INTERACTION OF JUGLANS SPECIES WITH PRATYLENCHUS VULNUS AND MELOIDOGYNE INCOGNITA

Transcription

1 INTERACTION OF JUGLANS SPECIES WITH PRATYLENCHUS VULNUS AND MELOIDOGYNE INCOGNITA T. Buzo, M. McKenry, nd J. Hsey ABSTRACT Nemtode-free micropropgted own-rooted English cultivrs Vin nd Chndler nd seedling rootstocks Northern Cliforni lck (NCB) nd Prdox hyrid were plnted into 0.5 m 3 hole of sndy lom soil contining 100 Prtylenchus vulnus nd two Meloidogyne incognit per 250 cm 3 of soil volume. Trees were frmed using micro-sprinkler irrigtion with 3 m y 4 m plnt spcing. Trees were removed from the field site fter 7 months nd ll new root growth prtitioned into three size groupings including fleshy root tips, secondry roots (<7 mm dimeter), nd primry roots (>7 mm dimeter). These two nemtodes preferred the fleshy root tips supporting 172, 293, 369 nd 882/grm of root on NCB, Prdox, Vin, nd Chndler, respectively. Secondry roots supported 22, 117, 204 nd 239/grm of root on NCB, Prdox, Vin, nd Chndler, respectively. Few nemtodes were present in primry roots lthough these roots were produced in the presence of inoculum. All Juglns spp. tested were susceptile or highly susceptile to P. vulnus. NCB ws poor host nd non-glled y M. incognit, Prdox ws intermedite, nd the two J. regi cultivrs proved susceptile. When present, the root knot glls were norml-sized nd occurred cross the root system, ut never on the fleshy root tips. Prdox nd J. regi cultivrs occsionlly developed 3 to 5 cm dimeter glls on their secondry roots. Plnting into high popultions of these nemtodes cn gretly restrict erly root explortion y Juglns spp. Totl tree iomss t termintion of the experiment rnged from 3.9 kg/tree for the more vigorous Prdox to 2.3 kg/tree for own-rooted Vin. This difference ws significnt t P = 0.05 with other growth differences eing intermedite nd non-significnt. INTRODUCTION Wlnut roots, Juglns spp., re dmged y three gener of plnt prsitic nemtodes: Prtylenchus vulnus, Meloidogyne spp., nd Mesocriconem xenoplx (Westerdhl nd McKenry, 1998). These nemtodes cn completely stunt the growth of young wlnut trees. It hs een uncler if this response is function of the replnt prolem, the high sensitivity of wlnut, or feeding preference y the nemtodes. The three wlnut rootstocks of contemporry interest in Cliforni include Northern Cliforni Blck wlnut (NCB), J. hindsii; English wlnut J. regi; nd the Prdox hyrid J. hindsii x J. regi. Prdox is the preferred rootstock lrgely due to its hyrid vigor. It is susceptile to crown gll, Agrocterium tumefciens, nd there re differing opinions reltive to its nemtode host sttus (Lownsery et. l., 1978; McGrnhn nd Ctlin, 1987; Ctlin, 1998). NCB is the trditionl rootstock tht served wlnut producers well ut is less vigorous nd more susceptile to Phytophthor root rot (McGrnhn et. l., 1998). English rootstock is unffected y lckline disese so is often used in loctions hving high incidence of this disese. A potentil lterntive to English rootstock in lckline disese res is micropropgted own-

2 rooted English cultivrs. Own-rooted Chndler ws found to e productive ut P. vulnus susceptiility my limit its usefulness where soil popultions exist. (Hsey et. l., 2004). English wlnut is lso known to e highly susceptile to Meloidogyne spp. NCB hs proven to e source of resistnce to common Meloidogyne spp. nd Prdox rootstocks re vrile in their response. The gol of this study ws to determine reltive susceptiility to P. vulnus nd Meloidogyne incognit mong own-rooted English cultivrs Chndler nd Vin compred to NCB nd Prdox seedling rootstocks. MATERIALS AND METHODS Nemtode-free, micropropgted own-rooted Chndler nd Vin (J. regi cultivrs) field grown for two sesons were plnted in completely rndomized pttern longside one-yer-old seedling rootstocks of NCB nd Prdox hyrid of similr size. Ten replictes of ech wlnut selection were spced t 3 m x 4 m intervls cross 0.25 h field site t Kerney Agriculturl Center ner Prlier, CA in The sndy lom soil (65% snd, 27% silt nd 8% cly) hd six-yer fllow history. Ech tree ws plnted into pre-dug 45 cm x 45 cm x 60 cm-deep hole nd ckfilled with ntive soil infested with 2.24 x 10 4 P. vulnus, nd 1.10 x 10 2 M. incognit per 5.5 L of soil. The inoculum soil ws gthered from two sites. One ws wlnut orchrd infested with P. vulnus nd the other n Actinidi delicios plnting infested with M. incognit. The two soils were mixed together in 1 m 3 continers nd ssyed for nemtode popultion density using the sieve-mist nemtode extrction procedure. Immeditely fter inocultion, ech tree ws heled in with 20 L wter. A micro-sprinkler irrigtion system ws instlled to provide uniform irrigtion nd to keep the soil moisture content close to field cpcity. Ech tree ws fertilized with 100 g of triple 15 (16.7 kg/h rte of NPK) plus 8.3 ml of SuperMicro contining five micronutrients t 20 dys fter plnting. Two generl contct weed sprys were necessry to keep the tree row free of weeds. The soil temperture rnge ws 11-25ºC from Mrch to Octoer At 210 dys fter plnting ech tree ws excvted y crefully removing moistened soil from either side of the tree nd then removing the complete tree nd root system using ckhoe with 1 m 3 ucket ttchment. Extrcted trees were ssessed for the following prmeters: 1) whole iomss, 2) iomss ove-ground nd elow, 3) weight of lterl roots excised into primry roots (> 7 mm dimeter), 4) secondry roots (<7 mm in dimeter), 5) numer of fleshy root tips orne on ech of the secondry roots, nd 6) length nd dimeter of fleshy root tips. This ltter mesurement of fleshy root tips occurred t oth the tip nd its proximl feeder root using n electronic digitl cliper hving mm cpcity with +/-.02 mm ccurcy. For ech selection, four replictions of the fleshy root ctegory were selected t rndom to serve s n unised representtive smple of the ten replictions. Oservtions were mde on gll formtion. The smller root ctegories were collected into polyethylene gs nd temporrily stored in ice chests. After wshing, mesuring nd weighing, ech root ctegory ws diced nd 20 g smple plced in 23ºC mist-chmer for 5 dys to extrct nemtodes within.

3 Extrcted nemtodes were identified to species nd quntified y use of dissecting scope t 40X. Nemtode numers were reported s nemtodes per grm of root. Dt were sujected to two-wy nd one-wy Anlysis of Vrince (SAS Institute, Inc., Cry, NC) for its fctoril tretment vriles, followed y men seprtion using Duncn s Multiple Rnge Test t the 95% confidence level. In this lortory the following scle hs provided yrdstick to define resistnce or susceptiility mong endoprsitic nemtodes ttcking Vitis nd Prunus rootstocks. The unit of mesure is extrcted nemtodes per grm of root. These sme criteri were used here. Resistnce = <0.2 nemtodes/grm of root Modertely resistnt = 0.21 to 0.6 Susceptile = 0.61 to 180 Highly susceptile = RESULTS AND DISCUSSION Biomss Chrcteriztion Totl tree mss ws seprted into seven components nd compred etween ech wlnut selection (Tle 1). Prdox produced significntly lrger totl iomss thn own-rooted Vin. Prdox lso produced significntly lrger root system thn Vin nd NCB. Compred to the other selections, Vin visily slowed its growth when mient tempertures wrmed to 35 o C t hundred dys fter plnting. Seedling Prdox root iomss ws 0.5 to 0.8 kg greter thn for ll other wlnut selections (Tle 1). Both Prdox nd own-rooted Chndler developed 2:1 rtio in mss of primry to secondry roots. Own-rooted Vin hd 1:1 rtio in the mss of primry to secondry roots. NCB seedlings developed n extensive root system of primry roots with reltively few secondry roots; 3:1 rtio of primry to secondry roots ws mesured (Tle 1). These differing root designs ltered the overll numer, length, nd dimeter of fleshy root tips mong the four wlnut selections. The root growth differences listed ove were visile ut few were significnt. Own-rooted Vin nd Chndler developed sttisticlly shorter fleshy root tips when compred to those of Prdox nd NCB; NCB hd the longest fleshy root tips (Tle 2). Prdox exhiited sttisticlly greter mss of fleshy root tips thn Chndler. Interestingly, Prdox developed root trits similr to its prents, with some fleshy root tips reltively short while others were lengthy (dt not shown). Nemtode Development We hve no dt to indicte tht nemtode presence ltered ny of the root chrcteristics or iomss mesurements listed ove. However, nemtode presence ws comprtmentlized cross the root system. Except for NCB, glling y M. incognit occurred on secondry roots nd to lesser degree on primry roots. Individul glls were not pprent on the lredy swollen fleshy root tips. Most notle ws the occsionl presence of reltively lrge (3-5 cm dimeter) glls on Prdox nd own-rooted Chndler roots. These glls were not in ssocition with Agrocterium tumefciens. Lesion symptoms cused y P. vulnus presence nd feeding were never visile in this 210-dy study. Field oservtions from mture orchrds revel tht

4 visile lesions, indictive of P. vulnus presence, occur lmost exclusively on wlnut roots tht re t lest two yers of ge. This study revels tht nemtode presence within older roots is occurring t reltively low popultion levels. At 210 dys fter inocultion the popultion levels of P. vulnus nd M. incognit were in sufficient numer to ctegorize ll rootstocks nd own-rooted cultivrs s highly susceptile or susceptile (Fig. 1 nd Tle 3). Own-rooted Chndler nd Vin were highly susceptile with 375 nd 191 nemtodes/grm of root, respectively. In the susceptile ctegory Prdox developed 138 nemtodes/grm of root, significntly fewer thn own-rooted Chndler. NCB t 65 nemtodes/grm of root ws sttisticlly poorer host thn Chndler or Vin (Tle 3). Both nemtode species exhiited preference for smller root sizes, lthough ll lterl roots exmined were developed during the 210-dy period. Dt were sujected to two-wy nlysis of vrince to determine the nemtode s preferred feeding sites nd ech root ctegory ws sttisticlly different. Tle 4 depicts the preferred feeding sites. Fleshy root tips supported 189 times the nemtode popultion s tht present in primry roots >7 mm. The secondry roots, <7 mm dimeter distl to the fleshy root tips, supported 143 nemtodes/grm of root. Compred to the Chndler cultivr, nemtode numers in roots of NCB nd Prdox were sttisticlly fewer in the secondry root ctegory (Fig. 1). In the fleshy root ctegory Prdox gin exhiited sttisticlly reduced nemtode numers when compred to own-rooted Chndler (Fig. 1). Further prtitioning of the specific nemtode into root ctegories indicted tht NCB nd Prdox hd sttisticlly reduced numers of M. incognit in their secondry nd fleshy root ctegories (Fig. 2). Aginst P. vulnus, NCB exhiited sttisticlly fewer nemtodes thn Prdox in the secondry, <7 mm root ctegory. The English prentge in own-rooted Chndler nd Vin ws ssocited with greter susceptiility to oth nemtodes. The reltive host sttus of ech of the own-rooted cultivrs nd seedling rootstocks ws determined y multiplying the comined nemtodes/grm of root y the weight of the three root ctegories. Own-rooted Chndler ws the most susceptile supporting 1.17 x 10 6 nemtodes within its totl root system (Fig. 3) t 210 dys fter inocultion. CONCLUSIONS This study revels the prevlence of enlrged, lengthy root tips mong Juglns spp. Roots of NCB, Prdox, own-rooted Chndler, nd own-rooted Vin were differentilly infected y these nemtodes. Bsed on the totl numer of nemtodes extrcted per grm of root, the fleshy roots of the two own-rooted cultivrs were highly susceptile wheres NCB nd Prdox hd susceptile rnking. Development of P. vulnus ppered to dominte over M. incognit cross these four selections. Regrdless of the nemtode type the most undnt infections occurred within youngest lterl roots nd notly within their fleshy root tips. Any estimtes of susceptiility or resistnce to these nemtodes must tke into ccount the ge of the smpled roots. NCB produces fewest fleshy roots lthough they were of greter length thn for the other cultivrs. NCB roots lso hd the lowest infection of M. incognit. To lesser extent this reduced host sttus lso occurred in Prdox. Resistnce to M. incognit is more likely to e found in J. hindsii rther thn in the Prdox hyrid. The oserved hyrid vigor inherent within J. hindsii x J. regi is lso expressed in its root system ut it remins n excellent host for these

5 two nemtode species. It ppers tht Juglns spp., prticulrly J. hindsii, offer degree of resistnce to nemtodes in roots older thn 210 dys, ut younger roots re extensively dmged y these nemtode species. This finding supports erlier studies indicting tht mtured roots nd shoots of Juglns spp. contin nemticidl properties tht cn e extrcted with wter (McKenry nd Anwr, 2003). Cliforni wlnut orchrds commonly support soil popultions of P. vulnus tht re fivefold the inoculum level utilized herein. The popultion levels tested here re more similr to those remining fter two yers of fllow period following wlnut orchrd removl. Our results suggest tht the most susceptile prt of the wlnut root is the terminl portion. This emphsizes the need for nemtode free soil to ensure extensive root explortion in newly plnted wlnut trees. ACKNOWLEDGEMENT We re grteful to Burchell Nursery, Inc. for providing the trees used in this study. LITERATURE CITED Ctlin, P.B Root physiology nd rootstock chrcteristics. p In: D.E. Rmos (ed.), Wlnut Production Mnul. UC DANR Puliction 3373, Oklnd, CA. Hsey, J.K., Westerdhl, B.B., nd Lmpinen, B Long-term performnce of own-rooted Chndler wlnut compred to Chndler wlnut on Prdox rootstock. Act Hort. (ISHS) 636: Lownsery, B.F., Moody, E.H., Moretto, A., Noel, G.R. nd Burlndo, T.M Pthogenicity of Mcroposthoni xenoplx to Wlnut. J. Nemtology. 10: McGrnhn, G.H nd Ctlin, P.B Juglns rootstocks. p In: R.C. Rom nd R.F. Crlson (eds.), Rootstocks for Fruit Crops. Wiley, New York. McGrnhn, G.H, Leslie, C.A., Philips H.A. nd Dndekr, A Genetic improvement. p In: D.E. Rmos (ed.), Wlnut Production Mnul. UC DANR Puliction 3373, Oklnd, CA. McKenry, M.V. nd Anwr, S.A Nemticidl ctivity of wlnut extrcts ginst root-knot nemtodes. J. Nemtology 35:353. Westerdhl, B.B. nd McKenry, M.V Controlling nemtodes tht prsitize roots. p In: D.E. Rmos (ed.), Wlnut Production Mnul. UC DANR Puliction 3373, Oklnd, CA.

6 Tles Tle 1. Totl iomss in kg/tree prtitioned into seven components cross four wlnut selections. Tree components Reps Chndler Vin Prdox NCB Totl tree Top Root Stump Primry roots >7 mm di Secondry roots <7 mm di Fleshy root tips Mens in the sme row followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P=0.05. Tle 2. Fleshy root tip mesurements (mm) of three prmeters cross four wlnut selections tested. Prmeter Reps Chndler Vin Prdox NCB Length c 35.44c Dimeter c 3.89c Dimeter of feeder root Mens in the sme row followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P=0.05. Tle 3. Popultion levels of Prtylenchus vulnus nd Meloidogyne incognit cross ll three root ctegories of ech wlnut selection. Selections Numer of Smples Nemtodes/grm of root Chndler Vin Prdox c NCB c Mens in the sme column followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P=0.05. Tle 4. Popultion level of Prtylenchus vulnus nd Meloidogyne incognit on three root ctegories within four wlnut selections. Root Ctegory Numer of Smples Nemtodes/grm of root Fleshy root tip Secondry roots < 7 mm di Primry roots > 7 mm di c Mens in the sme column followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P=0.05.

7 Figures Primry roots>7mm di. Nemtodes / g. of root Secondry roots<7mm di. Fleshy root tips c c 0.0 Chndler Vin Prdox NCB Primry roots>7mm di Secondry roots<7mm di Fleshy root tips Wlnut Selections Tested Fig. 1. Totl nemtode popultion per grm of root for ech root ctegory nd wlnut selection. Mens followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P= Primry roots>7mm di. Secondry roots<7mm di. Fleshy root tips Nemtodes / g. of root c 0.0 Chndler Vin Prdox NCB Chndler Vin Prdox NCB P.v. Primry roots>7mm di Secondry roots<7mm di Fleshy root tips Wlnut Selections Tested Fig. 2. Totl nemtode popultion per grm of root for ech nemtode species, root ctegory, nd wlnut selection. Log trnsformed mens followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P=0.05. M.i.

8 Nemtode popultion per tree Chndler Vin Prdox NCB Nemtode popultion per tree Wlnut Selections Tested Fig. 3. Nemtode uild-up on four wlnut selections 7 months fter exposure to 22,400 P. vulnus nd 110 Meloidogyne incognit + eggs. Mens followed y the sme letter re not significntly different ccording to Duncn s Multiple Rnge Test t P=0.05.