comparative invitro sensitivity of selected chemicals on phytophthora palmivora … papers/pert vol....

Pertanika 9(2), 183-191 (1986)

Comparative Invitro Sensitivity of Selected Chemicals onPhytophthora palmivora from Cocoa and Durian

LUZ G. CHAN and LIM TONG KWEEDepartment of Plant Protection,

Faculty of Agriculture,University Pertanian Malaysia,

43400 Serdang, Selangor, Malaysia.

Key words: Chemical control; Phytophthora palmivora; cocoa; durian.

ABSTRAK

Lima sebatian sistemik yang baru iaitu metalaxyl, benalaxyl, cyprofuram, propamocarb danfosetyl AI dan dua racun kulat pelindung biasa, etridiazol dan captafol telah dibandingkan dari segikesan invitro terhadap asingan-asingan Phytophthora palmivora daripada koko dan durian yangterpilih. Metalaxyl, etridiazol dan cyprofuram memberiperencatan yang tinggi kepada pertumbuhanmiselium, sporangium dan pengeluaran klamidospora, percambahan terus sporangium dan per-kembangan tiub cambahan kedua-dua asingan-asingan koko dan durian, sementara benalaxylmemberi perencatan yang sederhana. Etridiazol dan benalaxyl memberi halangan yang lebih ter-hadap percambahan zoospora tetapi metalaxyl dan cyprofuram secara perbandingan adalah tidakberkesan. Captafol juga memberi halangan tinggi terhadap pertumbuhan miselium, percambahanterus sporangium dan zoospora, tetapi kurang berkesan terhadap pengeluaran sporangium danklamidospora. Propamocarb dan fosetyl AI secara perbandingan adalah paling tidak berkesan ter-hadap semua peringkat perkembangan asingan-asingan melainkan bagi percambahan zoosporaasingan durian di mana fosetyl Al memberi perencatan yang tinggi.

ABSTRACT

Five new systemic compounds viz. metalaxyl, benalayxl, cyprofuran, propamocarb and fosetylAl and two standard protectants, etridiazole and captafol were compared for invitro effects on repre-sentative isolates of Phytophthora palmivora from cocoa and durian. Metalaxyl, etridiazole andcyprofuram were highly inhibitory to mycelial growth, sporangium and chlamydospore production,direct sporangium germination and germ-tube development of both cocoa and durian isolates whilebenalaxyl was moderately inhibitory. Etridiazole and benalaxyl were more suppressive en zoosporegermination but metalaxyl and cyprofuram were relatively ineffective. Captafol was also highly sup-pressive to mycelial growth, direct sporangium and zoospore germination but less so on sporangiumand chlamydospore production. Propamocarb and fosetyl Al were comparatively the least effectiveagainst all the developmental stages of the isolates except in the case of zoospore germination of thedurian isolate where the latter was highly inhibitory.

INTRODUCTION it attacks (Chee, 1969; 1974). Among the impor-tant agricultural crops attacked are cocoa and

The ubiquitous parasitism of Phytophthora durian. On cocoa, the fungus causes black podpalmivora is reflected by the wide array of crops rot, decay of flower cushions and cherelles,

Key to authors' names: L.G. Chan and T.K. Lim.

LUZ G. CHAN AND LIM TONG KWEE

stem canker, blight of shoots and chupon,dieback of budgrafted and hand pollinatedhybrid seedlings, and root rot. On durian, thefungus causes root rot, patch canker, leaf blightand dieback of seedlings and trees and recentlyfruit rot (Lim and Chan, 1986).

Control measures adopted to control thisfungus are mainly confined to cultural means orthe use of non-systemic fungicides which haveprovided little and erratic success. With theadvent of new systemic fungicides such as theacylalanines — metalaxyl (Urech, et aL, 1977),and furalaxyl (Wiertsema and Wissink, 1977) byCiba-Geigy; benalaxyl by Farmoplant Monte-dison (Bergamuschi et aL, 1981) and butryolac-tones (derivatives of acylalanines) like milfuramby Chevron (Lukens et aL, 1978) and cypro-furam by Schering, A.G. (Schering, 1982); thecarbamates — prothiocarb and propamocarb bySchering, A.G. (Pieroh et aL, 1978); cymoxanil,a cyanoacetamide oxime by E.I. dupont deNemours (Denis, 1976) and the ethyl phosphitese.g. fosetyl Al (Williams et aL, 1977); a markedimprovement in the chemical control ofOomycete diseases can now be realised. Thispaper reports on the comparative invitro effects

of some of these new compounds and a few con-ventional protectants on the mycelial growth,production of sporangia and chlamydospores,sporangium and zoospore germination on tworepresentative isolates of P. palmivora fromcocoa and durian.

MATERIALS AND METHODS

The systemic fungicides and protectantslisted in Table 1 were tested for comparativeinvitro effects against two representative isolatesof Phytophthora palmivora, PCI from cocoa andPDR from durian. For the studies, five-day-oldvegetable juice agar (VJA) cultures were usedand all experiments were carried out at 28 ±1.5°C unless otherwise stated.

Effects on Mycelial Linear Growth

Suitable dilutions of each chemical (Table1) were prepared separately with sterile distilledwater and incorporated into standardizedamounts of sterile molten Difco Corn Meal Agar(CMA) kept at 45°C to obtain the desired finalconcentrations of 0.01, 0.1, 0.5, 1.0, 2.5, 5.0,10.0 and 50.0 fJig/m\ a.i. A six-mm inoculum

TABLE 1Fungicides used in the toxicity studies on

cocoa (PCI) and durian (PDR) isolates of Phytophthora palmivora

Productname

Trivialname

Chemicalname

Ridomil25 WP

Galben25 WP

Aliette80 WP

Previcur-N70 EC

Vinicur20 WP

Difolatan4F

Terrazole25 EC

Metalaxyl

Benalaxyl

Fosetyl Al

Propamocarb

Cyprofuram

Captafol

Etridiazole

N-(2, 6-dimethylphenyl)-N-(methoxyacetyl)-DL-alaninemethyl ester

Methyl N-phenylacetyl-N-2, 6-xylyl-DL-alaninate

Aluminium tris-ethyl phosphonate

Propyl S-(dimethylamino) propylcarbamate

3-chloro-N-(2-oxoperhydro-3-furyl)-cyclopropane-carboxanilide

3a, 4, 7, 7a-tetrahydro-N-(l, 1, 2, 2, tetrachloroethane-sulphenyl phthalidamide)

5-ethoxy-3-trichloromethyl-l, 2, 4-thiadiazole

184 PERTANIKA VOL. 9 NO. 2, 1986

SENSITIVITY OF PHYTOPHTHORA PALMIVORA FROM COCOA AND DURIAN TO CHEMICALS

plug taken from the advancing margin of the VJAcolony of the test isolates was placed centrally oneach plate after solidification. The seeded plateswere incubated in the dark at 28 ± 1 .S^C. Eachchemical including the blank check agar whichcontained no chemical was tested in 4 replicates.Colony growth diameters of the fungus weremeasured at right angles regularly up to 7 days.Data at 7th day were subjected to probit analysis(Finney, 1971) where the probit inhibition of thefungal growth was plotted against the log con-centration of the chemical. A regression line wascalculated and the amount of fungicide requiredto inhibit 50% of the growth of the fungus (ED 5Q

value) was determined.

Effects on Production of Zoosporangium andChlamydospore

The procedure was similar to that used inmycelial growth studies except that VJA mediumwas used. The same chemicals were used at thefollowing concentrations: 0.1, 1.0, 10.0, 100,500 and 1,000 /i-g/ml. Blank check plates con-sisted of VJA minus the chemical. Test plateswere incubated in the dark at 28 ± 1.5°C in 3replicates.

After 7 days of incubation, colony measure-ments were made and a standardized amount ofsterile distilled water was added into each plate,A bent glass rod was used to dislodge the sporesand the suspension was filtered using muslincloth to remove mycelial fragments. A Neubauerhaemocytometer was used to determine thenumber of sporangia and chlamydospores pro-duced. Mean spore count data were transformedusing logarithmic transformation (log X +• 1)(Gomez and Gomez, 1976) and were subjected toANOVA statistical analysis.

Effects on Sporangia! Direct Germination

A cellophane transfer technique wasemployed. Sterilized 20 mm X 20 mm cello-phane (E.I. Dupont de Nemours & Co\, PUDO193) squares were laid on petri plates containingwater agar (WA) which were incorporated withappropriate concentrations of the test fungicide.Drops of sporangial/fungicide solution prepared

from equal volumes of double strength solutionof the fungicide and spore suspension wereplaced on these cellophane squares making thefinal concentration similar to that in thesporangial production test. Control consisted ofsterile distilled water plus the sporangial suspen-sion. Petri plates were kept in the dark at 25 ±1.2°C for 16 hrs after which cellophane squareswere mounted on glass slides and stained withlactophenol blue. Slides were gently flamed toprevent further germination of the sporangia.Percent germination and length of germ-tubebased on the first 200 sporangia encounteredwere determined. A sporangium was deemedgerminated when the germ-tube exceeded thewidth of the spore.

All data were analyzed using the probitanalysis to determine the ED 50 values.

Effects on Zoospore Germination

Coors porcelain plates with 12 depressions(112 mm X 87 mm; 5 mm deep) were used. Thedepressions were filled with 0.5 ml of doublestrength solution of each fungicide and a sporesolution with 2,000 sporangia/ml was addedgiving the final test concentrations of 0.1, 1.0,10.0, 100, 500 and 1,000 ug/ml a.i. Checktreatments consisted of half ml of sterile distilledwater added with another half ml of sporangiumsuspension of the isolate. Plates were incubatedin the dark for 4 hrs at 6°C and then returned toroom temperature (28 ± 1.5°C) to facilitate therelease of spores. With the use of a sterilizedpipette, drops of the mixed solution from theCoors porcelain plate were mounted on cleanglass slides, stained with lactophenol and gentlyflamed with an alcohol lamp. Percent germina-tion and length of germ-tube were determinedbased on the first 200 zoospores encounteredunder the X 40 magnification of the microscope.Data was then subjected to probit analysis.

RESULTS

Effects on Mycelial Linear Growth

The fungicides tested exhibited varyingdegrees of fungitoxicity on mycelial growth of

PERTANIKA VOL. 9 NO. 2, 1986 185


both isolates of P. palmivora from cocoa anddurian (Table 2). Metalaxyl and captafol werethe most effective with ED 50values of > 0 \ l f*g/ml for both isolates. Etridiazole was also effectiveagainst the two isolates with ED 50 value of 0.2# g / m l . Mycelial growth of the durian isolate

(PDR) appeared to be extremely sensitive toetridiazole with an ED 50 value as low as 0.0011*1 g /ml . Of the four remaining fungicides tested,

the order of fungitoxicity was cyprofuram,benalaxyl, fosetyl Al and propamocarb.

Effects on Sporangium Production

The invitro efficacy of fungicides againstsporangium production of P. palmivora cocoaand durian isolates is presented in Table 3.Metalaxyl displayed its superiority over the restof the fungicides tested. It significantly reducedsporangium production at 0.1 / /g /ml and com-pletely inhibited production of sporangia at 1.0/ ig /ml . Etridiazole and cyprofuram ranked

second best followed by benalaxyl. Captafol andfosetyl Al showed greater toxicity towards thecocoa isolate, completely inhibiting sporangiumformation at 500 / ig /ml . Adverse effects ofpropamocarb on both isolates were only observ-ed at 1,000 / ig/ml.

Effects on Chlamydospore Production

A similar trend was observed in chlamydo-3pore production as in sporangium production(Table 4). Metalaxyl and etridiazole were themost effective followed by cyprofuram. ThePDR isolate was, however, more sensitive toetridiazole compared to PCI, completely haltingchlamydospore production of the former isolateat 0.1 j ig/ml. Similarly, propamocarb dis-played greater toxicity towards the durian isolateeffecting 100% inhibition at 10 Mg/ml. FosetylAl was only effective at 500 / ig /ml .

Effects on Direct Germination of Sporangia

Metalaxyl, captafol and etridiazole had themost adverse effects on germination of sporangiaof P. palmivora (Table 5). On the cocoa isolate,these fungicides had ED 50 values of < 0 . 1 // g /mlwhile an ED i ovalue of 0.8 / /g /ml was recordedfor the durian isolate. Captafol and etridiazolewere, however, superior to metalaxyl in com-pletely suppressing direct germination ofsporangia of both isolates as indicated by thelower ED ioo values. Cyprofuram was also effec-tive against PDR in particular with an ED5 0

value of 0,08 / /g /ml . In contrast, benalaxyl andfosetyl Al displayed more toxicity towards PCI.

TABLE 2Effects of chemicals on mycelial growth of

Phytophthora palmivora cocoa (PCI) and durian (PDR) isolates

Chemical

ED5oValue (/ig/ml)

PCI

0.02

13.01

20.31

30.70

3.09

0.01

0.21

PDR

0.01

4.98

20.34

39.81

1.78

0.09

0.001

Metalaxyl

Benalaxyl

Fosetyl Al

Propamocarb

Cyprofuram

Captafol

Etriadiazole



TABLE 3Effects of fungicides on sporangium formation of


Chemical Isolate

Metalaxyl

Benalaxyl

Fosetyl Al

Propamocarb

Cyprofuram

Captafol

Etridiazole

PCIPDR

PCIPDR

PCIPDR

PCIPDR

PCIPDR

PCIPDR

PCIPDR

0

4.23 a**3.83 a**

1.50 a5.60 a

0.87 a8.60 a

2.09 a1.73 ab

5.43 a4.73 a

3.23 a1.83 a

3.53 a2.50 a

0.1

0.77 b0.80 b

1.07 a2.47 b

1.77 a8.53 a

1.17 ab2.20 a

5.57 a0.83 b

2.83 a1.30 a

2.13 b0.23 b

Mean sporangial count* (X 5 X 104)

Chemical concentration (fJ. g/ml)

1

0 c0 c

1.07 a1.67 c

0.90 a7.90 a

0.83 b0.97 abc

1.47 b0.13 c

1.23 b0.43 b

0.83 c0.13 b

10

0 c0 c

0.43 b0.30 d

0.77 a9.10 a

0.07 c0.27 c

0 c0.13 c

0.57 b0.27 b

0 d0 b

100

0 c0 c

0.43 b0.13 de

0.83 ab1.60 b

0.13 c0.57 abc

0 c0 c

0.33 be0.67 b

0 d0 b

00

00

00

00

00

00

00

500

cc

ce

.07 bec

.07 c

.13 be

cc

ce

db

00

00

00

00

00

00

00

1000

cc

ce

cc

cc

cc

ce

cb

*Each figure is an average of 3 replicates.

**Figures followed by the same letter in each row are not significantly different at P = 0.05 using transformeddata.

Propamocarb was the least effective among thefungicides tested.

The same pattern was also recorded for thegerm-tube development of sporangia of bothisolates (Table 5). Etridiazole, captafol andmetalaxyl were more effective in reducing thegerm-tube length in comparison with the otherfungicides tested. Benalaxyl, fosetyl Al andcyprofuram were intermediate in their effectswhile propamocarb remained comparativelyineffective.

Effects on Zoospore Germination

Among the fungicides tested, captafolshowed the most toxic effect on zoospore germi-nation of both isolates (Table 6). Captafol at 1.0Mg/ml and <0 .1 Mg/nil produced 100% and50% inhibition of zoospore germination of thetwo isolates, respectively. Although higher

amounts of fosetyl Al was needed against thecocoa isolate, it displayed greater toxicity againstzoospore germination of the durian isolate withan ED 5Q value of 0.29 //g/ml. Benalaxyl andetridiazole were moderate in action whereasmetalaxyl, propamocarb and cyprofuram wereonly effective at higher concentrations.

On zoospore germ tube development, asimilar trend was observed, with captafol main-taining its leading efficacy on the two isolates(Table 6). Captafol at 0.1 Mg/ml resulted in50% reduction in length of germ-tube of bothisolates. The rest of the chemicals requiredhigher dosages before they could bring about thesame effect. Metalaxyl, in particular, exhibitedless effects against the zoospores compared to itshigh toxicity against sporangium and clamydo-spore production, and sporangium germinationof the isolates.



TABLE 4Effects of chemicals on chlamydospore production of


Chemical Isolate

Metalaxyl

Benalaxyl

Fosetvl Al

Propamocarb

Cyprofuram

Captafol

Etridiazole

PCIPDR

PCIPDR

PCIPDR

PCIPDR

PCIPDR

PCIPDR

PCIPDR

0

1.370.20

1.830,60

0.670.77

1.200.37

1.770.33

0.770.27

0.830.27

a**a**

aa

aab

aa

aa

abcab

aa

0.1

0.63 b0.10 b

0.53 b0.50 a

0.20 a1.03 a

1.67 a0.33 a

1.07 b0,20 ab

1.57 a0.17 b

0.07 b0 b

Mean chlamydospore count*

Chemical

1

0 c0 b

0.30 b0.17 b

0.57 a0.90 a

1.30 a0.27 a

0.30 c0 b

1.00 ab0.43 a

0 b0 b

concentration

10

0 c0 b

0.23 b0 b

0.50 a1.07 a

0.17 b0 a

0 d0 b

0.20 c0.07 b

0 b0 b

(X 5 X

(jUg/ml)

100

0 c0 b

0 c0 b

0.43 a0.43 ab

0.30 b0 a

0 d0. b

0.43 be0.23 ab

0 b0 b

104)

00

00

00

0.0

00

00

00

500

cb

cb

ab

23 ba

db

dc

bb

00

00

00

00

00

00

00

1000

cb

cb

ab

ba

db

dc

bb

*Each figure is an average of 3 replicates.

**Figures followed by the same letter in each row are not significantly different at P = 0.05 using transformeddata.

TABLE 5Invitro effects of fungicides on direct germination of sporangia of

Phytophthora palmivora isolates from cocoa (PCI) and Durian (PDR)

Chemical

Metalaxyl

Benalaxyl

Fosetyl Al

Propamocarb

Cyprofuram

Captafol

Etridiazole

ED 50 value forgermination*

( jLtg/ml)

PCI PDR

0.05 0.68

0.53 >1000

>10<100 >1000

> 10000' >1000

3.92 0.08

<0.1 >0.1<l

<0.1 >0.1.<l

ED lQ0 value forgermination*

(Mg/

PCI

1000

>1000

100

>1000

^1000

1

1

ml)

PDR

500

>1000

>1000

">IOOO

500

10

100

ED tor germtube length**

( Mg /m!)

PCI PDR

0.29 0.74

20.59 486.05>10<100 >500<1000

>1000 > 1000

28.1 <100<500

<0.1 <0.1<l

<0.1 0.72

•based on the first 200 zoosporangia per replicate encountered.

**Basedon the actual number of germinated zoosporangia.



TABLE 6Effects of fungicides on zoospore germination of

Phytophthora palmivora cocoa (PCI) and durian (PDR) isolates after 4 hours of incubation

Chemical

Metalaxyl

Benalaxyl

Fosetyl Al

Propamocarb

Cyprofuram

Captafol

Etridiazole

ED 50 value forgermination*

(Wf/

PCI

> 100<B00

10

>100<500

100

>500<1000

<0.10

10.00

ml)

PDR

> 100< 500

6.92

0.29

277.21

79.22

< 0.10

69.64

ED 1OQ value forgermination*

(/ig/ml)

PCI

500

>1000

500

500

1000

1

1000

PDR

1000

>iooo1000

>1000

1000

1

500

ED 5Q value forgerm-tubtj length**

(/ig/ml)

PCI

>100<500

7.56

55.69

137.29

125.89

0.10

1.98

PDR

>100<500

281.84

1.70

85.60

60.23

0.10

69.64

•Based on the first 200 zoospores per replicate encountered.

**Based on the actual number of germinated zoospores.

DISCUSSION

A distinct variation in the invitro efficacy ofselected fungicides op the cocoa and durianisolates of P. palmivora was observed. A dif-ferential response was noted among the acyala-nines — metalaxyl, benalaxyl, and the acyala-nine derivative (butryolactones) — cyprofuram,although all these were reported to share similarbasic properties (Schwinn, 1983). Metalaxyl wasthe most active in inhibiting the various stages ofdevelopment except zoospore germination ofboth cocoa and durian isolates followed bycyprofuram. The low ED 50 values of below 1li g/ml recorded for metalaxyl on mycelialgrowth, sporangium and chlamydospore forma-tion and germination were also reported forother P. palmivora isolates from cocoa (Tey andWood, 1983), orchids (Lim and Nio, 1983) andother Phytophthora spp. (Staub and Young,1980; Farih et al, 1981; Coffey et al, 1984).Benalaxyl was more active in suppressing zoo-spore germination of the isolates than metalaxylor cyprofuram. The low invitro fungitoxicity ofmetalaxyl on zoospore germination was alsoobserved for P. parasitica (Farih, et al, 1981),P cinnamomi and P. citricola (Coffey, et al,1984).

The cocoa isolate of P palmivora appearedto be more sensitive to fosetyl Al duringsporangium germination whereas the durianisolate appeared to be more sensitive during zoo-spore germination. However, the overall invitroactivity of fosetyl Al is relatively low. Therelatively weak invitro toxicity of fosetyl Al wasalso reported by Farih, et al (1981); Lim andNio (1983), Schwinn, (1983) and Tey and Wood(1983). Compared to its breakdown product,phosphorus acid (Hai, et al, 1979), fosetyl Alwas less fungipotent invitro. However, recentlyFenn and Coffey (1984) reported that in lowphosphate medium, fosetyl Al exhibited muchhigher antifungal activity on P. cinnamomi.

The relatively low invitro efficacy ofpropamocarb (Previcur-N 70 EC) against all thedevelopmental stages of P. palmivora cocoa anddurian isolates suggest that it may not be activeagainst this particular species of Phytophthora.Negligible activity of propamocarb hydro-chloricje was similarly obtained invitro against P.palmivora cocoa isolate by Tey and Wood(1983). The invitro toxicity of propamocarbmight be similar to its analogue prothiocarbwhich was reported to exhibit full efficacy onlyat neutral pH of the substrate and against some



species of Phytophthora only at temperaturesaround 10°C (Kerkenaar and Kaars Sijpesteijin,1977).

Etridiazole, which was introduced in 1969for controlling diseases caused by Oomycetes,demonstrated a strong invitro efficacy againstalmost all the developmental stages of the twotest isolates, comparable to that of metalaxyl.Both etridiazole and metalaxyl were compar-atively less inhibitory to zoospore germination.The high invitro activity of etridiazole againstother Phytophthora spp. was also reported byGrant and Chew, (1981).

Captafoi, another non-systemic fungicide,demonstrated a very strong invitro efficacyagainst almost all the development stages of P.palmivora from cocoa and durian. Its highactivity was comparable to metalaxyl againstmycelial growth, sporangium germination andgerm-tube extension of both isolates. Unlikemetalaxyl, captafoi was highly toxic to zoosporegermination as well as its germ-tube develop-ment. The excellent invitro activity of captafoihas also been reported against mycelial growth,production of sporangia and zoospore of P.palmivora from cocoa (Tey and Wood, 1983).Mycelial growth of P. palmivora from orchid wassimilarly affected by captafoi (Lim and Nio,1983).

Taking into consideration the varyingefficacy of the fungicides reported here on thedifferent developmental stages of P. palmivoraas well as their strengths and weaknesses,integrating their use would result in a moreefficacious control. Besides, such a strategy canhelp to counteract the development of resistantpopulations of Phytophthora spp. when only onesystemic fungicide is used continuously(Schwinn, 1983).

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(Received 28 May, 1986)


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