A review of dipterocarps - Center for International Forestry Research

Pests and Diseases of Dipterocarpaceae 121
1961, Elouard unpublished). Schyzophyllum commune
has been reported as causing die-back of young saplings
of Shorea robusta, cankers caused by frost or fire
providing the route of entry. The fungus, once established,
attacks the living sapwood killing the stem beyond the
scars, and it progresses both up and down the stem
(Bagchee 1954).
Various fungi cause leaf diseases, an infection of
leaves characterised by spots, necrosis and leaf fall
(Hawksworth et al. 1983), and most of them belonging
to Imperfect Fungi (Deuteromycetes). In most cases,
growth of seedlings and saplings is not affected, except
when large spot areas (dead and necrosed cells)
significantly reduce the leaf area for photosynthesis. The
weakened plant becomes more susceptible to pathogen
and pest attacks, or is less competitive with other
seedlings and saplings in natural stands. Ultimately, the
leaf becomes completely necrosed and dry and falls. On
seedlings and young saplings, the defoliation can
eventually lead to death (Hong 1976, Mridha et al. 1984,
Charlempongse 1988, Harsh et al. 1989, Elouard l99l,
Zakaria personal communication, Elouard unpublished).
Some fungi, such as Meliola sp. develop a dense dark
mat on the leaf surface, sometimes entirely covering the
leaf area. Though the hyphae do not penetrate the leaf
cells, chlorophyll development is hindered (Elouard
l991). An alga, Cephaleuros virescens
(Trentepholiaceae), was also recorded causing leaf
disease on seedlings and saplings in India, Indonesia and
Malaysia and on trees in India (Mittal and Sharma 1980,
Elouard 1991).
Thread blights recorded on dipterocarps are caused
by Basidiomyceteae of the genera Marasmius and
Corticium. There are two kinds of thread blights, white
and dark. The white thread blights are produced by the
development of whitish mycelium sticking on the twigs,
branches and foliar system of the seedlings and saplings.
The black thread blights are horse hair-like and attached
to the host by byssus. The threads do not stick to the
host’s organs except by the byssus, but develop an aerial
network which, when too excessive, can hinder the host’s
development. These fungi were observed in plantation
and natural forests in India, Indonesia and Malaysia
(Symington 1943, Bagchee 1953, Bagchee and Singh
1954, Spaulding 1961, Smits et al. 1991, Elouard 1991,
Elouard unpublished).
Gall formation on shoots of seedlings and saplings
has been described in Shorea javanica plantations in Java
(about 60% of the seedlings affected), man-made
dipterocarp forests of Sumatra and on Shorea spp. and
Upuna borneensis (100% of the plants affected in
nursery) in Kalimantan (Ardikoesoema 1954, Torquebiau
1984, Smits et al. 1991). This gall formation is
commonly attributed to a bacterium, Agrobacterium
tumefaciens. According to Smits et al. (1991), the
youngest leaf remains smaller than the leaves developed
before infection, subsequent leaves no longer develop
from the top shoot and all buds in the zone with green
leaves produce side buds. This process continues until a
dense clump of tiny shoots is produced at the buds’
positions but without development of any normal shoots
from these clumps. The plant growth is then stopped. An
insect is suspected to be the vector for this bacteria
(Torquebiau 1984, Smits et al. l991).
Trees
About 150 fungal species have been recorded on trees,
mainly causing rots and decay. In addition, leaf damage,
flower necrosis and cankers were also reported.
Parasitic plants of the family Loranthaceae have severely
damaged Shorea robusta in India.
Leaf disease on trees is harmful if the damaged area
covers a large area of the foliar system. The fungal leaf
diseases are mainly caused by species of Asterina,
Capnodium, Cercospora, Colletotrichum
(Thirumalachar and Chupp 1948, Bagchee 1953, Bagchee
and Singh 1954, Chaves-Batista et al. 1960, Spaulding
1961, Bakshi et al. 1967-1972, Elouard 1991).
Cankers and rots were recorded on various
dipterocarp species in Peninsular Malaysia, Thailand,
Singapore, Indonesia and India (Bagchee 1954, 1961,
Bagchee and Singh 1954, Bakshi 1957, 1959, Bakshi et
al. 1967, Panichapol 1968, Hong 1976, Charlempongse
1985, Kamnerdratana et al. 1987, Corner 1987, l991,
Elouard 1991).
Few fungal species are able to attack healthy trees.
Aurificaria [Polyporus] shoreae, a fungus only reported
on Shorea robusta, is capable of infecting healthy and
uninjured roots, causing root rot and bark and sapwood
decay. The disease results in top die back and death of
trees (Bakshi and Boyce 1959). Most of fungal species
are secondary parasites infecting the trees through
wounds and are distinguished from the primary parasites
which produce active root and stem rot. According to
Bagchee (1954), at least 24 species of Hymenomycetes
behave as facultative parasites of Shorea robusta.