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1 The Afrin Journl of Plnt Siene nd Biotehnology 8 Glol Siene Books Reltive Suseptiility of Nine Potto (Solnum tuerosum L.) Cultivrs to Artifiil nd Nturl Infetion y Rhizotoni solni s Mesured y Stem Cnker Severity, Blk Surf nd Plnt Growth Mejd Dmi-Remdi * Smi Zmmouri Mohmed El Mhjou Centre Régionl des Reherhes en Hortiulture et Agriulture Biologique,, Chott-Mriem, Sousse, Tunisi Institut Supérieur Agronomique de Chott-Mriem,, Chott-Mriem, Sousse, Tunisi Corresponding uthor: * dmi_rm@yhoo.fr ABSTRACT The reltive suseptiility of nine potto ultivrs ginst Rhizotoni solni ws tested vi nturl seed tuer infetion nd rtifiil ulture sustrte inoultion. The ssessment ws sed on stem nker nd lk surf severity nd negtive effet on plnt growth nd expeted impt on yield. In oth experiments, symptoms of Rhizotoni stem nker were oserved on ll inoulted nd nturlly infested plnts ompred to non-infested ontrols. Furthermore, ultivrs tested showed vrile retion to R. solni, expressed y vrying degrees of stem nker nd lk surf severity nd susequent plnt growth, ut no totlly immune ultivrs were found. Under either rtifiil or nturl infetion y R. solni, v. Spunt, nd to lesser degree Elodie, were shown to e the most suseptile to this pthogen wheres Alsk nd Disy were the most tolernt. However, lthough its higher suseptiility to Rhizotoni disese nd redued growth ompred to other ultivrs tested, Spunt showed the highest progeny tuer weight ut with pronouned inidene of lk surf. Keywords: ultivr ehviour, disese inidene, inoulum soure, seed tuer, yield INTRODUCTION Rhizotoni solni Kühn [teleomorph Thntephorus uumeris (Frnk) Donk] is destrutive soil-orne pthogen tht uses diseses in mny plnt speies world-wide (Crling et l. ). Rhizotoni stem nker or lk surf is n eonomilly importnt disese of pottoes round the world. It redues the qulity nd the yield of pottoes nd hs eome n importnt impediment for export of pottoes nd self seed prodution in Tunisi (Dmi-Remdi et l. 8). Furthermore, when infeted tuers re used s seeds, they will serve s inoulum soures for future potto rops euse old nd wet soil onditions re fvourle to sleroti germintion t seed tuer surfes (Fig. ). Thus, dmge to potto plnts y R. solni egins primrily eneth the soil surfe where developing suterrnen stems nd stolons re prtiulrly suseptile to ttk (Bnville 978). Soures of infetion inlude seed tuers nd the soil itself, whih my ontin different types, s well s vrile levels of inoulum (Jger et l. 99). In ft, urrently, R. solni Fig. Germinting R. solni sleroti on potto seed tuer of Spunt. isoltes hve een divided into groups sed on their nstomosis ehviour (Crling et l. ) nd isoltes elonging to AG-, whih usully ttks emerging shoots nd survives s sleroti on infeted tuers (Rolnd 6), re well dpted to proliferte over rnge of soil wter potentils well eyond the limits of their potto host nd this must e one of the ftors involved in its suess s soil-orne plnt pthogen (Rithie et l. 6). In Tunisi, Rhizotoni disese is mnged y ulturl prties nd methods tht minimize prolonged ontt of the plnt or tuers with the pthogen (Dmi-Remdi et l. 8). Furthermore, s potto res re limited, nd rottion is often diffiult to pply, the use of resistnt ultivrs would oviously improve the ontrol of this disese. Potto ultivrs/reeding seletions showed rnge of suseptiility retions to R. solni, preisely to lk surf nd stem nker, ut none of these ws ompletely resistnt to these diseses (Anderson 98; Chnd nd Logn 98; Jeger et l. 996; Bins et l. ). In ft, ording to survey relized y the Ntionl Federtion of potto growers in Frne, vs. Akersegen, Be, Regle, Stell, Ultimus, Viol were lssified s less suseptile wheres Arrrn, Bnner, B.F.5, Bintje, Frfdette, Ke Pondy, Sski nd Sirt were suseptile (Betenourt 97). In other reent surveys, Estim nd Kennee were shown to e modertely suseptile to Rhizotoni disese (Simons nd Gillign 997; Wolski et l. 6) wheres Niol, Rosvll nd Clustr were reported to e suseptile (Tsror (Lhkim) nd Peretz-Alon 5). Furthermore, Ruf et l. (5) found tht, mong germplsm lines nd ultivrs of potto tested, the ultivrs SH-5, SH- nd the line CIP-965 were found to e resistnt to the disese using fungus R. solni AG (isolte SL-) nd tht Fisld white ws the most susep- Reeived: 7 June, 8. Aepted: July, 8. Originl Reserh Pper

2 The Afrin Journl of Plnt Siene nd Biotehnology (), Glol Siene Books tile vriety. In Tunisi, s potto rhizotonis were not deeply studied, ultivrs ehviour ginst this disese is still unknown lthough Niol nd Spunt seem to e suseptile to this pthogen (Dmi-Remdi et l. 8). As ultivrs used re quite speifi to eh ountry due to their ptitude to dpttion to lol environmentl onditions, onlusions on the ehviour of potto ultivrs reported in others ountries re not pplile in Tunisi. Consequently, informtion on omprtive suseptiility of most ultured lol potto ultivrs will help growers mke informed deisions regrding the mngement of this disese. Furthermore, disese inidene nd severity on dughter tuers is strongly influened y the ontminted seed tuer nd soil inoulum soures (Tsror (Lhkim) nd Peretz-Alon 5) nd oth inoulum soures hve the ility to use disese individully or in ssoition (Pltt et l. 99; Whrton et l. 7). Thus, the reltive ultivr s suseptiility to Rhizotoni disese ws ssessed, in the present study, vi nturl seed tuer infetion nd rtifiil ulture sustrte inoultion. MATERIALS AND METHODS Plnt mteril: origin nd preprtion Potto tuers of severl ultivrs (lss A) used were kindly provided y the Tehnil Center of Potto, Essïd, Tunisi. A frtion of tuers nturlly infeted y R. solni sleroti (originting from n initil stok showing 5 to % of nturl infetion depending on ultivrs) ws used without ny pthogen inoultion nd their level of infetion ws determined ording to the Frenh sle used in Dmi-Remdi et l. (8). The seond frtion of tuers ws mrosopilly free of lk surf symptoms nd these were to e used for the inoultion trils. Two weeks efore plnting, tuers were superfiilly disinfeted in ommeril sodium hypohlorite solution (ommeril leh ontining % of tive hlorine) diluted to 5% for 5 min then rinsed with wter nd ir dried. They were pled under environmentl onditions fvourle for pre-germintion (5- C, 6-8% reltive humidity nd nturl room light). Germinting tuers (non-inoulted ontrol, inoulted or nturlly infeted) were then individully plnted in plsti pots (6 litres) ontining mixture of perlite nd pet (5:75) previously sterilized for 6 min t 7 C. After emergene, plnts were irrigted every to dys. Pthogen Isoltes of R. solni were otined during 6 from Tunisin potto-growing res (Essïd, Gfs, Testour, Kiroun) y isolting from tuers showing typil lk surf symptoms (two isoltes) nd plnts with nkers t their stem ses (two isoltes). Disesed tissues (stem nker or tuer periderm tissue with sleroti) were rinsed thoroughly in tp wter nd ut into m piees. After surfe-disinfesting in sodium hypohlorite (%) for min, the piees were rinsed three times in sterile distilled wter nd dried on sterile filter pper. Piees were plted on PDA (Potto Dextrose Agr) medium ontining mg/l of streptomyin sulphte (Phrmdrug Prodution Gmh). Fungl ultures were inuted for dys t 5 C in the drk nd were lened up y suulturing suessively on PDA pltes from the edge of tively growing olonies. Isoltes pthogeniity ws previously onfirmed on potto plnts Spunt from whih the pthogen ws then re-isolted, purified nd stored on PDA t C until further use. Myelium nd sleroti of eh isolte of R. solni were srped from dys old ultures (Petri dishes, 9 m in dimeter) on PDA with sterile flmed slpel then mixed with other isoltes with sterile distilled wter (one plte per isolte nd per litre). The pthogen mixture ws homogenized y n eletri mixer for 5 min efore plnt inoultion. Assessment of the ehvior of potto ultivrs ginst R. solni As soures of R. solni infetion inlude seed tuers overed in sleroti nd myelium, nd the soil itself (Jger et l. 99), the ssessment of the ehviour of some potto ultivrs ginst this pthogen ws relized y using two soures of inoulum. In ft, in first ssy, seed tuers were nturlly infeted with R. solni sleroti t level ording to the Frenh sle desried in Dmi-Remdi et l. (8). For the seond ssy, pprently non-infested seed tuers of eh ultivr were individully plnted s desried ove nd the inoultion ws mde y dding ml of pthogen mixture to eh pot t the ollr level dys fter plnt emergene. plnts were irrigted y similr volume of sterile distilled wter. During growth period nd until the end of oth ssys, plnts were irrigted every to dys. Four nd five weeks post-plnttion of the different ultivrs of the first nd the seond ssy respetively, plnts were uprooted nd their roots were wshed with tp wter, ir dried then exmined for Rhizotoni disese indution nd severity. The ollr nerosis index (CNI) nd the index of progeny tuers (IPT) infetion y R. solni sleroti were determined for ll tretments ording to the sles used y Dmi-Remdi et l. (8) then verged over the totl numer of developed stems or tuers. Other prmeters suh s tuer fresh weight nd eril nd suterrnen prts fresh nd dry weights were lso noted per plnt to eluidte the effet of the pthogen x ultivr intertion on potto growth nd yield. The pthogen ws isolted from disesed plnts nd from every tretment to onfirm tht R. solni ws responsile for the oserved symptoms. Sttistil nlyses The first ssy ws rrnged in ompletely rndomized experimentl design where the sole fixed ftor orresponded to the different potto ultivrs. Five replites were used per tretment. The seond essy ws rrnged in ompletely rndomised ftoril design where potto ultivrs nd tretments (inoulted or ontrol) re oth fixed ftors. Ten replites were used per tretment. Dt were nlyzed using SPSS (Ver. ) nd sujeted to nlysis of vrine nd Fisher s lest signifint differene test, LSD t p.5. RESULTS Reltive suseptiility of potto ultivrs to rtifiil inoultion with R. solni Two weeks post-plnttion, the first symptoms of Rhizotoni stem nker were oserved nd were ompnied y delyed plnt growth on inoulted plnts s ompred to ontrols. These symptoms progressed to nerosis nd nkers t the stem ses of inoulted plnts. Stem nker developed following inoultion y R. solni The ollr nerosis index (CNI), noted five weeks postplnttion, vried depending on the potto ultivr used nd the tretment relized; signifint intertion (t p.5) ws oserved etween oth fixed ftors. Fig. shows the vrile retion of ultivrs tested to inoultion y R. solni. In ft, the highest CNI, of out.8, ws reorded on Spunt nd to lesser degree Elodie, Mondil nd Arind (.676,.988 nd.98, respetively) whih seem to e the most suseptile to this disese where stem nker ws even ompnied y lk surf on dughter tuers of Spunt (Fig. ). However, for Alsk nd Disy, the CNI noted did not exeed on sle with mximum of 5 used (Dmi-Remdi et l. 8). All ontrol plnts of the mjority of ultivrs tested did not develop stem nker symptoms, exept for Spunt nd Tngo, 58

3 Rhizotoni disese severity nd potto ultivr ehviour. Dmi-Remdi et l..5.5 CNI d d de e f f f f f f f f f "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. Collr nerosis index (CNI), noted five weeks post-plnttion, on inoulted potto plnts of different ultivrs ompred to ontrols. A signifint ultivr tretment intertion ourred nd two-wy nlysis ws performed. For tretments (ontrol or inoulted), rs (for ultivrs) with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). The letters indite nlysis y ultivr tested for eh tretment. Eh r represents the men of plnts. Stem dry weight following inoultion y R. solni B A The stem dry weight, noted five weeks post-plnttion, vried depending on the potto ultivr used nd the tretment relized; the intertion (t p.5) etween oth fixed ftors ws non-signifint ut eh ftor individully ffeted this prmeter signifintly. In ft, stem dry weight ws redued y % on inoulted ompred to noninoulted ontrol plnts (Fig. 5). Moreover, the lowest vlue of vrile stem dry weight ws noted on Spunt nd Elodie (Fig. 6), whih seem to e most ffeted y Rhizotoni disese nd whih showed to e the most suseptile; this depended on the CNI prmeter (Fig. ). However, the highest stem dry weight ws noted on Mondil nd t lesser degree Atls nd Sfrne. The other ultivrs tested showed intermedite stem dry weights (Fig. 6). Root dry weight following inoultion y R. solni Fig. Severity of stem nker (A) nd lk surf (B), oserved five weeks fter plnttion, on potto Spunt plnts inoulted y R. solni. where slight stem nker developed on some non-inoulted plnts, nd where the CNI ws out. nd.66, respetively. Numer of stems formed per plnt following inoultion y R. solni The men numer of stems per plnt, noted five weeks post-plnttion, vried depending on the potto ultivr used nd the tretment relized; signifint intertion (t p.5) ws oserved etween oth fixed ftors. Fig. shows tht sustrte inoultion y R. solni, dys postemergene, did not negtively ffet the numer of stems developed per plnt exept for Spunt where this prmeter ws redued y out 8% ompred to the noninoulted ontrol. In the se of Atls nd Alsk, the numer of stems formed ws 7% higher in inoulted plnts thn in non-inoulted ontrols. The root dry weight, noted five weeks post-plnttion, vried depending on the potto ultivr used nd the tretment relized; the intertion (t p.5) etween oth fixed ftors ws non-signifint ut eh ftor individully ffeted this prmeter signifintly. In ft, root dry weight ws redued y 9% on inoulted plnts ompred to non-inoulted ontrols (Fig. 7). Fig. 8 shows the vriility in root dry weight noted on tested ultivrs. In ft, the lowest root iomss ws reorded on Spunt nd to lesser degree Alsk nd Disy. However, the highest root dry weight ws noted on Sfrne nd Atls (Fig. 8) s ws lso the se for the stem dry weight (Fig. 6). The other ultivrs tested showed intermedite root dry weights. Progeny tuer weight following inoultion y R. solni The progeny tuer fresh weight, noted five weeks postplnttion, vried only depending on the tretment relized while the potto ultivr used hd no signifint effet on this prmeter. Fig. 9 shows tht the tuer fresh weight ws signifintly redued y out 7% on inoulted plnts ompred to non-inoulted ontrols. This illustrtes the neg- 59

4 The Afrin Journl of Plnt Siene nd Biotehnology (), Glol Siene Books 8 7 Numer of stems/plnt 6 5 d "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. Numer of stems per plnt noted, five weeks post-plnttion, on inoulted potto plnts of different ultivrs ompred to ontrols. A signifint ultivr tretment intertion ourred nd two-wy nlysis ws performed. For tretments (ontrol or inoulted), rs (for ultivrs) with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). The letters indite nlysis y ultivr tested for eh tretment. Eh r represents the men of plnts. 8 Stem dry weight (g) Root dry weight (g) Tretment tested Fig. 5 Stem dry weight noted, five weeks post-plnttion, on potto plnts inoulted y R. solni ompred to non-inoulted ontrol. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). Eh r represents the men of 9 plnts. Tretment tested Fig. 7 Roots dry weight noted, five weeks post-plnttion, on potto plnts inoulted y R. solni ompred to non-inoulted ontrol. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). Eh r represents the men of 9 plnts. 9 8 Stem dry weight (g) "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. 6 Stem dry weight noted, five weeks post-plnttion, on potto plnts of different ultivrs. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). Eh r represents the men of plnts. 6

5 Rhizotoni disese severity nd potto ultivr ehviour. Dmi-Remdi et l..5 Root dry weight (g) "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. 8 Roots dry weight noted, five weeks post-plnttion, on potto plnts of different ultivrs. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). Eh r represents the men of plnts. Tuer fresh weight (g) 8 6 Tretment tested tive effet of R. solni on the expeted yield. All potto ultivrs tested hd signifintly similr tuer fresh weights. Reltive suseptiility of potto ultivrs under nturl infetion y R. solni. Stem nker developed under nturl infetion y R. solni The CNI, noted four weeks post-plnttion, vried signifintly depending on the potto ultivr used. In ft, the severity of vrile stem nker expressed y ultivrs in the presene of nturl infetion y R. solni hd the highest CNI of out. in Spunt nd to lesser degree in Atls, Elodie nd Sfrne (Figs., ) with CNI of out.,.8 nd.6, respetively; these ultivrs seem to e the most suseptile to this disese. However, the lowest CNI of out.95 ws noted on Alsk ; the CNI of Mondil, Tngo nd Disy did not exeed ; they seem to e less suseptile or tolernt to Rhizotoni disese. Tngo, showing CNI of.67 nd lssed s less suseptile y CNI, indued on the developed stem nker n typil formtion of sleroti-like strutures t the stem ses nd roots (Fig. ). A similr phenomenon ourred normlly on tuers, ondition ommonly known s lk surf. Fungl isoltions mde on Tngo plnts showing Fig. 9 Progeny tuers fresh weight noted, five weeks post-plnttion, on potto plnts inoulted y R. solni ompred to non-inoulted ontrol. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.5). Eh r represents the men of 9 plnts. these symptoms reveled tht R. solni is involved in this phenomenon.. Numer of stems formed per plnt under nturl infetion y R. solni When seed tuers nturlly infeted y R. solni were used, the numer of stems noted per plnt, four weeks post-plnttion, depended signifintly (t p.5) on the potto ultivr tested. In ft, the lowest stem numer developed per plnt, etween nd, ws reorded for Atls nd t lesser degree for Spunt (Fig. ); the ltter ultivr lso showed the highest stem nker severity (Fig. ). However, Arind, Disy nd Tngo showed 7 to 8 stems per plnt even when their initil seed tuers were infeted with R. solni sleroti t plnting.. Stem dry weight otined under nturl infetion y R. solni The stem dry weight noted, four weeks post-plnttion, vried depending on the potto ultivr used. All ultivrs derived from seed tuers nturlly infeted y R. solni t plnting hd signifintly omprle stem dry weights of out 6 to 9 g exept for Spunt, whih showed the lowest dry weight of out g (Fig. ); inidentlly, it lso hd the lowest stem numer per plnt (Fig. ).. Root dry weight otined under nturl infetion y R. solni In the presene of nturl seed tuer infetion y R. solni t plnting, ll potto ultivrs tested showed signifintly (t p.5) vrile root dry weights four weeks post-plnttion. In ft, two groups of ultivrs sed on root dry weight ould e distinguished (Fig. 5): the first one ontined primrily Elodie, Sfrne, Mondil nd Disy, with more thn g, nd the seond one, inluding Spunt, hd the lower root dry weight, followed y Atls, Arind nd Tngo, whih were intermedite to oth groups. 5. Progeny tuer weight otined under nturl infetion y R. solni The progeny tuer fresh weight noted, four weeks postplnttion, vried depending on the potto ultivr used. In ft, Fig. 6 shows tht Spunt plnts hd the highest tuer fresh weight (out 9 g), nd to lesser degree Elo- 6

6 The Afrin Journl of Plnt Siene nd Biotehnology (), Glol Siene Books.5 CNI d de de de e "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. Collr nerosis index (CNI), noted four weeks post-plnttion, on potto plnts of different ultivrs nturlly infeted y R. solni. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). Eh r represents the men of 5 plnts. A B Fig. Severity of stem nker (A) nd lk surf (B), oserved four weeks fter plnttion, on potto v. Sfrne derived from seed tuer nturlly infeted y R. solni t plnting. Fig. Sleroti of R. solni formed on stem nker, formed four weeks fter plnttion, on potto v. Tngo derived from seed tuer nturlly infeted t plnting. 8 7 Numer of stems/plnt 6 5 d "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. Numer of stems per plnt noted, four weeks post-plnttion, on potto plnts of different ultivrs derived from seed tuer nturlly infeted y R. solni t plnting. Brs with the sme letter re not signifintly different ording to Fisher's proteted lest signifint differene LSD test (p.5). Eh r represents the men of 5 plnts. 6

7 Rhizotoni disese severity nd potto ultivr ehviour. Dmi-Remdi et l. 6 Stem dry weight (g) 8 6 "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. Stem dry weight noted, four weeks post-plnttion, on potto plnts of different ultivrs derived from seed tuer nturlly infeted y R. solni t plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.5). Eh r represents the men of 5 plnts..5 Root dry weight (g) "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. 5 Roots dry weight noted, four weeks post-plnttion, on potto plnts of different ultivrs derived from seed tuer nturlly infeted y R. solni t plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.5). Eh r represents the men of 5 plnts. die, Atls nd Arind. However, Mondil nd Sfrne produed the lowest quntity, 5 to 5 g, of progeny tuers under experimentl onditions. 6. Blk surf severity on progeny tuers under nturl infetion y R. solni The indexes of progeny tuer (IPT) infetion y R. solni sleroti (lk surf), four weeks post-plnttion, on potto plnts derived from seed tuers nturlly infeted t plnting vried signifintly (t p.5) depending on the ultivr used. Severe lk surf ourred on progeny tuers (Fig. 7) of Spunt, Disy, Tngo (Fig. 8) nd Alsk where the IPT vlue ly etween. nd.66. However, the lest inidene of lk surf ourred on Atls nd Elodie where the IPT ws out.8; it less thn.6 for the other ultivrs tested. DISCUSSION The reltive suseptiility of nine potto ultivrs to Rhizotoni disese ws ssessed, in the present study, vi nturl seed tuer infetion nd rtifiil ulture sustrte inoultion. Both methods were used in sreening studies of the ehviour of potto ultivrs ginst R. solni (Hide nd Bell 978; Hide et l. 985, 989, 99; Csinos nd Stephenson 999; Tsror (Lhkim) nd Peretz-Alon 5). This ssessment of host resistne or suseptiility ws sed on the quntifition of symptoms (stem nker nd lk surf), plnt growth prmeters nd expeted impt on yield. In oth experiments, symptoms of Rhizotoni stem nker were oserved, ompnied y heterogeneous plnt growth depending on the ultivr used. Whether plnts were rtifiilly inoulted or nturlly infeted ompred to non-infested ontrols espeilly ffeted plnt growth. The infetion of potto plnts y R. solni ws initited, s reported y Pltt et l. (99), y soil-orne nd tuer-orne 6

8 The Afrin Journl of Plnt Siene nd Biotehnology (), Glol Siene Books Tuer fresh weight (g) 8 6 "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. 6 Progeny tuers fresh weight noted, four weeks post-plnttion, on potto plnts of different ultivrs derived from seed tuers nturlly infeted y R. solni t plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.5). Eh r represents the men of 5 plnts. IPT "Alsk" "Arind" "Atls" "Disy" "Elodie" "Mondil" "Sfrne" "Spunt" "Tngo" Cultivr tested Fig. 7 Indexes of progeny tuer (IPT) infetion y R. solni sleroti noted four weeks post-plnttion, on potto plnts of different ultivrs derived from seed tuers nturlly infeted t plnting. Brs with the sme letter re not signifintly different ording to Fisher s proteted lest signifint differene LSD test (p.5). Eh r represents the men of 5 plnts. Fig. 8 Blk surf (A) nd stem nker (B) oserved, four weeks post-plnttion, on potto Tngo derived from seed tuers nturlly infeted t plnting. A B inoulum. The indued stem nker ws shown to dely shoot emergene (Hide et l. 99), to derese the numer nd length of stems nd even to use inresed vrition in stem length; Hide et l. (989) lso reported tht these effets were ultivr-dependent. Both experiments onverged on the vrile retion of the ultivrs tested to R. solni, vi sustrte inoultion or nturl seed tuer infetion, on the vrying degrees of stem nker severity nd on the sene of totlly immune ultivrs. These results re in greement with those of El Bkli nd Mrtin (6), who reported tht potto vrieties differ in their suseptiility to Rhizotoni nd on the degree of resistne to sleroti formtion on tuers; these uthors lso limed tht to dte no vriety hs een found with immunity to stem lesions. Furthermore, ll shoots of ultivrs we tested showed stem nker symptoms, s lso found y Hide et l. (989). Plnts derived from seed tuers nturlly infeted y R. solni sleroti t plnting showed, four weeks lter, stem nker sore vrile etween.95 nd.. In ontrst, 6

9 Rhizotoni disese severity nd potto ultivr ehviour. Dmi-Remdi et l. when seed tuers were rtifiilly inoulted dys postemergene, this prmeter ly etween.86 nd.8 five weeks post-plnttion. These results showed tht soil-orne inoulum is potentilly s dmging s seed-orne inoulum whih is prtiulrly effetive in using disese euse of its lose proximity to developing sprouts nd stolons, s mentioned y Whrton et l. (7). However, our findings re not in greement with those of El Bkli nd Mrtin (6) who found tht tuer inoulum is more importnt thn soil inoulum liming tht it represented, in their study, the primry use of disese. In our experiments, plnt inoultion ourred following the irrigtion of inoulum suspension t the ollr level nd this, ording to Whrton et l. (7), fvours the infetion of plnt orgns developed in proximity to the inoulum suh s stem ses. This phenomenon ws shown to our mostly in the erly prt of the plnt growth yle, whih is lso the se in this sreening. Hide et l. (985) showed tht y inoulting seed tuers t the time of plnting with R. solni to stimulte seed tuer infetion, muh stem nker is used lthough shoots ould eventully grow from disesed plnts. However, Hrtill (989) reported less suseptiility of stems fter plnt emergene, nd lter infetion whih ourred minly on tuers nd tuer-ering stolons. Although Hide et l. (985) hd reported the resistne of shoots to infetion y R. solni fter eril leves development, severe stem nker ws developed in oth experiments nd espeilly on plnts inoulted dys post-emergene. This disese severity my e ttriuted to the virulene of the inoulum used nd to the onduive post-plnting onditions suh s regulr irrigtion every dys. In ft, Hide nd Firmger (989) reported tht moisture n gretly ffet the trnsmission of inoulum from seed tuers to the rop nd the susequent development of the disese. Moreover, the inidene nd severity of symptom expression re influened, ording to Csinos nd Stephenson (999), y severl ftors or omponents suh s infetion effiieny nd time from inoultion to symptom expression or inution period. Furthermore, positive orreltion etween the density of infetion strutures nd disese severity ws lso involved in pthogen penetrtion nd symptom progression on stems nd onsequently, disese severity (Mrshll nd Rush 98; Demiri nd Döken 998). Other ftors suh s soil-orne nd tuer-orne inoulum density, temperture nd soil moisture were lso shown to ffet the development nd severity of Rhizotoni stem nker on potto (Bolkn et l. 97; Simons nd Gillign 997; Kyritsis nd Wle ). The present results onfirmed, vi oth sreening methods used, tht Spunt nd to lesser degree Elodie were the most suseptile to R. solni wheres Alsk nd Disy were the most tolernt in oth ses, i.e. rtifiil or nturl infetion y this pthogen. These findings will hve prtil onsequenes in disese mngement nd my lso explin the greter nd higher inidene of potto rhizotonis in Tunisi euse in some lol potto res, Spunt is ultured in monoulture for more thn one rop within yer (erly, seson nd lte rops). In the sme wy, Gillign et l. (996) reported tht replenishment of inoulum (initilly originting from seed tuer, deris or soil) to soil ws rpid following the growth of suseptile rop, evidently of suseptile ultivr, with omprtively high levels of infetion nd disese, nd this phenomenon ourred even in long rottions. Sustrte inoultion y R. solni, dys post-emergene, did not negtively ffet the numer of stems developed per plnt exept for Spunt, whih ws shown to e the most suseptile to stem nker severity. Moreover, this numer ws redued y out 8% in inoulted plnts ompred to the non-inoulted ontrols. In ddition, even in the presene of nturl seed tuer infetion y R. solni, Spunt developed the fewest stems per plnt ssoited with the highest stem nker severity. This result onfirmed the findings of Hide et l. (985, 989) who showed tht severe stem nker n e ssoited with derese in the numer nd length of stems on the infeted plnts. In ontrst, Zimmer (988) reported tht there ws no definite orreltion etween the Rhizotoni index nd the numer of stolons or stems produed. Vrile stem nd root dry weights were noted. Following nturl nd rtifiil infetion y R. solni, Spunt plnts were most negtively ffeted y the pthogen, s ssessed y these prmeters. Moreover, the stem nd root dry weights redutions, on inoulted ompred to non-inoulted ontrol plnts (Figs. 5, 7), vried etween nd 9%, respetively for the mjority of ultivrs tested. These results re in greement with those of Hide et l. (985, 989) who found tht inoulting deresed the men weight of folige per plnt nd delyed tuer initition; delyed folige nd tuer growth were the diret result of severe stem nker. On some ultivrs tested, stem nker severity ws not lwys ssoited with redued plnt growth s is the se of the rtifiilly inoulted Mondil plnts whih hd reltively severe stem nker (CNI of out ) ut showed the highest stem dry weight. Similrly, Hide et l. (985) reorded n inrese in the folir dry mtter in infeted plnts due to elow-ground lesions interfering with the downwrd trnsport of ssimiltes. Sustrte inoultion y R. solni, dys post-emergene, signifintly redued the tuer fresh weight y out 7% more in inoulted thn in non-inoulted ontrol plnts: this illustrtes the negtive effet of R. solni on the expeted yield. However, in Spunt, whih showed the most severe stem nker produed under nturl infetion y R. solni, the highest fresh tuer weight ws ssoited with most severe lk surf on progeny tuers. The redution of tuer weight indued y sustrte inoultion y R. solni ws lso reported y Bnville (978) who showed tht severe infetion n redue yield. In the sme wy, Hrtill (989) reported tht infetion y R. solni inresed the numer of tuers initited ut redued their totl weight. Hide et l. (99) found tht inoulting delyed plnt growth nd deresed tuer numers nd yield. The redued yield due to the presene of R. solni depended on the inoulum soure. In ft, Hide et l. (985), in inoultion experiments, found tht soil-orne, ut not seed-orne, inoulum ws ssoited with loss in yield. However, Pltt et l. (99) reported tht infeted potto seed tuers used or plnted in ontminted soil n use redution in the mrketle tuer yield. Severe stem nker oserved on Spunt nd Elodie ws ompnied y severe lk surf on progeny tuers. These findings re in ordne with most reports inditing tht the severity of stem nker in the growing rop is positively orrelted with the susequent formtion of lk surf on progeny tuers (Bnville 978; Chnd nd Logn 98; Red et l. 989); other uthors reported diffiulties in relting stem nker nd lk surf (Hide et l. 989). However, Frnk nd Leh (98) sserted tht soil-orne inoulum is more idelly situted to infet tuers. Downgrded tuer qulity is not only ttriuted to tuerorne sleroti or lk surf symptoms (Jger et l. 99), ut lso to the possile development of mlformed (misshpen) tuers, ltertion of their trget size nd numer in ddition to redution in their mrketle yield (Hide et l. 97; Frnk 978, 98; Anderson 98; Crling et l. 989; Red et l. 989; Jeger et l. 996). Finlly, lthough the pot experiments re not onlusive in identifying, with ertinty, resistne mong ultivrs nd lthough they do not fully reflet the relity under field onditions, the present results re importnt euse they eluidted the ehviour of potto ultivrs, vi severl ssessment prmeters, ginst R. solni in the presene of two soures of inoulum (nturl seed tuer infetion or ulture sustrte inoultion) whih t independently in disese development. Furthermore, in oth our experiments onvergent results were otined regrding the most suseptile or the most tolernt ultivrs, the sene of resistne nd the vrile retion of ultivrs tested. These 65

10 The Afrin Journl of Plnt Siene nd Biotehnology (), Glol Siene Books onlusions will e useful for future disese ontrol strtegy s the ultivr ftor hd signifint effet not only on disese severity ut lso on fungiide effiy s reported y Zimmer (988, 988). These results should e onfirmed under field onditions, in different rops within yer, where disese-free seed tuers ould e plnted in infested fields nd nturlly infeted seed tuers in non-infested soils to eluidte more the effet of ultivr when onsidering oth possile soures of inoulum tht ontriute to Rhizotoni disese development in Tunisi. ACKNOWLEDGEMENTS Authors thnk the Tehnil Potto Center of Tunisi (CTPT) for finnil ontriution. REFERENCES Anderson NA (98) The genetis nd pthology of Rhizotoni solni. Annul Review of Phytopthology, 9-7 Bins PS, Bennypul HS, Lynh DR, Kwhuk LM, Shupmeyer CA () Rhizotoni disese of pottoes (Rhizotoni solni): Fungiidl effiy nd ultivr suseptiility. Amerin Journl of Potto Reserh 79, 99-6 Bnville GJ (978) Studies on the Rhizotoni disese of pottoes. Amerin Potto Journl 55, 56 Betenourt A (97) Le Rhizotone run de l pomme de terre. Phytom. L défense des Végétux 5, 7-9 Bolkn HA, Wenhm HT, Milne KS (97) Effet of soil temperture on severity of Rhizotoni solni infetion on potto shoots. Plnt Disese Reporter 58, Crling DE, Leiner RH, Westphle PC (989) Symptoms, signs nd yield redution ssoited with Rhizotoni disese of potto indued y tuerorne inoulum of Rhizotoni solni AG-. Amerin Potto Journl 66, 69-7 Crling DE, Bird RE, Gititis RD, Brinrd KA, Kuning S () Chrteriztion of AG- newly reported nstomosis group of Rhizotoni solni. Phytopthology 9, Chnd T, Logn C (98) Retion of ten potto ultivrs to stem nker nd lk surf of potto used y Rhizotoni solni. Annls of Applied Biology, - Chnd T, Logn C (98) Culturl nd pthogeni vrition in potto isoltes of Rhizotoni solni in Northern Irelnd. Trnstions of the British Myologil Soiety 8, Csinos AS, Stephenson MG (999) Evlution of fungiides nd too ultivr resistne to Rhizotoni solni inited trget spot, dmping off nd sore shin. Crop Protetion 8, 7-77 Dmi-Remdi M, Zmmouri S, El Mhjou M (8) Effet of the level of seed tuer infetion y Rhizotoni solni t plnting on potto growth nd disese severity. The Afrin Journl of Plnt Siene nd Biotehnology, -8 Demiri E, Döken MT (998) Host penetrtion nd infetion y the nstomosis groups of Rhizotoni solni Kühn isolted from pottoes. Trnstions Journl of Agriulture nd Forestry, 69-6 El Bkli AM, Mrtin MP (6) Blk surf of potto. Myologist, - Frnk JA (978) The Rhizotoni disese of pottoes in Mine. Amerin Potto Journl 55, 59 Frnk JA (98) The Rhizotoni nker (lk surf). In: Hooker WJ (Ed) Compendium of Potto Diseses, Amerin Phytopthologil Soiety, St. Pul, MN, pp 5-5 Frnk JA, Leh SS (98) Comprison of tuerorne nd soilorne inoulum in the Rhizotoni disese of potto. Phytopthology 7, 5-5 Gillign CA, Simons SA, Hide GA (996) Inoulum density nd sptil pttern of Rhizotoni solni in field plots of Solnum tuerosum: effets of ropping frequeny. Plnt Pthology 5, - Hrtill WFT (989) Some effets of Rhizotoni solni on growth nd yield of pottoes. Potto Reserh, 8-9 Hide GA, Bell F (978) Helthier seed pottoes. I. Effets of inoulting stem utting stoks with Polysytlum pustulns nd Rhizotoni solni on growth, yield nd disese. Annls of Applied Biology 9, 7-5 Hide GA, Firmger JP (989) Effets of soil temperture nd moisture on stem nker (Rhizotoni solni) disese of pottoes. Potto Reserh, 75-8 Hide GA, Hirst JM, Stedmn OJ (97) Effets of lk surf (Rhizotoni solni) on pottoes. Annls of Applied Biology 7, 9-8 Hide GA, Red PJ, Sndison JP (985) Stem nker (Rhizotoni solni) of minrop pottoes. I. Development of the disese. Annls of Applied Biology 6, - Hide GA, Red PJ, Firmger JP, Hll SM (989) Stem nker (Rhizotoni solni) on five erly nd seven minrop potto ultivrs I. Infetion of shoots, stolons nd tuers. Annls of Applied Biology, Hide GA, Red PJ, Firmger JP, Hll SM (989) Stem nker (Rhizotoni solni) on five erly nd seven minrop potto ultivrs. II. Effets on growth nd yield. Annls of Applied Biology, Hide GA, Red PJ, Hll SM (99) Stem nker (Rhizotoni solni) on three erly nd three min rop potto ultivrs: effets of seed tuer size on growth nd yield. Annls of Applied Biology, 9- Jger GH, Velvis JG, Lmers A, Mulder A, Roosjen J (99) of Rhizotoni solni in potto y iologil, hemil nd integrted mesures. Potto Reserh, 69-8 Jeger MJ, Hide GA, vn den Boogert PHJF, Termorshuizen AJ, vn Brlen P (996) Soil-orne fungl pthogens of potto. Potto Reserh 9, 7-69 Kyritsis P, Wle SJ () Effet of soil temperture nd moisture, inoulum level nd depth of plnting on the development of Rhizotoni solni on miropropgted potto seed tuers. Proeedings of Crop Protetion in Northern Britin, Dundee, Sotlnd, 9- Ferury, pp 5- Mrshll DS, Rush MC (98) Reltion etween infetion y Rhizotoni solni nd R. oryze nd disese severity in rie. Phytopthology 7, 9-96 Pltt HW, Cnle F, Gimenez G (99) Effets of tuer-orne inoulum of Rhizotoni solni nd fungiidl seed potto tretment on plnt growth nd Rhizotoni disese in Cnd nd Uruguy. Amerin Potto Journl 7, Ruf CA, Ysin SI, Khn HU, Rhmn F (5) Vrietl sreening of potto ginst Rhizotoni solni. Interntionl Journl of Biology nd Biotehnology, 7-7 Red PJ, Hide GA, Firmger JP, Hll SM (989) Growth nd yield of pottoes s ffeted y severity of stem nker (Rhizotoni solni). Potto Reserh, 9-5 Rithie F, MQuilken MP, Bin RA (6) Effets of wter potentil on myelil growth, slerotil prodution, nd germintion of Rhizotoni solni from potto. Myologil Reserh, 75-7 Rolnd F (6) Rhizotoni stem nd stolon nker of potto. Myologist, 6-7 Simons AS, Gillign CA (997) Reltionships etween stem nker, stolon nker, lk surf (Rhizotoni solni) nd yield of potto (Solnum tuerosum) under different gronomi onditions. Plnt Pthology 6, Tsror (Lhkim) L, Peretz I (5) The influene of the inoulum soure of Rhizotoni solni on development of lk surf on potto. Journl of Phytopthology 5, - Whrton P, Kirk W, Berry D, Snpp S (7) Mihign Potto Diseses: Rhizotoni stem nker nd lk surf of potto. Extension Bulletin E- 99-New-My, 6 pp Wolski EA, Mldondo S, Dleo GR, Andreu AB (6) A novel -, -glun eliits plnt defense responses in potto nd indues protetion ginst Rhizotoni solni AG- nd Fusrium solni f. sp. eumrtii. Physiologil nd Moleulr Plnt Pthology 69, 9- Zimmer RC (988) Chnge in the Rhizotoni solni index on the stems nd stolons of four potto ultivrs during the growing seson. Cndin Plnt Disese Survey 68, 5-6 Zimmer RC (988) Development of Rhizotoni solni on four fungiide treted potto ultivrs grown in virgin potto soil. Cndin Plnt Disese Survey 68,