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Crop Protection 27 (2008) 678–688

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Effects of limiting irrigation and of manual pruning on brown rotincidence in peach

Vincent Merciera,�, Claude Bussia, Daniel Plenetb, Franc-oise Lescourretb

aINRA (Institut National de la Recherche Agronomique), Domaine de Gotheron, Unite Experimentale Recherches Integrees, 26320 St.

Marcel-les-Valence, FrancebINRA, Domaine Saint-Paul, Site Agroparc, Unite Plantes et Systemes de culture Horticoles, 84914 Avignon Cedex 9, France

Received 10 August 2007; received in revised form 19 September 2007; accepted 26 September 2007

Abstract

To limit peach brown rot incidence in 4-year-old late maturing peach trees, cultivar ‘Nectaross’, four combinations of irrigation and

pruning treatments were assessed: conventional (Conv) irrigation (I) and pruning (P) (ConvI+ConvP); modified (Mod) irrigation

and conventional pruning (ModI+ConvP); conventional irrigation and modified pruning (ConvI+ModP); and modified irrigation and

pruning (ModI+ModP). Modified irrigation and pruning involved water deprivation and manual pruning, respectively. In 3 successive

years, in the conditions of the Middle Rhone Valley in France, the lowest brown rot incidences were detected under (ModI+ModP) and

the highest under (ConvI+ConvP), whereas brown rot incidences under (ModI+ConvP) and (ConvI+ModP) were intermediate. The

lower brown rot incidences under modified treatments occurred before fruit maturity and were maintained until post-harvest storage.

They suggest that appropriate cultural practices, water deprivation and manual pruning possibly decrease peach disease sensitivity, and

this could result in reducing use of pesticide sprays against brown rot in orchards. Moreover, water deprivation and manual pruning

tended to enhance peach taste quality—measured as a decrease of fruit firmness, and increase of total soluble solids—compared with

conventional irrigation and pruning, but the average fruit weight decreased under the modified treatments. Nevertheless, because of the

increase in marketable first-class fruit as a result of water deprivation and in fruit yield as a result of manual pruning, the relative

profitability of fruit production tended to be higher under the modified treatments than under conventional conditions.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Prunus persica; Monilinia; Disease sensitivity; Water restriction; Fruit quality

1. Introduction

Brown rot, mainly caused by Monilinia fructicola

(G. Wint.) in California and Monilinia laxa (Aderh. andRuhl.) in Europe (Palou et al., 2003; Mari et al., 2004), isthe leading stone fruit disease in Southern France (Mercieret al., 2003). Weather conditions conducive to brown rotlead to considerable economic losses in the peach sector(Barkai-Golan, 2001). Prophylactic measures, like remov-ing cankers and mummies from the orchard every winter inorder to limit brown rot inoculum, mostly fail in reducingbrown rot incidence to tolerable levels (Arnoux, 1981).Thus, this pathogen is mainly controlled by fungicide spray

e front matter r 2007 Elsevier Ltd. All rights reserved.

opro.2007.09.013

ing author. Tel.: +334 75 59 92 16; fax: +33 4 75 58 86 26.

ess: mercier@avignon.inra.fr (V. Mercier).

programmes in the field and alternative methods tofungicide spraying in the orchard have not been assessed,with the exception of rain protective covering in sweetcherry (Borve et al., 2007).Now, an important challenge exists for fruit growers

concerning the reduced use of pesticides in peach orchards,in compliance with integrated pest management rules.More generally, guidelines referring to sustainable agricul-ture systems emphasize reducing inputs (irrigation water,pesticides, etc.). Cropping practices in peach orchards canbe adapted to contribute to these aims; with regard to thistopic, irrigation scheduling and pruning managementappear of particular interest (Arnoux, 1981).When applied throughout the entire peach-growing

period, including that of rapid fruit growth (Stage III),water restrictions in orchards were shown to be highly

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decisive in terms of peach quality, notably by increasingtotal soluble solids and by decreasing fruit size (Naor et al.,2001). Crisosto et al. (1994) also detected a decrease in fruitwater loss with restrictive irrigation, due to the formationof a thicker fruit cuticle. Miller et al. (1997) corroboratedthis finding, adding that microcracking of the fruitepidermis might be reduced by limiting the water supply.Given that fruit cracks are assumed to be the preferentialpathway of pathogen invasion (Kamamoto et al., 1990;Gibert et al., 2005), water restrictions in the peach orchardwere logically reported to reduce the sensitivity of thepeach to brown rot (Li et al., 1989a). But this effect hadonly been assessed in post-harvest storage conditions. Theimpact of water restriction on brown rot incidence duringthe entire fruit-growing period in the peach orchard shouldtherefore be determined.

Light transmission through the tree canopy appears tobe crucial for improving peach tree growth, cropping andfruit quality (Walcroft et al., 2004). A new concept of treepruning—centrifugal pruning—was proposed in apple forthis purpose (Willaume et al., 2004). The aim of thismethod is to optimize the relationship between vegetativegrowth and fruiting, especially by encouraging the close-ness of leaves and fruit at the periphery of the tree (Lauriet al., 2004). Pest incidence, notably scab, was reduced inapple orchards where centrifugal pruning was used,compared with those that were conventionally pruned; itwas hypothesized that the microclimate created inside thecanopy was less favourable to pest development (Simonet al., 2006). When applied to the peach tree (Navarro andPlenet, 2002), this innovative pruning method was referredto as manual pruning because it was performed by hand(Plenet et al., 2004). It mainly consists of removing shootsof the tree that limit light penetration inside the canopymuch earlier than in conventional summer pruning. Sincescab control appeared to be effective in apple orchardsunder centrifugal pruning (Simon et al., 2006), weproposed to test the effect of manual pruning on theincidence of brown rot in peach trees.

Combinations of different irrigation and pruning prac-tices were studied over a 3-year period in a 4-year-oldpeach tree orchard, cultivar ‘Nectaross’, in Middle RhoneValley conditions, to compare the effects of waterdeprivation and manual pruning (specific or combinedeffects) on the incidence of peach brown rot with that ofconventional irrigation and pruning practices. Since theadoption of alternative methods depends on their ability tomaintain sound agronomic performance, the effects ofthese cultural practices on tree growth, fruit yield andquality were also assessed.

2. Materials and methods

2.1. Orchard description

This study was carried out in a peach tree orchardplanted in 2000 at INRA’s Gotheron Experimental Station

near Valence in the Middle Rhone Valley in France. Thesoil was stony alluvial with 15% clay, 30% silt and 54%sand, considered particularly suitable for growing peachtrees (Bornand, 1968).The area of the experimental orchard was 0.45 ha.

‘Nectaross’, a late maturing nectarine (Prunus persica (L.)Batsch) cultivar, grown on GF305 rootstock, was plantedin an open vase training system (4� 5m). Approximatedates of flowering, beginning of Stages II and III, andharvest were 20 March, 10 June (80 d after full bloom,DAFB), 10 July (110 DAFB) and 10 August (150 DAFB),respectively. Routine horticultural care for fertilization andsoil management was provided (Huguet, 1978). Hand-thinning was carried out in May to leave 10–15 cm betweenfruit along the fruiting shoots in order to ensure suitablefruit size (Mitcham, 1980). Crop phytoprotection wasmanaged according to the integrated pest managementsystem (ACTA, 1979). However, no phytoprotectionmeasures were taken against brown rot in order to observethe effect of water and pruning management on theincidence of this disease. Cankers and mummies wereremoved from the entire orchard every winter in order tostandardize brown rot inoculum among the differenttreatments. Furthermore, in summer, pathogens wereisolated from infected fruit and incubated on potatodextrose agar (Merck) in Petri dishes at 25 1C, with 12 hdark/12 h light cycles for 10 d (Mercier et al., 2003). M.

fructicola and M. laxa were identified, but their relativeimportance in the orchard had not been determined.A microjet irrigation system was installed with two

emitters per tree, at a distance of 1m from the tree. Eachemitter had a discharge rate of 30 l h�1. Rainfall wasmeasured at the site (about 800mm on the average for thepast 10 years) and evapotranspiration (ETo) was calculatedusing the Penman equation.

2.2. Experimental set-up

In 2003, the homogeneity of the experimental area waschecked by measuring tree trunk circumferences of theexperimental orchard, which comprised nine tree rows.The experiments were performed on four tree rows, the fiveother tree rows being considered to be guard rows. Guardrows were arranged so that all experimental units weresurrounded by an equal number of trees. Two irrigationand two pruning treatments (defined below) were com-bined so as to carry out four treatments: conventional(Conv) irrigation (I) and pruning (P) (ConvI+ConvP);modified (Mod) irrigation and conventional pruning(ModI+ConvP); conventional irrigation and modifiedpruning (ConvI+ModP); and modified irrigation andpruning (ModI+ModP). Modified irrigation and pruningconsisted in water deprivation and manual pruning,respectively. These four treatments were randomly appliedin four blocks. Each of the 16 experimental units comprisedfive trees, and the three central trees were used forsampling. All the guard trees of the area were stripped of

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fruit early each year in May to prevent the experimentaltrees from being contaminated by brown rot.

2.3. Irrigation treatments

A tensiometer was installed at three sites of theconventional irrigation plots at a distance of 0.50m fromthe emitter and a depth of 0.35m. The first irrigation wascompleted when the soil water potential (C soil) reached�40 kPa for at least two of the three tensiometers (Li et al.,1989b). The soil water potential was then monitored duringthe irrigation period in order to verify that no water excessoccurred during the season, which was effectively the case(data not shown). The following irrigations were calculatedto replace crop evapotranspiration (ETc), minus anyeffective rainfall. ETc was estimated by multiplyingreference ETo by a crop coefficient (Kc) adapted to peach(Goldhamer and Snyder, 1989). Kc was modified accordingto the stage of fruit development (Ayars et al., 2003): initialKc was 0.6 during Stage I, mid-season Kc was 1.0 duringStage II and 1.2 during Stage III, late season Kc was 0.6after harvest. These crop coefficients corresponded to thoseusually recommended to fruit growers in the area byagricultural extension services.

For water-deprived trees, no water was applied duringthe first phase of fruit development (Stage I), and irrigationwas applied at one-third the frequency of the controlirrigation during the fruit pit-hardening phase (Stage II).During the final phase of rapid fruit growth (Stage III),irrigation was applied at 20% of the control irrigationamount in 2003 and 2004, and at 40% in 2005. Afterharvest (Stage IV), the irrigation supply remained equiva-lent to that of the conventional plot. The volumes of waterapplied during the 3 years at the various fruit stages for thetwo irrigation treatments are given in Table 1. Globally,irrigation water applied to water-deprived (ModI) treesrepresented 29%, 27% and 38% of irrigation water appliedto conventional irrigation (ConvI) plots in 2003, 2004 and2005, respectively. In 2003 and 2004, micromorphometric

Table 1

Water (mm) applied in the peach orchard, cultivar ‘Nectaross’, at various

stage of fruit development

Year Treatment Stage I Stage IIa Stage III Stage IV Total

mm % ConvI

2003 ConvIb 120 270 230 40 660

ModIc 0 100 50 40 190 29

2004 ConvI 90 260 290 40 680

ModI 0 80 60 40 180 27

2005 ConvI 100 230 280 50 660

ModI 0 80 120 50 250 38

aOn average, Stages II, III and IV begin at 80, 110 and 145 DAFB (days

after full bloom), respectively.bConvI: conventional irrigation according to crop evapo-transpiration.cModI: modified irrigation (water deprivation).

sensors were installed on the branches of water-deprivedtrees (Katerji et al., 1994). These sensors made it possible tocontrol tree response to water deprivation (data not shown)(Huguet et al., 1992).

2.4. Pruning treatments

Conventional pruning consisted of a dormant (beginningof March) and a summer (mid-July) pruning (Marini,1985). Our conventional pruning corresponds to themethod usually performed by the fruit growers in the area,which can be defined as ‘short’ pruning, leading toconsiderable leaf density and shade inside the canopy(Li et al., 1994). Manual pruning is qualified by the growersas a ‘long’ pruning system. More precisely, it is a type oflong pruning that encourages light penetration within thecanopies as in the centrifugal apple training system(Willaume et al., 2004). Manual pruning consisted in themanual removal of all young vigorous shoots (potentialwater sprouts), which can shade the fruits after they arefully developed (Plenet et al., 2006). This pruning systemtends to favour the shoots located at the end of the 1-year-old shoots and to reduce the damage done by pruningshears, which results in vigorous growth of epicormic-shootin some parts of the tree (Lauri et al., 2004; Gordon andDejong, 2007). Manual pruning also required twofoldhandling. First, at the same time as the dormant pruning ofthe control treatment, 1-year-old shoots limiting lightpenetration inside the canopy were manually removed.Second, so-called manual pruning particularly consisted ofthe removal, in spring (mid-May), of vigorous shoots of theyear, mainly located in the centre of the tree on the basalpart of the vigorous 1-year-old shoots and 2-year-oldwoods. Work time devoted to conventional and manualpruning was identical (data not shown).

2.5. Brown rot incidence and fruit diameter measurements

The fruits from 10 tagged 1-year-old shoots of the threesampled trees in each experimental unit were observedevery twice a week from mid-July to a few days beforeharvest, so as to evaluate the percentage of fruits infectedby brown rot at each observation date. Infected fruits wereremoved to prevent the other fruit on the shoot from beingcontaminated. The kinetics of infected fruit was assessed ineach experimental unit on a sample comprising about 100fruit, from around 3 weeks before fruit maturity. Thus,each year, brown rot incidence was assessed at least seventimes before fruit harvest. At harvest, the brown rotincidence was evaluated on all the fruit of the three centraltrees in each experimental unit (Mercier et al., 2005).Moreover, in 2005, 40 fruits were sampled at the firstpicking in each of the 16 experimental units, and the maindamage to these peaches was identified so as to evaluate therelative importance of brown rot incidence compared withother pests. Each year, the post-harvest brown rot inci-dence was evaluated on 30 chosen fruits (same diameters,

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Fig. 1. Time-course of cumulative brown rot incidence on peach for the

combined 3 years (2003, 2004 and 2005) according to irrigation and

pruning treatments. ConvI+ConvP: conventional irrigation and pruning;

ModI+ConvP: water deprivation and conventional pruning; ConvI+-

ModP: conventional irrigation and manual pruning; ModI+ModP: water

deprivation and manual pruning. Brown rot incidence was assessed twice a

week from around 3 weeks before fruit maturity until few days before

harvest (seven measurements). Vertical bars denote positive or negative

standard error of the averaged cumulative percentage of infected fruits in

each treatment. Different letters indicate statistical difference at Pp0.05

using Fisher’s test (LSD); ns, not significant.

V. Mercier et al. / Crop Protection 27 (2008) 678–688 681

without epidermis defects) sampled at maturity in eachexperimental unit 1 d before the first picking date.Fruits were carefully arranged in fruit crates equippedwith special packaging material in order to prevent anydamage. The fruits were transported from the orchard to agrowth chamber and stored under controlled conditions(temperature: 20 1C, hygrometry: 70%) for 6 or 12 d. Theinfected fruits were removed every day to prevent the otherfruit from being contaminated.

On the central sampled tree in each experimental unit, thediameters of the fruit from 10 tagged 1-year-old shoots weremeasured twice a week from pit hardening to harvest with ahand-held digital micrometer to determine their growthpattern. Data collected at the first measurements were notsignificantly different for fruit growth, so that further growthwere calculated from these first measurements considered asthe zero points of the experiment for the 3 years. The fruitdiameters at the zero points were close to 35mm.

2.6. Agronomic performance

The percentage of fruit drop was evaluated by countingand comparing the total numbers of fruit in the centralsampled trees at thinning and just before the firm-ripestage. Fruit yield was determined at harvest for the trees ofeach experimental unit, with the exception of the centraltree that was used for other purposes (see below). Theharvest was completed in three pickings, and the fruits wereselected in the orchard to differentiate them according tomarket standards used in the area: damaged fruit wasconsidered to be second-class fruit, as opposed to first-classfruit that was well-suited to the market. Average fruitweights were calculated on a representative sample of thefruit production (about 20% of the total harvest, as definedby Marini and Trout, 1984). In 2003, the peaches were notharvested because major hailstorm damage occurred atfruit maturity.

At harvest, the first-class fruits of the central sampledtrees were graded. Firmness and total soluble solidconcentration of each peach were measured for each fruitgrade (Bussi et al., 1994). In 2004 and 2005, relativeeuros ha�1 returns were calculated on the basis of treeyield, fruit size distribution and fruit market class of thiscentral sampled tree, and were expressed for non-controltreatments as a percentage of the result of the controltreatment. Fruit sale prices were provided by the LorifruitCooperative, where area fruit growers delivered theirproduce.

Tree growth was partly evaluated every year in winter bymeasuring trunk circumference of all the trees at 0.30m fromthe ground. The annual increase in trunk cross-sectional area(TCA) was thereby evaluated in 2004 and 2005.

2.7. Statistical analysis

A classical analysis of variance was used includingarcsine square root transformation of the data when

needed (brown rot incidence) (Dagnelie, 1975). The least-square difference (LSD) was performed for averagediscrimination when F was significant (Statgraphicss Plussoftware). The results were statistically tested at each yearof experimentation, except for kinetics of infected fruitbefore harvest where data of the 3 years were included inthe same analysis of variance. Fruit grade partitioning wascompared for the four treatments using a w2 test (Scherrer,1984).

3. Results

3.1. Brown rot incidence

Brown rot incidence assessed on the tagged shoots variedaccording to the treatments (Fig. 1). For the combined 3years, the lowest and highest brown rot incidences occurredunder ModI+ModP and under ConvI+ConvP, respec-tively; significant differences were detected around 10 dbefore harvest and close to fruit maturity. At the last dateof measurement, brown rot incidence under ModI+ModPrepresented one quarter of that under ConvI+ConvPfor the 3 years; brown rot incidence under ModI+ConvPand ConvI+ModP appeared intermediate between these(Fig. 1). Brown rot incidence tended to be greater underModI+ConvP than under ConvI+ModP from around 2weeks before harvest. At harvest (Fig. 2), brown rotincidence measured on the entire tree mainly confirmed the

ARTICLE IN PRESSV. Mercier et al. / Crop Protection 27 (2008) 678–688682

results obtained at the last measurement date for the taggedshoots: 12–14% under ConvI+ConvP and below 5%under ModI+ModP; these differences were significant forthe 3 years (Fig. 2). Brown rot incidence at harvest tendedto be higher under ModI+ConvP than under ConvI+ModP in 2003 and 2005, but the opposite trend wasobserved in 2004 (Fig. 2). During post-harvest storageconditions in 2003 and 2004, brown rot incidence wassignificantly higher under ConvI+ConvP conditions thanunder ModI+ModP at each measurement date (Fig. 3).Brown rot incidence appeared lower under ModI+ConvPthan under ConvI+ConvP for these 2 years (significant in2003).

3.2. Fruit development

From the beginning of Stage III of fruit growth in 2003and 2004, fruit growth was significantly lower underModI+ModP than under ConvI+ConvP (�13% at thelast date of measurement; Fig. 4A and B), whereas fruit

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Trea

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Fig. 2. Brown rot incidence on peach at harvest in 2003 (A), 2004 (B) and 2

conventional irrigation and pruning; ModI+ConvP: water deprivation and c

pruning; ModI+ModP: water deprivation and manual pruning. Vertical bars d

Different letters indicate statistical difference at Pp0.05 using Fisher’s test (L

diameters under ModI+ConvP and ConvI+ModP wereintermediate between these. In 2004, ModI+ConvP tendedto induce a lower fruit growth than ConvI+ModP (�3%at the last date of measurement); in 2003, the fruit growthunder these two treatments was quite similar. In 2005, thefruit diameters were equivalent under all the treatments(Fig. 4C).The relationship between fruit growth and brown rot

incidence was analysed by plotting the fruit diameter vs.the incidence of brown rot at harvest (Fig. 5). In 2003 and2004, these two variables were linearly related (Pp0.01); in2005, this relationship was an exponential curve, but wasnot significant.

3.3. Agronomic performance

Compared with the other treatments, ModI+ModPinduced less fruit drop and lower average fruit weight(Table 2). Trees under ModI+ModP and ConvI+ModP,i.e., under manual pruning, showed higher yields than trees

b b

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tments

ab

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005 (C) according to irrigation and pruning treatments. ConvI+ConvP:

onventional pruning; ConvI+ModP: conventional irrigation and manual

enote standard error of the percentage of infected fruits in each treatment.

SD).

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Postharvest storage (days)

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Fig. 3. Time-course of brown rot incidence on peach in post-harvest

storage conditions in 2003 (A) and 2004 (B) according to irrigation and

pruning treatments. ConvI+ConvP: conventional irrigation and pruning;

ModI+ConvP: water deprivation and conventional pruning; ConvI+-

ModP: conventional irrigation and manual pruning; ModI+ModP: water

deprivation and manual pruning. Vertical bars denote standard error of

the averaged cumulative percentage of infected fruits in each treatment. *

and different letters indicate significant differences at Pp0.05 using

Fisher’s test (LSD); ns, not significant.

**

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∗∗

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∗∗

Fig. 4. Time-course of peach diameter in 2003 (A), 2004 (B) and 2005

(C) according to irrigation and pruning treatments. ConvI+ConvP:

conventional irrigation and pruning; ModI+ConvP: water deprivation

and conventional pruning: ConvI+ModP: conventional irrigation and

manual pruning: ModI+ModP: water deprivation and manual pruning.

The zero points corresponded to the first fruit diameter measurements

(see Section 2). Vertical bars denote standard error of the averaged peach

diameter. * and ** indicate significant differences P at p0.05 and p0.01,

respectively, using Fisher’s test (LSD).

V. Mercier et al. / Crop Protection 27 (2008) 678–688 683

under ConvI+ConvP and ModI+ConvP, i.e., underconventional pruning, probably as a result of the highertree fruit load at fruit thinning (ca. +20%) under manualpruning (Table 2). At harvest, the percentage of marketablefirst-class fruit was low (ca. 50%; Table 2) due todowngrading as a result of fruit damage. The damagemainly resulted from epidermis defects and peach pestattacks as observed at the first picking in 2005, brown rotbeing the main pest detected (data not shown). Consideringthe mean result of the 2 years (2004 and 2005), the highestpercentage of marketable first-class fruit was detectedunder ModI+ModP and the lowest under ConvI+ConvP(Table 2). The percentage of marketable first-class fruittended to be higher under ModI+ConvP than underConvI+ModP (+ 20%; Table 2).

In 2005, fruit firmness was significantly higher underConvI+ConvP than under ModI+ModP, with intermedi-ate firmness under ModI+ConvP and ConvI+ModP(Table 3). Fruit grade partitioning varied significantly

between ModI+ModP (lower grades) and ConvI+ConvP(higher grades) in 2004 and 2005 as detected with a w2 test(data not shown). In 2004 and 2005, fruit total solublesolids (TSS) generally seemed higher for the high fruitgrades than for the low ones, and they varied slightly undermodified treatments (Table 3). However, depending on the

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y = - 98 + 1.04 x

r = 0.69∗∗

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y = 0.0005e0.143x

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Fig. 5. Relationship between the average fruit diameter at fruit maturity

and the percentage of peaches infected by brown rot in 2003 (A), 2004 (B)

and 2005 (C) according to irrigation and pruning treatments. ConvI+-

ConvP: conventional irrigation and pruning; ModI+ConvP: water

deprivation and conventional pruning; ConvI+ModP: conventional

irrigation and manual pruning; ModI+ModP: water deprivation and

manual pruning. Significance levels: **Pp0.01; ns, not significant.

V. Mercier et al. / Crop Protection 27 (2008) 678–688684

year, fruit soluble solids differences between modifiedtreatments were significant for certain fruit grades. TSSwere higher under water deprivation (ModI+ConvPand ModI+ModP) than under conventional irrigation(ConvI+ModP and ConvI+ConvP) for grades C andAA in 2004; they were higher under manual pruning(ConvI+ModP and ModI+ModP) than under conven-

tional pruning (ModI+ConvP and ConvI+ConvP) forgrades B and A in 2005 (Table 3). Furthermore, comparedwith those under conventional irrigation and pruning,relative monetary returns tended to increase, ca. +20%and +23%, under water deprivation in 2004 and manualpruning in 2005, respectively (Table 3). The increase inprofit was mainly due to a higher percentage of marketablefirst-class fruit in 2004, and of a higher fruit yield in 2005(Table 2).The increase in TCA in 2004 tended to be lower (�10%)

under water deprivation than under conventional irrigation(Table 2). In 2005, this tendency was no longer observed,probably as a result of the additional water supplied to thewater-deprived trees compared with 2004 (Table 1). TheTCA increase under manual pruning was equivalent to thatunder conventional pruning (Table 2).

4. Discussion

For the 3 years of experimentation and from around 2weeks before harvest until fruit storage, the lowestincidence of brown rot in the peach orchard was detectedunder ModI+ModP, i.e., water deprivation and manualpruning, and the highest incidence under ConvI+ConvP,i.e., conventional irrigation and pruning. Intermediatetreatments, ModI+ConvP and ConvI+ModP, each con-tributed to reducing brown rot incidence compared withConvI+ConvP, but less than did ModI+ModP. Thissuggests that water restriction and manual pruning eachcontribute to decreasing peach sensitivity to brown rot, andan accumulation of these effects may occur when bothpractices are combined. English et al. (1989) and Houma etal. (1998) demonstrated that Botrytis bunch rot of grapecould be suppressed by the removal of leaves from aroundflower clusters; Holb (2005) showed that scab was limitedin apple under severe pruning compared with unprunedtrees. These disease limitations were mostly caused by thedifference in the moisture content of air in the plantcanopy. Under our conditions, a similar hypothesis can beproposed to explain limited brown rot incidence undermanual pruning. According to this hypothesis, this pruningmethod would adversely affect the germination andsporulation of the fungus by inducing more aeration andlower humidity around the peach. This would take effect assoon as manual pruning is carried out in spring, probablyexplaining the early occurrence of brown rot limitationunder ConvI+ModP compared with that under ModI+ConvP, i.e., around 2 weeks before fruit ripeness.A limitation of fruit infection related to a direct limitationof fruit growth caused by the modified treatments wasrevealed by the significant correlation of fruit diameterwith brown rot incidence at harvest. This observation is inaccordance with the finding that fruit epidermis micro-cracking is particularly limited under low fruit growth, thuslimiting pathogen invasion (Gibert et al., 2007). Under ourconditions, the relationship between fruit growth andbrown rot incidence was only significant in 2003 and

ARTICLE IN PRESS

Table 2

Productivity and vegetative growth of ‘Nectaross’ peach trees in relation to irrigation and pruning treatments

Year Treatment Fruit

number per

tree at

thinning

Fruit drop

(%)

Total yield

per tree (kg)

1st

marketable

class (%)

Average

fruit weight

(g)

TCAa

increase

(cm2)

2004 ConvI+ConvPb 425bc 14ab 52.6b 46.1ab 145.6a 31.5

ModI+ConvP 455b 16ab 56.4ab 57.8ab 148.0a 29.4

ConvI+ModP 560a 22a 65.6a 43.7b 148.5a 33.0

ModI+ModP 485ab 7b 61.0ab 60.4a 135.0b 29.6

LSD (5%)d 100 14 11.2 14.8 8.3 9.0

2005 ConvI+ConvP 380 18 56.3bc 44.8c 180.8a 31.5

ModI+ConvP 380 19 53.6c 54.9ab 180.1a 29.0

ConvI+ModP 510 13 74.5ab 48.7bc 168.7ab 30.5

ModI+ModP 500 4 78.6a 57.9a 163.8b 38.5

LSD (5%) 130 16 19 7.1 12.4 10.0

aTCA: trunk cross-sectional area.bSee Section 2 for treatment labels.cFor each year, values within columns followed by different letters are significantly different at P ¼ 0.05.dLeast-square difference at P ¼ 0.05.

Table 3

Peach quality at harvest (firmness, total soluble solids—TSS—by fruit grade) and monetary returns as related to irrigation and pruning treatments

Year Treatment Firmness (kg/0.5 cm2) Fruit TSS by gradea Monetary returnsb (%)

TSS C TSS B TSS A TSS AA

2004 ConvI+ConvPc 6.2 10.2abd 11.2 11.4 12.5b 100b

ModI+ConvP 6.4 11.0a 11.2 11.6 14.0a 122ab

ConvI+ModP 6.3 9.2b 10.6 11.6 12.1b 103ab

ModI+ModP 6.0 10.8ab 10.9 12.0 12.9ab 124a

LSD (5%)e 0.7 1.7 0.9 0.8 1.5 22

2005 ConvI+ConvP 6.5a – 8.5c 9.8ab 10.3 100

ModI+ConvP 6.4a – 9.1bc 9.4b 9.8 98

ConvI+ModP 5.8ab – 11.4a 10.2ab 9.5 116

ModI+ModP 5.0b – 10.0b 10.4a 10.6 130

LSD (5%) 1.2 1.4 0.9 1.2 35

aGrade AA corresponds to a diameter of 73–80mm, A to 67–73, B to 61–67, C to 56–61. Total soluble solids are evaluated in every first-class fruit of the

sampled trees; they are indicated for each peach grade. TSS AA represents fruit TSS for grade AA, TSS A for grade A, TSS B for grade B, TSS C for grade

C.bMonetary returns are expressed as a percentage of that of ConvI+ConvP in each year.cSee Section 2 for treatment labels.dValues within columns followed by different letters are significantly different at P ¼ 0.05.eLeast-square difference at P ¼ 0.05.

V. Mercier et al. / Crop Protection 27 (2008) 678–688 685

2004. For these 2 years, compared with 2005, a higherwater restriction was applied to the trees, and thecorrelation of fruit diameter with brown rot incidencewas probably significant as a consequence of the resultingdiscrepancies in fruit growth between the treatments. In2005, despite a lack of significant correlation of fruitgrowth with brown rot incidence, the brown rot incidencewas actually limited under water deprivation and manualpruning, suggesting that the limitation of fruit growth wasnot the only factor to explain the limitation in brown rotincidence under our conditions (Mercier et al., 2003). Asmentioned above in relation to the pruning method, it

could be also assumed that irrigation scheduling modifiesclimatic parameters that promote fungus development,particularly the hygrometry around the fruit (Guelfat-Reich and Ben-Arie, 1980). Further studies will benecessary to better understand how these croppingpractices affect brown rot incidence.Fruit technological quality was modified by irrigation

scheduling and tree pruning. Decreasing fresh fruitfirmness observed under water restriction and manualpruning compared with that under conventional irrigationand pruning would suggest that modified treatments mightencourage early peach maturity (Table 3). Greater fruit

ARTICLE IN PRESSV. Mercier et al. / Crop Protection 27 (2008) 678–688686

softening can be identified as a quality improvementbecause softer peaches are generally preferred by theconsumer (Gelly et al., 2004), even if it usually induces ashorter life of the peach (Genard et al., 1994). Peach totalsoluble solids at harvest were not lower than 9.5% Brix, avalue considered as acceptable for quality fruit productionat harvest (CEMAGREF, 1988), and their increase withincreasing fruit grade was in accordance with previousresults (Marini and Trout, 1984). The trend towards highertotal soluble solids in 2004 under ModI+ConvP andModI+ModP compared with the other treatments,significant for a few peach grades, supported the expectedresult of improved sugar content in peach under waterrestriction (Genard and Huguet, 1996; Bussi et al., 1999).The simultaneous reduction in peach diameter detectedin 2004 suggested that this sugar content increase couldjust be the result of a passive concentration of sugarsrelated to fruit dehydration (Lescourret and Genard, 2005).Moreover, under manual pruning (ConvI+ModP andModI+ModP), a total soluble solids increase was detectedin 2005 compared with the other treatments, particularlyaffecting fruits at the lower grades. Overall, these resultsshowed that restrictive irrigation and manual pruning arelikely to improve the potential taste quality of peach.

Even if water irrigation was largely limited under waterdeprivation, representing less than 40% of the waterapplied in the conventional irrigation treatments for the 3years of the study, fruit yield was not significantly reduced,probably as a result of the decreasing fruit drop, as alreadymentioned (Li et al., 1989b). Nevertheless, fruit diameterunder water deprivation declined in 2003 and 2004, leadingto lower average fruit weights and fruit diameters atmaturity compared with conventional irrigation, as usuallyobserved (Naor et al., 1999; Mahhou et al., 2005). Despitethis limitation in fruit growth, relative monetary returnsincreased in 2004 under water restriction compared withconventional irrigation, mainly due to the higher percen-tage of marketable first-class fruit at harvest. Similareconomic conclusions were obtained under water depriva-tion applied to French prune (Lampinen et al., 1995).Under our conditions, higher commercial fruit qualityunder water restriction has to be related to lower fruitdamage in the orchard, principally caused by brown rot.Finally, severe water deprivation as applied in 2003 and2004 improved taste and marketable fruit quality, butvegetative growth evaluated by trunk cross-sectional areatended to decrease, which could induce the limitation offlowering and yield for the following years (Goldhameret al., 2002). Less severe water restriction, as in 2005, madeit possible to maintain the positive effects of the waterdeprivation treatments and reduced their disadvantages, aspreviously observed (Mitchell and Chalmers, 1982; Gironaet al., 2005). The irrigation scheduling performed in 2005should therefore be promoted. Relative monetary returnsalso increased under manual pruning (ConvI+ModP andModI+ModP) compared with conventional pruning,mainly due to higher fruit yield. However, higher fruit

yield might reduce fruit production for the following yearsby favouring an alternation in flower setting (Chalmers andWilson, 1978). Further experiments involving the main-tenance of fruit production under manual pruning at thesame level as under classic pruning would make it possibleto more effectively assess peach quality improvement undermanual pruning.In conclusion, brown rot incidence in the peach orchard

was limited under water deprivation and manual pruning,suggesting a decreased disease sensitivity of peach underappropriate irrigation scheduling and tree pruning man-agement possibly leading to reduction of the use ofpesticide sprays in the orchard. Moreover, these methodsappeared likely to improve peach quality without reducingfruit yield, possibly even increasing their market valueunder our particular conditions of production. Theconsiderable savings in water was also of great interest,especially with regard to recent drought cycles in theMiddle Rhone Valley in 2002–2006. Further studiesfocused on the intensities of water deprivation and manualpruning that have to be implemented in order to optimizefruit production for the entire life of the orchard will benecessary for transferring our methods to fruit growers. Wemust be able to shed light on the contribution ofenvironmental and physiological effects to the observeddisease limitation if we are to increase our understanding ofthe brown rot–peach crop connections.

Acknowledgements

The authors would like to thank the French Ministry ofEcology and Sustainable Development for its financialsupport within the framework of the programme, ‘Evalua-tion and reduction of risks linked to pesticide use’. Wegratefully acknowledge E. Neraudeau, C. Millet, andJ. Besset for their work in the plot.

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