Download Pyrenopeziza brassicae

Poznań University of Life Sciences, Poznań, Poland
DEVELOPMENT OF LIGHT LEAF SPOT
(PYRENOPEZIZA BRASSICAE) ON BRASSICAS
Z. Karolewski
Abstract
Pyrenopeziza brassicae, causing agent of oilseed rape (Brassica napus) light leaf
spot, produces initial inoculum in the form of airborne ascospores, released from
apothecia on not ploughed oilseed rape debris and conidia from oilseed rape volunteers, brassica weeds or cultivated brassicas. Under controlled environment conditions the development of light leaf spot on currently cultivated commercial
vegetable brassicas and winter oilseed rape was compared. Light leaf spot did not
occur only on radish – Raphanus sativus var. radicula and R. sativus var. sativus. The
progress of light leaf spot on other vegetable brassicas was similar to that observed
on winter oilseed rape. Maximum percentage of leaf area with symptoms was the
highest for oilseed rape cv. ‘Polo’ (99.2%) and it was not significantly different for
Chinese cabbage, white cabbage and cauliflower. The lowest values of the parameter were noticed for turnip (69.2%), kohlrabi (71.7%) and kale (72.5%).
Key words: Cylindrosporium concentricum, disease assessment, resistance, infection
criteria
Introduction
Light leaf spot (Pyrenopeziza brassicae) is an important disease of oilseed rape
(Brassica napus) in European countries: in the UK (Boys et al. 2007), France (Brun
et al. 1979) and Germany (Amelung and Daebeler 1991). In Poland the disease occurs mainly in western part of the country, usually after mild wet winters. Severe
epidemics of light leaf spot were noticed in 1992, 1999 and the last one in 2002
(Karolewski 1999, 2005).
The disease can develop on plants at wide range of temperatures – from 4 to
24°C (Gilles et al. 2000), the most favourable is 16°C and high humidity lasting
24–48 h (Karolewski et al. 2002). Under the conditions, parameters of the disease
Phytopathologia 55: 13–20
© The Polish Phytopathological Society, Poznań 2010
ISSN 2081-1756
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Z. Karolewski
development on oilseed rape leaves (maximum percentage of leaf area with
sporulation, maximum rate of increase in percentage leaf area with sporulation,
time from inoculation until the day on which the rate of increase in percentage leaf
area with sporulation was at a maximum) were the highest (Karolewski et al.
2004).
The main initial inoculum of the pathogen for winter oilseed rape are airborne
ascospores, released from apothecia formed on not ploughed oilseed rape debris
(Rawlinson et al. 1978, Gilles et al. 2001). Other potential sources might be
conidia from oilseed rape volunteers, brassica weeds or cultivated brassicas. It is
possible that these plants can be a bridge over the gap in the pathogen life cycle between autumn sown a new winter oilseed rape crop and the previous one harvested
in summer. Pyrenopeziza brassicae can infect Brassica oleracea, incl.: broccoli, Brussels
sprouts, cabbage, cauliflower (Rawlinson et al. 1978, Cheah et al. 1980). Symptoms of light leaf spot were found in controlled environment experiments on artificially inoculated species: B. nigra, B. rapa, B. juncea (Maddock and Ingram 1981) and
B. campestris (Maddock et al. 1981). However, the progress of light leaf spot on
Brassica species, except oilseed rape, have not been investigated. This study describes controlled environment experiment to compare the development of light
leaf spot on currently cultivated commercial vegetable brassicas and winter oilseed
rape.
Material and methods
The development of light leaf spot was tested on 28 cultivars belonging to B.
campestris, B. oleracea, B. napus, B. rapa and Raphanus sativus (Table 1). The experiment was performed in two replicates in controlled environment cabinet (80% relative humidity, 12 h light/12 h dark, supplied by fluorescent and tungsten
lighting) at 16°C. To obtain a sufficient amount of conidial inoculum, leaves of oilseed rape (cv. ‘Polo’) at GS 1.6–1.7 were sprayed using an aerosol sprayer with
a suspension of P. brassicae conidia (0.5 × 106 conidia per 1 ml) produced on MA
medium from mixed six Polish and six UK isolates collected from naturally infected winter oilseed rape plants between 2002 and 2007. Directly after inoculation, plants were covered with polyethylene bags for 48 h. After 18 days from
inoculation, conidia were washed off from the leaves by shaking them in distilled
water and conidial suspensions were adjusted to the desired concentration using
a haemocytometer slide (Weber Scientific International Limited, Teddington, UK)
for inoculating plants (GS 1.6–1.7) in the experiment. Plants were inoculated with
conidia by spraying the leaves with a conidial suspension (0.5 × 106 conidia per
1 ml) with an aerosol sprayer until droplets had begun to run off the leaves. Severity of light leaf spot was assessed by visual estimation of percentage of leaf area
with sporulation (lesions) every day, starting from inoculation until the percentage of leaf area with lesions did not increase any more. For each treatment data on
changes in the percentage of leaf area with symptoms (y) in order to describe dis-
Development of light leaf spot (Pyrenopeziza brassicae) on brassicas
15
Table 1
Parameters (estimated values) for logistic equation describing the change
in percentage of leaf area with symptoms (y) with time (t, days after inoculation)
on brassica leaves inoculated with Pyrenopeziza brassicae conidia
Species
Common
name
Brassica napus
Oilseed rape
Brassica rapa
Brassica oleracea
Raphanus sativus
var. radicula
Brassica oleracea
Brassica oleracea
Brassica oleracea
Brassica oleracea
Brassica rapa
Raphanus sativus
var. sativus
Brassica oleracea
SED (135 d.f.)
c (%)
r (% per day)
l (day)
‘Polo’
99.17
20.83
17.92
Chinese
cabbage
‘Hilton’
90.83
19.17
16.39
White
cabbage
‘Agat’
84.17
19.16
18.92
‘Balbro’
87.50
20.00
18.50
‘Ditmarska’
93.33
24.17
18.33
‘Rowa’
0.00
0.00
0.00
‘Carmen’
0.00
0.00
0.00
‘Krakowianka’
0.00
0.00
0.00
‘Claudia’
88.33
18.33
16.78
‘Wiarus’
85.00
15.84
17.00
‘Sebastian’
80.00
17.50
17.67
‘Pionier’
90.83
20.00
17.63
‘Barcelona’
91.67
14.17
18.78
‘Trevi’
92.50
15.84
17.50
‘Niebieska Masłowa’
75.83
15.00
18.58
‘Delikates Weiser’
71.67
15.00
18.27
‘Dvorskyego Pol’
76.67
14.16
15.78
‘Maczuga’
72.50
12.50
18.30
‘Dolores’
73.33
15.83
18.67
‘Groninger’
75.83
17.50
18.08
‘Purple Top White Globe’
85.83
13.34
18.39
‘Snowball’
75.00
12.50
16.00
‘Goldball’
69.17
15.00
18.92
Radish
Broccoli
Cauliflower
Kohlrabi
Brussels
sprout
Turnip
Radish
Kale
Cultivar
‘Murzynka’
0.00
0.00
0.00
‘Montang Hong’
0.00
0.00
0.00
‘Sugi F1’
0.00
0.00
0.00
‘Lerchenzungen’
72.50
12.50
20.40
‘Vitesse’
72.50
12.50
20.40
4.45
1.34
2.01
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Z. Karolewski
ease progress with time (t, days after inoculation) were fitted by the logistic equation used earlier by Karolewski et al. (2002, 2004):
y=
c
 4r

1+ exp− (t − l )
 c

The fitted equation enabled estimates to be made of the predicted maximum
percentage of leaf area with symptoms (c), maximum rate of increase in percentage
of leaf area with symptoms (r) and time from inoculation until the day on which
the rate of increase in percentage of leaf area with symptoms was maximum (l).
Results
The experiment revealed that P. brassicae was able to infect four out of five
tested species: B. napus, B. campestris, B. oleracea and B. rapa (Table 1). Disease
symptoms were not found on any of six cultivars of both radish species – R. sativus
var. sativus and R. sativus var. radicula. The differences between brassicas in the occurrence of symptom types were found (Phot. 1). In general, sporulation of P.
brassicae was less abundant on vegetable crops, than on oilseed rape cv. ‘Polo’.
However, on broccoli, many white acervuli occurred, whilst on white cabbage dark
lesions were mainly observed on inoculated leaves. In comparison, on kohlrabi,
both types of symptoms appeared simultaneously.
The logistic curves fitted well the data for changes with time (t) in the percentage of leaf area with symptoms occurring on inoculated brassicas (Fig. 1), however
parameter value for six cultivars of radish was ‘0’, as no symptoms of light leaf spot
were observed. The statistical analysis of estimated parameters showed that predicted maximum percentage of leaf area with symptoms (c) was the highest for oilseed rape cv. ‘Polo’ (99.2%) and it was not significantly different for Chinese
cabbage (‘Hilton’), white cabbage (‘Ditmarska’) and all cauliflower cultivars (Table 1). The lowest values of c were noted for turnip cv. ‘Goldball’ (69.2%), kohlrabi
cv. ‘Delikates Weiser’ (71.7%) and kale cv. ‘Lerchenzungen’ and ‘Vitesse’ (72.5%).
The value of parameter r reached 20.8% per day for oilseed rape cv. ‘Polo’ and was
similar again for Chinese cabbage (‘Hilton’), white cabbage (‘Ditmarska’, ‘Balbro’), cauliflower (‘Pionier’) and also for broccoli (‘Claudia’). The day on which
the rate of increase in percentage of leaf area with symptoms was maximum (l) did
not differ for all brassicas cultivars (except for not infected radish cultivars) and
varied from 15th to 20th day.
Development of light leaf spot (Pyrenopeziza brassicae) on brassicas
17
Phot. 1. Symptoms on brassica leaves 21 days after inoculation with Pyrenopeziza brassicae conidia:
a – white cabbage ‘Agat’ – dark spots, b – broccoli ‘Sebastian’ – acervuli, c – kohlrabi ‘Niebieska
Masłowa’ – dark spots and acervuli, d – radish ‘Murzynka’ – no symptoms (photo by Z. Karolewski)
Discussion
The majority of tested cultivars belonging to Brassicaceae family could be infected by P. brassicae at high infection pressure and under conditions favourable for
the disease. Light leaf spot did not occur on radish R. sativus var. radicula and R.
sativus var. sativus only. The progress of light leaf spot on vegetable brassicas was
often similar to that observed on winter oilseed rape. Although the differences between maximum and minimum value of parameter c (maximum percentage of leaf
area with symptoms) for tested species/cultivars (except radish) was ~30%, the
lowest level of infection reached 70% (turnip cv. ‘Goldball’). Also maximum rate
of increase in percentage of leaf area with symptoms of disease progress (r) suggested high infection of different brassicas. The lowest value of the parameter –
12.5% per day (kale, turnip) showed, that light leaf spot can develop quickly on
these species. It seems, that optimum temperature and humidity duration for light
leaf spot development on vegetable brassicas are similar to oilseed rape. Little differences for P. brassicae infection were found on cauliflower between 15 and 20°C
(Hartill and Cheah 1984).
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Z. Karolewski
Fig. 1. Logistic curves fitted to data on changes in the percentage of leaf area with symptoms (y)
with time (t, days after inoculation) on brassica leaves inoculated with Pyrenopeziza brassicae:
a – white cabbage ‘Agat’, b – broccoli ‘Claudia’, c – Chinese cabbage ‘Hilton’, d – kale
‘Lerchenzungen’, e – Brussels sprout ‘Maczuga’, f – radish ‘Murzynka’, g – kohlrabi ‘Niebieska
Masłowa’, h – cauliflower ‘Pionier’, i – oilseed rape ‘Polo’, j – turnip ‘Purple Top White Globe’.
c
was fitted to the data for each cultivar
Logistic equation y =

 4r
1 + exp− (t − l )

 c
Development of light leaf spot (Pyrenopeziza brassicae) on brassicas
19
Pyrenopeziza brassicae has a broad host range of brassicas, however, differences
in susceptibility of cultivars to light leaf spot were found (Maddock and Ingram
1981). Some species were known as less susceptible – Brussels sprout and kale
(Maddock et al. 1981). Progress of light leaf spot in this study on the species was
similar to that on the other hosts, except radish, suggesting that these current
cultivars of Brussels sprout and kale were susceptible.
The results of the experiments indicate that vegetable brassicas cultivated in
autumn can play an important role in the light leaf spot life cycle in Poland. During
vegetation season on majority of these species acervuli may be formed after infection with conidia come from different brassica crops. Cultivated brassicas can also
be infected with ascospores, released from infected oilseed rape debris in autumn
and then rain splash dispersed conidia can initiate epidemics on winter oilseed
rape. To avoid such primary infections of winter oilseed rape, fields with vegetable
brassicas should not be located near oilseed rape crops, due to fact that P. brassicae
conidia can be transmitted only a short distance (Evans et al. 2003).
Acknowledgements
I would like to thank Dr. Jan Bocianowski for advice on statistical analysis of the
data.
Streszczenie
ROZWÓJ CYLINDROSPORIOZY (PYRENOPEZIZA BRASSICAE)
NA ROŚLINACH KAPUSTOWATYCH
Cylindrosporioza, powodowana przez Pyrenopeziza brassicae, jest groźną chorobą
rzepaku w wielu krajach Europy, m.in. w Wielkiej Brytanii, Francji, Niemczech
i Polsce. Głównym źródłem pierwotnej infekcji rzepaku ozimego są rozprzestrzeniane z wiatrem askospory, uwalniane z apotecjów powstających na nieprzyoranych resztkach pożniwnych rzepaku. Innym źródłem infekcji mogą być konidia pochodzące z samosiewów rzepaku, chwastów z rodziny kapustowatych oraz uprawnych kapustowatych. W pracy przedstawiono doświadczenie wykonane w warunkach kontrolowanych, którego celem było porównanie rozwoju cylindrosporiozy
na uprawnych warzywach kapustowatych i rzepaku ozimym. Objawy cylindrosporiozy nie występowały jedynie na rzodkiewce – Raphanus sativus var. sativus i rzodkwi – R. sativus var. radicula. Przebieg choroby na pozostałych badanych warzywach
kapustowatych był zbliżony do obserwowanego na rzepaku ozimym. Maksymalny
procent powierzchni liści z objawami był najwyższy w przypadku rzepaku odm.
‘Polo’ i nie różnił się istotnie od wartości zanotowanych dla kapusty pekińskiej, kapusty białej i kalafiora. Najmniejszą wartość tego parametru odnotowano w przypadku rzepy jadalnej (69,2%), kalarepy (71,7%) i jarmużu (72,5%).
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Z. Karolewski
Literature
Amelung D., Daebeler F., 1991: Occurrence of fertile apothecia and the epidemiology of Pyrenopeziza
brassicae Sutton and Rawlinson (anamorph: Cylindrosporium concentricum Grev.) in the German
Democratic Republic. IOBC Bull. 14: 147–150.
Boys E.F., Roques S.E., Ashby A.M., Evans N., Latunde-Dada A.O., Thomas J.E., West J.S., Fitt B.D.L.,
2007: Resistance to infection by stealth: Brassica napus (winter oilseed rape) and Pyrenopeziza
brassicae (light leaf spot). Eur. J. Plant Pathol. 118: 307–321.
Brun H., Renard M., Jouan B., Tanguy X., Lamarque C., 1979: Observations préliminaires sur quelque
maladies du colza en France. Sclerotinia sclerotiorum, Cylindrosporium concentricum, Ramularia armoraciae. Sci. Agron. Rennes: 7–17.
Cheah L.-H., Hartill W.F.T., Corbin J.B., 1980: First report of the natural occurrence of Pyrenopeziza
brassicae in brassica crops in New Zealand. N. Z. J. Bot. 18: 197–202.
Evans N., Baierl A., Brain P., Welham S.J., Fitt B.D.L., 2003: Spatial aspects of light leaf spot
(Pyrenopeziza brassicae) epidemic development on winter oilseed rape (Brassica napus) in the United
Kingdom. Phytopathology 93: 657–665.
Gilles T., Fitt B.D.L., Jeger M.J., 2001: Effects of environmental factors on development of Pyrenopeziza
brassicae (light leaf spot) apothecia on oilseed rape debris. Phytopathology 91: 392–398.
Gilles T., Fitt B.D.L., Kennedy R., Welham S.J., Jeger M.J., 2000: Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation of Pyrenopeziza brassicae on
leaves of oilseed rape. Plant Pathol. 49: 498–508.
Hartill W.F.T., Cheah L.-H., 1984: Some effects of climate and plant growth on the development of light
leaf spot in cauliflower. N. Z. J. Agric. Res. 27: 441–449.
Karolewski Z., 1999: The occurrence of light leaf spot on winter oilseed rape in Western Poland in
1991–1996 and the characteristics of Pyrenopeziza brassicae isolates. Phytopathol. Pol. 18: 113–121.
Karolewski Z., 2005: Podatność odmian rzepaku na cylindrosporiozę (Pyrenopeziza brassicae). Progr.
Plant Prot. / Post. Ochr. Rośl. 45, 2: 768–771.
Karolewski Z., Evans N., Fitt B.D.L., Baierl A., Todd A.D., Foster S.J., 2004: Comparative epidemiology
of Pyrenopeziza brassicae (light leaf spot) ascospores and conidia from Polish and UK populations.
Plant Pathol. 53: 29–37.
Karolewski Z., Evans N., Fitt B.D.L., Todd A.D., Baierl A., 2002: Sporulation of Pyrenopeziza brassicae
(light leaf spot) on oilseed rape leaves inoculated with ascospores or conidia at different temperatures and wetness durations. Plant Pathol. 51: 654–665.
Maddock S.E., Ingram D.S., 1981: Studies of survival and longevity of the light leaf spot pathogen of
brassicas, Pyrenopeziza brassicae. Trans. Br. Mycol. Soc. 77: 153–159.
Maddock S.E., Ingram D.S., Gilligan C.A., 1981: Resistance of cultivated brassicas to Pyrenopeziza
brassicae. Trans. Br. Mycol. Soc. 76: 371–382.
Rawlinson C.J., Sutton B.C., Muthyalu G., 1978: Taxonomy and biology of Pyrenopeziza brassicae sp. nov.
(Cylindrosporium concentricum), a pathogen of winter oilseed rape (Brassica napus ssp. oleifera).
Trans. Br. Mycol. Soc. 71: 425–439.
Author’s address:
Dr. Zbigniew Karolewski, Department of Phytopathology, Poznań University
of Life Sciences, ul. Dąbrowskiego 159, 60-594 Poznań, Poland, e-mail:
[email protected]
Accepted for publication: 3.02.2010