HISTOLOGICAL RESPONSE OF SUSCEPTIBLE AND RESISTANTDATE-PALM CULTIVARS TO THE ROOT-KNOT NEMATODE,

MELOIDOGYNE INCOGNITA INFECTION.

Eissa*, M.F.MI.; EI-Sherief, M.A2.; Abdel-Gawad, M.M.I.; Ismail, A.AI.;and EI-Nagdi, W.M.AI.

1.Nematology Unit, Plant Pathology Dept., National Research Centre.

2. Nematology Dept., Fac. Agric., Cairo Univ.

ABSTRACT

The cellular alteration in M incognite infected roots of susceptible andresistant date-palm cultivars were histologically studied. The most obvious cellreaction of the susceptible cultivar "Zaghlool" was the giant cell formation. Inresistant cultivars "Deglet Noor" and "Samani" the infected roots reacted to thenematode infection by forming necrotic area around the invading nematodelocalities. Deformed portions of dead nematodes were found surrounded bydeeply stained necrotic cells. In few cases, malformed small giant cells wereobserved in association with nematode larval stages.

INTRODUCTION

Numerous nematode pests were reported to attack date-palm rootscausing considerable damage to the plants especially in their early stages. Theroot-knot nematodes, Meloidogyne spp. are some of the serious date-palmnematode pests. In 1993 Buhrer et al reported the occurrence of root-knotnematodes on date-palm in USA. Carpenter (1964) proved that cultivars ofDeglet-Noor and Amhat were tolerant to root-knot nematode infection, whileBraim, Hayany and Honey were rated as susceptible cultivars. Lamberti andGreco (1977) reported Deglet-Noor cultivar as least susceptible to Mjavanicain Algeria. Minz (1963) from Palestine; Stephan (1986) ITomIraq; Eissa et a1.(1979) from Saudi Arabia and Ismail & Eissa (1993) and Youssef & Eissa(1994) from Egypt reported root-knot pathogenicity to date-palm. Griffin andKoshy (1990) stated that young seedlings of date-palm were killed (90%) inheavily ifested soil by root-knot nematodes.

Objective of this work is to illustrate the histological alterations of theinfected date-palm roots.

MATERIALS AND METHODS

Date-palm seeds cvs. Zaghlool, Deglet Noor (Tunisian source) andSamani was prepared and planted . One inoculum level of M incognita wasintroduced to the 4-weeks-old seedlings of each cultivar grown in 20 cm

291

---- -- - -- -- ---

diameter clay pots. The inculum level was 5000 newly hatched M incognitalarvae/plant. For each cultivar four replicates were made. Inoculation was madeby pipetting the proper aliquot into three holes around the root system of eachseedling. All pots were kept in a greenhouse at 30 :!: 5°C in a completerandomized block design and agronomically treated the same. After fourmonths from inoculation time, the experiment was terminated and plants wereuprooted and data on plant growth criteria and nematode populations weredetermined.

Portions of M incognita infested roots of date-palm cvs. Zaghlool,Deglet Noor and Samani were fixed in F.A.A. and processed for histologicaltechnique according to the standard methods ofSass(1964). Dehydration wascarried out : in a serial concentrations of known volume of ethanol and butanolalcohols. Dehydrated root tissues were then infiltrated and imbedded in paraffinwax at 52°C for 10 days. During the wax infiltrationprocess, air bubbles wereremoved from root tissues by vacuum. Sectioning of the processed root partswas made by a rotary microtome at 12 microns thickness. Staining was made bySafranin and Fast green and the stained sections were mounted in canadabalsam. Sections were then examined under a light microscope.

RESULTS AND DISCUSSION

Stained root sections of the susceptible (Zaghlool) and resistant (DegletNoor and Samani) cultivars of date-palm were examined under stereoscopicmicroscope. Cross and longitudinal sections of the susceptible cultivar rootrevealed that the nematode developed and reproduced normally within the roottissues. The most obvious cell reactions to the nematode infection were cell

hyperplaisa and hypertrophy in comparison with the healthy date-palm rootsection (Fig.I). The hypertrophied giant cells were initiated in both cortical andstelar regions of the roots which then developed abnormal xylem elementsexpanding into the cortex (Fig.2). Parenchyma type cells bordering the giantcells were small, have dense protoplasm, and irregular in shape. The welldevloped giant cell had uniformly dense cytoplasm, numerous large nuclei andthickened walls. The number of nuclei per giant cell ranged from 10 to 18,which were scattered within the giant cell or aggregated in the center (Fig.2) . agroup of giant cells consisting many clusters are usually located close toanterior part of the nematode. The giant cells were irregular in shape, however,they tend to be elongated or rounded (Figs. 2b and 2c).

On the other hand, the root tissues in the resistant cultivars reacted in adifferent way. It seems that as the nematode have invaded the cortical layer, anegative reaction to nematode existence was exhibited by forming a necroticarea around the nematode body (Figs. 3 and 4). In few cases, the nematodesucceeded to survive for a while, hence a slight host reaction was noticed. Insuch cases, vaculated and empty giant cells were found. Vacuoles. andapparently empty regions were often associated with the cytoplasm of such

292

---

giant cells and frequently seemed to lack turgidity, in comparison to adjacenthealthy tissues. Poorly developed larvae usually observed in association withthose giant cells (Figs. 3and4). Ismail 1985 obtained similar results on cornplants.

Observations on M incognita infected roots of the highly susceptiblecultivar Zaghlool indicated an acute histological respons. Differentdevelopmental stages could be easily observed within the infected root tissueeither in cortex or in close vicinity to the stelar regions (Fig. 2). The cells sitesbecame hypertrophied with several swollen nuclei (Fig. 2). The formation ofcharacteristic multinucleate and well developed giant cells was found at theanterior part of the the nematode in the infected plant tissues with the root-knotnematode, M incognita (Fig.2). The secreted nematode enzyme throughparasitism dissolved cell walls in susceptible host. Such host do not secreteample or any phenols and/or other nematistatic compounds to contradictnematode parasitism.

In unsuitable host, nematodes are always faced with antagonisticreaction initiated by the host plant. The most common reaction in resistant orless suceptible (Deglet Noor and Samani) cultivars was cell necrosis (Figs.3and 4). Often, after inducing necrosis, the nematodejuveniles migrated to non-necrotic cells and commended feeding these cells subsequently became

..necrotic. Necrosis can result in death of the nematode either through directtoxicity or by destruction of the plant tissues, thus causing starvation.

LITERATURE CITED- Buhere, E.M.; C.K. Cooper and G. Steiner 1933. A list of plantsattacked by the root-knot nematode (Heterodera marioni) Plant Diseasereporter 17: 64-96.

- - Carpenter, J.B. 1964. Root-knot nematode damage to date-palmseedlings in relation to germination and stage of development. DateGrowers Inst., Ann. Rept., 44:10-14.

- Eissa,M.F.M.; G.B. Beinhart and S.AI-Uyayed 1979. Co-operationwith the International Meloidogyne Project in the Kingdom of SaudiArabia. Proc. 2nd. Res. Planning Cont: on root-knot nematode,Meloidogyne spp., Athens, Greece, Nov. 26-30, 1979, p.l05-112.

- Griffth, R. and P.K. Koshy 1990. Nematode parasites of coconut andother palms. In: Plant Parasitic Nematodes in subtropical and TropicalAgriculture (M.Luc, R.A. Sikora and J.Bridge eds.) C.A.B. International,363-386.

- Ismail, A.E. (1985). Biological and Pathological studies on pathogenicnematodes of some field crops in Egypt. M. Se., ZooI. Dept, Fac. Agric.,Cairo Univ., PP 121.

293

-- ---

- --- - - .- -.- - -. - -- .. - - ---- -- . - - -. - -- ----- - --.

- Ismail, A.E. and M.F.M. Eissa1993.Plant parasitic nematodesassociated with ornamental palms in three botanical gardens. Pak.J.Nematol., 11 (1):53-59.

- Lamberti, F. and E.N. Greco1977.Pathogenecity of two species ofMeloidagyne on four varities of date-palm. Nematol. Medit., 5: 159-172.

Minz, G. 1963. Additional hosts of the root-knot nematode,Meloidogyne spp. recorded in Israel during 1960/1962. Israel J. Agric.Res., 13:133-134.

- Sass,J.E. 1964.Botanical Microtechnique. The Iowa State Univ. Press,228 p.

- Stephan, Z. 1986. Host status of cyst nematodes in Iraq. NATO AsiSeries. A, Life Sciences, Vol. 121.Proc. NATO Advanced study on cystnematodes, Sept. 21-0ct. 30 , New York, 1985.

- Youssef, M.M.A. and M.F.M. Eissa 1994. Population dynamics ofcertain nematodes associated with date-palm in Egypt. Afro-Asian J.Nematol. 4: 68-72.

294

- - - --- - --

Figure 1: Cross section of healthy date-palm root.

295

---

B

~ . ."~r:. .~" 1ift. ill ~ ~ ~ o.iiiiiiiiIiio;'_-

S

A

Figure 2: Cellular reaction of the susceptible Zaghlool date-palm cultivar to. M. incognitainfection.

A. Cross section of Zaghlool cultivar infected root showing thehypertrophied cells

B. Cross section of Zaghlool cultivar infected root (note the groupsof giant cells and abnormal xylem).

296

- - - - - - --- -----

c

D

Figure 2: Cellular reaction of the susceptible Zaghlool date-palm cultivar toM. incognita infection.

C. Longitudinal section of zaghlool dultivar infected root (note themature females and giant cells inside stellar tissues).

D. Cross section of Zaghlool cultivar infected root (note themature female and egg-mass).

ax =abnormal xylem; ge= giant cell; ne=nematode;em= egg-mass; ht= hypertrophy.

-

297

A

B

Figure 3: Cellular reaction of the resistant Deglet Noor date-palm cultivarto M. incognita infection.

A,B= Cross section of cv. Deglet Noor infected root by M.incognita (note the necrotic tissues around nematode body).

--

298

,.

c ..

Figure 3: Cellular reaction of the resistant Deglet Noor date-palm cuItivarto M. incognita infection.

C= Cross section of cv. Deglet Noor infected root by M. incognita(note the necrotic tissues around nematode body).

299

- - ---

B

A

..

Figure 4: Cellular reaction of the resistant Samani date-palm cultivar toM. incognita infection.

A,B= Cross section of cv. Samni infected root by M. incognita(note the necrotic tissues around nematode body).

300

- ---

c.

_,10

II

1..,....

Figure 4: Cellular reaction of the resistant Samani date-palm cultivar toM. incognita infection.

C= Cross section of cv. Samni infected root by M. incognita (notethe necrotic tissues around nematode body).

- -

301

- ---