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Synergistic effect of fungicides on resistant strains of Penicillium italicum and Penicillium digitatum
lnternattonal Journal of Food Mtcrobtologv, 7 (1988) 79-85
79
Elsevier JFM 00224
Short Communication
Synergistic effect of fungicides on resistant strains of Penicillium italicum and Penicilliurn digitatum Angeles Diaz Borr~s 1, Rafael Vila Aguilar and Enrique Hernfindez Gim6nez 2 I C.S 1 C Inst:tuto de Agroqulm:cay Tecnologia de Ahmentos, Valencia, Spare and e Escuela T~cmca Superior de lngemeros Agrbnomos, Valenc:a, Spain
(Received 28 September 1987, revised version recewed 18 April 1988, accepted 9 May 1988l
In vitro and m VlVO tests were carried out to study the lnhlbttory, effect of rmxtures of sodium orthophenylphenate, methyl-l-(butyl-carbamoyl)-2-benzlrmdazole ('Benomyl') and sodmm orthophenylphenate. 2-(4-ttuazohl)-benzlrmdazole ('Ttuabendazole') on growth of strains of Pemcdhum :tahcum and P d:gttatum resistant to sodmm orthophenylphenate, "Benomyl' and "Ttuabendazole" 'In vitro' tests showed a synerglsuc effect of the ratxtures. 10 ppm of sodmm orthophenylphenate and 10 ppm of the benzlrmdazohc compound m most cases resulted m complete growth mhtbttton Navel oranges inoculated with P ~tahcum spores showed no damage after 7 days of incubation at 25°C and 80-90% relative humldtty when treated with a nuxture of 100 ppm of sodium orthophenylphenate and 100 ppm of Ttuabendazole Key words Pemctlhum ttahcum, Pemcdhum dtg:taturn. Fungtclde, Resistance, Synergtstlc effect
Introduction T h e increasing n u m b e r of p a t h o g e n i c r m c r o o r g a m s m s cau si n g spotlage of harvested citrus fruits a n d being resistant to c h em i cal s strongly indicate the n e e d for further research w o r k (Sylakakls, 1980). A possible solution hes m b l e n d i n g fungicxdes of d i f f e r e n t m o d e s of action (Delp, 1980) as in the case for the m i x t u r e of s o d m m o r t h o p h e n y l p h e n a t e a n d b e n z l r m d a zoles, e.g. ' B e n o m y l ' a n d ' T h i a b e n d a z o l e ' . N o n e of t h e m is satisfactory w h e n used alone due to resistance a m o n g fungj (Dekker, 1977: H o u c k , 1977; Brown, 1982) H o w e v e r , they can be e f f e c t w e w h e n used in c o m b i n a t i o n . E x a m p l e s can be f o u n d m the h t e r a t u r e showing v a r y i n g results with the use of m i x t u r e s of f u n g t o d e against fruit p a t h o g e n i c fungi ( K o f f m a n et al., 1978: Sutton, 1978; Prusky et al., 1985). T h e m a i n objective of the present p a p e r was the st u d y of the effect of c o m b i n e d use of f u n g i o d e s on growth, on a l a b o r a t o r y m e d i u m a n d N a v e l oranges, of
Correspondence address A Diaz Borr~ts, C S.I C. Insmuto de Agroquirruca y Tecnologia de Ahmentos, Jaime Rolg 1l, 46010 Valencia, Spare
0168-1605/88/$03 50 9 1988 Elsevter Sctence Pubhshers B V (Btomedlcal DIvaston)
80
Penlcllhum ttahcum and P dlgltatum strains resistant to sodium orthophenylphenate, Benomyl and Thlabendazole.
Material and Methods In vitro tests The strains of P ltahcum and P. dlgltatum used In this work were Isolated from Spanish cTtrus packing plants and were identified according to PTtt (Pitt, 1979). The number of strains used as well as their resistance towards fungicides as determined previously (unpublished data) are shown in Table I. A strain is considered resistant or sensmve to the fungicides sodium orthophenylphenate (SOPP), methyl-l-(butylcarbamoyl)-2-benzimidazole (Benomyl), and 2-(4-thiazolil)-benzlmidazole (Thxabendazole) depending on its ability or inability to grow on Orange serum agar (Dffco) pH 5 5 wTth 50 ppm of the fungicTde. To test synergastic effects, Orange serum agar were added mixtures used of SOPP and Benomyl or SOPP and Thiabendazole in ratios of 10 : 1 ppm, 25 : 1 ppm, 50 : 1 ppm, 10' 10 ppm, 2 5 : 1 0 ppm, 5 0 : 1 0 ppm, 1 0 : 2 0 ppm, 2 5 : 2 0 ppm and 5 0 : 2 0 ppm. These ratios were established following the theoretTcal models proposed by Sylakakis (1981). The fungicides were added as aqueous solutions (SOPP) or a suspensTons (Benomyl and Thmbendazole). The peru dTshes were inoculated with circular cuts of 5 mm dmmeter, and about 5 mm thickness, taken with a sterlhzed glass puncher from the margins of colonies grown, on Orange serum agar, for 7-10 days at 2 5 ° C and 80-90% relative hurmdlty. Inoculation was done in quadruplicate, using four peru dishes and placing on each one of them three different strains at equal distances. After 7 days of incubation under the above mentToned conditions the diameters of the colonies were measured. The average value was compared with the control to calculate the percentage of growth reduction (Geeson, 1976). 11l UIUO t e s t s
Nine lots consisting each of 15 freshly harvested Washington Navel oranges (Koffman et al., 1978) were inoculated with spores of P ttahcum, grown for 7 days at 25 ° C on petrl dishes with Orange serum agar and suspended in sterile water. The oranges were first washed to remove dirt and initial contamination, air-dried at room temperature and scarified uniformly on the surface. Each of the 4 lots were treated according to one of the following treatments. 1 Immersmn of the fruits for 2 man in a pool with water containing 7 × 10 ° spores per ml (determined by the use of a haemocytometer) followed by drying at room temperature and treatment by 7mmerslon m aqueous solutTons or suspensTons of the fung~cTdes for 4 man. 2 Treatment of the fruit by immersmn with aqueous solutions or suspension of the fungicides for 4 min followed by drying at room temperature and immersion for
81
TABLE
I
Remstance t of different strains of Pemcdhum and Thtabendazole
SOPP P
ttahcum
and
P
to 50 ppm
dtgztatum
2
Benomyl 3
Ttuabendazole
Itahcum
b
+
+
-
d
•
+
+
e
+
+
-
j
+
+
-
k
+
+
+
1
+
4-
-
m
-
-
-
o
-
-
-
p
+
--
_
r
--
4-
--
s
+
+
+
t
--
+
+
A~
+
-
-
Ft
-
+
-
G l
+
+
-
Jl
+
+
--
K~
+
+
-
Pt
+
+
-
R]
+
+
X]
+
+
WI
-
+
-
A 2
+
+
--
-
-
--
F2
+
+
--
G2
+
+
-
a 3 B3
+ +
+ +
+ +
D3
+
+
+
K 3
+
+
+
N3
+
+
+
M 3
+
+
+
03
+
-
-
P3
+
+
+
R 3
+
+
+
V3
+
+
+
Z 3
+
+
+
a
-
+
+
c
--
+
+
01
+
+
-
B2
+
+
-
02
+
+
+
H 2
+
+
+
T2
+
+
+
P
1
dlgltatum
+
resistant,
2 SOPP
-
sodmm
3 Benomyl
= non remstant orthophenylphenate
methyl-l-(butyl-carbamoyl)-2-benztmldazole
4 Thmbendazole,
of SOPP,
added to Orange serum agar
2-(4-thtazohl)-benzarmdazole
4
Benomyl
'~
I
I
I
I
I
I
I
d
l
~
l
l
l
l
l
l
F
I
d
l
l
N < = , ~ O- ~ Z ~ ~, ~ = >: _~ ~> __~_ × = ~ ~ >
l
l
----
l
l
l
t
l
~
l
~
l
l
~
o ~ --~
l
~ ~
o©
'J'
o©
B
0
0
E~
0
0
o
,-i
~o
©o
,..,~
0
o
83 TABLE IIl Mean values of colony dmmeters (ram) and percentages of growth reducuon of tested stratus of
Pen,cllhum dlgttatum treated with different combmatmns of SOPP and Benomyl (ppm) added to Orange serum agar Strain
d 1
a c OI B, D2 H2 T2
32 33 28 24 33 30 31
i 2 3 4
SOPPBenomyl 10 14
SOPP Benomyl 25 1
SOPP Benomyl 50 1
SOPP Benomyl 10.10
d
%:
d
%
d
d
22 17 26 21 25 27 28
30 48 8 15 24 8 13
15 14 23 16 25 23 19
52 59 19 8 24 22 33
% 6
21 10 24 23 11
81 100 27 26 27 22 68
4,
_ 3
100 100 100 100 68 64 100
11 11 -
Mean of colony dmmeters Percentage of growth reduction _ = no growth SOPP and Benomyl see Table I
2 min
in w a t e r
haemocytometer).
containing
7 × 10 s p o r e s p e r
ml (determined
by
the use of a
T h e n i n t h l o t w a s u s e d a s c o n t r o l , i.e. it w a s m o c u l a t e d
with
spores but not treated with fungicides. The following fungmides and doses were included: ppm;
Tbaabendazole, 1000 ppm. These concentrations
S O P P , 2%; B e n o m y l ,
1000
are normally used m citrus
fruit p a c k i n g p l a n t s . T h e b l e n d of S O P P (100 p p m ) w i t h T h i a b e n d a z o l e
(100 ppm)
w a s i n c l u d e d , to i n v e s t i g a t e the s y n e r g i s t i c effect of S O P P a n d b e n z i m i d a z o l e s .
TABLE IV Percentages of spoiled Navel oranges inoculated w,lth strains of Pemctlhum ttahcum resistant to SOPP, Benomyl and Ttuabendazole Treatment
Control (untreated) Treated with SOPP (2%) 3 Treated with Benomyl (1000 ppm) 3 Treated with Thlabendazole (1000 ppm) 3 Treated wtth SOPP (100 ppm) and Ttuabendazole (100 ppm) t Samples inoculated and then treated 2 Samples treated and then inoculated 3 SOPP, Benomyl and Ttuabendazole see Table I
Percentage spoiled 3rd day
7th day
93 87 100 47 47 0 0 0 0
100 100 1 100 2 67 1 53 2 33 1 33 2 0 1 0 ~
1 2 i 2 ~ 2 1 2
84
Oranges were packed m crates and stored at 25 ° C and 90% of relative humidity. The frmts were checked daffy for rune days to observe fungal growth. A frmt was considered damaged when green-blue spots with a diameter of at least 15-20 mm due to spore growth were observed on the scarified surface.
Results
Percentages of m vitro growth reduction (in relation to control samples) of P
ltahcum and P. dtgttatum caused by SOPP and Benomyl blends are shown m Tables II and III. No growth was observed when using the blend consisting of 25 ppm of SOPP and 10 ppm of Benomyl and higher levels (results not included). At 10 ppm of SOPP and 10 ppm of Benomyl, most of the moulds were completely inhibited. Blends of SOPP and Thiabendazole gave very sirmlar results (data not included). As seen from Table IV no frmt damage was observed after 3 and 7 days m fruits treated with 100 ppm of SOPP and 100 ppm of Tinabendazole. Tins agrees with the synergistic effect observed in the in wtro tests.
Discussion
These present results have shown a synergistic effect between SOPP and benzimldazoles ("Benomyl" and "Tinabendazole") on stratus of P ltahcum and P dlgltatum resistant to these fungicides. Tins finding ~s important considering that the problem of resistance can be solved avoiding the use of new fungicides winch, m addition to an increase in costs could cause new resistance problems (E1-Goorani et al., 1984: Prusky et al., 1985; Diaz and Vfla, 1987). It ~s also ~mportant to take into cons~deratton the occurrence of resistant moulds at citrus packing plants when defining the most statable types and blends of fung~ctdes (Bancroft et al., 1984).
References Bancroft, M N , Gardner. P D and Bantelle. J L (1984) Comparison of decay control strategxes m Cahforma lemon packing-houses Plant Dis 68, 24-28 Brown, G E (1982) Resistance of deca} fungi to benzlrmdazole fungicides used in Florida cttrus packang-houses Proc Fla State Hort Soc 95, 239-242 Dekker, J (1977) The fungaclde resistance problem Neth J Plant Pathol 83, 159-167 Delp, C J (1980) Coping w~th resistance to plant disease Plant Dis. 64, 652-657 Diaz, A and Vda, R (1987) Estudlo de la flora ffingma presente en c~.maras fngoriflca de conservacl6n de citncos A h m e n t a n a 183, 77-82 EI-Gooram, M A and E1-Kashelr, H M (1984) Resistance to benzimtdazole fungicides of Penlctlhum ttahcum and P dlgttaturn isolated from packmghouses and orchards m Egypt Plant D~s 68. 100-102 Oeeson, J D (1976) Comparanve studies of rnnethyl-benzlmadazol-2-ylcarbarnate tolerant and sensmve ~solates of Botrytts cmerea and other fungi Trans Br Mycol Soc 66. 123-129
85 Houck, L G (1977) Problems of resistance to citrus funglc~des Proc Int Soc Citric 1, 263-269 Koffman, W , Penrose, L J , Manzles, A R , Davas, K C and Kaldor, J (1978) Control of benzamidazoletolerant Pemcllhum expansum m pome frmt Scl Hortlc 9, 31-39 Pitt, J I. (1979) The G e n u s Pemctlhum and its Teleomorphic States Eupemcdhum and Talaromyces Acadermc Press. London Prusky, D , Bazak, M and Ben-Arle, R (1985) Development, persistence, survival, and strategies for control of Thaabendazole-reslstant stratus of Pemcdhum expan~um on pome fruits Phytopathology 75, 877-882 Sutton, T B (1978) Failure of combmations of Benom3l with reducted rates of non-benzarmdazole fungicides to control Venturta maequahs resistant to Benomyl and the spread of resistant stratus in North Carohna. Plant Dis. 62, 830-834 Sylakakis, G (1981) Effects of alternating and mixang pesticides on the budd-up of fungal resistance Phytopathology 71, 1119-1121
79
Elsevier JFM 00224
Short Communication
Synergistic effect of fungicides on resistant strains of Penicillium italicum and Penicilliurn digitatum Angeles Diaz Borr~s 1, Rafael Vila Aguilar and Enrique Hernfindez Gim6nez 2 I C.S 1 C Inst:tuto de Agroqulm:cay Tecnologia de Ahmentos, Valencia, Spare and e Escuela T~cmca Superior de lngemeros Agrbnomos, Valenc:a, Spain
(Received 28 September 1987, revised version recewed 18 April 1988, accepted 9 May 1988l
In vitro and m VlVO tests were carried out to study the lnhlbttory, effect of rmxtures of sodium orthophenylphenate, methyl-l-(butyl-carbamoyl)-2-benzlrmdazole ('Benomyl') and sodmm orthophenylphenate. 2-(4-ttuazohl)-benzlrmdazole ('Ttuabendazole') on growth of strains of Pemcdhum :tahcum and P d:gttatum resistant to sodmm orthophenylphenate, "Benomyl' and "Ttuabendazole" 'In vitro' tests showed a synerglsuc effect of the ratxtures. 10 ppm of sodmm orthophenylphenate and 10 ppm of the benzlrmdazohc compound m most cases resulted m complete growth mhtbttton Navel oranges inoculated with P ~tahcum spores showed no damage after 7 days of incubation at 25°C and 80-90% relative humldtty when treated with a nuxture of 100 ppm of sodium orthophenylphenate and 100 ppm of Ttuabendazole Key words Pemctlhum ttahcum, Pemcdhum dtg:taturn. Fungtclde, Resistance, Synergtstlc effect
Introduction T h e increasing n u m b e r of p a t h o g e n i c r m c r o o r g a m s m s cau si n g spotlage of harvested citrus fruits a n d being resistant to c h em i cal s strongly indicate the n e e d for further research w o r k (Sylakakls, 1980). A possible solution hes m b l e n d i n g fungicxdes of d i f f e r e n t m o d e s of action (Delp, 1980) as in the case for the m i x t u r e of s o d m m o r t h o p h e n y l p h e n a t e a n d b e n z l r m d a zoles, e.g. ' B e n o m y l ' a n d ' T h i a b e n d a z o l e ' . N o n e of t h e m is satisfactory w h e n used alone due to resistance a m o n g fungj (Dekker, 1977: H o u c k , 1977; Brown, 1982) H o w e v e r , they can be e f f e c t w e w h e n used in c o m b i n a t i o n . E x a m p l e s can be f o u n d m the h t e r a t u r e showing v a r y i n g results with the use of m i x t u r e s of f u n g t o d e against fruit p a t h o g e n i c fungi ( K o f f m a n et al., 1978: Sutton, 1978; Prusky et al., 1985). T h e m a i n objective of the present p a p e r was the st u d y of the effect of c o m b i n e d use of f u n g i o d e s on growth, on a l a b o r a t o r y m e d i u m a n d N a v e l oranges, of
Correspondence address A Diaz Borr~ts, C S.I C. Insmuto de Agroquirruca y Tecnologia de Ahmentos, Jaime Rolg 1l, 46010 Valencia, Spare
0168-1605/88/$03 50 9 1988 Elsevter Sctence Pubhshers B V (Btomedlcal DIvaston)
80
Penlcllhum ttahcum and P dlgltatum strains resistant to sodium orthophenylphenate, Benomyl and Thlabendazole.
Material and Methods In vitro tests The strains of P ltahcum and P. dlgltatum used In this work were Isolated from Spanish cTtrus packing plants and were identified according to PTtt (Pitt, 1979). The number of strains used as well as their resistance towards fungicides as determined previously (unpublished data) are shown in Table I. A strain is considered resistant or sensmve to the fungicides sodium orthophenylphenate (SOPP), methyl-l-(butylcarbamoyl)-2-benzimidazole (Benomyl), and 2-(4-thiazolil)-benzlmidazole (Thxabendazole) depending on its ability or inability to grow on Orange serum agar (Dffco) pH 5 5 wTth 50 ppm of the fungicTde. To test synergastic effects, Orange serum agar were added mixtures used of SOPP and Benomyl or SOPP and Thiabendazole in ratios of 10 : 1 ppm, 25 : 1 ppm, 50 : 1 ppm, 10' 10 ppm, 2 5 : 1 0 ppm, 5 0 : 1 0 ppm, 1 0 : 2 0 ppm, 2 5 : 2 0 ppm and 5 0 : 2 0 ppm. These ratios were established following the theoretTcal models proposed by Sylakakis (1981). The fungicides were added as aqueous solutions (SOPP) or a suspensTons (Benomyl and Thmbendazole). The peru dTshes were inoculated with circular cuts of 5 mm dmmeter, and about 5 mm thickness, taken with a sterlhzed glass puncher from the margins of colonies grown, on Orange serum agar, for 7-10 days at 2 5 ° C and 80-90% relative hurmdlty. Inoculation was done in quadruplicate, using four peru dishes and placing on each one of them three different strains at equal distances. After 7 days of incubation under the above mentToned conditions the diameters of the colonies were measured. The average value was compared with the control to calculate the percentage of growth reduction (Geeson, 1976). 11l UIUO t e s t s
Nine lots consisting each of 15 freshly harvested Washington Navel oranges (Koffman et al., 1978) were inoculated with spores of P ttahcum, grown for 7 days at 25 ° C on petrl dishes with Orange serum agar and suspended in sterile water. The oranges were first washed to remove dirt and initial contamination, air-dried at room temperature and scarified uniformly on the surface. Each of the 4 lots were treated according to one of the following treatments. 1 Immersmn of the fruits for 2 man in a pool with water containing 7 × 10 ° spores per ml (determined by the use of a haemocytometer) followed by drying at room temperature and treatment by 7mmerslon m aqueous solutTons or suspensTons of the fung~cTdes for 4 man. 2 Treatment of the fruit by immersmn with aqueous solutions or suspension of the fungicides for 4 min followed by drying at room temperature and immersion for
81
TABLE
I
Remstance t of different strains of Pemcdhum and Thtabendazole
SOPP P
ttahcum
and
P
to 50 ppm
dtgztatum
2
Benomyl 3
Ttuabendazole
Itahcum
b
+
+
-
d
•
+
+
e
+
+
-
j
+
+
-
k
+
+
+
1
+
4-
-
m
-
-
-
o
-
-
-
p
+
--
_
r
--
4-
--
s
+
+
+
t
--
+
+
A~
+
-
-
Ft
-
+
-
G l
+
+
-
Jl
+
+
--
K~
+
+
-
Pt
+
+
-
R]
+
+
X]
+
+
WI
-
+
-
A 2
+
+
--
-
-
--
F2
+
+
--
G2
+
+
-
a 3 B3
+ +
+ +
+ +
D3
+
+
+
K 3
+
+
+
N3
+
+
+
M 3
+
+
+
03
+
-
-
P3
+
+
+
R 3
+
+
+
V3
+
+
+
Z 3
+
+
+
a
-
+
+
c
--
+
+
01
+
+
-
B2
+
+
-
02
+
+
+
H 2
+
+
+
T2
+
+
+
P
1
dlgltatum
+
resistant,
2 SOPP
-
sodmm
3 Benomyl
= non remstant orthophenylphenate
methyl-l-(butyl-carbamoyl)-2-benztmldazole
4 Thmbendazole,
of SOPP,
added to Orange serum agar
2-(4-thtazohl)-benzarmdazole
4
Benomyl
'~
I
I
I
I
I
I
I
d
l
~
l
l
l
l
l
l
F
I
d
l
l
N < = , ~ O- ~ Z ~ ~, ~ = >: _~ ~> __~_ × = ~ ~ >
l
l
----
l
l
l
t
l
~
l
~
l
l
~
o ~ --~
l
~ ~
o©
'J'
o©
B
0
0
E~
0
0
o
,-i
~o
©o
,..,~
0
o
83 TABLE IIl Mean values of colony dmmeters (ram) and percentages of growth reducuon of tested stratus of
Pen,cllhum dlgttatum treated with different combmatmns of SOPP and Benomyl (ppm) added to Orange serum agar Strain
d 1
a c OI B, D2 H2 T2
32 33 28 24 33 30 31
i 2 3 4
SOPPBenomyl 10 14
SOPP Benomyl 25 1
SOPP Benomyl 50 1
SOPP Benomyl 10.10
d
%:
d
%
d
d
22 17 26 21 25 27 28
30 48 8 15 24 8 13
15 14 23 16 25 23 19
52 59 19 8 24 22 33
% 6
21 10 24 23 11
81 100 27 26 27 22 68
4,
_ 3
100 100 100 100 68 64 100
11 11 -
Mean of colony dmmeters Percentage of growth reduction _ = no growth SOPP and Benomyl see Table I
2 min
in w a t e r
haemocytometer).
containing
7 × 10 s p o r e s p e r
ml (determined
by
the use of a
T h e n i n t h l o t w a s u s e d a s c o n t r o l , i.e. it w a s m o c u l a t e d
with
spores but not treated with fungicides. The following fungmides and doses were included: ppm;
Tbaabendazole, 1000 ppm. These concentrations
S O P P , 2%; B e n o m y l ,
1000
are normally used m citrus
fruit p a c k i n g p l a n t s . T h e b l e n d of S O P P (100 p p m ) w i t h T h i a b e n d a z o l e
(100 ppm)
w a s i n c l u d e d , to i n v e s t i g a t e the s y n e r g i s t i c effect of S O P P a n d b e n z i m i d a z o l e s .
TABLE IV Percentages of spoiled Navel oranges inoculated w,lth strains of Pemctlhum ttahcum resistant to SOPP, Benomyl and Ttuabendazole Treatment
Control (untreated) Treated with SOPP (2%) 3 Treated with Benomyl (1000 ppm) 3 Treated with Thlabendazole (1000 ppm) 3 Treated wtth SOPP (100 ppm) and Ttuabendazole (100 ppm) t Samples inoculated and then treated 2 Samples treated and then inoculated 3 SOPP, Benomyl and Ttuabendazole see Table I
Percentage spoiled 3rd day
7th day
93 87 100 47 47 0 0 0 0
100 100 1 100 2 67 1 53 2 33 1 33 2 0 1 0 ~
1 2 i 2 ~ 2 1 2
84
Oranges were packed m crates and stored at 25 ° C and 90% of relative humidity. The frmts were checked daffy for rune days to observe fungal growth. A frmt was considered damaged when green-blue spots with a diameter of at least 15-20 mm due to spore growth were observed on the scarified surface.
Results
Percentages of m vitro growth reduction (in relation to control samples) of P
ltahcum and P. dtgttatum caused by SOPP and Benomyl blends are shown m Tables II and III. No growth was observed when using the blend consisting of 25 ppm of SOPP and 10 ppm of Benomyl and higher levels (results not included). At 10 ppm of SOPP and 10 ppm of Benomyl, most of the moulds were completely inhibited. Blends of SOPP and Thiabendazole gave very sirmlar results (data not included). As seen from Table IV no frmt damage was observed after 3 and 7 days m fruits treated with 100 ppm of SOPP and 100 ppm of Tinabendazole. Tins agrees with the synergistic effect observed in the in wtro tests.
Discussion
These present results have shown a synergistic effect between SOPP and benzimldazoles ("Benomyl" and "Tinabendazole") on stratus of P ltahcum and P dlgltatum resistant to these fungicides. Tins finding ~s important considering that the problem of resistance can be solved avoiding the use of new fungicides winch, m addition to an increase in costs could cause new resistance problems (E1-Goorani et al., 1984: Prusky et al., 1985; Diaz and Vfla, 1987). It ~s also ~mportant to take into cons~deratton the occurrence of resistant moulds at citrus packing plants when defining the most statable types and blends of fung~ctdes (Bancroft et al., 1984).
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