Salinity Effects on Fusarium Wilt Severity and Tomato Growth

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1 Dynmi Soil, Dynmi Plnt 29 Glol Siene Books Slinity Effets on Fusrium Wilt Severity nd Tomto Growth Mejd Dmi-Remdi 1* Ahmed Souissi 2 Hedi Ben Oun 2 Mohsen Mnsour 1 Bouzid Nsroui 2 1 Centre Régionl des Reherhes en Hortiulture et Agriulture Biologique, 442, Chott-Mriem, Sousse, Tunisi 2 Eole Supérieure d Agriulture du Kef, 7119 Le Kef, Tunisi Corresponding uthor: * dmi_rm@yhoo.fr ABSTRACT The im of the present study ws to eluidte the effets of wter slinity nd Fusrium oxysporum f. sp. lyopersii (FOL) on tomto (v. Ventur ) growth, wilt severity nd susequent yield loss. The six slt tretments tested showed no signifint effet on pthogen myelil growth in vitro ut inresed sporultion ws reorded with the highest NCl doses (8 nd 1 g/l). Inresing slinity stress (2 to 1 g of NCl/l) to the inoulted tomto plnts enhned the severity of Fusrium wilt disese nd resulted in signifint inrese in the lef dmge index (LDI) reorded from 3 to 62 dys post-plnting (DPP). Moreover, the LDI noted on plnts under highest slt stress (8 nd 1 g of NCl/l) ws inresed y nd 6%, respetively ompred with the LDI reorded on unstressed plnts. Slinity tretment in wtering tomto plnts (inoulted or not with FOL), from 1 DPP until the end of the ssy (i.e., 62 DPP), deresed plnt height y 9.7 nd 3% when the slinity level vried from 2 to 1 g/l. A similr effet ws noted fter inoultion with FOL. The fresh nd dry weights of the eril prt were generlly lower with the inrese in NCl dose; these prmeters were redued y 4-% nd y 34-41% with higher slt tretments tested (8 nd 1 g of NCl/l), respetively, ompred to the non-sline wter. The rnge of derese in root fresh nd dry weights ws nd 13-7%, respetively, when slinity levels were 2 nd 1 g of NCl/l, ompred to the unstressed plnts. Fruit fresh weight ws lso dversely ffeted y the highest NCl doses tested (8 nd 1 g/l) nd ws redued y 4 nd 78%, respetively ompred to non-sline wter. Keywords: disese inidene, Fusrium oxysporum f. sp. lyopersii, Lyopersion esulentum Mill., lef dmge, myelil growth, slt stress, yield INTRODUCTION In the pst, slt stress hd little importne s it ws speifi of ostl regions or ourring in prtiulr environments with evportion of slt-rih wters (Rivero et l. 23). Thus, due to the low-qulity nd high-sline irrigtion wter originting from the ontmintion of the groundwter, griulture in ostl regions my e dversely ffeted (FAO 199). In ddition to these sewter slinity effets, limti hnges inluding inresed tempertures, redued irrigtion wter vilility, flooding nd slinity, re lso onsidered s limiting ftors in sustining nd inresing vegetle produtivity (FAO 21). Hene, environmentl stress ws found to e the primry use of rop losses worldwide, reduing verge yields for most mjor rops y more thn % (Boyer 1982; Bry 1997). Slinity, in prtiulr, is one of the mjor ftors tht limit rop produtivity in rid nd semi-rid ountries. Almost 1 million h of ultivted lnds re ffeted y high slinity (Szols 1994) whih hs eome more prolemti due to the inrese in irrigtion round the world (Deou et l. 27) nd due to its impt on soil fertility (Ad-All nd Omr 1998). Moreover, seondry sliniztion, ourring vi indequte irrigtion mngement, ws reported to ffet 2% of irrigted lnds worldwide (Ghssemi et l. 199). Indeed, prtiulrly in irrigted roplnds, vegetle prodution, whih provides 4% of the world s food, is thretened y inresed soil slinity (FAO 21). Amongst vegetle rops, tomtoes re the most importnt hortiulturl rop worldwide nd re grown on over 4 million h of lnd re (FAO 26) nd more thn 3% of world prodution omes from the Mediterrnen ountries (FAO 199). In Tunisi, tomto, whih is strtegi rop shown to e modertely sensitive to slinity (Ayers nd Westot 198; Kterji et l. 2), is dversely ffeted y irrigtion with sline wter t levels exeeding 1.7 g/l of totl slts. However, the mjority of wter ville for plnt irrigtion is rkish (Dvet 1967; El Mhjou et l. 1979), espeilly in ostl zones where tomto is intensively ultured under greenhouse or field onditions. This sitution is more evident in the Shel region where slt onentrtion rehed 7 g/l nd % of surfe wells ville for irrigtion presented slinity level higher thn 4 g/l. Slinity hs een reported to inrese the suseptiility of some rops to soil-orne fungus-like miroorgnisms suh s Phytophthor spp. (Bouhii et l. 199; Snpp et l. 1991; Snogo 24) nd Pythium ultimum (Mrtin nd Hnok 1981; Rsmussen nd Stnghellini 1988) nd fungi inluding Alternri solni, Vertiillium dhlie nd V. lo-trum (Livesu et l. 199; Nhmis et l. 1993; Howell et l. 1994). However, the intertion of Fusrium oxysporum with slt stress vried depending on forme speiles (f. sp.) nd host-plnts involved. In ft, inresed disese inidene following irrigtion with high-slinity wter hd een reported in severl pthosystems inluding vriety of F. oxysporum f. sp., inluding vsinfetum (Rgzzi et l. 1994; Rgzzi nd Mori 199; Turo et l. 22), rdiis-lyopersii (Woltz et l. 1992; Jones et l. 1993; Triky-Dotn et l. 2) nd lyopersii (Besri 198). However, sodium hloride (NCl) hs een used for suppression of Fusrium diseses on mny plnts suh s F. oxysporum f. sp. sprgi nd F. moniliforme on sprgus (Elmer nd LMondi 1999; Elmer 23) nd F. oxysporum f. sp. ylminis on ylmen (Elmer 22). In tomto, numerous investigtions hve een reported on the effets of slt stress on growth redution (Minmide nd Ho 1986; Att-Aly et l. 1992; Al-Rwhy et l. 1992; Knight et l. 1992), ut the intertive effets of ioti nd ioti stresses on tomto diseses were limited to those Reeived: 14 Novemer, 29. Aepted: 6 Deemer, 29. Originl Reserh Pper

2 Dynmi Soil, Dynmi Plnt 3 (1), Glol Siene Books used y F. oxysporum f. sp. rdiis-lyopersii (Woltz et l. 1992; Jones et l. 1993; Triky-Dotn et l. 2), F. oxysporum f. sp. lyopersii (Besri 198, 1981), V. dhlie (Besri 198, 1981; Regrgui et l. 23; Dmi-Remdi et l. 29) nd Phytophthor prsiti (Snpp et l. 1991). In Tunisi, Fusrium wilt is the most severe disese of tomto ultivted in summer (Dvet 1967) whih is minly monitored with geneti resistne nd ulturl prties. However, little informtion is ville on the effets of the onomitnt ourrene of wter slinity nd F. oxysporum f. sp. lyopersii (FOL) on tomto growth ssoited with wilt severity. Furthermore, in the forementioned Besri (198, 1981) studies, only pthogen development nd survivl in vitro nd disese severity with regrd to soil nd irrigtion wter qulity were onsidered. Thus, the mjor ojetive of the present work ws to study the tion of NCl on FOL development in vitro, prtiulrly the slinity pthogen intertion, nd the in vivo effets of slinity nd pthogen on severl tomto growth prmeters s well s wilt severity. MATERIALS AND METHODS Plnt mteril Tomto seeds (Lyopersion esulentum Mill. v. Ventur ) used were resistnt to FOL re 1. They were grtefully provided y the lortory of seed nd plnt ontrol of the Generl Diretion of the Protetion nd Control of the Agriulturl Produt Qulity, Tunisi. Tomto seeds were superfiilly disinfeted y immersion in solute ethnol for 2 min, followed y extensive rinsing in sterile distilled wter. Seeds were then sowed in lveolus pltes filled with previously sterilized pet. Seedlings were grown in greenhouse nd wtered dily until use. Experiments were performed with 4-week-old tomto plnts. Pthogen FOL tested in the present study ws isolted from tomto plnts v. Riogrnde (resistnt to FOL re 1) showing typil Fusrium wilt symptoms nd vsulr disolortion. Monospore FOL isoltes were ultured t 2 C on Potto Dextrose Agr (PDA) medium dded with 3 mg/l of streptomyin sulphte (Phrmdrug Prodution Gmh, Hmurg, Germny) nd their pthogeniity ws previously verified on v. Riogrnde tomto plnts (unpulished dt). Liquid ultures used for sustrte inoultion were prepred on Potto Dextrose Broth (PDB) medium nd inuted t 2 C under ontinuous gittion t 1 rpm during 4 to dys. The spore suspension onentrtion used ws djusted to 1 7 spores/ml y Mlssez ytometer. For their long-term preservtion, FOL isoltes were stored up to 12 months t -2 C in 2% glyerol solution. Effet of different slinity levels on FOL myelil growth Osmoti potentil of PDA ws modified y the ddition of different quntities of NCl (Chemi-Phrm, Tunisi) into Erlenmeyer flsks ontining 2 ml of PDA just efore pouring it in Petri dishes (9 m dimeter). Agr plugs (dimeter 4 mm), removed from the leding edges of olonies on 1 dys-old pthogen ultures, were plted in the enter of eh treted Petri dish. The men dimeter of the pthogen developing olonies ws noted fter 7 dys of inution t 2 C. These in vitro FOL NCl dose intertions were ompleted y severl mrosopi nd mirosopi oservtions of pthogen olonies. Sttistil nlyses were performed following ompletely rndomized design where slt tretments represented the sole fixed ftor. Six replites (six Petri pltes) were used per slinity level nd mens were seprted using Fisher s proteted LSD test (t p.). All sttistil nlyses were performed using SPSS (Sttistil Pkge for Soil Sienes) version 11. Effet of different slinity levels on tomto Fusrium wilt severity nd plnt growth Seedling inoultion ws performed ording to the root-dip method (Hir et l. 26). Seedlings t two- to three-lef stges were uprooted, their roots wshed with tp wter, rinsed in sterile distilled wter nd dipped during 3 min in pthogen spore suspension (1 7 spores/ml). Seedlings dipped in only sterile distilled wter served s uninoulted ontrol. All the seedlings were trnsplnted, immeditely fter inoultion, to pots (16 m dimeter) filled with mixture of pet nd perlite (7%: 2%), previously sterilized t 17 C for 1 h, nd mintined under unheted greenhouse onditions where the temperture rnged etween 9 nd 23 C (minimum nd mximum, respetively). During the first 1 dys following inoultion, plnts were wtered regulrly with tp wter to fvor revivl following trnsplnting. Therefter, pots were wtered, every 2 dys, with wter mended or not with NCl. The dded quntity of wter ws dequte to replenish the wter level in the ulture sustrte to pot pity. Six NCl doses were tested:, 2, 4, 6, 8 nd 1 g/l. Tomto plnts uninoulted with FOL were inluded in the experiment to eluidte the effet of slinity lone. Five plnts were used per elementry tretment. Fusrium wilt severity ws estimted 62 dys post-plnting (DPP), vi the lef dmge index (LDI) nd ording to -4 sle whih depends on symptom severity on leves (Dmi- Remdi et l. 27). Plnt height nd LDI were reorded weekly. At the end of the ssy, the dry nd fresh weights of roots nd stems, nd the fruit weight were noted for ll tomto plnts. Sttistil nlyses were performed, for ll mesured prmeters, following ompletely rndomized ftoril design where FOL inoultion nd NCl dose were the fixed ftors. Five replites per elementry tretment were used nd mens were seprted ording to Fisher s proteted LSD test (t p.). RESULTS Effet of NCl on FOL myelil growth in vitro The effets of six NCl doses dded to PDA on the men dimeter of FOL olonies, formed fter 7 dys of inution t 2 C, ws shown to e insignifint t p.. Otherwise, pthogen olony development under diverse slt stresses is sttistilly omprle to those of the untreted ontrol (Fig. 1). Mirosopi oservtions showed tht inresing the NCl dose in the growth medium did not lso negtively ffet pthogen sporultion. Moreover, with highest NCl doses tested suh s 8 nd 1 g/l, FOL olonies showed undnt sporultion ssoited with n importnt differentition of sporogenous philide ells (i.e. enhned sporulting proess) ompred to the unmended ontrol olonies. Effet of NCl on tomto Fusrium wilt severity The effets of slinity on the severity of tomto Fusrium wilt used y FOL were investigted. Sine uninoulted ontrol plnts were symptomless under ll stress onditions, only dt of inoulted plnts re presented. Fig. 2 showed tht inresing the slinity stress (2 to 1 g of NCl/l) to the inoulted tomto plnts enhned the progression of Fusrium wilt disese nd resulted in signifint inrese in the LDI reorded from 3 to 62 DPP. Hene, higher LDI ws noted t 8 nd 1 g/l slinity levels. At the end of the ssy i.e. 62 dys post-inoultion, the LDI reorded depended on the fungl pthogen inoultion nd the NCl dose tested; signifint intertion ws otined etween oth fixed ftors t p.. Fig. 3 shows tht wilt severity ws signifintly enhned in inoulted plnts wtered with inresing wter slinity ompred to plnts wtered with non-sline wter. LDI of plnts under highest slt stress (8 nd 1 g of NCl/l) inresed y nd 6%, respetively ompred to the LDI reorded t 62

3 Slt stress nd Fusrium wilt. Dmi-Remdi et l Colony dimeter (m) NCl dose (g/l) Fig. 1 Effet of different NCl-sed tretments on Fusrium oxysporum f. sp. lyopersii rdil growth noted on PDA medium fter 7 dys of inution t 2 C. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.).,6 3 dys 42 dys 49 dys 6 dys 62 dys, Lef dmge index,4,3,2, NCl dose (g/l) Fig. 2 Effet of inresing wter slinity on the disese severity of tomto v. Ventur plnts inoulted with Fusrium oxysporum f. sp. lyopersii reorded 3 to 62 dys post-plnting.,7,6 Lef dmge index,,4,3,2, NCl dose (g/l) Fig. 3 Effet of inresing wter slinity on the disese severity of tomto v. Ventur plnts inoulted with Fusrium oxysporum f. sp. lyopersii reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.). g/l. Nevertheless, NCl t 2, 4 nd 6 g/l showed signifintly omprle LDI with the unstressed ontrol. 63

4 Dynmi Soil, Dynmi Plnt 3 (1), Glol Siene Books Effet of NCl on tomto growth nd prodution 1. Plnt height Plnt height inrese, from 21 to 62 DPP, ws independently relted to NCl dose nd fungl pthogen inoultion, s the intertion etween oth fixed ftors ws sttistilly insignifint (t p.). In ft, slinity tretment in wtering tomto plnts from 1 DPP until the end of the ssy negtively ffet plnt growth s height deresed with inresing slinity (Fig. 4). The inrese in plnt height over time ws gretest in the se of plnts irrigted with non-sline wter. In ontrst, under highest slt tretments (8 nd 1 g of NCl/l), plnt growth ws strongly redued ompred to unstressed plnts ( g/l). The inrese in plnt height relted to the fungl pthogen inoultion (FOL tretment) ws slowed down ompred with the uninoulted ontrol (Fig. ). The sme oservtion ws noted with sline wter irrigtion. Plnt height, noted 62 DPP, depended signifintly on NCl dose (Fig. 6). This growth prmeter derese rnged etween 9.7 nd 3% when slinity level inresed from 2 to 1 g/l, respetively. Also, plnt height deresed fter inoultion y the fungus nd ws out 18% less tht the uninoulted ontrol (Fig. 7). 2. Aeril prt weight The fresh nd dry weights of the eril prt, noted 62 DPP, depended signifintly (t p.) on slinity levels tested only s fungl pthogen inoultions were shown to hve n insignifint effet on oth these growth prmeters. Dt presented in Fig. 8 shows tht slinity dversely ffeted the vegettive growth of tomto plnts. The fresh weight of the eril prt ws generlly lower s sliniztion level inresed; this prmeter ws redued y more thn 4% with higher slt tretments tested (8 nd 1 g of NCl/l) ompred to the non-sline wter ( g/l). Similrly, the dry weight of the eril prt ws lso negtively ffeted y inresing slinity levels (Fig. 9) nd the redution reorded, ompred to the ontrol plnts wtered with unslinized wter, vried from 17 to 41% when the NCl dose rnged etween 2 nd 1 g/l, respetively. 3. Root weight The root fresh weight, noted 62 DPP, ws signifintly ffeted (p.) when independently ompred to the slinity level nd the fungl pthogen inoultion. The intertion etween oth fixed ftors ws sttistilly insignifint. In ft, the root fresh weight of tomto plnts deresed y 12 to 74% when the NCl dose ws inresed from 2 to 1 g/l ompred to the unstressed ontrol (Fig. 1). The most signifint dereses, ompred to ontrol, were reorded with 8 nd 1 g of NCl/l. Dt presented in Fig. 11 shows tht root dry weight ws redued y 13 to 7% when NCl dose rnged etween 2 nd 1 g/l. A signifint negtive effet, ompred to the unstressed ontrol, ws otined with 6, 8 nd 1 g/l NCl. 4. Fruit weight The fruit fresh weight, noted 62 DPP, depended signifintly (t p.) on slinity levels tested only. In ft, s shown in Fig. 12, this prmeter ws dversely ffeted y the highest NCl doses tested (8 nd 1 g/l); it ws redued y 4 nd 78%, respetively, when ompred to non-sline wter. The redution reorded with less thn 8 g of NCl/l vried etween 12 nd 2%, ut ws sttistilly insignifint. DISCUSSION A plnt disese is the result of the intertions etween three mjor omponents: the host plnt, the pthogen nd the ioti nd ioti environment. Any externl ftor introdued into this system n positively or negtively ffet some or ll of these omponents, leding to derese, inrese or no effet on disese inidene nd severity. In ft, slt stress ws shown to indue vrious types of physil nd hemil stress in plnts, using omplex responses involving hnges in plnt morphology, physiology nd metolism (Cheeseumn 1988; Borohov-Neori nd Borohov 1991; Ymguhi nd Blumwld 2). This environmentl stress my led to derese in other nutrient ions in plnt tissues (Bernstein nd Kfkfi 22; Prid nd Ds 2), inluding K +, whih is frequently relted with resistne to pthogens. However, prtiulr minerl nutrient my e ssoited with n inrese in severity of ertin disese in one rop, ut with suppression of the disese in nother rop or hve simply no effet. In ft, high slinity my inrese the inidene nd severity of Fusrium wilt of otton (Turo et l. 22) nd Fusrium rown nd root rot of tomto (Triky-Dotn et l. 2) nd my suppress Fusrium wilt of dte plm (Br de l Perriere et l. 199), Fusrium rown nd root rot of sprgus (Elmer 23), nd Fusrium wilt of ylmen (Elmer 22). Eh intertion is speifi for prtiulr minerl nutrient, plnt nd pthogen. Furthermore, slinity levels, pthogen popultions (pthogen physiologil res) nd plnt mteril (ultivrs) vry etween ountries, nd etween res within ountry; the ove-mentioned intertions my e lso site-speifi. Thus, the present study is the first one to desrie the in vivo multiple effets of the triprtite omplex slinity FOL tomto on plnt growth, wilt severity nd susequent yield loss. The pthogen slinity intertion ws evluted in vitro vi rdil growth, whih is relile prmeter for the ssessment of the effet of n environmentl stress on given pthogen (Suro et l. 1993), nd whih my reflet the pthogen ehvior in vivo, inside plnt tissues (Cook 1973). The present results showed tht six slinity levels tested did not ffet negtively the in vitro development of FOL. Moreover, t the highest NCl doses, FOL showed enhned sporultion ompred with the unstressed ontrol. These findings re in ordne with those of Besri (1981) who found tht irrigtion nd soil slinity hve ig effet on FOL popultion nd tht this pthogen tolertes very low wter potentils (-144 rs) nd sporultes profusely in sline environments. Similrly, El-Ayed et l. (1988) nd Rgzzi et l. (1994) reported tht myelil growth nd sporultion of different Fusrium speies, inluding F. oxysporum, were motivted under slt stress onditions. In the sme wy, Triky-Dotn et l. (2) lso reported tht F. oxysporum f. sp. rdiis-lyopersii growth in ulture or survivl of onidi, when dded to soil, ws not ffeted y sline wter. Moreover, neither growth in ulture nor onidil germintion ws ffeted y wter slinity t 1 mm NCl, high level of slinity t whih even rop growth is dmged. Convergent results were reported in in vitro V. dhlie slinity intertions (Besri 198; Regrgui et l. 23; Dmi-Remdi et l. 29). Tolerne of soil-orne fungus-like miroorgnisms nd fungi to high slinity levels hs een lso demonstrted in severl other studies (MDonld 1982; Blker nd M- Donld 198; Rsmussen nd Stnghellini 1988; Rgzzi nd Vehio 1992; Rgzzi et l. 1994; Rgzzi nd Mori 199). The present study showed tht y inresing the slinity stress from 2 to 1 g of NCl/l to inoulted Ventur tomto plnts enhned the progression of Fusrium wilt disese nd tht the highest LDI were noted t 8 nd 1 g/l slinity levels. In previous work (Dmi-Remdi et l. 29), under similr environmentl onditions nd slt stress, inresed Vertiillium wilt severity ws lso oserved on tomto v. Ventur plnts wtered with sline wter. In Moron Atlnti ostl tomto-growing res, known y their high slinity levels, Fusrium nd Vertiillium wilts of tomtoes re reported to e the most serious 64

5 Slt stress nd Fusrium wilt. Dmi-Remdi et l. 4 g/l 2 g/l 4 g/l 6 g/l 8 g/l 1 g/l 4 3 Plnt height (m) Post-plnting period (dys) Fig. 4 Effet of inresing wter slinity on the plnt height of tomto v. Ventur plnts reorded 21 to 62 dys post-plnting. Six NCl doses were tested:, 2, 4, 6, 8 nd 1 g/l. 4 Control FOL 3 3 Plnt height (m) Post-plnting period (dys) Fig. Plnt height of tomto v. Ventur plnts inoulted or not with Fusrium oxysporum f. sp. lyopersii (FOL) reorded 21 to 62 dys post-plnting Plnt height (m) NCl dose (g/l) Fig. 6 Effet of inresing wter slinity on the plnt height of tomto v. Ventur plnts reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.). 6

6 Dynmi Soil, Dynmi Plnt 3 (1), Glol Siene Books Plnt height (m) Control FOL Fungl pthogen inoultion Fig. 7 Plnt height of tomto v. Ventur plnts inoulted or not with Fusrium oxysporum f. sp. lyopersii (FOL) reorded 62 dys postplnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.). 6 Aeril prt fresh weight (g) NCl dose (g/l) Fig. 8 Effet of inresing wter slinity on the eril prt fresh weight of tomto v. Ventur plnts reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.). 8 7 Aeril prt dry weight (g) NCl dose (g/l) Fig. 9 Effet of inresing wter slinity on the eril prt dry weight of tomto v. Ventur plnts reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.). diseses (Besri 1981). This enhned wilt severity is due to plnt osmoti stress, to lowered wter potentil, nd to the wter defiit imposed y slt stress (Bernstein nd Kfkfi 22; Munns 22). Slt wter in the root zone indues osmoti hnges nd interferes with nutrient uptke (Cornillon nd Plloix 1997; Hlperin et l. 23; Ben-Gl et l. 29). Furthermore, the effet of slinity on root exudtes is onsidered s ruil ftor in the erly stges of infetion y soil-orne pthogens (Bernstein nd Kfkfi 22). In ddition to the osmoti stress nd nutritionl disruption used y slinity, the ove-mentioned inresed FOL sporultion under sline onditions seems to lso e involved 66

7 Slt stress nd Fusrium wilt. Dmi-Remdi et l. 3 2 Root fresh weight (g) NCl dose (g/l) Fig. 1 Effet of inresing wter slinity on the root fresh weight of tomto v. Ventur plnts reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.) Root dry weight (g) NCl dose (g/l) Fig. 11 Effet of inresing wter slinity on the root dry weight of tomto v. Ventur plnts reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.). 3 2 Fruit fresh weight (g) NCl dose (g/l) Fig. 12 Effet of inresing wter slinity on the fruit fresh weight of tomto v. Ventur plnts reorded 62 dys post-plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.). in suessful plnt infetion. These findings re lso in greement with those of Triky-Dotn et l. (2). In ft, irrigtion with sline wter signifintly inresed disese severity in tomto trnsplnts inoulted with F. oxysporum f. sp. rdiis-lyopersii. Disese onset ws shown to our erlier nd more severely in plots irrigted with sline wter thn those preirrigted with tp wter. Similrly, inresed Fusrium wilt severity of otton under slt stress, estimted 67

8 Dynmi Soil, Dynmi Plnt 3 (1), Glol Siene Books vi the perentge of infeted lef re nd the dte of onset of wilt, ws reported y Rgzzi nd Mori (199). Even though plnt sensitivity to slt stress is generlly expressed y loss of turgor, growth redution, wilting, lef urling nd epinsty, lef sission, deresed photosynthesis, respirtory hnges, loss of ellulr integrity, tissue nerosis, nd potentilly deth of the plnt (Jones 1986; Cheesemn 1988), Gour et l. (199) suggested the involvement of Fusrium infetion in wilting nd yellowing of plnts t high slinity levels. The present results showed tht the mjority of growth prmeters were negtively ffeted y wter slinity levels. Only the highest NCl onentrtions ffeted ll of the onsidered prmeters nd used signifint redution in root nd shoot growth. These findings joined those of severl uthors who found tht slinity dversely ffeted the vegettive growth of tomto nd redued plnt length, dry weight (Adler nd Wilor 1987), fresh weight, shoot weight nd root weight (Omr et l. 1982; Shnnon et l. 1987; Hjer et l. 26). Inresing NCl onentrtion in nutrient solution dversely ffeted tomto shoot nd roots nd plnt height (Al-Krki 2). Furthermore, the lef nd stem dry weights of tomto were lso signifintly redued in plnts irrigted with sline nutrient solution in ontrst with ontrol plnts (Stti nd Al-Yhyi 199). Similrly, Stti et l. (1994) noted tht oth stem height nd lef growth were the most ffeted growth prmeters in slt-stressed tomto. It is supposed tht leves re the most sensitive plnt tissue to high slinity, while root growth is only modertely ffeted (Munns nd Termt 1986). However, Cruz nd Curtero (199), ited y Curtero nd Fernández-Mu oz (1999), mentioned tht in spite of the negtive effet of slt on roots, root growth in tomto ppers to e less ffeted y slt thn shoot growth nd so the root/ shoot dry weight rtio is higher in plnts grown under slt stress thn in ontrol plnts t ll their stges of development. The fruit fresh weight ws dversely ffeted, s the other growth prmeters, y higher NCl doses tested (8 nd 1 g/l). Similrly, Triky-Dotn et l. (2) found tht the erlier disese onset nd the inresed disese severity, reorded on plnts irrigted with sline wter, were ssoited with lower yield. Also, greter yield losses were used y slinity stress sumitted to lflf plnts previously inoulted with V. lo-trum (Howell et l. 1994). Plnt responses to slinity depend upon vrious ftors, suh s the durtion nd degree of the stress nd the growth stge t stress exposure (Triky-Dotn et l. 2). Consequently, the redued plnt growth nd the enhned wilt severity reported in the present work re expeted to e more pronouned under nturl onditions due to the durtion of exposure to slt stress, nd to the greter soil inoulum. Moreover, slt stress my weken the geneti resistne of plnts to disese y induing hnges in suseptiility of root tissue to pthogens (MDonld et l. 1984). Rgzzi nd Mori (199) reported tht even otton vriety GSC 2, whih is normlly modertely resistnt to F. oxysporum f. sp. vsinfetum, exhiited firly high perent infeted lef re fter exposure to the lowest postinoultion wter potentils. A similr phenomenon ws noted on potto where disese expression nd oloniztion levels of the fungus were found to e more severe in V. dhlie-tolernt ultivrs irrigted with sline wter ompred with plots irrigted with fresh wter (Nhmis et l. 1993). 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