PertanikaJ. Trop. Agric. Sci. 27(2): 143 -149 (2004) ISSN: 1511-3701© Universiti Putra Malaysia Press

Effect of Partial Rootzone Drying (PRD) on Growth, Water Use Efficiency(WUE) and Yield of Tomatoes Grown in Soilless Culture

]HASSAN IBRAHIM ALI, 'MOHD RAZI ISMAIL, HALIMI MOHD SAUD 8c2MOHD MOKHTARUDDIN MANAN

department of Crop Science,department of Land Management,

Faculty of Agriculture,Universiti Putra Malaysia 43400 UPM Serdang,

Selangor, Malaysia

Keywords: Partial rootzone drying (PRD), water use efficiency (WUE), yield, tomatoes

ABSTRAK

Satu kajian telah dijalankan di Jabatan Sains Tanaman, Universiti Putra Malaysia (UPM) untuk mengkajipengaruh pengeringan separa akar menggunakan kultur tanpa tanah, campuran 70% habuk sabut kelapa dangambut (3:2) ditambah dengan 30% kompos jerami padi. Tanaman tomato (Lycopersicon esculentum Millcv Red Rock) diberikan dua rawatan air, iaitu pengairan sepenuh (kawalan) dan pengairan secara pengeringansepara akar (PRD). Pengurangan kedapatan air dalam media secara PRD menyebabkan pengurangansignifikan bagi perkembangan daun, luas daun dan konduksi stomata. Prolina meningfcat dengan PRD. Tidakterdapat pengurangan yang signifikan dalam pembahagian bahan kering tanaman dan hasil di antarapengairan penuh dan PRD. Kecekapan penggunaan air meningkat secara signifikan dengan PRD.

ABSTRACT

An investigation was carried out at the Department of Crop Science, Universiti Putra Malaysia (UPM) to examinethe effect of PRD using soilless media, a mixture of 70% coconut coir dust and peat (3:2 respectively) amendedwith 30% rice straw compost Tomato (Lycopersicon esculentum Mill cv Red Rock) plants were exposed totwo different water treatments, which was either well-watered (control) or partially irrigated on half of the roots(PRD). Reduction in water availability in the media with PRD treatment caused a significant decrease in leafexpansion, leaf area and stomatal conductance. Proline was significantly increase with PRD. There was nosignificant reduction in dry matter partitioning and yield between well-watered and PRD-treated plants. Wateruse efficiency also was significantly increased with PRD.

INTRODUCTION

Increasing water use efficiency (WUE) is one ofthe main strategic goals for the researchers aswell as decision makers world wide due to waterscarcity and continuing high demand of waterfor agricultural irrigation. The efficiency ofutilization of irrigation water is often low leadingto around 50% increase in the demand forwater that could be met by increasing theeffectiveness of irrigation. However, theagricultural irrigation uses over 70% of the worldsupplies of clean water and most of this cleanwater is especially used in the protectedenvironments (Ismail and Razi 2002). The useof clean water and chemical solutions as fertilizers

are very cosdy. In addition, the fast growingindustrial sector competes with agriculture forwater resources and the pollutants emitted werethe source of underground water pollution andthis will push the agricultural activities to remoteareas where water and salinity are the majorproblems.

Tomato has more acreage than any vegetablecrop in the world (Ho 1996) and is the secondmost common grown vegetable crop in Malaysia.Therefore, studying the effect of low costirrigation technique such as partial rootzonedrying (PRD) could make substantialcontribution to saving water especially withsoilless culture, since many studies conducted

HASSAN IBRAHIM ALI, MOHD RAZI ISMAIL, HALIMI MOHD SAUD 8c MOHD MOKHTARUDDIN MANAN

under a protected environment showed thesignificance of the use of a soilless culture (Ismailand Razi 2002). Thus, the use of this lowtechnological agronomic manipulation can alsoexploit recent understanding of plant functionsand physiological basis of yield production underlimited resources. In this way, yield can besustained and resource use can be optimized.

PRD is a relatively new irrigation strategy,where at each irrigation time only a part of theroot system is wetted with the complement beingleft to dry to a pre-determined level or time. Itcould save water by 50% and yet maintain yieldas shown for some grape cultivars (Loveys et al2000). Implementing PRD technique is simple,requiring only the adaptation of irrigation systemsto allow alternate wetting and drying part of therootzone. Although the theory of PRD has beendeveloped, little is known about how tomatoesgrowing under warm and humid climaticconditions will respond to this irrigationtechnique. However, it is also important tounderstand the basis of the plant's finely-tunedsensitivity to environmental stresses to overcomethe problems by using either agronomic orgenetic techniques and the advantages of cropgrowth and food production may be substantial.The objective of this study therefore, is tounderstand how PRD works within soilless mediaamended with rice straw compost throughmonitoring of water use efficiency; fruit yieldand vegetative growth, as well as quantifying theimpacts of PRD on proline accumulation withinthe leaf. The hypothesis is that PRD may decreaseleaf area and growth of the plant withoutsignificant reduction in yield and hence, increasewater use efficiency. Stomatal conductance willbe significantly reduced and proline will beincreased in response to PRD technique andthat will be correlated with soil drying.

MATERIALS AND METHODS

Plant Materials

A study was conducted at the Department ofCrop Science, Faculty of Agriculture, UPM,Malaysia. Tomato (Lycopersicon esculentum Mill.)cv Red Rock F1 hybrid was used in this study.Seeds were sown on germination trays with mediaof peat amended with rice straw compost (3:1)and transplanted four weeks later. Seedlingswith the same vigor were transplanted to doublepots, where taproot was removed and the rootsof each plant were approximately divided into

two pots. The plants were placed under shade-house condition with daily average temperaturesof 32 and 28°C day and night, respectively andaverage relative humidity of 65% and 80% dayand night respectively. The plants were trainedvertically, as single stems. Plants were also stakedor trained by using raffia string tied to anoverhead support. At weekly intervals, all auxiliarybuds were removed. When the plants hadproduced a total of three trusses, the maingrowing stem was terminated at the point of twoleaves after the final truss.

Treatments and Experimental DesignSoilless media (coconut coir dust and peat 3:2v/v, respectively) 70%+ 30% rice straw compostwere' used in this study. Two treatments wereused which were either irrigated to drip pointdaily (100% field capacity) with drip irrigationas a control (C) or partial irrigation PRD on halfof the roots alternately (until the moisturecontent reached within 10% of the controlplants). Each cycle of drying was 12 days. Eachpot was irrigated with a single drip emitter, withone irrigation per day to maintain soil waterclose to field capacity. An auto timer was usedand the amount of the water used for eachtreatment was monitored with flow meters placedin each irrigation line and calculated thereafterin kg. Half-Copper solution was used asfertigation fertilizer. The pots were raised toavoid direct contact with the ground and twoweeks later the treatments started.

Parameters

Four pots from each replicate were selectedrandomly from either the both pots irrigatedor half of the roots irrigated for determinationof soil moisture content. The samples were takenfrom a depth of 0-5cm and oven dried at 90°Cfor 72 hours and the moisture content of thesoil sample was determined.

Measurements were carried out on maturedfully expanded leaves (leaf number four fromthe apex of the plant). The measurements weretaken on the abaxial surface of the leaf dailybetween 11:00 and 14:00. All readings wereaccomplished within a one-hour period to avoidthe diurnal pattern of variation in leaves, usinga transit- time promoter (AP-4, Delta T DevicesLtd., Cambridge, UK). Similar leaves were usedfor leaf water potential determination using apressure chamber (PMS, Soil Moisture

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EFFECT OF PRD ON GROWTH, WUE AND YIELD OF TOMATOES GROWN IN SOILLESS CULTURE

Equipment, Santa Barbara, USA). Leaf waterpotential was measured between 12:00 and 15:00.

Newly emerged leaves from four plantswithin each treatment were chosen randomly,labeled and tagged and the length of leaf bladewas measured from the point of petiole insertionwith the leaf blade to the tip of the leaf. Thelength was measured every two days at middayusing a standard ruler.

Determination of free concentration ofproline was based on the method described byBates et al (1973). Proline was extracted fromliquid nitrogen-frozen tissue by homogenizing0.5 g of sampled leaves with 10 ml of 3% aqueoussolution of sulfosalsilic acid at 25°C. Thehomogenate was filtered through Whatman No.2 filter paper. Two ml of the filtrate was reactedwith two ml of glacial acetic acid and two-mlacidninhydrin in a test tube for one hour in awater bath at 95°C. The reaction mixture wasthen cooled in an ice bath. Following that, 4 mlof toluene was added to the reaction mixtureand mixed vigorously with a test tube stirrer for20 seconds. The toluene layer at the top, whichis a pink-red color, was collected with a pipette.The absorbency of the toluene layer was read at520 nm with a spectrophotometer using tolueneas a blank. Standard curve was produced rangingfrom 0 to 30 g/ml of L-proline (Sigma ChemicalCo., St. Louis, Mo.) dissolved in 3% sulfosalsilicacid. Proline standard curve was used to calculateproline concentrations in the samples on freshweight basis.

A destructive sample method was used todetermine leaf area and dry matter production(dry biomass). Total leaf area was measured incm2 using leaf area meter (Delta-T Cambridge,U.K.). Each plant part was put in a paper bagand placed in an oven at 85°C for 72 hr till aconstant weight was reached for dry weightdetermination. Root to shoot ratio and total drymatter production in g per plant was calculatedthereafter. Yield per plant was determined aftereach harvest from an average of ten plants.

Water use efficiency (WUE) was calculatedfor each treatment as function of the harvestyield and total dry biomass (shoot + roots)divided by the actual total amount of waterirrigated as described by Kang et al (2001).

WUEl =Yield(g)

Gross irritation(kg)(1)

Gross irritation(kg)(2)

Statistical Design and Analysis of DataThe treatments (control (C) and PRD (P)) werearranged in a completely randomized designwith three replicates. Data were analyzed usinganalysis of variance and means separationperformed using least significant differences(LSD) at 0.05 levels. Both analyses were doneusing SAS (1997).

RESULTS AND DISCUSSION

Stomatal behavior varied significantly (p< 0.05)in response to ?RD(Fig. 1). PRD significantlyreduced the stomatal conductance gradually. Thisgradual reduction in stomatal was also shown inmany studies with different crop species (Loveyset al 1998; Stoll et al 2000; Awad 2001) might beattributed to the signal coming from the drypart of the root system through the xylem stream.The signal, which may lead, to the partial closureof stomata of PRD plant may be attributed toroot sourced chemical signals. Media dryingpresumably enhanced different hormones andenzymes such as proline and the accumulationresulted in stomatal closure and leaf growthrestriction (Fig. 6).

Fig. 1: Stomatal conductance as affected by PRDapplications or tomato plants groum on soilless culture

Leaf water potential (LWP) showed differenttrend in response to PRD treatment (Fig. 2).This clearly suggested that LWP is stronglyaffected by plant age and the amount of waterapplied under environment of high evaporativedemand occurred, although there were no visualsymptoms due to desiccation in PRD treatment.

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LWP values measured for control and PRDtreatments as a mean for the whole cycle periodwere -0.41 and -0.51 MPa, respectively. MeanLWP value at day 0 was -0.39 MPa and reached-0.64 MPa on day 12. The minimum LWPobserved with two tomato species under completedrying of media to all plant roots under waterstress were -1.8 and -1.4 MPa for L. esculentumand L. pennelliiy respectively after seven days ofwithholding water from the plants as stated byTorrecillas et al (1995). In most split-rootexperiments, where half of the root was irrigatedby 50% of the control, conducted under lowevaporative demand (Ague1 and Duan 1991;Blackman and Davies 1998; Zegbe-Dominguez etal 2003) concluded that leaf water status didnot change under water deficit. However, themaintenance of leaf water potential withdecreasing soil water status is expected due tolow evaporative demand of the atmosphere asreiterated by Hsiao (1990). This might be thereason why differences were not measurable ordue to other limitations such as sensitivity ofinstrumentation, sporadic measurement of waterstatus or the behavior of the stomata to maintainrelatively stable leaf water potential during milddrought (Ague' and Moore 2002).

-025

grapevine stomatal conductance and leafexpansion in order to regulate shoot growth(Loveys 1991).

-0.662 4 6 6 10 12

Day* from atari of ttw traatmanta

Fig 2: Leaf water potential (LWP) as affected by PRDapplication for tomato plants grown on soilless culture

PRD significantly reduced leaf expansion(Fig. 3). There was also a significant relationship(r2 • 0.98) between media drying and leafexpansion (Fig. 6). The concept of using PRD asa technique to control water deficit responsesoriginated from observation that root-derivedabscisic acid was an important factor in regulating

0 2 4 6 8 10Days from start of the treatment

14

Fig. 3: Leaf expansion as affected by PRD application fortomato plants grown on soilless culture

Free proline accumulation seems to be awidespread stress response in higher plants, whichcan reach very high levels within a short timeafter stress induction (Gzik 1995). Thisaccumulation is always induced by hydraulic stressfor osmotic adaptation. However, litde was knownabout the role of non-hydraulic signaling inresponses to PRD in accumulation of the proline.However, proline increased significantly inresponse to PRD (Fig. 4). This indicates thatproline accumulation was dramatically influencedby the root drying. The increase in prolinecontent in stressed plants parts was predo-minantly due to de novo synthesis (Gzik 1995).Therefore, understanding the mechanism behindthe accumulation of proline in response to PRDunder non-hydraulic signaling needs furtherclarification.

PRD significantly reduced leaf area as shownin Table 1. The reduction of leaf area of PRDplant was almost 13% compared to control plants.These results were quite similar to those observedwith PRD tomato plants (Davies et al 2000). Drybiomass, dry shoot and root weights and root toshoot ratio were not significantly differentbetween them for both PRD and control plants.There was very little data that suggested thatroot growth can actually be increased by soildrying in support of this present study. Authorsthat do (Sharp and Davies 1979), attribute sucheffects to a stress of particular magnitude which

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EFFECT OF PRD ON GROWTH, WUE AND YIELD OF TOMATOES GROWN IN SOILLESS CULTURE

10

12 142 4 6 8 10

Days from start of th« treatment*

Fig. 4: Proline accumulation as affected by PRD

application for tomato plants grown on soilless culture

TABLE 1Effect of partial rootzone drying system (PRD) on leaf area, dry matter partitioning, total and marketable

yields and water use efficiency (WUE) of tomato plant grown on soilless culture

Parameter Control PRD LSD C.V.

Leaf area (cm2)Dry whole plant biomass (g)Dry shoot wt (g)Dry root wt. (g)Root to shoot ratioTotal yield (g)Marketable yield (g)Water use efficiencyl (g/kg)Water use efficiency2 (g/kg)

1739.53a45.67a40.00a5.67a0.14a852.8a786.76a1.56b

34.48b

1507.45b41.67a35.17a6.50a0.19a

744.30a721.77a2.39a43.99a

156.79.396.583.310.07

292.12113.320.477.49

4.269.497.7224.0219.5216.146.6310.408.42

Means with the same letter in the same row is not significant difference with Least Significant Difference (LSD)at p< 0.05.

results in increased availability of assimilates toroots, as shoot growth is limited by water deficitin the absence of any effect on carbon gain.More recently, however, Mingo (2003) reportedthat root growth can be stimulated when rootsare dehydrated after a drying episode, relative toroots in moist soil.

In the well-watered plants in which bothsides of the roots were irrigated, moisture contentremained high. Moisture content decreasedprogressively in PRD with time until 10% of thecontrol plants (Fig. 5). This suggested that duringthe stress cycle, part of the plant receivedsufficient water when the other part received asign of water deficit conditions resulting in

different physiological and biological changes,and thus sustain crop yield with minimum water

use.Tomato yield was not significantly affected

by PRD application (Table 1). This result wassupported by numerous studies demonstratingthat PRD application resulted in no significantreduction of crop yield (Loveys 1991). Recentevidence had showed that fruit growth wasregulated by non-hydraulic regulations (Mingoet al 2003). They concluded that restrictions infruit growth rate in plant growing in a partialdrying soil can occur in the absence of anychanges in fruit cellular turgor. It was suggestedthat signals borne within the xylem can travel

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0 2 4 0 8 10Days from Start Crf tn# traatmants

Fig. 5: Media drying as affected by PRD application fortomato plants grown on soilless culture

0.1 0 60.2 03 0.4 0.5

Madia molatura content g/g

Fig, 6: Relationships between media dryingy prolineaccumulation and leaf expansion as affected by PRD

application for tomato plants grown on soilless culture

from root-to-shoot and shoot-to-fruit to elicit apowerful regulatory effect on fruit cell expansion.Other evidence might be that carbohydratelimitations, as showed in this study (data notshown) increased in both leaf and fruit inresponses to PRD application. This might bedue to maintenance of carbohydrate eitherdirectly by some active mechanism or indirectlyvia a relative increase in the sink strength of thefruit (Davies et al 2000). This idea was stronglysupported by Baldet et al (2002) who contrasted

responses to carbohydrate limitation in tomatofruit at two stages of development. They statedthat the plant responses to sugar depletion wereusually by a rapid consumption of carbohydratereserves and/or an arrest of the processes ofcarbon storage. However, in tomato fruit wherethe sugar consumption is slowest when comparedto other sink organs such as tomato young rootsand this may explain why yield did notsignificantly decrease with PRD applicationdespite the significant reduction of the sourceorgan such as leaf expansion (Fig. 3) and leafarea (Table 1).

The pattern of water use by the crop can beused strongly affect by the agronomic means,widely fertilizers, type of soil, water and irrigationtechnique. In this present study PRD significantlyincreased WUE in the two different calculationsas presented in Table 1. These results were inagreement with many findings dealing with PRD(Loveys et al 1998; Stoll et al 2000; Davies et al2000; Zegbe-Dominguez et al 2003). Thesefindings strongly support the idea behind usingPRD with grapes to save and increase water useefficiency without significant reduction (Loveys1991).

CONCLUSIONPRD decreased leaf expansion, stomatalconductance as well as plant leaf area, whereas itincreased proline accumulation. PRD, on theother hand, increased water use efficiency(WUEs) of tomato plants by up to 50%and 28%compared to control plants as dry biomass andtotal yield espectively, without a significantreduction in yield.

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(Received: 10 November 2003)(Accepted: 29 November 2004)

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