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Resistance to
nude Jens.)
carboxin and fenfuram in Ustilago
Rostr., the causal agent of barley
loose smut
P.
EROUX AND G. BERTHIER*
I NRA, St at i on de Phy t opharm acie, Etoi l e de Choi sy, 78000 Versai l l es, France and
* NRA , SRIK La Verri -e, 78320 Le M esnil -Saint- Den France
ABSTRACT.
Two types
of strains of
U ago
nudu,
resistant to carboxin and fenfuram, were detected
on winter barley crops in 1986. The most frequent strains are similar to those found previously and
they are characterized by their great susceptibility to mepronil and flutolanil. This negative correlation
between two groups of carboxamide fungicides is not found when the other type of carboxin-resistant
isolates is considered. From these observations, we elaborate a simple teliospore-germination test which
can be used for routine survey of resistance. In field trials, when the resistant strains are prevalent (in
the absence of treatment), the efficacy of seed dressings with carboxin or fenmram against barley loose
smut is low. In such situations, which are common with the winter barley varieties Panda or Viva,
inhibitors of sterol biosynthesis such as flutriafol or triadimenol remain very active in practice.
KEYWORDS: Fungicide resistance; carboxamides; carboxin; fenfuram; barley; Ustilugo nudu
Introduction
The discovery, 20 years ago, of carboxin provided the
possibility of an efficient chemical control of barley
loose smut caused by
Ustilago nuda
(Richard and
Cognet, 1967; Ventura, Bourdin and Piedallu, 1968).
Since that time, this fungicide and several related
carboxamides (e.g. fenfuram, methfuroxam, pyra-
carbolid) have been intensively used as seed dressings,
in France and many other countries.
During the last three seasons, several cases of
reduced efficacy of these carboxamides have been
reported on winter barley crops in France. In some
situations it has been shown that heavy rainfall just
after sowing, or low dosage of chemicals applied to
seeds, were the causes of these failures. As resistance in
practice towards oxycarboxin (an analogue of
carboxin) has been found in
Puccinia horiana
(Grouet,
Montfort and Leroux, 1981), this possibility has also
been considered with the barley loose smut. The
monitoring which was conducted in France during the
spring of 1985 has indicated the presence of U
nuda
isolates, resistant to carboxamides, on several varieties
of barley (Leroux, 1986). This enabled us to collect
barley seeds contaminated with sensitive or resistant
strains. These samples were used for field experiments
during the season 1985-1986, to test the field
resistance of barley loose smut to carboxamides. This
paper presents the results of these trials (efficacy of
seed dressings and characteristics of U.
nuda
strains).
0261-2194/88/01/0016-04 03.00
0 1988 Butterworth & Co (Publishers) Ltd
CROP PROTECTION Vol. 7, February 1988, 16-19
Materials and methods
Varieties of w int er barl ey
The various samples of seeds were harvested during
summer 1985 in plots where smutted heads were
present. The resistance of teliospores from some of
these heads has been investigated (Leroux, 1986).
The three samples of cv. Viva, collected near Lyon,
Niort and Orleans, respectively, as well as the sample
of cv. Panda, were obtained from fields where
resistance to carboxin was widespread. In contrast, the
sample of cv. Thibaut came from a field where only
sensitive strains of U.
nuda
were detected. With regard
to cv. Gerbel, the sample was collected in a plot in
which resistant and sensitive isolates were present
simultaneously.
Seed dressi ngs
The seeds were treated by agitation with fungicide
powders for 15 min using a rotary shaker. For
carboxin, fenfuram and triadimenol formulations, the
rates were 1OOg a.i./quintal seed (q)f 80g a.i./q and
30 g a.i./q respectively; these are rates recommended in
France (Bourdin, 1983). Mepronil and flutriafol were
tested at 1OOg a.i./q and 5 g a.i./q respectively.
t
1 quintal=05g 100kg).
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P. LEROUXAND G . BERTHIER 17
TABLE 1. Effect of various chemicals on the germination ofteli ospores and the length ofpromyceli a of different strains of Ustilago nuda (each value is t h e
average obtained on at l e a s t t h r e e d i f f e r e n t i s o l a te s of each type)
S i s o l a t e
Concentra tion (mg/1) inhibi ting isolates of U. nuda
R1 isolate R2 i s o l a t e
Chemical* Spore st Promycelia~ Spores Promycelia Spores Promycelia
Benodanil 1 5 0.70 12 4.0 6.5 3 0
3.5 2.5 15 8.0 12 8 0
Carbox in 0 20 0.12 1 0 0.60 2.4 1.0
0.35 0.25 2.4 1.5 4 .6 3.0
Cyclafluramid 0 70 0.30 6- 0 2.5 13 5.0
1.0 0.70 7 5 4.0 25 8-0
Fen fura m 1.0 0.80 20 12 32 20
2.5 1.6 30 20 45 40
Flutolanil 15 7- 0 50 30 0 70 0 30
60 20 80 60 2.0 0 80
Furcarbanil 0 15 0.06 1.0 0.60 0.70 0.50
0.20 0.15 1.4 1.0 1.5 0.80
Furmecyclox 30 20 ND ND 30 18
70 45 ND ND 70 50
Mepronil 6.0 3.0 15 12 0.80 0.40
10 8.0 > 20 > 20 1.6 1.0
Methfur oxam 0 10 0 05 0.40 0.30 1.2 0 80
0.16 0.12 0 70 0.50 3.0 2.0
Oxycarboxin 65 30 > 200 200 200 100
120 90 > 2 0 0 >200 >200 180
Pyracarbol id 1 1 0. 80 6 5 4 .0 32 18
1.8 1.5 10 7 0 90 60
Antimycin A 0.04 0.05 0.04 0.04 0.06 0.08
0.12 0.20 0.12 0.20 0.20 0.20
2,4-Dinitrophenol 40 40 55 40 45 40
ND ND ND ND ND ND
Thenoy ltri fluoroacet one 25 25 25 25 25 25
80 90 70 90 90 100
* Chemical names:benodanil, 2-iodobenzanilide; carboxin, 5,6-dihydro-2-methyb1,4-oxathi-ine-3-carboxanilide; cyclafluramid, N-cyclohexyb2,5-dimethyb3-furamide; enfuram,
2-methyl-3-furanilide; flutolanil, a,cr,cr-trifluoro-Y-isopropoxy-o-toluanilide; urcarbanil, 2,5-dimethyl-3-furanilide; furmecyclox, methyl N-cyclohexyl-2,5-dimethylfuran-3-
carbohydroxamate; mepronil, Y-isopropoxy-o-toluanilide; methfuroxam, 2,4,5.~rimethyl-3-furanilide; oxycarboxin, 5,6.dihydro-2-methyl-l,4-oxathi-ine-3-carboxanilide
4,4-dioxide; pyracarbolid, 3,4-dihydro-6-methyl-2H-pyran-5-carboxanilide.
** EC50 upper number; EC90 lower number, in each column.
t Wi th eliospores, the EC50 and ECo0represent the concentrrations which give an inhibition of spore germination of 50% and 90%, respectively.
:1: Withpromycelia, the EC50 and EC90 represent the concentrations which give an inhibition of promcelial length of 50% and 90%, respectively.
ND: E C5 0 a nd
EC90 values
no t det erm i ned .
TABLE 2. Laboratory conditions for the routine monitoring of resistance
t o
carboxamides in
Ustilago nuda
Carboxin
Mepronil (0.5 mg/1)
(2- 5 mg/1) + meproni l
Strain Control or (2.5 mg/1)
of (without Carboxin Fenfuram flutolanil or flutolanil
U. nuda fungicides) (0 .5 mg/l) (7. 5 mg/l) (5 mg/1) (5 mg/l)
S + - - +
-
R 1
R2 + + + - -
+, germination of teliospores (presence of promycelium); -, no germination.
rial conditions
F o r e a c h
p l ot o f l m
2 1 8 g
s e e d w a s u s e d . S e e d w a s
s o w n o n 3 0 O c t o b e r 1 9 8 5 , e x c e p t f o r s e e d tr e a te d w i t h
m e p r o n i l w h i c h w a s s o w n o n 8 N o v e m b e r 1 9 8 5 .
C o n t r o l p l o t s w e r e s o w n a t b o t h d a t e s . T h e t r i a l h a d
t w o r e p l ic a t es a n d w a s c o n d u c t e d a t L a V e r r i ~ r e n ea r
V e r s a il le s . A t t h e b e g i n n i n g o f J u n e 1 9 8 6 , a t th e
f l o w e r i n g s t a g e , s m u t t e d a n d h e a l t h y h e a d s i n e a c h
p l o t w e r e c o u n t e d .
I n v i t r o
t e st s w i t h t el i o spo r es o f U .
n u d a
F o r e a c h e x p e r i m e n t a l c o n d i t i o n , 1 0 s m u t t e d h e a d s
w e r e c o l l e c t e d o n 1 0 d i f f e r e n t p l a n t s f i v e i n e a c h p l o t ) .
A s u s p e n s i o n o f t e li o s p o r e s i n s t e ri le w a t e r w a s
o b t a i n e d f r o m e a c h d i s e a s e d h e a d a n d p i p e t t e d o n t o
t h e s u r fa c e o f a g l u c o s e - a g a r m e d i u m w i t h o r w i t h o u t
f u n g i c i d e s. A f t e r a n i n c u b a t i o n o f 2 4 - 3 0 h a t 2 2 C ,
s p o r e g e r m i n a t i o n w a s o b s e r v e d u n d e r t h e m i c r o s c o p e
L e r o u x , 1 9 8 6 ) .
R e s u l t s
Ch a ra c t e r i s t i c s o f i s ol a t es o f
U . n u d a
T h r e e t y p e s o f s t r a in s h a v e b e e n d e t e c t e d i n o u r t r i a ls
Tab l e 1 .
T w o S a n d R 2) a r e s i m i l a r t o t h o s e d e s c r i b e d
p r e v i o u s l y L e r o u x , 1 9 8 6 ) a n d ar e c h a r a c t e r i z e d b y t h e
p h e n o m e n o n o f n e g a t iv e c r o s s r e s is t a n c e b e t w e e n
c a r b o x i n a n d m e p r o n i l . B e n o d a n i l , c y c l a f u r a m i d , f e n -
f u r a m , f u r c a r b a n i l , m e t h f u r o x a m , o x y c a r b o x i n a n d
p y r a c a r b o l i d e x h i b i t p o s i t i v e c r o s s r e s i s t a n c e w i t h
c a r b o x i n w h e r e a s f l u t o l a n i l h a s t h e s a m e e f f e c t a s
m e p r o n i l . T h e t h i r d ty p e o f s t r a in , r e s is t a n t t o
c a r b o x i n , fe n f u r a m , m e p r o n i l a n d f l u t a lo n i l R 1 ,
Tab l e 1 )
h a s b e e n f o u n d o n c v s G e r b e l a n d V i v a
see
Tab l e 4 ) .
T h e t h r e e t y p e s o f s t r ai n s d o n o t d i f f e r i n
t h e i r s e n s i t i v i t y t o t h e n o n - c a r b o x a m i d e r e s p i r a t o r y
i n h i b i to r s a n t i m y c i n A , 2 , 4 - d i n i t r o p h e n o l a n d t h e n o y l -
t r i f l u o r o a c e t o n e Tab l e 1 ) .
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18 Resistance to carbo xamides in Ust i lago nuda
TABLE 3. Efficacy o f various fungicides against barley loose smut (resul ts expressed as the percentage of smutt ed heads at the flowering stage)
Sowing date 30 October 1985
Sowing date 8 November 1985
Variety Carboxin Fenfuram Triadimenol * Flutri afolt Mepronil
of barley Cont rol (100 g/q) (80 g/q) (30 g/q) (5 g/q) Cont rol ( 100 g/q)
Viva (Lyon) 19.5 15.1 19.7 0.0 0.2 18.2 5.6
Viva (Niort) 17.0 15.3 19.5 0.0 0.0 18.7 11.7
Viva (Orleans) 8.6 6.0 7.1 0.0 0.0 9.1 3.6
Panda 13.9 6.2 12.0 0.0 0.0 12.7 2.2
Gerbel 2.8 0.9 2.4 0.0 0 0 2.6 1.8
Thibau t 13.0 0.0 0.0 0 0 0' 0 13 2 13.9
T r i a d i m en o l , 1 - 4 - ch l o r o p h en o x y ) - 3 , 3 - d i m et h y l - l - 1 H- 1 , 2 , 4 - t r i azo l - l - y l ) b u t an - 2 - o l .
t F l u t r l a f o l
(RS)-2,4 -di f luore~a.(1H-1,2,4-tr lazol-l -ylmethyl)benzhydryl
a l co h o l .
TABLE 4. Phenot ypes of strains of stilago nuda collected at the floweri ng stage of barley plants obtained from untreated o r carboxamide-treated seed
Sowing date 30 October 1985 Sowing date 8 November 1985
Carboxin Fenfura m Mepronil
Variety of barley Control (100 g/q) (80 g/q) Control (100 g/q)
Viva (Lyon) 1R1, 9R2 10R2 10R2 1S, 9R2 10R2
Viva (Niort) 10R2 10R2 10R2 10 R2 10R2
Viva (Orleans) 10R2 10R2 10R2 10R2 5R2 *
Panda 10R2 10R2 10R2 10R2 2R2 *
Gerbel 3S, 3R1, 4R2 3R1, 5R2 4R1, 6R2 2S, 1R1, 2R2 IS, 1R2*
Thibau t 10S -- -- 10S 10S
* L e s s t h a n 1 0 s m u t t e d h e a d s h a v e b e e n t e s t e d i n e a c h o f t h e s e c o n d i ti o n s .
TABLE 5. Carboxin resistance in stilago nuda in France (monitored in
June and July, 1985)
Variety
Number of plots* with:
Seed dressings Mixtures of
with (+ ) or Sensitive sensitive and Resistan t
without ( - ) isolates resistant isolates
carboxamides only isolates only
Antares - 2 0 0
+ 2 0 0
Barberousse - 4 0 0
+ 2 1 4
Cabro - 3 0 0
+ 0 2 1
Capri - 2 0 0
+ 0 1 1
Castel + 0 0 1
Gerbel - 2 1 0
+ 0 1 2
Igri + 1 2 0
1 0 3
Illia - 1 0 0
+ 0 2 3
Mogador - 0 2 0
Nefta + 1 0 0
Nymphe + 1 0 0
Panda - 3 2 5
+ 2 3 15
Pirate + 1 1 0
Plaisant + 1 0 0
Smash + 0 0 1
Sonja - 3 0 0
+ 2 4 1
Thibau t - 2 0 0
+ 2 1 0
Viva - 3 3 4
+ 2 4 11
* F r o m e a c h p l o t 5 - 1 0 s m u t t e d h e a d s w e r e t e s t e d a n d t h e r e s i s ta n t i s o la t e s c a n b e
e i t h e r t y p e R 1 o r t y p e R 2 .
D u r i n g o u r in v e s t i g a ti o n s i n 1 9 8 6 w e a l w a y s f o u n d
o n l y o n e t y p e o f st r ai n i n e a ch s m u t t e d h e a d . I n o u r
r o u t i n e m o n i t o r i n g w e u s e d t h e c o n d i t i o n s s e t o u t i n
Table 2
t o c h a r a c t e r i z e t h e i s o l a t e p r e s e n t o n e a c h
d i s e a s e d p l a n t .
Field act iv i t y o f fungicides
C a r b o x i n a n d f e n f u r a m d i d n o t c o n t r o l lo o s e s m u t o n
c v s V i v a a n d P a n d a w h e r e a s 1 0 0 c o n t r o l w a s
o b t a i n e d o n c v . T h i b a u t ( T a b l e 3). T h e s e r e s u lt s c a n b e
e x p l a i n e d b y t h e f a c t t h a t r e s i s t a n t s t ra i n s p r e d o m i n a t e
o n t h e f i r s t t w o v a r i e t i e s a n d a r e a b s e n t o n t h e t h i r d ( i n
t h e a b s e n c e o f s e e d d r e s s i n g s ) ( T a b l e
4).
O n c v . G e r b e l ,
c a r b o x i n h a d a n e f f ic a c y o f 7 0 w h e r e a s f e n f u r a m w a s
i n e f f e c t iv e . T h i s c a n b e e x p l a i n e d b y t h e d i f f e r e n c e s in
a c t i v it y b e t w e e n t h e s e t w o c a r b o x a m i d e s o n s t r a in s o f
t y p e R 1
Table 1) .
H o w e v e r , t h e l e v e l o f d i se a s e w a s
l o w , s o t h i s c o n c l u s i o n c a n n o t b e g e n e r a l i z e d .
S e e d d r e s s i n g w i t h m e p r o n i l d i d n o t e r a d ic a t e l o o s e
s m u t b u t s o m e t i m e s i t g a v e c o n t r o l g re a t e r t h a n 5 0 .
T h i s w a s o b s e r v e d o n l y w h e n s t ra i n s o f t y p e R 2
( s e n s i t i v e t o me p r o n i l ) w e r e p r e s e n t . O n t h e o t h e r
h a n d , t h e a b s e n c e o f a c ti v i ty o n c v . T h i b a u t c a n b e
c o r r e l a t e d w i t h t h e p r e s e n c e o f s tr a i n S w h i c h i s
t o l e r a n t t o me p r o n i l ( T a b l e s
3
and 4 ) .
D i s c u s s i o n
T h e t r i a l s c o n d u c t e d i n 1 9 8 6 c o n f i r m t h e p r e s e n c e , i n
n a t u r a l c o n d i t i o n s , o f U .
n u d
i s o l a t e s r e s i s t a n t t o
c a r b o x in . T h o s e w h i c h h a v e t h e h i g h e s t le v e l o f
r e s i st a n c e t y p e R 2 ) a r e p r e v a l e n t a n d h a v e t h e s a m e
c h a r a c t e r is t ic s a s t h e o n e s d e t e c t e d i n 1 9 8 4 a n d 1 9 8 5
L e r o u x , 1 9 8 6 ) . T h e i r m a i n p r o p e r t y i s t h e i r h i g h
s e n s i t i v i t y t o m e p r o n i l a n d f lu t o l a n i l . T h i s c a n b e
i n t e r p r e t e d a s n e g a t i v e c r o s s r e s i s t a n c e b e t w e e n t w o
t y p e s o f c a r b o x a m i d e f u n g i c i d e s . A s i m i l a r n e g a t i v e
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P. LEROUX AND G. BERTHIER
c o r r el a ti o n b e t w e e n c a r b o x a m i d e s h a s b e e n f o u n d i n
s t u d i e s w i t h l a b o r a t o r y m u t a n t s o f Ust i l a g o ma y d i s
( W h i t e , T h o r n a n d G e o r g o p o u l o s , 1 9 7 8 ) ; t h e c a r b o x -
a m i d e s s e l e c ti v e l y t o x i c t o m u t a n t s t ra i n s ( s u c h a s
m e p r o n i l o r f i u t o l a n i l ) w e r e c a r b o x i n a n a l o g u e s a l s o
s u b s t i t u t e d o n t h e p h e n y l r i n g . S u c h s i m i l a r i t i e s
b e t w e e n
U. maydis
a n d
U~ nuda
c a n a l so i nd i c a t e t ha t
r e s i s t a nc e t o c a r box in i s a t t r i bu t a b l e , i n bo th c a se s , t o
m o d i f i c a ti o n o f t h e s u c c i n i c d e h y d r o g e n a s e c o m p l e x .
H o w e v e r , b i o c h e m i c a l a n d g e n e t i c s tu d i e s a re r e q u i r e d
t o e l u c i d a t e th e m e c h a n i s m s o f r e s i st a n c e to c a r b o x i n
in U. nuda.
U n d e r f i e l d c o n d i t i o n s , w h e n t h e v a r i e t i e s V i v a o r
P a n d a a r e c o n t a m i n a t e d b y s tr a in s o f U. nuda
r e s i st a n t t o c a r b o x i n , t h i s f u n g i c i d e a n d a l s o f e n f u r a m
a r e i n e f fe c t iv e . I n c o n t r a s t , 1 0 0 % c o n t r o l o f l oo s e s m u t
is a c h i e v e d w h e n t h e f u n g u s i s se n s it iv e , a s w a s t h e
c a s e w i t h t h e s a m p l e o f cv . T h i b a u t . S u c h r e s u l ts
i n d i c a t e t h a t c a r b o x a m i d e r e s i s t a n c e i s a p r o b l e m i n
pr a c t i c e f o r t he c on t r o l o f l oose sm ut o f ba r le y .
I n F r a nc e a t p r e se n t i t i s poss ib l e t o de t e c t r e s i s t a n t
s t ra i n s o n t h e m o s t c o m m o n v a r i e ti e s o f w i n t e r b a r l e y
Table 5) . Ho we ve r , t he i r JT re que nc ie s r e m a in ge ne r a l l y
l o w i n t h e a b s e n c e o f s e e d d re s s i n g s a n d t h e y a r e
d e t e c t e d o n l y w h e n c a r b o x a m i d e s a r e s t i l l e f f e c t i v e
a g a i n st t h e l o o s e s m u t o f b a rl e y . I n t h o s e f e w s i t u a ti o n s
i n w h i c h h i g h f r e q u e n c i e s o f r e s is t a n t i s o la t es a r e
f o u n d i n t h e a b s e n c e o f t r e a t m e n t w i t h r e g i s t e r e d
c a r b o x a m i d e s , t h r e e s o l u t io n s c a n b e c o n s i d e r e d :
1 . I n v i e w o f t h e l o w l e v el o f r e s is t a n c e to w a r d s s o m e
c a r b o x a m i d e s , w e c a r l u s e t h e m a t h i g h e r d o s e
l e v e l s . S o m e p r e l i m i n a r y t r i a l s w i t h e x p e r i m e n t a l
c h e m i c a l s h a v e g i v e n u n e n c o u r a g i n g r e s u l t s ( G .
B e r t h i e r , u n p u b l i s h e d d a t a ) .
2 . T h e m i x t u r e o f t w o n e g a t i v e l y c o r r e l a t e d c a r b o x -
a m i d e s c a n b e c o n s i d e r e d (e .g . c a r b o x i n +
m e p r o n i l ) . T h i s s o l u t i o n i s o f li m i t e d i n t e r e s t i n
p r a c t i c e , m a i n l y b e c a u s e s o m e s t r a i n s w i l l n o t b e
a f f e c t e d ( R1 type ) .
19
3 . A t p r e se n t , t he on ly p r a c t i c a l poss ib i l i t y i s s e e d
d r e s s i n g w i t h i n h i b i t o rs o f s t e ro l C - 1 4 d e m e t h y l a -
t i o n . I n F r a n c e , t r i a d i m e n o l a n d f l u t r i a f o l a r e
r e g is t e re d a n d a r e r e c o m m e n d e d f o r u se o n t h e
v a r ie t ie s V i v a a n d P a n d a ( E s c h e n b r e n n e r , 1 98 6) .
c k n ow l e d g emen t s
W e a r e i n d e b t e d to t h e C o m p a n i e s D o w C h e m i c a l a n d
L a Q u i n o l e i n e w h i c h p r o v i d e d s a m p l e s o f s m u t t e d
h e a d s a n d s e e d s o f b a rl e y .
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R e c e iv e d 9 M a rc h 1 98 7
Revised 17 June 1987
A c c e p te d 9 S e p te mb e r 1 9 87
C R O P P R O T E C T I O N V o l. 7 F e b r u a ry 19 88