesis of ssimiltes required for the plnt growth. There ws more increse in totl dry mtter up to 54.2 DAT for the control, 55. DAT for the Aluminet nd 55.9 DAT for the Somrite nets, followed y period of reduction. Then, the mximum symptotic vlues were Hortic. rs., v. 29, n. 1, jn.- mr

6 FHF Pereir et l g/plnt t full sun, followed y g/plnt using Aluminet, g/plnt using Cromtinet nd g/plnt using Somrite cloths (Figure 1). The highest ccumultion of dry mtter t full sun ccounted for the higher vlues of stem, roots nd fruits dry mtter (Figures 2B, C nd D), once these plnts hd similr vlues for the lef dry mtter found for the Aluminet cloth (Figure 2A). Accumultion of totl dry mtter per plnt reched its highest level under full sun, which cn e ttriuted to the etter use of photo ssimiltes in promoting higher root growth; nd s consequence, the use of ll soil resources, which ws fvored y the higher soil temperture (Tle 1). Such fvorle growing conditions llowed n erlier increment of mss nd numer of leves, s well s the mximum symptotic mximum vlues. Thus, the comintion of such fvorle conditions could e responsile for the performnce in ccumulting dry mtter in the different plnt orgns under full sun. Under the Aluminet net, some morphologicl chnges such s expnsion of the lef lmin nd numer of leves per plnt, contriuted to the increment of lef, stem, fruit nd totl dry mtter compred to Cromtinet nd Somrite (Figures 1F, 2A nd 2D). Accumultion of dry mtter y the plnt is the result of the lnce etween totl PAR nd the sored y the leves, y the efficiency in converting to dry mtter nd the prtition etween sources nd sinks (Lrcher, 2). Therefore the synthesis of photo ssimiltes nd their prtition to different orgns t full sun propitited erlier growth nd mximum vlues for the lef, stem, root, fruit nd totl dry mtter compred to the shded tretments. Crneiro Filho (21) found tht t full sun the melon plnts hd higher eril dry mtter compred to plstic greenhouse plnts. And in lettuce, the reduction of solr rdition under Aluminet 3%-O, Aluminet 4%-O nd Cromtinet 3%-O nets reduced the ccumultion of dry mtter in the leves nd roots (Aurre, 24). Higher totl nd commercil fruit production ws otined under full sun nd Aluminet conditions, compred to Cromtinet nd Somrite yields (Figure 3). The highest solr rdition otined under full sun conditions (Tle 1), nd erlier increment on the numer of leves s well s its symptotic vlue (Figure 1E), certinly contriuted to the growth nd ccumultion of dry mtter in the fruits, due to etter use of the solr rdition. Under Aluminet, the lrger expnsion of the lef lmin nd the numer of leves per plnt (Figures 1D nd 1E), which were fvored y the ir temperture nd diffuse light, seem to compenste the reduction of solr rdition, resulting in higher yield compred to Cromtinet nd Somrite environments. The response of melons nd wtermelon to shde hs een controversil. Sin et l. (1991) working with melon nd Nknsh et l. (1996) with wtermelon found higher mss production of fruits under higher rdince intensity of 1,2 μmol m -2 s -1 PAR nd lower ir tempertures (< 33 o C). Even under low rdince intensity of 6 μmol m -2 s -1 PAR, the photosynthesis nd production of fruits were fvored y the lower tempertures. But, Nishizw et l. (1998) concluded tht the shding of 5% did not reduce the melon fruit mss production when compred to full sun yield. Also for wtermelon plnts, the highest yield ws otined under shding conditions with 8 μmol m -2 s -1 PAR compred to the 1,8 μmol m -2 s -1 PAR present under full sun conditions (Cltyud et l., 2). On the other hnd, Nishizw et l. (2) nd SngGyu et l. (23) found tht shding ws responsile for the reduction of melon fruit mss. The melon species presents light sturtion point etween 1, nd 1,2 μmol m -2 s -1 PAR (Kitroongrung et l., 1992; Vlntin et l., 1998), thus well elow the 1,8 μmol m -2 s -1 PAR light present under tropicl full sun shine dy (Nknsh et l., 1996). Under cler skies without clouds, it cn e ssumed tht the reduction of rdition imposed y the nets, did not ffect the photosynthesis nd susequently the growth nd yield of melon, since the vlues of rdition re still within the optimum level required y the crop. But, during the 9 dys of the crop cycle, the numer of hours of full light per dys ws in verge 4.47, much lower thn the 9 hours found in the semi-rid conditions of the Northestern (Silv & Cost, 23). Thus, under cloudy dys, the reduction of solr rdition imposed y the nets could limit the photosynthesis, the plnt growth nd production, ecuse the levels of rdition were elow the sturtion point for the crop, which might reduce the eneficil effects given y the shding cloths. The incidence of low dily sun light nd the good growth nd yield under 3.85% shding given y the Aluminet 3%-O net, indicte tht this melon species does not require elevted levels of light s thought efore. Under semi rid conditions present in the North of Mins Geris Stte nd the Brzilin Northestern, where the dily numer of full light verges 9 hours, the growth under shding cn e promising, opening the possiility for groforestry nd intercrop systems of cultivtion. ACKNOWLEDGEMENTS To CAPES for the concession of D.Sc. scholrship to the fist uthor. REFERENCES ABAURRE MEO. 24. Crescimento e produção de dus cultivres de lfce so mlhs termorrefletors e difusor no cultivo de verão. Viços: UFV. 79 p (Tese mestrdo). CALATAYUD A; DELTORO VI; ALEXANDRE E; BARRENO E. 2. Acclimtion potentil to high irrdince of two cultivrs of wtermelon, Biologi Plntrum 43: CARNEIRO FILHO J. 21. Produção e qulidde de frutos de melão Cntloupe influencids pel pod e pelo tutormento, em condições de estuf e cmpo. Viços: UFV. 12 p (Tese mestrdo). DASKALAKI A; BURRAGE SW The effect of zone temperture on the growth nd root ntomy of cucumer (cucumis stivus L.). 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