© 2004 Plant Management Network.
Accepted for publication 16 January 2004. Published 2 March 2004.
Mango Dieback and Gummosis in Sindh,
Pakistan Caused by Lasiodiplodia theobromae
Muhammad Ali Khanzada, Abdul Mubeen Lodhi, and Saleem
Shahzad, Pest and Disease Research Lab, Department of Botany,
University of Karachi, Karachi-75270, Pakistan.
Corresponding author: Saleem Shahzad. [email protected]
Khanzada, M. A., Lodhi, A. M., and Shahzad, S. 2004. Mango dieback and gummosis in
Sindh, Pakistan caused by Lasiodiplodia theobromae. Online. Plant Health Progress
doi:10.1094/PHP-2004-0302-01-DG.
Disease: Dieback and gummosis
Primary Economic Host: Mango (Mangifera indica L.)
Pathogen: Lasiodiplodia theobromae (Pat.) Griffon & Maubl.
Synonyms: Botryodiplodia theobromae Pat.; Diplodia theobromae
(Pat.) Nowell; Lasiodiplodia tubericola Ell. & Ev.; Diplodia tubericola
(Ell. & Ev.) Taubenh; Botryodiplodia tubericola (Ell. & Ev.) Petrak.
Teleomorph: Botryosphaeria rhodina (Berk. & Curt.); synonym:
Physalospora rhodina Berk. & Curt.
Taxonomy
The fungus is commonly known as Botryodiplodia theobromae (Pat.).
However, Sutton (5) has adopted the name Lasiodiplodia theobromae Griff. &
Maubl. as suggested by Zambettakis (6). L. theobromae has also been
recognized by Hawksworth et al. (4), and B. theobromae is now, therefore,
considered to be a synonym of L. theobromae. The current Latin binomial for
the fungus can be obtained online from the CABI Bioscience Databases (2).
Symptoms and Signs
Dieback. In affected plants, twigs die from the tips back into old wood,
giving a scorched appearance to the limb (Fig. 1). The young green twigs start
withering first at the base and then extending outwards along the veins of leaf
edges. The affected leaf turns brown and its margins roll upwards. Leaves scorch
and fall, leaving a dead branch. In severe conditions, branches start drying one
after another in a sequence (Fig. 2) resulting in death of the whole tree (Fig. 3).
Fig. 1. Dieback of branches on a mango
tree.
Plant Health Progress
2 March 2004
Fig. 2. A mango plant
showing sequential death of
branches.
Fig. 3. Death of mango tree
caused by dieback disease.
Gummosis. The infected plants show abundant gum secretion from
branches, stem, and main trunk. Initially the gum appears as a small droplet
(Fig. 4). However, as the disease progresses, it increases and covers most of the
branch (Fig. 5) and trunk (Fig. 6). Under severe conditions, the outer wood of a
branch cracks and splits (Fig. 7) and exudes a yellow to brown, gum-like
substance (Fig. 8).
Fig. 4. A small droplet of gum exuded by a
branch of a mango tree.
Plant Health Progress
Fig. 5. Heavy gummosis on branches of a
mango tree.
Fig. 6. Heavy gummosis on main trunk of a
mango tree.
Fig. 7. A branch of a mango tree showing
splitting of bark.
Fig. 8. Gum oozing-out from the split bark.
2 March 2004
Browning of vascular tissues. In infected plants, the twigs and branches
show internal discoloration. Brown streaks in vascular regions are visible upon
splitting the twigs lengthwise (Fig. 9).
Fig. 9. Browning of vascular tissues.
The disease may occur any time throughout the year in Pakistan. Plants
growing under water stress conditions show more severe symptoms compared to
regularly watered plants, indicating that water stress apparently predisposes the
plant and enhances the severity of disease.
Host Range
This fungus has a wide host range. It attacks more than 280 species of plants
in different parts of the world (3,5). In Pakistan, the fungus has been reported
on more than 50 plant species (1).
Geographical Distribution
The fungus is a common soil-borne saprophyte or wound parasite,
distributed throughout the tropics and subtropics (3).
Pathogen Isolation
Root and stem samples were cut into 1-to-2-cm pieces, surface sterilized with
5% sodium hypochlorite solution for 2 min and placed in sterilized Petri plates
containing either potato sucrose agar (PSA) or two layers of moistened blotter
paper and incubated at 30°C with 12-h alternating periods of light and darkness.
Specimens were examined after 1 week for fungal growth.
Pathogen Identification
On PSA, colonies were initially white, soon becoming black and fastspreading with immersed and superficial, branched, septate mycelium. Shiny
black pycnidia were produced on the surface (Fig. 10).
Fig. 10. Colony of Lasiodiplodia
theobromae showing pycnidia.
Plant Health Progress
2 March 2004
Conidia were initially hyaline, unicellular, subovoid to ellipsoidal, with a
granular content (Fig. 11). Mature conidia were two-celled, cinnamon to dark
brown, thick walled, ellipsoidal, often with longitudinal striations 18 to 30 × 10
to 15 µm in size (Fig. 12).
Fig. 11. Immature, hyaline,
unicellular conidia of Lasiodiplodia
theobromae.
Fig. 12. Mature, dark brown, bi-celled,
thick walled conidia of Lasiodiplodia
theobromae.
The morphological characters for pycnidia and conidia were similar to those
given by Sutton (5).
Pathogen Storage
The pathogen was maintained on PSA slants at room temperature and in a
refrigerator for several months.
Cultures were also maintained on wheat meal-soil medium. Wheat meal was
mixed in sandy-loam soil at 5% w/w and 10 ml distilled water was used to
moisten 100 g medium. The mixture was transferred in 250-ml flasks at 100 g
per flask and sterilized at 15 p.s.i. for 20 min. A 1-cm2 block of agar containing
mycelium of L. theobromae was added in each flask and the flasks were
incubated at room temperature for 2 wk with frequent shaking.
Storage for an extended period was accomplished by inoculating the fungus
on chopped, moist sterilized wheat straw in 250-ml conical flasks. The flasks
were incubated at room temperature.
Pathogenicity Test
Pathogenicity tests were carried out at farmers’ fields and in the screen house
of the Pest & Disease Research Lab (PDRL). A famous and widely cultivated
variety Langra was used in these experiments.
In farmers’ fields, 3 to 4 years old, apparently healthy plants were selected.
Specimens were taken from branches and roots, cut into 1-cm-long fragments,
surface sterilized with 5% sodium hypochlorite solution, and placed on the
surface of PSA medium to confirm the absence of the pathogen. Plants found
infected with the test pathogen were not used in the study.
Roots and stems of separate plants were inoculated by making a cut in the
stem (Fig. 13) or root (Fig. 14) using a sterilized knife. A 1-×-2-cm inoculum
block from 5-days-old culture on PSA was placed in the gap and the inoculated
portion was wrapped with Para film. A 1-×-2-cm PSA block without fungus was
placed in control plants. Plants were irrigated after inoculation and the
wrapping material was removed from the stems after 2 wk of inoculation. Plants
were monitored for the development of disease symptoms and the pathogen was
re-isolated from roots, stem, and branches of the test plants to confirm the
pathogenicity. The experiment was conducted at 3 different orchards. In each
experiment, four different sites in an orchard were used and the experiment was
laid down in a randomized complete block design.
Plant Health Progress
2 March 2004
Fig. 13. A cut made in stem of a mango
tree for inoculation with Lasiodiplodia
theobromae.
Fig. 14. Bark removed from root of a
mango tree for inoculation with
Lasiodiplodia theobromae.
After one month of inoculation, plants inoculated with L. theobromae
showed typical symptoms of the disease as observed during the survey.
Symptoms included wilting and death of leaves at the tip (Fig. 15), gum
exudation (Fig. 16), and internal browning of the vascular tissues (Fig. 17).
Control plants did not exhibit the typical symptoms and remained normal and
healthy. It clearly indicated that the decline and gummosis is caused by L.
theobromae. It was interesting to note that the symptoms appeared early and
more prominently in stem inoculated plants as compared to root inoculated
plants. Re-isolation from the dead and green branches of L. theobromaeinoculated plants showed up to 95% recovery.
Fig. 15. Wilting and death of
leaves in apical region of an
inoculated plant.
Fig. 16. Exudation of gum
from an inoculated plant.
Fig. 17. Browning of vascular tissues in
stem of an inoculated plant.
Plant Health Progress
2 March 2004
In the screen house experiment, seeds obtained from an apparently healthy
tree of variety Langra were surface-sterilized with 5% sodium hypochlorite
solution and sown in sterilized sandy-loam soil kept in 8-cm diameter plastic
pots. After 2 months of germination, roots and shoots of the plants were
inoculated with the pathogen using the method described above.
The inoculated plants showed defoliation and necrosis of the shoot tip.
Gradually, all the plants were killed. Shoot inoculated plants died earlier as
compared to the root inoculated plants.
Literature Cited
1. Ahmed, S., Iqbal, S. H., and Khalid, A. N. 1997. Fungi of Pakistan. Sultan Ahmed
Mycolog. Soc. Pakistan, Dept. Bot., Univ. Punjab, Lahore, Pakistan.
2. CABI Bioscience. 2003. IndexFungorum: The CABI Bioscience and CBS Database of
Fungal Names. Online.
3. Domsch, K. H., Gams, W., and Anderson, T. H. 1980. Compendium of Soil Fungi.
Vol.1. Academic Press, NY.
4. Hawksworth, D. L., Kirk, P. M., Sutton, B. C., and Pegler, D. N. 1995. Ainsworth &
Bisby’s Dictionary of the fungi. Eighth edition. CAB Int., Wallingford, Oxan OX10
8DE, UK.
5. Sutton, B. C. 1980. The Coelomycetes. Commonw. Mycolog.l Inst., Kew, Surrey,
England.
6. Zambettakis, E. C.1954. Recherches sur la systematique des “SphaeropsidalesPhaeodidymae”. Bull. Trimest. Soc. Mycol. Fr. 70:219-349.
Plant Health Progress
2 March 2004