A review of dipterocarps - Center for International Forestry Research

Pests and Diseases of Dipterocarpaceae 120
and Sharma 1982, Mohanan and Sharma 1991). Most of
these fungi belong to Fungi Imperfecti
(Deuteromycetes). Though a large number of species are
recorded on dipterocarp seeds, their disease transmission
and seed degradation is not well documented. In general,
poor seed storage conditions affect seed quality and
facilitate fungal infection and spread of fungi (see
Chapter 4). There have been few fungicidal studies on
stored dipterocarp seeds and there is a need for seed
pathology research to establish suitable control methods
for fungal infection both during storage and in nurseries.
Two categories of seed fungi can be identified, the
storage fungi and the seedborne fungi. The first category
includes saprophytic fungi growing on the seed testa, and
the second refers to pathogenic fungi developing from
the internal part of the seed. Both cause significant
damage during storage.
Storage fungi
Storage fungi grow fast, developing from the ever-present
spores in the air or on the seed testa. They rapidly invade
the embryo, causing damage and decreased germination
(Neergard 1977). These saprophytes do not feed on the
seeds, but their excessive development leads to the
rotting of the seeds. The most common species belong
to the genera of Aspergillus, Penicillium, Pestalotia,
Pestalotiopsis, Gliocladium, Fusarium,
Cylindrocladium and Lasiodiplodia. Most of these fungi
produce enormous quantities of spores spreading rapidly
and infecting the whole seed stock.
Aspergillus niger was widely recorded on
dipterocarp seeds (Pongpanich 1988, Singh et al. 1979,
Mittal and Sharma 1981, 1982, Hong 1976, 1981a, Lee
and Manap 1983, Hadi 1987, Elouard and Philip 1994).
In India, fungicidal trials were conducted on fungi
infecting Shorea robusta seeds, namely Aspergillus
niger, Penicillium albicans, P. canadense,
Cladosporium cladosporioides, C. chlorocephalum
and Rhizopus oryzae (Mittal and Sharma 1981).
Brassical, Bavistin and Dithane-45 proved effective. In
Malaysia, Elouard and Philip (1994) tested fungicides
on Hopea odorata seeds, and Benlate 50 and Thiram
were effective without preventing germination or
affecting seedling development.
Seed-borne fungi
Seed-borne fungal infection most probably takes place
during the flowering period or at the early stage of
fructification. The infection occurs through spores
present in the environment or through inoculation of
spores or mycelium by pollinating insects or predispersal
insect predators while laying their eggs. Seed-borne
fungi feed on living tissues, destroying the embryo and
the cotyledons. The mycelium develops inside the seed
and eventually covers the whole fruit. In natural stands,
seed destruction is mainly caused by seed-borne fungi.
The most common seed-borne fungi belong to the
genera Fusarium, Cylindrocladium, Lasiodiplodia,
Colletotrichum, Curvularia and Sclerotium (Hong
1976, 1981a, Lee and Manap 1983, Charlempongse et
al. 1984, Pongpanich 1988, Mohanan and Sharma 1991,
Elouard 1991, Elouard and Philip 1994). The
Basidiomyceteae Schyzophyllum commune has been
observed on several dipterocarps (Hong 1976, Vijayan
and Rehill 1990, Elouard and Philip 1994), developing
on the cotyledons and embryo and ultimately covering
the whole seed and producing carpophores. Infection
leads to high levels of mortality: 70% of Shorea
leprosula and S. ovalis seeds were rotted by a Fusarium
species and 90% of Shorea glauca seeds were destroyed
by Schyzophyllum commune (Elouard and Philip 1994).
Seedlings and Saplings
Over 40 species have been identified causing seedling
diseases. The most common are in the genera
Colletotrichum, Cylindrocladium, Fusarium and
Lasiodiplodia, which are responsible for damping-off,
wilting, root and collar rots, cankers, leaf diseases, thread
blights and gall formation.
Damping-off is the rotting of seeds and young
seedlings at soil level (Hawksworth et al. 1983) and is
in most cases caused by seed-borne fungi (Hong 1981a,
Lee and Manap 1983, Pongpanich 1988, Elouard l991,
Elouard and Philip 1994). Collar rot, root rot and wilting
(loss of turgidity and collapse of leaves (Hawksworth et
al. 1983)) are mainly caused by Fusarium species
(Foxworthy 1922, Thompson and Johnston 1953, Hong
1976, Lee and Manap 1983, Elouard, l991, Elouard and
Philip 1994).
A canker is a plant disease in which there is sharplylimited
necrosis of the cortical tissue (Hawksworth et
al. 1983). Though most of the time stem cankers are not
lethal, they still can be harmful decreasing the strength
of the stem and causing it to fracture. Root and collar
cankers can affect the vascular system of the plant and
eventually result in plant death by wilting (Spaulding