MARDI Res. J. I8( l ) 1990: 6- l -69

Studies on sclerotic layer hardness of cocoa pods(Ka j ian kekerasan lap isan sk le ro t i k buah koko)

I . A z h a r *

Kcv words : sc le ro t i c layer hardness , penet ra t ion ho les . emergence ho les , cocoa pod

borer . hos t -p lan t res is tance

Abstrak

Lubang masuk instar pertama dan lubang kcluar instar terakhir pengorek

buah koko (PBK) telah ditcl i t i pada buah koko daripada klon-klon ICS 98.

UIT 5 dan UA .17. Kckcrasan lapisan sklerot ik telah juga dicatat pada

beberapa tempat ( lu rah pr imcr . lu rah ,sckunder . dan d i a tas permatang) dan

bahagian (atas. tcngah dan bau'ah) buah koko dari klon-klon terscbut.

Lubang masuk dan lubang kcluar didapati banyak tcrdapat di kau'asan 2 mm

dari lurah primcr dan sckunder dan jarang sekal i di atas lurah-lurah tersebut.

Lapisan sklerot ik di bawah lurah primcr cian sckundcr adalah lcbih kcras

daripada kawasan-kawasan vang berhampiran dengannya. Kawasan 2 mm

dar i lu rah pr imcr sesua i d igunakan un tuk menentukan kckerasan lap isan

sk lc ro t i k da lam pemi l ihan k lon-k lon vang r in tang te rhadap PBK.

Abstract

The penetrat ion holes of f i rst instars and cmcrgcncc holes of f inal instars ot

cocoa pod borcr (CPB) were examined on cocoa pods of clones ICS 98, UIT

-5 and UA 37. The sclerot ic laycr (SCL) hardncss was also recordcd on

diffcrcnt si tcs (primary furrow - PF. sccondarv furrow - SF. and on r idgc -

R) and port ions (top. middlc and bottom) of thc pod of thcsc cloncs. The

entry and emergencc holcs occurrcd ncar thc PF in thc middlc port ion of the

pod. Genera l l y . the en t ry ho les occur red less than 2 mm f rom e i ther the PF

or SF but seldom direct ly on the furrows. Hardness test indicated that.thc

SCL direct ly beneath the PF and SF wcrc hardcr than those from other sites

of the pod. The sites around 2 mm from the PF would bc appropriatc to

dctcrmine SCL hardness when scrccning for CPB rcsistant clones.

IntroductionThe cocoa pod borer (CPB).Cono po morp ha cramerella (Snellen)(Lepidoptera: Graci l lar i idae) . is the mostdamaging pest of cocoa in Malaysia andother growing areas in South East Asia.-Ihe

pest, if left uncontrolled, is capable ofcausing severe economic loss. Althoughinsecticidal control has been widely used

to manage the pest , cu l tura l pract ices,such as sleeving the pods, are also popularamong the smallholders. Biologicalcontro l . us ing egg parasi tes. is vcr lpromising but not widely used due to highestablishment cost and other technicalproblems. The use of pheromones in CPBcontrol is currently under investigation(Azhar 1986a, b, c) .

*Cocoa and Coconut Research Div is ion. MARDI Hi l i r Perak. P.O. Box 25.36307 Sunsai Sumun. MalavsiaAuthor 's fu l l namc: Azhar Ismai loMalal -s ian Agr icul tural Rescarch and Devekrpment Inst i tute 1990

63

Sclcrot ic laver hardncss ol cocoa pods

One componcnt usefu l in theIntegrated Pest Management ( lPM) ofth is pest . and current lv underinvest igat ion. is host p lant res is tancc(HPR). The possib i l i tv of incorporat ingt lPR in the management of CPB was { ' i rs tsugges ted bv Roepke (1912 ) whoobserved that Djat i Roenggo (DR) andForastero hybrids suffered less CPBinfestat ion bv v i r tue of thei r smooth podsurface and hard sc lerot ic la-v"er (SCL).

However. Azhar and L im (1987) found ncrevidence o l ' res is tance to CPB due tosmooth pod sur face but noted h ighcrlarval morta l i tv in c lones wi th hard SCL asrepo r ted by Day (1985 ) .

An important s tcp in developingHPR for CPB management is thcic lcnt i f icat ion of genet ic resources (Azhar

anc l L im 1987 ) . Day (1985 ) and Azha r andLim (1987) suggested compar ison of thcSCL hardness as a cr i ter ion ic l r the in i t ia lident i f icat ion of potent ia l l .v res is tantckrnes. This requi res a techniquc tomeasure SCL hardness accuratelv andrapid ly . Current ly . there is no def in i temethod of measur ing the SCL hardness.Day (1985) mcasured the SCL hardnessusing the convent ional 15 kg weighingscale by paring away the presclerotic layerbefore p lunging the 2.35 mm cyl indr ica lp lunger in the area of the SCLcorresponding to each of the ridges on thecomplete pod. The SCL measurementshave also been repclrted to be recordedusing a penetrometer wi th a modi f iedplunger on unpaired ripe cocoa pods (Lim

D. H. K. , BAL Plantat ions Tawau, pers.

comm. 1987). Thus, there is a need tostandardize the method such that the SCLhardness measurements are accurate.consistent and b io logical ly meaningfu l .This study ascertained the site and portionon the cocoa pod where SCL hardnessshould be measured based on larval entryand emergence ho les .

Materials and methodsThe study was conducted at the Cocoa

64

Research Stat ion. Quoin Hi l l , - l -awau.

- I 'hree c lones. ICS 98. UI- f 5 and UA 37.

were used in the study. These c l t tnes wcrcselcctcd based on a range t t f to lerance(L im and Phua 1986 ) . ICS 98 i s ve rvsuscept ib le whi le UI I ' 5 and tJA 37 arepart ia l l l ' to lerant to CPB infestat ion.

Itlumber of penetration holes' fen

newl l , r ipc pods were used to examinepcnetrat ion holes of CPB f i rs t instars. Thesi tes and por t ions of thc pod where thelarvae penetrated were determined bvpeel ing the epicarp of the pod husk (P/c le

1, , | . Thc s i tcs on the pod were categor izedas primary" furrows (PF) and secclnclarrvfurrows (SF), and r idge (R). The por t ionson the pod were c lass i f ied as top ( f rom thebase of f ru i t s ta lk to thc basal point ofin f lex ion) . middle ( f rom thc basal point ofin f lex ion to the adaxia l point of in f lex ion)and bottrxr (from the aclaxial pttint ofinflerion to the pod tip) (Plate 21. Thedistance of the pcnctrat ion hole s f rom thePF and SF were then measured using apair of vern ier ca l l ipers. In cases wherelarval penetrat ion occurred on R onlv theport ion of the pod and the number ofentrv holes was recorded.

llumber of emergence holesData on the CPB larval emergence holeswere taken f rom a study on the in festat ionpat tern of CPB on d i f ferent c lones. In th isstudy. a l l r ipe pods were harvested andtheir infestation rates recorded. The sitesand por t ions on the pods whereemergence holes occurred were alsorecorded. Data for the month of Augustand September 198-5 were used in theanalys is .

Sclerotic layer hardnessThe hardness of the SCL (expressed aspenetrabi l i ty in kg) of ten pods per c lonewas measured using a penetrometer(Mode l OSK 2713 , Ogawa Se i k iCo . L td . .Japan) wi th a modi f ied p lunger head ( 1.55mm in d iam.) Two measurements were

I. Azhar

l ' ,9::irillg

Plate 1. A cocoa pod with the pod husk peeled-off showing the point of penetration ol

the newly emerged first larval instar (a) and a line indicating the middle of the furrow (b)

Plate 2. Cocoa pods of three dffirent clones (A : UIT 5; B : UA 37; C-- ICS 98). The lines indicate the rough border separating three dffirentportions of the pod (a : top; b : middle; c : bottom)

65

Sclerot ic layer hardness of cocoa pods

taken at the PF and SF, respectively (eachdirectly on and adjacent to these sites)and only a measurement was taken fromthe R ( i .e . d i rect lv on i t ) . Thesemeasurements were taken from threedifferent portions of the cocoa pod viz.top, middle and bottom (Plate 2).

Data analysisAll the data rvere subjected to analysis ofvariance and means were separated usingDuncan's mul t ip le range test (DMRT).Before analysis, the number of holes wastransformed using the SQRT (x + 1) tos tab i l i ze t he va r i ances .

Results and discussionNumber of penetration holesThere were significantly higher number( p <0.05) of f irst larval instar penetrationholes in the middle por t ion (2.07) of thepod than e i ther the top (1.26) or bot tom(1.19) of the pod (Table 1) . This may bedue to the greater pod surface area andgreater accessibil i ty of the female moth tolay thei r eggs on the middle por t ions ofthe pod.

A significantly higher number ofpenetration holes ( p <0.05) occurred onthe PF (1 .87 ) t han on SF (1 .40 ) o r R(1.25) ; no s igni f icant d i f ference wasobserved between SF and R (Table 1) .The large surface area at the PF (exceptthe UA 37) may allow for a relativelyhigher mean number of eggs at this site.Placement of eggs in the PF also allowsthe newly hatched larvae to penetratemore directly into the placenta (where the

larva normally settles down to develop)through the interbean space (Plate ,11.

Generally. no significant difference( p >0.05) was observed on the d is tanceof penetration holes of the larvae from thePF. SF and the R (Table 2). In most cases(more than 70Vc), the penetrat ion holesoccurred at a point less than , mm awayfrom either the PF or SF. It was alsoobserved that the penetration holesseldom occurred directlv on the furrows.

Larval emergence holesGenerally, significantly higher numbers( p <0.05) of larval emergence holesoccurred in the middle por t ion (1.64) ofthe pod fo l lowed by the bot tom (1.2,1) andthe top por t ions (1.1a) in a l l the c lones(Table,3) . However. there was nosignificant difference between the numberof emergence holes in the bot tom and topport ions of the pod of UA 37.

The number of larval emergenceholes was s igni f icant ly h igher (p<0.05) onthe PF followed by SF and R in both ICS98 and UIT 5.

-l 'he interbean space and

the comparatively thinner pod wall at thePF may facil i tate passage for larvae toemerge from the pod as compared to theother sites of the pod (Plate -l). There wasno significant difference in the number ofemergence holes bctween the three s i teson the pods of UA 37 (Table -1).

SCL hardnessThe results of the SCL hardness at varioussites and portions on cocoa pods ofdifferent clones are shown in Table 1. ln

Table 1. Number of f i rst larval instar penetrat ion holes in relat ion to

the port ion and site on cocoa pod of the 3 clonesr

Portion on pod Site on pod

Top Middle Bottom SF

ICS 98UIT 5UA 37

1 . 3 1 b1 .33bl . l 8 b

2.32al . - b a

1.63a

1.27bl t 3 bl . l 3 b

38b25cl3b

.r5b54b20b

2.07a1.92a1.62a

rMeans between the port ions and s i tes on cocoa pods of respect ive c lonefol lowed by the same let ter are not s igni f icant lv d i f ferent (p <0.05: Duncan's

mult ip le rangc test) .

66

[. Azhar

Plate 3. Cross-sectional view of cocoa pods of three difkrent clones (A

C : ICS 98) showing the primary (a) secondary (b) funows, ridge (c),

space p)

Table 2. Average distance (mm) of the first larval instar

penetration holes from primary (PF) and on secondary (SF)

furrows in various portions on the cocoa pod of the 3 clones

: U I T 5 ; B : U A 3 7 ;

SCL (d) and interbean

Portion onthe pod

ICS 98 UIT 5 UA 37

TopMiddleBottom

1 . 2 71 . 1 80.86

1.480.990.39

1.30

1 .61

1 . 2 60.920.60

0.68 1.650.99 1 .291.56 0 .90

Table 3. Number of emergence holes in

site on cocoa pod of the 3 clonesr

relation to the portion and

Portion on pod Site on pod

SFTop Middle Bottom PF

ICS 98UIT 5UA 31

1 .10c1.20c1.02b

1.93a1.74a1 .16a

1.28b1.32b1.02b

1.55a 1 .51ab 1 .36b1.65a 1 .39b 1 .22c1.74a 7.04a 1.04a

tMeans between the portions and sites on cocoa pods of respective clonefollowed by the same letter are not significantly different (p <0.05; Duncan'smultiple range test).

general, significantly harder SCL ( p<0.05) was recorded in the SF than anyother site in any of the clones. Theanatomical features of SCL in the SF showthat the sclerenchymatous cells arecompactly ananged and raised into aprojection within the preSCL (Plate. 4).

This feature may deter the newly emergedfirst instars from penetrating at this site.The less harder SCL recorded at the APFand ASF, especially of the ICS 98 andUIT 5 clones, may explain for the highernumber of penetrations by the newlyemerged first instars.

67

Sclerotic layer hardness of cocoa pods

Table 4. Mean hardness of SCL (kg) at various portions and sites and on

cocoa Dods of the 3 clonesl

Portionon the pod

Sites on pod2

PF APF ASF

ICS 98

UIT 5

U A 3 7

TopMiddleBottom

TopMiddleBottom

TopMiddleBottom

2.56cC2.86bB3.01aA

2.66b82.57bC2.82a8

3.17a4 2.56cC3.17a4 2.70bC3.06bA 2.97a4

3.71a4 2 .59bB3.55bA 2 .51bC3.39cA 2.78aB- 2.77b1^- 2.93a8- 2.95a8

2.69c8 1.38cD2.82bB 2.51bD2.94a4 2.69a8

2.66b8 2.62b82.50cC 2.85aB2.82a8 2.77a8

2.82b4 2.85bA3.0 laA 2 .90bB3.05aA 3.06aA

rMeans within each clone followed by the same letter are not significantly different (p

<0.05; Duncan's multiple range test). Lower case letter within column difference and

upper case letter between column difference2PF - directly on primary furrow; SF - directly on secondary furrow; APF -

adjacent to primary furrow; ASF - adjacent to secondary furrow; R - on the ridge.

Plate 4. A photomiuograph of cocoa pod husk

showing the sclerenchymatous cells of the SCL

(A; red stained) compactly ananged

Comparatively, the SCL of UA 37was harder than that of UIT 5 and ICS 98.For UA 3J, lhe hardness was notmeasured in PF or SF because thehardness was greater than the maximumreading that could be recorded by the

68

penetrometer. A significantly harder SCLwas recorded at the bottom portion of thepod of all the clones on the sites otherthan in SF. This may also explain why thebottom portion of the pod had lowervalues for penetration and emergence bythe first and final larval instars,respectively.

This study indicated that penetrationand emergence of the first and final larvalinstars of CPB, respectively, oftenoccurred at the middle portion and withinthe PF of the pod. Therefore, the SCLhardness readings are suggested to bemade at a point within 2 mm adjacent toPF and in the middle portion of the pod.By having a standardized procedure forSCL hardness measurement. results onCPB clonal screening program can becompared and validated amongorganizations. However, similar types ofpenetrometer and standard size(diameter) of plungers should also beused, bearing in mind that other factorssuch as environment and podcharacteristics should also bestandardized.

AcknowledgementsThe author thanks the Director-Generalof MARDI and Director of DeDartment

- *

l%'

of Agr icu l ture Sabah I 'or thei r permiss ionto publ ish th is paper. He appreciz t tes thesupport and encouragements prov ided byDr Hashim Abd. Wahab and Dr M. J .Musa, who a lso k indly prov ided thephotomicrograph of SCL. Mr Roslan S.and Mr Norhazazi M. A. ass is ted in datacol lect ion and Mr Amiruddin Z. A.p rov ided s ta t i s t i ca l expe r l i se .Appreciat ion is a lso extended to DrGarre l l E. Long. Mr A. Sivapragasm andtw( ) anonvmous rev iewers l i r r ( he i r

c ( )mmen ts und sugges t i ons i n improv ingthe manuscr ipt . This paper forms par t ofthe MARDI-JPNS col laborat ive researchproJect .

ReferencesAzha r . I . ( 1986a ) . Ancan ran pengo rek buah koko

( Conopomorpha <'ranrerelh) terhadap industrikoko d i Ma lavs i a . I . Pc r i ha l b i o l os i dankcrosakan. Teknol . Koko-Kelupu i l | ,4RDI 2:

-5-t 60- ( 19 t l 6b ) . Ancaman penqo rck buah koko

( ( .onopontLtrp l t t t < ' ranterel ln ) tcrhadap industr i

L Azha r

koko d i Ma l i r v s i r i . I L Tckn rk - t ekn i k kawa lan .Teknol . k tko-Kelapu I IARDI 2: 61 9

- ( 1986c ) . Ancaman pcngo rek buah koko( ( 'onoponorpl ta cramerel lu) tcrhadap industr ikoko di l \ ' la lavsia. l l l . Pcngurusirn pcroslk

bcrscpadu dan langkah- langkah awalpcnccgahan scrangan perosak in i . leknol .

Kok t -Kehpa MARDI 2 :71 6

Azha r . I . and l - im . D . H . K . ( l t ) 87 ) . Aninvest igat ion on the use of host p lant rcs istancc

and c rop man ipu la t i on i n t he managcmen t o f

cocoa pod borcr. In Management ct.l the cocouy td ho re r (Oo i e t a l . cd . ) . p . t t - 3 101 . Kua la

Lumpur: Malaysian Plant Protect ion Societv( N4 APPS)

Day . R . K . ( 1985 ) . Con t ro l o f cocoa pod ho re r(Conopomorpl tu t rutnerel lu) . Ph. D Thcsis.Uni ."ers i t l of London

I- i rn. Ci . ' l ' .

and Phua. P. K ( l9E6). Ef fect of cocoapod borcr Acnx'ercops crumerel lo Sncl lcn on

I i c l d and bcan s i zc . h t ( o t ou und t o tonu t . s :Progre.ss ttnd otrtktok (Pushparajah. E. anclChcu ' , P . S . . cd . ) p . 325 -36 . Kua la L -un rpu r :Incorpomtcd Socictv of Plrntcrs

Rocpkc . \ \ ' . ( l 9 l l ) . \ ' oo r l oop igc n r cdcc lec l i ng, ) n l l r cn l h r ' l ' )P l r ! r l d cn r l t t t n t o l i t tr c r sch i l l cndc t \ pcn \ an dcn D ja t i -Rocnggo -cacao. rl|d.1e./.,elingen Prot.fstution M idden-. l uvu 3 : 1 -3

Accepted .for publication on I7 Novetnber 1988

69