colletotrichum coccodes.pdf

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JUN09
Colletotrichum coccodes
(Wallr.) Hughes
a
b
Pathogen of the month – June 2009
c
d
Fig. 1.
Colletotrichum coccodes ;
Tomato Brown Root Rot coverd with black sclerotia (a); Acervuli with setae on the root
(b); conidia (c); and appressoria (d). Photo credits H. Golzar.
Common Name
:
Black Dot
Disease:
Tomato Brown Root Rot
Classification:
K: Fungi, P: Ascomycota , C: Sordariomycetes , O: Phyllachorales , F: Phyllachoraceae
Colletotrichum coccodes
(Wallr.) Hughes is an important pathogen of tomato and potato worldwide. The fungus is the
causal agent of tomatoes anthracnose on the fruit, black dots on the roots and blemishes on the surface of potato tubers.
It also causes early senescence (1). During summer 2009, symptoms were observed on root and stem bases of tomatoes
in both field and glasshouse hydroponics systems at two Perth locations. Although
C. coccodes
has been previously
reported on potato in Australia, this is the first report on tomato
.
Symptoms and Impact:
Black Dot symptoms appear as brown lesions on the
roots, progressing to larger brown areas covered with
small black sclerotia (Fig 1a). The root cortex rots and
abundant dark sclerotia form (diam. <1 mm). These
symptoms are particularly evident on older roots where
the tissues are grey to brown.
Anthracnose symptoms appear on fruit as discolored
lesions, and as the disease progresses, the lesions turn
into large circular, sunken areas. Black sclerotia and
acervuli may form on the fruit in moist conditions.
Lack of vigor, premature senescence and necrosis of
foliage can result in crop losses.
Fungal Characteristics:
C. coccodes
is an anamorph of
Glomerlla
which belongs
to the Phyllachoraceae family. The fungus produces
sparse, white to grey, aerial mycelium on potato dextrose
agar and forms abundant dark sclerotia on agar surface.
Acervuli and sclerotia form in culture and on the outer
layer of infected roots. Conidia are cylindrical, hyaline and
aseptate (16-25 µm x 3-4 µm) which form on cylindrical,
phialidic conidiophores (Fig 1c). Acervuli on the roots are
almost rounded (diam. 150-300 µm) with septate setae on
the surface (Fig 1b). Appressoria are ovate to elliptical (av.
12 x 7
μm)
(Fig 1d).
Host Range:
The fungus occurs on tomato, potato and a wide range of
plant species representing 13 families mostly from the
Cucurbitaceae, Leguminosae and Solanaceae. Some
asymptomatic hosts carry fungal propagules (1).
Fungal Survival:
Conidia and sclerotia of
C. coccodes
survive on tomato
roots and infested soils. The sclerotia have been reported
as a source of inoculum and can survive in the soil for up to
8 years (2).
Management and Control:
Good cultural and sanitation practices can reduce inoculum
and disease dispersal. For example, crop rotation with non-
host crops and elimination of wild hosts to reduce levels of
inoculum and survival of the pathogen in the soil. Planting
resistant cultivars is recommended, but known resistant
cultivars are limited. Fungicide application is inefficient,
however, soil fumigation in integrated disease control has
been effective (3).
Further Reading:
1- Chesters & Hornby (1965a,b)
Trans. Br. mycol. Soc.
48, 73–581, 583–594.
2- Dillard and Cobb (1998) Plant Dis. 82, 235-238.
3- Garibaldi
et al.
(2008) Phytoparasitica. 36, 483-488.
Key Contacts:
Hossein Golzar, DAFWA. Email: hgolzar@agric.wa.gov.au, Ph: 08 9368 3693

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