M Groenewald

P W Crous

S Denman

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Fungicide Sensitivity of Phaeomoniella chlamydospora, the Causal 
Organism of Petri Grapevine Decline 
M. Groenewald, S. Denman and P.W. Crous 
Department of Plant Pathology, University of Stellenbosch, Private Bag Xl, 7602 Matieland (Stellenbosch), South Africa 
Submitted for publication: February 2000 
Accepted for publication: December 2000 
Key words: Petri grapevine decline, esca, fungicides, grapevines, Phaeomoniella chlamydospora 
Twelve fungicides, benomyl, chlorothalonil, fenarimol, fosetyl-Al, iprodione, kresoxim-methyl, mancozeb, 
metalaxyl, prochloraz manganese chloride, quintozene, tebuconazole and thiram were screened in vitro for their 
ability to inhibit mycelial growth of Phaeomoniella chlamydospora, the causal organism of Petri grapevine decline. 
Isolates of Pa. chlamydospora were obtained from different geographical areas in the Western Cape province. The 
effective concentration at which 50% of mycelial growth was inhibited (ECso) was calculated for each fungicide. 
Benomyl, fenarimol, kresoxim-methyl, prochloraz manganese chloride and tebuconazole were the most effective in 
inhibiting mycelial growth of Pa. chlamydospora with ECso values ranging from 0.01 to 0.05 J.lglmL. Data obtained 
in this study represent the base-line sensitivity of local isolates to these fungicides, which is important for 
monitoring the development of pathogen resistance to fungicides. 
Grape production is an important agricultural industry in South 
Africa that earned an estimated Rl,4 billion in 1998 (Anon., 
1998). Losses caused by pests or diseases are thus of great con-
cern to the industry. It has only recently been proven that the con-
dition in which young grapevines show stunted growth and slow 
die-back is a disease caused by fungal pathogens (Morton, 1995; 
Ferreira, 1998; Scheck et al., 1998; Mugnai et at., 1999). This 
disease is widespread and causes serious losses in South African 
vineyards. 
Several fungi have been associated with slow die-back of vines 
worldwide, but the organism most commonly isolated from 
affected vines in South Africa was identified as Phialophora par-
asitica (Ferreira et at., 1994). However, after an extensive study, 
Crous et at. (1996) established the genus Phaeoacremonium for a 
group of fungal pathogens associated with die-back diseases of 
woody hosts. Although several species of Phaeoacremonium 
have been associated with the disease, namely Pm. aleophilum, 
Pm. chlamydosporum and Pm. inflatipes (Morton, 1995; 
Larignon & Dubos, 1997; Scheck et at., 1998; Mugnai et at., 
1999), Pm. chlamydosporum is the dominant fungus isolated 
from symptomatic young grapevines in South Africa 
(Groenewald et at., unpublished data) and Italy (Sidoti et at., 
2000). A re-examination of numerous Pm. chlamydosporum iso-
lates from diverse geographical regions showed several promi-
nent morphological differences between this species and others 
accommodated in Phaeoacremonium. Based on molecular 
(Dupont et at., 1998), morphological and pathological differ-
ences, a new genus Phaeomoniella Crous & W. Gams was there-
fore introduced, typified by Phaeomoniella chlamydospora 
(=Phaeoacremonium chlamydosporum) (Crous & Gams, 1999). 
Much confusion has surrounded the name of the disease. 
Morton (1995) reported a mysterious disease from young vines in 
California in which diseased vines had shiny black streaks in their 
vascular vessels and showed poor vine growth, sometimes lead-
ing to a sudden collapse of the vine. In response to the disease, 
plants produced black gum and thus the name 'black goo' origi-
nated (Morton, 1995). In older vines the disease has been referred 
to as esca, apoplexy and black measles, but in young vines it is 
called Petri grapevine decline (Mugnai et at., 1999). 
In order to effectively implement integrated control of Pa. 
chlamydospora, it is important to know how infection becomes 
established. Recently it was discovered that Pa. chlamydospora 
was present in apparently healthy propagation material (cuttings 
and rootstock) in a latent or endophytic form (Bertelli et aI., 1998; 
J.H.S. Ferreira, pers. comrn.). This evidence supports the belief 
that the disease could have its origin in propagation material. 
Preplant treatment of nursery material to eradicate the pathogen 
would thus be of practical use to the industry. 
One possibility of eradicating the pathogen from cuttings is to 
soak them in a solution of systemic or other fungicides so that the 
chemicals can be taken up and transported through the vascular 
tissue of the cuttings. Similarly, fungicide drenches could be 
taken up by the rooted cuttings and transported through the plant 
and this may also offer good control. The purpose of this experi-
ment was to screen a number of fungicides against Pa. chlamy-
dospora isolates to determine their effect on mycelial growth. 
Results of this screening test also provide base-line sensitivities 
of South African isolates of Pa. chlamydospora. Data obtained in 
these in vitro tests should thus lead to further testing in pot and 
field trials. 
MATERIALS AND METHODS 
In vitro tests on mycelial inhibition: Twelve fungicides repre-
senting contact and systemic products were screened (Table 1). 
The screenings were carried out in a block repetition conducted 
in December 1998 and January 1999. All twelve fungicides were 
tested at the following concentrations: 0.005,0.01,0.05,0.1,0.5, 
1 and 5 Ilg a.i.lmL. Chlorothalonil, thiram and mancozeb were 
also tested at 10, 50 and 100 Ilg a.i.lmL. One litre of stock solu-
tion was prepared for each fungicide and appropriate dilutions 
were added to 1000 mL 2% malt extract agar (MEA, Biolab) 
(50DC). Only MEA was present in the control medium. Within 24 
h after they had been poured, plates were inoculated with a 5 mm 
S. Afr. J. Enol. Vitic., Vol. 21, No.2, 2000 
59 
60 Fungicide Sensitivity of Phaeomoniella chlamydospora 
TABLE 1 
Fungicides screened against Phaeomoniella chlamydospora. 
Active ingredient Trade name Fungicide group 
benomyl Benlate Benzimidazoles 
chlorothalonil Bravo miscellaneous 
fenarimol Rubigan DMI-pyrimidine 
fosetyl-Al Aliette Organic compounds 
iprodione Rovral Flo Dicarboximide 
kresoxim-methyl Stroby Strobilurin 
mancozeb Dithane Dithiocarbamates 
metalaxyl Ridomil Acylanalines 
prochloraz manganese chloride Octave DMi-imidiazole 
quintozene PCNB Aromatic compounds 
tebuconazole Folicur DMl-triazoles 
thiram Thiram Dithiocarbamates 
a According to Nel et at. (1999). 
diam. mycelial disc from the cultured Pa. chlamydospora iso-
lates. Two mycelial discs were placed opposite each other on 
plates. Six isolates of Pa. chlamydospora from different geo-
graphical regions (STE-U 2863-2868) were used for the tests. 
These isolates are maintained at the Department of Plant 
Pathology, University of Stellenbosch (STE-U). Linear mycelial 
growth was recorded after 14 days incubation at 22°C in the dark 
by measuring the perpendicular diameters. 
The effective concentration at which mycelial growth was 
inhibited by 50% relative to the control (ECso) was calculated. 
Percentage inhibition of mycelial growth relative to the control 
was plotted against fungicide concentration for each 
fungicidelisolate combination. Different regression functions 
were fitted to the percentage inhibitions and the r2 were recorded. 
A linear function y = a+b( conc) was fitted for iprodione, meta-
laxyl and quintozene. For fungicides benomyl, chlorothanonil, 
fenarimol, kresoxim-methyl, mancozeb, prochloraz manganese 
chloride, tebuconazole and thiram the function y = a(l-exp(bx)) 
was fitted and the ECso value calculated. An analysis of variance 
was conducted on the ECso values to determine significant differ-
ences between the inhibitory effects of the various fungicides. 
RESULTS 
Differences between the means of the two repetitIOns (1998, 
1999) were not significant (P = 0.2538). Therefore, the pooled 
data of the two repetitions were used to calculate the ECso values. 
Since there were no significant differences between isolates (P = 
0.3354) in response to the fungicides, each isolate was regarded 
as a replicate in the statistical analysis. Interaction between the 
isolates and fungicides (P = 0.6110) was not significant. 
However, the effects of the various fungicides on mycelial 
growth were significantly different (P = 0.0001). No ECso values 
could be calculated for fosetyl-Al, due to the lack of inhibition of 
mycelial growth. ECso values calculated for the remaining 11 
fungicides are shown in Table 1. 
DISCUSSION 
Ferreira (1998) reported that fosetyl-Al and metalaxyl depressed 
Phaeoacremonium growth in the laboratory and in glasshouse 
Type 
Systemic 
Contact 
Systemic 
Systemic 
Contact 
Locally-systemic 
Contact 
Systemic 
Systemic 
Contact 
Systemic 
Contact 
EC" value 
(lJg a.i.!mL) 
0.206 
1.379 
0.254 
5.13 
0.457 
10.891 
13.59 
0.015 
11.199 
0.148 
1.677 
Registered on grapevines 
in Sonth Africa" 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
tests. Our results showed no inhibition of mycelial growth at 
effective concentrations by fosetyl-Al or metalaxyl. Fosetyl-Al 
is reported to have weak curative action and is known to stimu-
late host resistance (Schwinn & Staub, 1995) rather than being 
fungicidal. Since it has a broad spectrum of applications ranging 
from foliar sprays to trunk injections and dip treatment (Schwinn 
& Staub, 1995), and is also known to move symplastically in 
plant tissue, it may be able to stimulate host defence mechanisms 
which would prevent the spread of the pathogen. Although fos-
etyl-Al was found to be unsuccessful for the control of the esca 
disease complex (Mugnai et al., 1999), Ferreira (1998) reported 
success in glasshouse trials and hence further testing to determine 
the exact effect of this chemical on disease control should be car-
ried out. 
Metalaxyl is known to target some chromistan fungi, specifi-
cally the Oomycetes (Kerkemaar & Kaars Sijpesteijn, 1981). It 
has been effectively used to control Pythium and Phytophthora in 
soil (Schwinn & Staub, 1995). Ferreira (1998), however, report-
ed effective disease control of Pa. chlamydospora with metalaxyl 
in laboratory and glasshouse tests. Results from our study showed 
that metalaxyl had no inhibiting effect on the in vitro mycelial 
growth of this fungus. The unexpected effective control of Pa. 
chlamydospora by metalaxyl, as reported by Ferreira (1998), is 
therefore unexplained by this study. 
An important management aspect of vascular diseases is pre-
vention rather than the cure of the disease. The use of 
Phaeomoniella-free cuttings is of primary importance, and 
healthy pathogen-free propagation material should be planted in 
pathogen-free soil. However, it is difficult to ensure pathogen-
free nursery stock, because the fungus could be latent or endo-
phytic in rootstock cuttings (Bertelli et at., 1998). Therefore, pre-
plant treatments with fungicides might be useful in eradicating 
the pathogen from cuttings. Benomyl, fenarimol, kresoxim-
methyl, prochloraz manganese chloride and tebuconazole showed 
mycelial inhibition of Pa. chlamydospora at low concentrations 
(0.01-0.5 ppm). This in vitro test gives a good indication of 
which fungicides can be selected for further studies in glasshous-
es and nurseries. These data could therefore contribute to inte-
S. Afr. J. Enol. Vitic., Vol. 21, No.2, 2000 
Fungicide Sensitivity of Phaeomoniella chlamydospora 61 
grating an effective fungicide application programme. When used 
in combination with sanitation and stress relief, healthy, produc-
tive grapevines are an achievable goal. 
LITERATURE CITED 
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(SAWIS). PO Box 238, Paarl, 7620. 
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CROUS, PW., GAMS, w., WINGFIELD, MJ. & VAN WYK, P.S., 1996. 
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Fungicide Sensitivity of Phaeomoniella chlamydospora, the Causal Organism of Petri Grapevine Decline

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Fungicide Sensitivity of Phaeomoniella chlamydospora, the Causal Organism of Petri Grapevine Decline

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